All Projects

This is a list of projects I've had time to write up, completed, currently being built or being planned, feel free to contact me about any of these projects as feedback is always welcomed.

Cosmic Ray Detectors

Cosmic Rays

These projects were conceived from an interest in Radio Astronomy and Particle physics. I’ve now come to see cosmic ray detection as kind of poor man’s version of particle physics experiments.  As the journey of construction, experimentation and interpretation of the results has meant learning a little bit more about the fascinating world of particles and forces that make up the universe. 

This website has become a little cluttered, some projects are dated and so I have setup a new website dedicated only to Cosmic Ray Astronomy at cosmicray.com.au

What are Cosmic Rays?

Cosmic Rays

Cosmic rays are energetic particles originating from deep space that hit our atmosphere 30km above the Earth’s surface. They come from a variety of sources including our own Sun, other stars and distant interstellar objects such as black wholes, but most are the accelerated remnants of supernova explosions.

Although commonly called cosmic rays the term "ray" is a misnomer, as cosmic particles arrive individually as a primary particle, not as a ray or beams of particles. 90% are Protons, 9% helium nuclei, and the remainder electrons or other particels.

Matter smashing energy
When these primary particles hit, they do so with such tremendous energy they rip their way into our atmosphere with atom smashing power. Cosmic rays are commonly known to have energies well over 1020 eV (electron volts), far more than any particle accelerator built here on earth, like the Large Hadron Collider (LHC).

These interactions produce an exotic zoo of high energy particles and anti-particles high in the earth's atmosphere such as positive and negative pions and kaons that subsequently decay into muons and muon neutrinos (including cascades of protons and neutrons as a result of nucleonic decay). Where uncharged pions decay into pairs of high energy photons they become the starting points of large cascades of electrons, positrons and gamma rays. The resulting flux of particles at ground level consists mainly of muons and electrons/positrons in the ratio of roughly 75% : 25% still with energies greater than 4GeV travelling at near the speed of light ~0.998c.

Common interstellar events on earth of which most people are unaware
Muons created by the interaction of cosmic rays and our atmosphere lose their energy gradually. Muons start with high energies and therefore have the capacity to ionise many atoms before their energy is exhausted. Further, as muons have little mass and travel at nearly the speed of light, they do not interact efficiently with other matter. This means they can travel through substantial lengths of matter before being stopped. Consequently, muons are all around us, passing through just about everything. They can penetrate mountains, buildings, our bodies, and deep into the Earth’s surface, without anyone really being aware of their existence other than scientists and obsessive geeks

Time Travellers
Muons created by the interaction of cosmic rays are an everyday demonstration of Einstein's theory of relativity. A muon has a measured mean lifetime of 2.2 microseconds. Consequently, they should only be able to travel a distance of 660 metres even at near the speed of light and should not be capable of reaching the ground. However Einstein's theory showed that time ticks slowly for particles moving at speeds close to that of light. Whilst the mean lifetime of the muon at rest is only a few microseconds, when it moves at near the speed of light its lifetime is increased by a factor of ten or more giving these muons plenty of time to reach the ground.

Theory of Detecting Cosmic Rays

Unfortunately a muon created as a result of Cosmic Rays is not easily seen, but their after-effects when passing through is a little more easier, typically most forms of radiation detectors will do the job. The oldest and most famous example of this is the Cloud chamber. There is an operational cloud chamber installed and running at the South Australian Museum and is well worth a look (I think its fascinating).

Other radiation detectors can be used like Geiger Counters, Spark Chambers, Resistive Plate Chambers and materials called Scintillators which give off light when an ionizing particle passes through them.

The problem using a radiation detector for a cosmic ray observation is that there is larger amounts of terrestrial radiation as much 73% of background radiation is due to the natural decay of matter. Although in small quantities it is sufficient to make it difficult to discriminate between a terrestrial or cosmic source.

Consequently at least two detectors are needed placed one above the other, feed into electronics that can monitor coincidence between the two detectors quickly thus potentially filtering out most terrestrial radiation.

directional coincidence

Cosmic particles travel at nearly the speed of light and so do not ionise very efficiently and hence can travel through matter very easily passing through both detectors without effort, whereas the terrestrial radiation may not. Consequently anything detected in both detectors simultaneously is more likely to be a cosmic event than terrestrial.

Well almost simultaneously, if a muon is travelling at 0.998c and the detectors where spaced 5cm apart the actual flight time of a muon would be just 0.16ns. However as the detector and electronics response and delay times would be much slower than this, we can say in "real-life" terms it is simultaneous.

The main idea of coincidence detection in signal processing is that if a detector detects a signal pulse in the midst of random noise pulses inherent in the detector, there is a certain probability, p, that the detected pulse is actually a noise pulse. But if two detectors detect the signal pulse simultaneously, the probability that it is a noise pulse in the detectors is p2. Suppose p = 0.1. Then p2 = 0.01. Thus the chance of a false detection is reduced by the use of coincidence detection.

Issues to consider in the design of Muon (cosmic ray) Detectors

Muon Energy
Muons created by the interaction of cosmic rays and our atmosphere lose their energy gradually by ionisation of the material through which they pass. As they start with high energies they have the capacity to ionise many atoms before their energy is exhausted. Also, as they travel at nearly the speed of light, they tend not to ionise very efficiently and hence can travel through substantial lengths of matter, some metres of lead, before being stopped. Consequently, coincidence detection methods are the only real reliable way to discriminate between terrestrial radiation and cosmic sources.

Penetrative Terrestrial Radiation
I've been very surprised how penetrative local terrestrial radioactive sources can be. For example natural Cobalt-60 gammas can have energies up to 1.3 MeV and so could penetrate upto 10mm of lead. In all detector array designs either Geiger–Müller or Scintillator-Photomultiplier configurations, this can cause a substantial number of false detections. This particularly becomes a problem of detectors with small surface areas (aperture). Consequently, it is recommended that radiation shielding be included in your design to reduce the problem and increase reliability.

Compton Scattering
Compton Scattering is an effect where an interaction between charged electrons within the detector and high energy photons result in the electron being given part of the energy, causing a recoil effect of another high energy photon, which may enter into the adjacent detector causing a false coincidence detection.

In other words placing detectors too close to each other may cause cross-talk interference in coincidence mode, and so radiation shielding should be added or the detectors spaced further apart. However increased spacing also has the negative effect of decreasing the aperture of the detector and so the expected count.

Geiger–Müller Tube Detector Pulse Width
The Geiger–Müller tube is a very good detector of Muons however it would seem that filtering out background radiation using a simple coincidence detector systems alone is problematic due to the Geiger–Müller tube response and decay time (Pulse Width) when a muon has passed through and is detected.

Consequently, the wider the Pulse Width the greater the number of false positives. The means a pulse shorting or quenching circuit is also needed to shorten the Pulse Width to a period closer to the expected flight time of the Muon between tubes, but not too narrow that the electronics cannot measure relative coincidence. Some improvement might also be achieved by spacing the tubes further apart, but this also has the negative effect of decreasing the aperture of the detector.

Detector using Scintillators
As muons travel at nearly the speed of light, they tend not to ionise very efficiently and hence can travel through substantial lengths of matter, some metres of lead, before being stopped. This means that although a Scintillator-Photomultiplier detector has the potential to measure the energy of an ionising particle they can not discern between a muon and any other radiation caused by terrestrial sources and so must be used in a coincidence detection mode.

The major advantage of Scintillator-Photomultiplier detectors over a Geiger–Müller Detector is that a photomultiplier has a very fast response time and so more accurate than Geiger–Müller Detector in coincidence mode. Also as Scintillator panels can be made to have a much larger surface areas means a greater number of muons can be detected compared to other radiation caused by terrestrial sources, further increasing accuracy.

The major disadvantage of Scintillator-Photomultiplier detectors is cost and complexity.

Lead Shielding
Lead plays an important role as a material to shield against environmental radioactivity due to its high density and atomic number together with reasonable mechanical properties and acceptable cost. This role is however hindered by the unavoidable natural presence of Pb-210, which undergoes beta decay, with the consequent emission of gamma radiation.

Again why coincidence detection methods are the only real reliable way to discriminate between terrestrial radiation and cosmic sources.

Cosmic Ray (Muon) 18 Tube Drift Hodoscope

This project was an experiment to see if a multilayered array of Geiger–Müller Tubes (GMT) could track ionizing particles as they pass through.  The result is an interesting display demonstrating how cosmic rays travel down through the atmosphere at different angles.

Called a Hodoscope (from the Greek "hodos" for way or path, and "skopos:" an observer) it is a type of detector commonly unsed in particle physics that make use of an array of detectors to determine the trajectory of an energetic particle.
Cosmic Ray Drift Hodoscope

In the video random flashes are the result of terrestrial background radiation in and around the 18 GMTs but when you see a line of 3 or more simultaneous flashes these are the result of a muon (cosmic ray) passing though. The red LED flashes when more than three blue LED flashes and the level control sets the sensitivity.  


This is a very rough animation of how I first imagined the tubes would be triggered when a Cosmic Ray (Muon) flies through the detector array.
 
New version Cosmic Ray Hodoscope
Second Prototype still more work to do 24th March 2012, but getting there.
 
Rough Layout
First prototype above (June 2011) used 20GMT

In my first prototype I soon realised that doing coincidence in software was too difficult as the processing speed was fast then expected and so a gate array would be needed to pre-process the coincidence. Needless to say this would have made the detector quite large.
 
Consequently I redesigned a more compact designed using a smaller 18 GMT array and double sided PCBs rather than the stripboard I used above.
 
schematic of array
Schematic of 400V and 5 V power supply
 
9 Channel Detector Circuit

Circuit design for the 9 Channel  Geiger–Müller Tube Detector to 5V TTL this detector uses two of these giving a total of 18 outputs.

Note: The IC used in this desing a 74HC14 and not 74LS14.  The 74HC14 is a high-speed Si-gate CMOS device Low-power Schottky TTL. It provides six inverting buffers with Schmitt-trigger action. It transforms slowly changing input signals into sharply defined, jitter-free output signals.

 

The above circuit is design to discriminate between terrestrial background radiation and strikes that are the result of a muon passing through. This is achieved by adding a resistor in series with the LED array and measuring the voltage drop across it.  The greater the number of LEDs are lit simultaneously the higher the voltage across it.  A darlington transistor amplifier increases the voltage to set a level using a schmitt trigger which drives an LED indicating a muon was detected.  

9 Channel Detector PCB

Final PCB design of the 9 Channel  Geiger–Müller Tube Detector to 5V TTL

 
Geiger–Müller Array
20 wired GMTs installed between two plastic brackets which was changed to 18 for practical reasons.
 
Bracket for array
Drilled completed bracket for holding GMTs

 

Bracket for array
Drawing dimensions of the bracket for holding GMTs

Geiger-Müller Tube (GMT) CI-1G
I'm also using Russian Geiger-Müller tubes in this experiment which are described as being Gamma sensitive and available on ebay at very low cost less than the common SBM-20 Tubes that I have use before.

Specifications
Gamma Sensitive: unknown rate
Working Voltage: 360 - 440V
Plateau: Length/ Inclination: 80V/0,125%/V
Own Background: 0,4 Pulses/s
Load Resistance: 5 - 10 MOhms
Working Temperature Range: -400 +500 С
Length: 90mm
Diameter: 12mm

Cosmic Ray (Muon) 81 (9x9) Pixel Hodoscope

This  cosmic ray  detector works by detecting  muons which are a by-product of cosmic rays hitting our atmosphere. It detects these muons using Geiger Muller tubes - the very same type of detector used in a Geiger counter to measure radiation. However, this detector uses 18 Geiger Muller tubes that are arranged in an XY array of 9 tubes oriented on an X-axis and 9 tubes on a Y-axis.

Called a Hodoscope (from the Greek "hodos" for way or path, and "skopos:" an observer) it is a type of detector commonly used in particle physics that make use of an array of detectors to determine the trajectory of an energetic particle.

When a muon flies through the detector, it will trigger two tubes simultaneously.  By graphing which of the two tubes are triggered on an array of 81 LEDs, it gives an indication that a muon was detected as well as where it struck. 

The detector minimises background radiation using some shielding (brass plates) between the layers of tubes and also method of called coincidence detection.  Muons travel through matter very easily passing through the brass plates and both axes of the detector without effort, whereas the terrestrial radiation will not.  Consequently anything detected in both axes of the detector simultaneously is more likely to be a muon than local background radiation in, around and near the detector.

Matrix of GM Tubes

Figure 1. Basic overview operation of the 81 (9x9) Pixel hodoscope

Overview circuit

Figure 2 Primary overall circuit  using a simple LED Matrix for coincidence detection.

9 Channel Detector Circuit

Figure 2. 9 Channel Geiger–Müller converter to 5V TTL

Note: The IC used in this desing a 74HC14 and not 74LS14.  The 74HC14 is a high-speed Si-gate CMOS device Low-power Schottky TTL. It provides six inverting buffers with Schmitt-trigger action. It transforms slowly changing input signals into sharply defined, jitter-free output signals.

I made this PCB very generic so the design could be used in other projects like the 18 tube Drift Hodoscope.

9 Channel Detector PCB

Final PCB design of the 9 Channel  Geiger–Müller Tube Detector to 5V TTL

Geiger-Müller Tube (GMT) SI-22G

I'm using those good old Russian tubes again for this project. These are quite large 220mm with a diameter of 19mm. 

SI-22G

SI-22G Specs.

Working Voltage 360 - 440V
Initial Voltage 285 - 335V
Recommended Operating Voltage 400V
Plateau Length 100V
Plateau Slope 0.125% / 1V
Inherent counter background (cps) 1.16 Pulses/s
Cobalt-60 Pulse Gamma Sensitivity 540 pulse/mkR
Interelectrode Capacitance 10pF
Load Resistance 9 - 13 MOhms
Working Temperature Range -500 +700 ?
Length 220mm
Diameter 19mm

Case Wired
Complete Assembly with labling
 
Inside electronics
Complete wiring inside Box Arduino Mega PCP (not yet used) mounted on top of the passive parallel voltage summing circuit see figure 3.
 
Green LED Matrix
New Green 81 Pixel (9x9) LED Matrix Display Enclosure Inside
 
Green LED Matrix Outside
New Green 81 Pixel (9x9) LED Matrix Display Enclosure Outside
 
LED Matrix Display
Old Blue 81 Pixel (9x9) LED Matrix Display Enclosure Outside
 
Installing LED Matrix
Old Blue Inside the 81 Pixel (9x9) LED Matrix Display Enclosure
 
LED Matrix Display
81 Pixel (9x9) LED Matrix Display
 
Wiring Up
Wiring of each Geiger–Müller Tube
 
Connectors
Geiger–Müller Tube Anode and Cathode Clips each tube has been wired with LDR316 to reduce RFI
 
9 GMT Row
Basic arrangement of the tubes
 

Bottom Layer

Bottom Layer (foam layer is to prevent tube damage and prevent slipage)

Radiation Sheild

Assembled with shielding

Cosmic Ray (Muon) 81 Pixel Hodoscope with Midi Sound

The raw audio output from the Cosmic Ray (Muon) 81 (9x9) Pixel Hodoscope was a little hard on the ears so in an attempt to make this more pleasant, I modified the 9 x 9 matrix output by dividing into a 3 x 3 output using triple input NAND gates (74LS10) then monitoring coincidence between the resulting 3 x 3 matrix using AND gates (74LS08) to convert it to 9 channels, in order to drive a hacked MIDI Korg Nanokey 2 MIDI controller.

electronics inside midiconvertor

To do this, I modified the 9 x 9 matrix output by dividing into a 3 x 3 output using triple input NAND gates (74LS10) then monitoring coincidence between the resulting 3 x 3 matrix using AND gates (74LS08) to convert it to 9 channels in order to drive a MIDI keyboard.

Midi Convertor Circuit

Korg NanoKey2 USB Midi Keyboard
Hacked MIDI Korg Nanokey 2 MIDI controller

Midiconvertor

Cosmic Ray Pixel Hodoscope with generative graphics and music

My Cosmic Ray (Muon) Hodoscope now produces live generative graphics and music using an Arduino Mega and Ethernet Sheild over a network to a computer running software called Processing (PDE) and MaxMSP.

Arduino-Mega

Arduino-Mega Pin outs

Inside Hodoscope

Many thanks go to Sacha Panic for his enthusiasm for cosmic 
ray detection and talented imagination, time and skill in 
coding and graphics to make this work on my detector. 

I would also like to thank Luke Stark who has developed 
some wonderful music using MAX/MSP.

Code & Graphics by Sacha Panic:
http://omnime.blogspot.com

Music by Luke Stark
http://lukestark.com

Software 
arduino
Processing
MAX/MSP

Detector Hardware
Robert Hart 
Cocmic Ray Hodoscope
http://www.hardhack.com.au

Cosmic Ray (Muon) Detector using Geiger–Müller Tubes

This detector is to be used as test unit, to measure the performance of my other project using Fluorescent Tubes against in order to clarify and identify any issues, also to better understand and to also demonstrate the principles of a cosmic ray telescope.

Audio Recording of the Detector Outputs (1.35 MB Mp3)

Above is one of the first visual test of the circuit, which has been updated a number of times since this video. Although the new circuit produces less false positives and hence less flashes, the video here offers a good demonstration of what the output data looks like. The LED flash times are slowed by a one-shot timer, as the pulses are so short they would not be visible if the LEDs where driven directly.

 


Version 7. 1st August 2009

 

After a number of different configurations and tests, I have distilled the design down to a simple circuit seen here. The outputs 4,5,6 give a positive 5V logic pulse when a coincidence is detected in two or more of the tubes.

 

 

Although Geiger–Müller tubes are sensitive to Muons, the response time to decay (Pulse Width) when a muon is detected is relatively long for measuring the probability of coincidence in two or more the tubes. This means the wider the Pulse Width the greater the number of false positives. Consequently some means of pulse shortening is required to shorten the Pulse Width to a shorter period to decrease the probability that it is terrestrial radiation hitting the tubes in close succession.

 

 

The CRO trace above demonstrates what happens in this circuit when a wider pulse in feed in. The bottom trace is the output and only responds to a negative travelling pulse regardless of pulse shape. This is also important as the Geiger–Müller tube is positively biased and when a particle is detected the output swings negative, so the circuit ensures that only the first micro second of the detector pulse is processed in the coincidence circuit.

 

 

Why 3 tubes? I hear you say, well it is all about increasing the detectors aperture size to muons as most Geiger–Müller tubes available are longer than they are wide. So as an attempt to achieve a larger aperture as well as coincidence detection without using rows of tubes in each layer I am combining the coincidence outputs from top-middle and middle-bottom detectors.

 

 

The prototype provides six positive 5V logic outputs to a din socket. 1) Top tube - all detections 2) Middle tube - all detections 3) Bottom tube - all detections (all detections) meaning both cosmic and background radiation 4) Top and Middle - coincidence detection 5) Bottom and Middle - coincidence detection 6) "Top & Middle" or "Middle & Bottom" - coincidence detection (coincidence detection) meaning a stronger likelihood of a cosmic source than terrestrial source being detected. Outputs 4 and 5 are the main outputs, but to give some visual information that the detector is working I've added some LEDs driven by one-shot timers to give a 1/8 second flash, as the output pulses are only a micro second and wouldn't be seen if used to drive the LEDs directly. Output 6 drives the blue LED indicating a confirmed coincidence in two or more tubes and where outputs 1,2 & 3 drive the red LEDs indicating any detection in the adjacent tube.

 

 

Coincidence Detection The main idea of 'coincidence detection' in signal processing is that if a detector detects a signal pulse in the midst of random noise pulses inherent in the detector, there is a certain probability, p, that the detected pulse is actually a noise pulse. But if two detectors detect the signal pulse simultaneously, the probability that it is a noise pulse in the detectors is p2. Suppose p = 0.1. Then p2 = 0.01. Thus the chance of a false detection is reduced by the use of coincidence detection.

 

Detector Using 2 Pancake Geiger–Müller Tubes

I'm also making a two tube variation of the 3 tube design using Pancake Geiger–Müller tubes as they have a larger surface area.

Issues with detectors using Geiger–Müller Tubes

What should the count rate be?
The theoretical rate of cosmic rays is of the order of 1 count per minute per cm2 of active area, but it does depend on solid angle, so this number is only approximate. Assuming each GM tube has a broadside active area about 10 cm2, the number of counts maybe 10 per minute.

If the rate of each tube; S1, S2, and S3 counts per second and the coincidence gate width is τ seconds, then if counter #1 is ON S1τ , and the random coincidences in tube #2 at a rate R12 = S1S2τ random coincidences per second. So the random coincidence rate should be less than 1% of what is expected for the real coincidence rate, or about 0.1 counts per minute for a 10 cm2 Detector. (Many thanks to Bob S for this information)

Compton Scattering
One of the reasons for false counts in a Geiger–Müller array detector maybe due to Compton Scattering, where an interaction between charged electrons within the detector and high energy photons result in the electron being given part of the energy, causing a recoil effect of a high energy photon into the adjacent detector causing a false coincidence detection. In other words this causes cross-talk interference between GM Tubes

Consequently radiation shielding is required between each GM Tube of either 6mm of lead, 12mm of copper or 25mm of aluminium (note Iron is unsuitable). (Many thanks to Bob S for this information)

August 13th 2009 - To date tests carried out using radiation shielding between the GM tubes don't indicate that this is a real problem, however any cross-talk between each the tubes or the electronic is a real concern and should be design into any detector array.

Detector pulse width
In theory the Geiger–Müller tube is a very good detector of Muons (Cosmic Rays) however it would seem that filtering out background radiation using a simple coincidence detector is problematic due to the Geiger–Müller tube response and decay time (Pulse Width) when an ionising particle has been detected.

Consequently, the wider the Pulse Width the greater the number of false positives. The means a pulse shorting or quenching circuit is also needed to shorten the Pulse Width to a period closer to the expected flight time of the Muon between tubes, but not too narrow that the electronics cannot measure relative coincidence. Some improvement might also be achieved by spacing the tubes further apart, but this also has the negative effect of decreasing the aperture of the detector.

Coincidence
Although coincidence implies simultaneously, in reality we are talking about almost simultaneous, this is because a muon created by a cosmic event is travelling at near the speed of light 0.998c, so if the detectors are only spaced 2.5cm apart the actual flight time of a muon would only be 0.08ns. However as the detector and electronics response and delay times are slower than this, we can say in "real-life terms" it is simultaneous.

Sonification of Muons via Arduino and Max/MSP

I loaned my 3 Tube Muon Detector to Sebastian Tomczak who has rigged it up for some experimental sonification.

More information available on his website Little-scale

Cosmic Ray (Muon) Detector using Geiger–Müller tubes within lead shielding

This Geiger–Müller Array (or Geiger tube telescope) exploits an effect called Electromagnetic Cascade as a means of significantly increasing the effective aperture of the detector while reducing other issues I've identified in experiments with cosmic ray detection.

 

Muon Detector using Geiger–Müller Array and Lead Sheilding
Prototype v1. Construction of Lead Block Array

In a 1964 publication Bruno Rossi first described an experiment where cosmic rays could penetrate dense materials. Finding that cosmic radiation at sea level could penetrate over 1m of lead. In these same experiments he was also surprised to record a higher rate of detection as the thickness of lead increased peaking at 1.5cm and then falling slowly.

Consequently using a similar approach it is possible to improve a standard Geiger–Müller Array using a lead block in which the tubes are placed in an area which optimise these effects.

 

Muon Detector using a Geiger–Müller Array in  Lead Shielding
A Muon passing through lead will create electromagnetic cascades where they are detected by Geiger–Müller tubes.

The benefit of using this method not only enhances the count rate, but also allows the tubes to be moved into a parallel arrangement doubling the aperture of the detector over a conventional Geiger–Müller Array where the tubes are placed one above the other. While at the same time significantly reducing terrestrial interference with 15mm of lead shielding between each tube.

 

Muon Detector using a Geiger–Müller Array in  Lead Shielding
Prototype v1. Cut Lead Block block to size, drill holes, insert tubes and terminate.

Worse case terrestrial radiation may have energies up to 1.3 MeV but do not have enough energy to penetrate more than 10mm of lead and also cannot produce Electromagnetic Cascades, where muons created as a result of cosmic rays at sea level still have a mean energy of 4 GeVh or more and so can penetrate a metre of lead easily creating numerous Electromagnetic Cascades as they pass through.

 

Geiger–Müller Array Schematic
Prototype 1. Schematic of a two tube Geiger-Müller Coincidence Detector.

Using the circuit above the negative sawtooth pulses from each Geiger–Müller Tube (GMT) is converted into brief 5V square wave signals through a 74HC14 Schmitt Inverter and then further shorted to around 5uS. Unfortunately a Geiger–Müller tube response time to decay (Pulse Width) is relatively long for measuring the probability of coincidence in two or more the tubes. This means the wider the Pulse Width the greater the number of false positives. Consequently some means of pulse shortening is required to shorten the Pulse Width to a shorter period to decrease the probability that it is terrestrial radiation hitting the tubes in close succession.

 

The CRO trace above demonstrates what happens in this circuit when a wider pulse in feed in. The bottom trace is the output and only responds to a negative travelling pulse regardless of pulse shape. This is also important as the Geiger–Müller tube is positively biased and when a particle is detected the output swings negative, so the circuit ensures that only the first 5 micro seconds before entering a 74HC02 NOR gate which acts as a coincidence detector. Only when pulses are detected from both GMTs simultaneously within a 5uS window will there be an output, confirming the presents of an Electromagnetic Cascade within the Lead Block as a result of a high energy particle passing through.

 

Note that the output of the above circuit uses a 5V TTL to USB PCB this is because they are so cheap and I see no reason to reinvent the wheel, thank you to all Arduino enthusiasts everywhere. This PCB was purchased from Little Bird Electronics.

5V TTL to USB PCB

This allows me to link the output to the computer and log the count and even upload a live graph to the website. Unfortunately there aren't any win32 freeware or linux packages around and as I'm not a coder, I purchased a software package called Rad 2.4.5 which allows this and runs on both Win32 and MacOS.

 

 

Geiger–Müller Array prototype
Prototype 1. First rough prototype built - still more refinements but basically it works!.

Data-sheets of components used in the design
74HC02.pdf (451.58 KB)
74HC14.pdf (318.64 KB)
LM2575.pdf (725.34 KB)

Geiger-Müller Tube - SBM-20 / SBM-20U

I'm using Russian Hard Beta/Gamma sensitive Geiger-Müller tubes which are commonly available on ebay at low cost. I've purchased a few of these and they work quite well for gamma and xray sources. Which is ideal for this experiment as they are insensitive to low energy radiation and detect radiation along the wall of the metal tube.

Geiger–Müller Tube SBM 20

Specifications
Minimum Anode Resistor (meg ohm) 1.0
Recommended Anode Resistor (meg ohm) circuit diagram 5.1
Recommended Operating Voltage (volts) 400
Operating Voltage Range (volts) 350 - 475
Initial voltage (volts) 260 - 320
Plateau length (volts) at least 100
Maximum Plateau Slope (%/100 volts) 10
Minimum Dead Time (at U=400V, micro sec) 190
Working range (mkR/s) 0.004 - 40
Working range (mR/h) 0.014 - 144
Gamma Sensitivity Ra226 (cps/mR/hr) 29
Gamma Sensitivity Co60 (cps/mR/hr) 22
Inherent counter background (cps) 1
Tube Capacitance (pf) 4.2
Life (pulses) at least 2*1010
Weight (grams) 10 / 9

Cosmic Ray (Muon) Detector using Si Pin Photodiode

Just a note to say this project is currently having a rethink, due to some problems with noise induced by the PCB, even with shielding. So looks like I'm going to do a complete redesign. I still think it will work but each diode may will need to be FET buffered before amplification.

A Silicon Pin Photo-diode like the VBPW34FAS has been successfully used for the detection of Gamma Radiation and so in theory should also detect Cosmic Rays (Muons).  However, one very big drawback is their very small surface area. This is further complicated as they cannot easily be wired in parallel without decreasing sensitivity due to their inherent capacitance.

Cosmic Ray Draft Mechanical Layout

Experimentation has shown that 8 x photo-diodes can be paralleled before the problem becomes too over whelming.  This experiment will also use lead shielding to take advantage of electromagnetic cascade which can increase the aperture of a detector by allowing coincidence to be measured between individual detectors laying side by side and so providing a surface area of 16 x VBPW34FAS spaced apart evenly.

The below schematic is the first photo-diode amplifier stage which is based around the MAX4477 low-noise dual opamp and will be latter amplified using a high speed comparator and then coincidence circuit.  I will be develop this latter once the photo-diode amplifier stages are enclosed in shielding and optimum component values are determined.

 

Pin Diode Array Amplifier Stage PCB

Draft PCB of Pin Diode amplifier section

Si Pin Photo_Doide Array

Silicon Pin Photo-diodes are attached with a modified polyester varnish coating to reduce moisture

Array covered with light-proof shielding

Silicon Pin Photo-diodes covered in black resin and foil to block light

Cosmic Ray Neutron Monitor

Using a neutron detector to measure cosmic rays may sound odd, but this has been a common way to measure the level of cosmic ray levels since 1948. This is because if the primary cosmic ray that starts a cascade has an energy well over 500 MeV, and so many of its secondary by-products will be neutrons that will reach ground where they can be detected.  These systems are commonly called Neutron Monitors

Russian Neutron Pulse Corona boron Counter SI-19N

Recently some Russian Boron Coated Cathode Corona Pulse Neutron Tubes (SI-19N) became available on ebay at low cost and so I thought I'd see if I could also make one these guys.

List of materials required to build a Neutron Monitor:

  1. Reflector - 75mm of UHMWPE (Ultra-high-molecular-weight polyethylene)  or 280mm of Paraffin Wax.  Low energy neutrons cannot penetrate this material, but are not absorbed by it. consequently, non-cosmic ray induced neutrons are kept out of the monitor and low energy neutrons generated in the lead are kept in which is largely transparent to the cosmic ray induced cascade of neutrons.
  2. Producer - 40mm of Lead . Fast neutrons that get through the reflector interact with the lead to produce, on average about 10 much lower energy neutrons. This both amplifies the cosmic signal and produces neutrons that cannot easily escape the reflector.
  3. Moderator20mm of UHMWPE (Ultra-high-molecular-weight polyethylene) or 32mm of Paraffin Wax.  This slows down the neutrons now confined within the reflector, and makes them more likely to be detected.
  4. Nuetron Detector Tube - Boron Coated Cathode Corona Pulse Neutron Tube SI-19N. After very slow neutrons are generated by the reflector, producer, moderator, and so forth, they encounter a nucleus within the proportional counter which causes it to disintegrate. This nuclear reaction produces energetic charged particles that ionizes the gas in the proportional counter, producing an electrical signal. 
  5. Electronics - Very similar to a typical Geiger Counter circuit but with an adjustable High Voltage Regulated DC Supply 2-3kv

Neutron Monitor Layout

Draft Neutron Detector Circuit

Boron Coated Cathode Corona Pulse Neutron Tube SI-19N

Russian Neutron Pulse Corona boron Counter SI-19N

Specifications:
Operating  Voltage - 2000-2800 V
Working Voltage - 2400 V
Slop of plateau, % per 100 V - ≤ 3
Neutron sencitivity, pulses per neutron/ cm2 - 100
Plateau Length - 800 V
Own background, pulses/min - 5
Temperature range , 0 C  -  -50... +150
Diameter - 33.3 mm
Length  - 218 mm

 

Four Colour Cosmic Ray Detector

This Cosmic Ray detector uses three Geiger–Müller Tubes (GMT) where the detection of coincidence between any 2 or 3 GMT is displayed as a colour.

4 colour cosmic ray detector circuit

Cosmic Ray (Muon) Detector using Scintillators and Photomultipliers

Recently I obtained some blocks of Plastic Scintillator BC412 which measure 89mm x 89mm x 38mm and is ideally suited for detecting muons.

Scintillation occurs in the BC412 when exposed to ionising radiation with an energy between 100 KEV and higher and emits light between 420nM and 450nM (i.e. blue light)

Plastic scintillator Block BC412

The scintillator block will be coupled using Dow Corning DC4 to a 10 stage photomultiplier BURLE S83020F which is very sensitive to light between 350nM to 500nM.

10 stage photomultiplier BURLE S83020F

Dow Corning DC4 is mainly used in Aviation as an electrical insulator but because it is clear with a refractive index range of 1.4 to 1.5 it is similar to glass making it an ideal low cost choice Optical Coupling Grease between the scintillator plastic and photomultiplier glass envelope.

Layout sketch of muon telescope
Proposed layout of Prototype Version 2

More information soon...

Cosmic Ray (Muon) Detector using Fluorescent Tubes

This project was deliberately aimed at developing a very low cost cosmic ray detector using common Fluorescent Tubes. It was based on variation of an experiment performed in 2000 by the CERN (European Organization for Nuclear Research) laboratories by Dr. Schmeling which found a simple method for detecting and visualizing cosmic rays using everyday fluorescent tubes inside a wire mesh of feed with a high voltage.

There is a link here at the Teachers CERN Website at the bottom of their page, unfortunately there is little/no information about how this actually works.

However one of the very best websites I have found on working Fluorescent Tube cosmic ray detectors is www.astroparticelle.it if you are interested in this type of design you could do no better.

I have now begun building a number of other types of detectors due to a number of issues I've identified in experiments using Fluorescent Tubes.

Issues using Fluorescent Tubes

I have been testing a number of different design variations and have identified the following issues.

1) Power supply requires good filtering and regulation - Completed High Voltage Regulated Power Supply
2) Tubes vary in voltage requirements from one tube to another even between the same make, model and age
3) Oscillation is a problem as the supply voltage and/or coupling plate surface area increase
4) Internal filament electrodes must be insulated, even loose coupling increases oscillation and spurious pulses
5) Coupling plates should be positioned back 1cm from the tip of the internal filament electrodes
6) Oscillation occurs as the circuit forms a basic relaxation oscillator

Although oscillation is an unwanted artifact, it would also seem there is a point before oscillation begins where the tube increases sensitivity to radiation as the voltage increase and approaches a point where oscillation begins. However, radiation (cosmic or terrestrial) is also what first triggers the tube to jump into an unstable state before free oscillation begins.

Nevertheless, I will investigate this further to see how oscillation could be regulated through some form of negative feedback or quenching circuit as this may yield useful results.

Compton Scattering
Tests using a Geiger–Müller array detector have revealed a problem which will equally effect fluorescent tubes detector called Compton Scattering, this is where an interaction between charged electrons within the detector and high energy photons result in the electron being given part of the energy, causing a recoil effect of a high energy photon into the adjacent detector causing a false coincidence detection. In other words this causes cross-talk interference between Detector Tubes

Cosmic Ray induced radio emissions

The first experiment in which radio emission was detected from high energy particles was an array of dipoles was operated by a team of British and Irish physicists in 1964-5 at the Jodrell Bank Radio Observatory in conjunction with a simple air shower trigger. The array operated at 44 MHz with 2.75 MHz bandwidth. Out of 4,500 triggers a clear bandwidth-limited radio pulse was seen in 11 events. This corresponded to a cosmic ray trigger threshold of 5x10^16 eV and was of intensity close to that predicted. This has been further confirmed by many otherexperiments over the years and is now currently used in many well known projects such as LOFAR and at the Pierre Auger Observatory.

Cosmic rays are known to initiate a cascade of particle collisions in which large multiplicities of secondary particles of all kinds are produced. In the creation and annihilation of these secondary particles air-showers of charged particle are produced and travel down through the atmosphere near the speed of light to the ground. A large part of these charged particles consist of electron-positron pairs which emit a radio signal as they are deflected by the Earth's magnetic field. This process is known as a geo-synchrotron emission.

Radio signals produced are in the region of 10-100 MHz where most power received is at the lower frequencies due to coherence effects and so the spectrum begins to fall off at around 50 MHz. However due to short duration of the radio pulse typically less than 10nS it becomes increasingly difficult to measure at low frequencies and so most observations of cosmic ray induced radio emissions are made between 40 and 60Mhz.

Further due to the relativistic motion of these radio emissions they are concentrated into a beam in a forward direction so the footprint of the radio signal is concentrated around the particle shower by only several hundred meters. This makes the method of particle showers detection an ideal companion for other traditional particle shower observations by providing reinforcing information about the trajectory and energy of the incoming shower. 
 
As the number of particles in the air shower and peak radio signal correlate with the energy of the original primary particle and so the radio emission increases with the angle between the particle showers trajectory and the Earth’s magnetic field.

Cosmic Ray effects on Earths' climate

From the available research, there is no convincing evidence confirming  cosmic rays have a “major factor” in determining cloud cover. The ionising of air by cosmic rays will impart an electric charge to aerosols, which in theory could encourage them to clump together to form particles large enough to form cloud droplets, called "cloud condensation nuclei".

However, the majority of physicists who research this area say such clumping has yet shown to occur. Even if it does, it seems far-fetched to expect any great effect on clouds in the atmosphere. Most of the atmosphere, even relatively clean marine air, has plenty of cloud condensation nuclei already.

It is also not even clear whether the satellite measurements of changes in cloudiness are correct or how these changes have affected temperature, as it is unknown if clouds cover may mitigate global warming or amplify it.

Visit the CERN CLOUD experiment.

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For the record, the Administrator of this website agrees with the findings of the IPCC assessment of the scientific, technical and socio-economic information relevant for the understanding of the risk of human-induced climate change.

Radio Astronomy

Radio Astronomy only differs from traditional optical telescope astronomy in that they operate in the radio frequency portion of the electromagnetic spectrum where they can detect and collect data on natural radio emitting sources.

Atmospheric Transparency Spectrum
Atmospheric Transparency to different wavelengths of the Electromagnetic Spectrum

Using a number of radio receiving techniques, an astronomer can observe high energy interactions in distant celestial objects such as Pulsars or closer natural interactions within the earth’s magnetic field, solar flares and radio storms on Jupiter. Further, since radio waves penetrate dust, radio astronomy can be used to study regions of the sky that are not visible to conventional optical telescopes, such as the dust-shrouded regions where stars and planets are born, and the centre of our own Galaxy the Milky Way.

The radio Sky
For simplification Radio Telescopes come in five basic flavours:

  • Basic Receiver
  • Interferometer
  • Phase Switched Interferometer
  • Any combination of the above
  • Passive Radar (Meteorite Observation)

More information about Radio Astronomy and Radio Telescopes:

The Basic Radio Telescope

A basic radio telescope has the following attributes:

  • A sensitive radio which can receive one of the frequency identified for radio astronomy
  • The radio has "No" AGC (automatic gain control) or has the ability to turn it off.
  • It uses a high gain low noise pre-amp and a directional antenna which can be pointed at the sky.
  • A Data Logger is used to record total signal strength of the radio over a period of time

The signal strength of the radio is recorded over a period of time, signal levels will increase and decrease as a radio emitting object passes across the sky. Over number of days it is possible isolate radio astronomical observations from terrestrial and satellite interference.

Of cause everything is always a little more complicated. But it is possible and there are many examples of success to be found on the internet. The most famous of these is the NASA RadioJove Projects.

Radio interferometry

Radio interferometry is a powerful tool that can be used for a number of diverse applications. A radio interferometer consists of more than one antenna tuned to receive radio emissions from the desired frequency.

The antenna must be spaced more than 10 lambdas (baseline) apart East to West and following the natural rotation of the earth. The signals from the antenna is then cross-correlated in a Summing Amplifier at the input of the main radio receiver. As a radio emitting object passes above it produces a "fringe pattern" in the receivers measured signal strength, as the wave front of the radio emitting object passes in and out phase between each antenna.


From the Hans Michlmayr - Amateur Radio Astronomy Website

This fringe pattern can then in theory be analysed to produce a result ranging from an image of a distant astronomical object to the location of a nearby terrestrial or extra-terrestrial radio emitter.

The main limitation to the Amateur Radio Astronomer is not really the electronics but more the available space on your property. This is because in order to obtain a suitable fringe pattern the two antenna must be spaced at least 10 wave lengths (or 10 lambdas) apart. For example at 74Mhz VHF the distance between the to receiving antenna is more then 40 metres.

Radio Interferometry
Phase Interferometry
Interferometry

Phase-Switched Interferometer

Phase Switching is a system used to increase the discrimination and sensitivity of an interferometer; where an extra half-wave path difference is switched in, at well defined frequency, between the two interfering signal sources. In-phase signals then become out of phase and vice versa, so that the signal output becomes modulated by the switching frequency, and can be more easily filtered from the internally-generated noise. (The discrimination is highest for sources which are small compared with the interferometer-fringe spacing)

In the block diagram a phase switch is used to introduces either 180° or 360° (equivalent to 0° zero degrees) of phase shift into the right-hand transmission line, at a specific frequency easily demodulated by the receiver detector.

This switching signal generator is a square wave which changes periodically from one state to the other, many times per second, so that at one instant the first interference pattern is obtained, and at the next a second pattern. The same switching signal is applied to a phase-sensitive detector, which acts in synchronism with the phase switch and so subtracts the second pattern from the first. The resulting pattern is shown in the third part of Figure 1.; below, each maximum of the first pattern appears as a positive peak, but each maximum of the second pattern appears as a negative peak.

The instrument known as a phase-switching interferometerwas invented by Sir Martin Ryle in 1951, and is one of the major innovations in radio astronomy for which he was awarded the Nobel prize in 1974. This principle and later versions are now very widely used in radio astronomy.

You might ask, why go to so much trouble? Why not just use the simple adding interferometer and eliminate the phase switch and phase-sensitive detector? Although it is true the same information about a cosmic source is available in either type, the phase-switching instrument can be made much less sensitive to variations inherent in the receivers' electronics. Also, the phase switch causes the cosmic signal to be modulated at the switching frequency before it is amplified in the receiver. The noise generated by the receiver has the same general character as the cosmic noise, and this switch modulation acts as an identification tag helping to distinguish it from the receiver noise.

Also, the phase-switching interferometer responds less to extended sources, such as the general background radiation of the Milky Way, which might otherwise obscure the fainter radiation from weaker and small-diameter sources. In summary phase switching interferometers or more current versions, the correlator interferometer, are vastly superior to a simple adding interferometer and now universally used in preference to it.

"Phase switching is a clever trick how to make a basically additive interferometer behave like a multiplicative one. A plain additive interferometer has some undesired traits, like it outputs the fringes on a big DC pedestal, and needs the channels to be reasonably amplitude balanced to give good results. The phase switching is a way to avoid these." - Marko Cebokli

Information based on articles from Sky & Telescope by G.W. Swenson & W. Swenson, Jr.

Radio Astronomy Frequencies

Natural radio emissions from space cover the total range of the electromagnetic spectrum. However, on the earth's surface the majority of this spectrum is blocked by the earth's magnetic field and atmosphere only allowing few regions to pass. In the radio spectrum the earth’s atmosphere becomes increasingly transparent above 18Mhz and then increasingly opaque at around 40Ghz.

Atmospheric Transparency Spectrum
Atmospheric Transparency to different wavelengths of the Electromagnetic Spectrum

Any frequency above 18Mhz free from terrestrial and satellite interference can be used for radio astronomy. The lower segments of the spectra are used for solar and Jupiter observations; the 73, 150 and 406 MHz segments are quite popular for pulsar, and the 1.4 Ghz band and above is used for spectral line or energy measurements.

The following frequencies below are generally accepted spectral regions for radio astronomical observations and so have just chosen list the official regions as a reference, most accessible for an amateur radio astronomer.

  • 25.550 – 25.670 Mhz
  • 37.5 – 38.25 Mhz
  • 73 – 74.6 Mhz
  • 150.05 – 153 Mhz
  • 322 – 328.6 Mhz
  • 406.1 – 410 Mhz
  • 608 – 614 Mhz
  • 1.4 – 1.427 Ghz
  • 1.6106 – 1.6138 Ghz
  • 1.66 – 1.67 Ghz
  • 2.655 – 2.700 Ghz
  • 4.8 – 5 Ghz
  • 10.6 – 10.7 Ghz
  • 18.28 - 18.36 GHz

Amateur Radio Astronomy Frequency Choices

Most natural cosmic sources have spectra that fall off with frequency, so even if you keep the same antenna aperture (effective area) the signals will decrease with frequency.

Consequently the lower the frequency that is still transparent to the ionosphere (e.g. above 18Mhz) the greater the energy (signal strength) that can be collected by a specific gain of antenna. Said another way the better chance you have in detecting it.

What you gain by going up in frequency is:
- a narrower antenna beam (if you keep the same antenna area),
- less man made interference,
- more transparency to the ionosphere,
- a bigger possible bandwidth (if your hardware can eat it)

The relation between gain and effective area is

G = 4 * PI * A / L2 or A = G * L2 / 4 / PI

Where G is gain (linear, not dB), A is the effective area, PI is 3.14... and L2 is wavelength squared. Units for A and L2 are not important, but both must be given in the same units. The same area means more gain at a higher frequency, and the same gain means less area at a higher frequency.

Consequently from this reasoning the best choice of frequency would then be the lowest frequency that is free of interference that can be installed on the land area available to the Amateur Radio Astronomer. Land area becomes even a greater concern with interferometry as the antenna must be space apart East to West by 15 or more wavelengths to achieve a suitable fringe pattern.

74Mhz 16 Element Collinear Broadside Array

16 Element Collinear Broadside Array

In selecting an antenna for Radio Astronomy it is important to achieve a high degree of gain, low noise and have a a reasonable bandwidth for the frequency chosen.

After a review of many antenna designs, I have settled on a 16 Element Collinear Broadside Array as the most cost effective and high gain system to deploy on the 74Mhz band.

Element dimensions for 74Mhz
Each 1/2 wave feeder element = 1.948M
Each 1/2 wave reflector element = 2.064M
Spacing between feeder and Reflector = 0.771M
Overall dimensions = 6M X 4.2M X .771M

This is the basic electrical layout of the antenna it has balanced feed-line with an output impedance of between 300 to 400 ohms and an expected gain of 16dbi and a beam width of about 30 degrease.

16 Element Collinear Broadside Array

Each element is made of aluminium tubing and can be mounted directly using a simple U-clamp to welded steel frame without insulators. Affixed in the centre of the 1/2 wave element the impedance is at its lowest, so an insulator is not required.

16 Element Collinear Broadside Array

Collinear Broadside Arrays can also be connected in pairs simply, without the need of complex impedance matching networks.

16 Element Collinear Broadside Array

Antenna Aperture

A receiver antenna aperture or effective area is measured as the area of a circle to incoming signal as the power density (watts per square metre) x aperture (square metres) = available power from antenna (watts).

the aperture of different antenna

Antenna gain is directly proportional to aperture and generally antenna gain is increased by focusing radiation in a single direction, while reducing all other directions. Since power cannot be created by the antenna the larger the aperture, the higher gain and narrower the beam-width.

The relation between gain and effective area is

G = 4 * PI * A / L2 or A = G * L2 / 4 / PI

Where G is gain (linear, not dB), A is the effective area, PI is 3.14... and L2 is wavelength squared. Units for A and L2 are not important, but both must be given in the same units. The same area means more gain at a higher frequency, and the same gain means less area at a higher frequency.

Simply increasing the size of antenna does not guarantee an increase in effective area; however, other factors being equal, antennas with higher maximum effective area are generally larger.

It seems obvious to optical astronomers that a parabolic dish antenna that is many wavelengths across, will have an aperture nearly equal to their physical area. However other antenna such as a Yagi and Collinear arrays my not look to be the same at first glance but they do achieve the same result using other means at radio frequencies.

the aperture of different antenna

Basic VHF Radio Telescope

A few years back I bought some large VHF Broadside Antennas at a stock-take sale. So during one weekend, I thought I'd just weld up a stand and see if I could use them as a simple radio telescope.

Backyard radio telescope

Using a WinRadio WR-3700e Wide-band receiver and small preamp, I scanned the VHF spectrum within the antenna's designed frequency range for a radio quiet area where I could conduct a meridian drift scan of the sky.

WinRadio

After a week of scanning and logging, the quietest frequency identified was 231.58Mhz which was reasonably clear either side by about 1Mhz. The scans where conducted at a receive sensitivity less than 1uV, the bandwidth was 17Khz and was logged at 1khz steps, AGC (Automatic Gain Control) was disabled.

The purple line indicates the maximum signal strength detected over the 24 hours and similar the green the average and orange minimum. Note that over the 24 hour period, some RFI interference occurred at different times of the day. Nevertheless this could be reduced using a band-pass filter at a latter stage.

WinRadio

The audio of the receiver was connected to a computer using the sound card and was logged over 24 hours from 7pm to 7pm using the the famous amateur radio astronomer software Radio-SkyPipe and the results so far are not to bad for a first attempt.

Strip chart trace

The antenna was aligned approximately by eye to line up with the sun as it passed over, if there are any extraterrestrial objects it is difficult to verify, as no planning at all was attempted.

The next trace was recorded from 9pm to 9pm where the antenna was tilted directly vertical to zenith.

Strip chart trace

The last is an example of the noise generated by heat in the equipment without an antenna over a similar 24 hour period. Note that the noise floor has been amplified significantly.

Strip chart trace

The two antenna where stacked to offer a 32 element collinear phased array and should in theory offers a gain of around 20dbi and a beam width of about 18 degrees. Although the gain may seem low compared with microwave radio telescopes the all important aperture size is over 4 metres square. Also note that galactic noise is very bright compared to microwave in the VHF spectrum.

32 element collinear array

Interferometer Baseline

Most interferometers for radio astronomy are built on an east-west baseline and although this is not strictly necessary the operation of an east-west interferometer is the easiest to visualise. Also it is the easiest to interpret as the fringes recur more rapidly than those of any other baseline.

So how long should the baseline be?
In the vicinity of the meridian a baseline n wavelengths long would produce n/4 fringes per hour when a source on the celestial equator is observed. For example if the wavelength was 4 Meters (e.g. 74Mhz) then a baseline of 80 metres or 20 wavelengths would have a fringe rate approximately 5 fringes per hour or a fringe every 12 minutes.

Mapping the Radio Sky

Using a method called “Meridian Drift Scan Observation” it is possible to build up an image of the sky at radio frequency not visible using optical telescopes. As seen below.



The Radio Sky: Tuned to 408MHz Credit: C. Haslam et al., MPIfR, SkyView

Drift scans plot the sky line by line using the earths rotation from East to West then adjusting the antenna every 24 hours over a series of elevations separated by somewhat less than the angular beamwidth of your antenna. If you had a beamwidth of say 10 degrees, you would then lower the elevation by about five to seven degrees and making a strip chart for that elevation. You would continue the process until the beam was point a bit above your horizon and then combine the data to make a 2 dimensional map of the sky. In reality, there is quite a bit more to do this, but this is the basic Idea.

Here are some more examples:

The Infrared Sky (and more)

Polarisation of Radio Astronomy Antennas

Most natural signals (i.e cosmic sources) are almost always non-polarised (which is the same as "random polarised"), so the use of any single polarisation method either linear or circular will achieve the same result. The slight polarisation present in such signals do not bring any significant "power advantage" so in practice linear polarised antennas are preferred more in Radio Astronomy as they are more practical to construct for a specific gain over a circular polarised antenna.

Polarisation can however carry interesting information about the source, so radio astronomers sometimes want to measure this. However it is quite difficult to do, because the signal characteristics are so weak, and below a few 100 MHz, the polarisation information is usually too mixed up by the ionosphere to be of any practical use.

Information about Antenna Polarisation.

High Voltage Regulated Power Supply

This circuit is based around a cheap CCFL inverter module, in this case a surplus inverter from an old LCD monitor and the common LM2576 3 Amp Adjustable Switchmode Regulator which can be bought over the counter at any electronics shop like Jaycar.

HV Regulator

The output of the inverter is rectified and filtered and and then feed back into the feedback of pin 4 on the LM2576 through a voltage divider. The output of the LM2576 is then used to supply of the inverter.

The LM2576 maybe seem like over-kill but my aim is to be both accessible  and cost effective, and although there are better chips available unless your building a few hundred of these, it would be harder to choose a cheaper and more accessible alternative. The spin-off of cause is you can use this circuit with higher wattage inverters for other applications, and the LM2576 is fairly indestructible with thermal overload and short circuit protection built in.

High Voltage Regulated P0wer Supply

**note The component values in the circuit below maybe changed to achieve higher voltages by changing the value of the 1M resistor or R fb, the basic rule of thumb is for every 1M added the voltage is increase by 600V. So if you require 1.2Kv for a PMT, then the value would be 2M. Where the 2k2 trimpot offers the ability to adjust the output by 100V. The IN4007 is rated for 1000V so two diodes in series will be quite ok up to 2Kv. The capacitors in the HV filter are wired in series for higher voltages, although this does decrease capacitance and so increases ripple these inverters operate at a high frequency >20khz - 50Khz and so this is really not a big problem.

High Voltage Regulated Power Supply

Fake Geiger Counter Prop. for use in movie

I was asked by Christopher Jacobs of Longview Pictures a Melbourne based film company to build a Geiger Counter for his new movie LONE WOLVES

MK OUTLIER

As this project is a film prop, it dose not need to actually detect radiation nor will it need have any audio, as this will be dubbed in during editing. However, the unit must give the impression that it is operating and be able to be controlled both internally or remotely to indicate high and low levels of radiation during filming.

Fortunately, I had damaged 1960's British Army Geiger Counter which still had a meter inside which I extracted to form the basis of the Geiger Counter, (Any meter would do really) which not only added a certain realism, but also gave a familiar feel to old 50's nuclear scifi films which I personally love.

In the process I tried out a few different layouts and knobs, etc. before I got the right look.

Layouts and cases

Then I printed a Fascia label to give an impression that the knobs actually do something (which they do but not real Geiger Counter related).

But don't expect to see this unit looking so shiny in the film, as it will be most likely scuffed up and spray painted to give the impression it survived a strange apocalyptic disaster along with it's user.

Final Layout

The control circuitry is very basic and robust using an off-the-shelf flashing LED for the Power Indicator, this also provided a pulsating voltage source through a resistor network to modify the meters movements implying strange activity. 10K Linear Potentiometers are used to control the voltage to the meter from a small 6V battery pack and a 2 pole 4 position switch was used to switch between external or internal controls, and pulsating or smooth control.

 

Layouts and wiring

I installed a small 3.5mm phono socket at the rear that allows for the attachment of a remote control so that the meter can be controlled off-camera in a similar way to the internal knob in the video below. Where the different selections between smooth and pulsating control of the meter will give the film makers the flexibility for different scenarios during the film.

 

Lone Wolves - Teaser Trailer from Chris Jacobs on Vimeo.

250kv Hand Crank Marx Generator 20 Stage

The aim of this project is to build a hand cranked Marx Generator for display purposes. Where someone can wind a handle a few times and a loud bright snap of lightning ~10cm long accompanied with a cascade of 20 smaller spark gaps flashes at the same time.

An interactive, dangerous and loud electricity display. 

Marx Generator is a very simple and old circuit first described by Erwin Otto Marx in 1924. It generates a very high-voltage by charging a cascade of capacitors wired in parallel, then suddenly connecting them in series using spark gaps. Air breaks down at about 30kV/cm depending on humidity and temperature and when the arc forms it is virtually a short circuit and this is used to join the capacitor in series.  

The project part list so far

  1. The generator in this case will be a 200W 24V DC Motor with a gearbox.
  2. A High Voltage Invertor to step-up a voltage from about 9 to 20VDC to around 10 to 15Kv DC
  3. A 20 stage cascade of high voltage resistors and capasitors 42 x 1M 5Kv 3 Watt Rusian Resistors and 20 x 10nf 15Kv Capacitors
  4. Spark Gaps are 15mm round nickle plated solid brass draw handles x 40
  5. Full circuit diagram here : http://www.hardhack.org.au/files/Maxgenerator_0.jpg

HV Invertor  Marx Generator Stages

High voltage Invertor 15KV DC

 

First rough test of spark cap and RC combo

 

Second rough test of 2 stages in the correct circuit configuration

Capacitor Discharge Vortex Cannon

Vortex cannons are a device that fires doughnut-shaped air vortices. The vortices are able travelling several metres and can be visualised using smoke. Vortex cannons have been around for a long time from large weather cannons to everyday science toy.

Vortex Cannon

The aim of this project is to build portable rapid fire electric vortex cannon using a large woffer speaker and high voltage capacitor discharge circuit.

Capacitor discharge circuit

Vortex Cannon Front

Bush Button

Capacitor Discharge Box

 

Direct Conversion Software Defined Receiver

I recently purchased and built a low cost Soft66Lite kit which is a Direct Conversion (DC) Software Defined Receiver (SDR) the simple cousin of the well known Software Defined Receivers and unlike the early Direct Conversion Receivers of the past, as the mixer stages are based on a Quadrature Sampling Detector (QSD).

Direct Conversion Software Defined Receiver

In the Direct Conversion SDR version, the radio frequency (RF) signal is first down converted to an audio frequency (AF) where it is then sampled by a high performance stereo audio card or Analogue-to-digital converter (ADC). Then through the use of digital signal processing (DSP) it can be filtered and enhance to demodulate many modulation systems including AM, CW, SSB, FM and a variety of digital modes.

Direct Conversion Software Defined Receiver

Quadrature sampling detector (QSD)

A QSD is a system that switches the incoming RF signals into in-phase signals (I) and quadrature signals (Q) by the frequency of the local oscillator. The in-phase signal is the first 90º of the RF signals waveform (I) and the quadrature signal is the second 90º segment of the RF signals waveform (Q).

Mathematical functions can be used by the software to calculate the phase and amplitude of the original signal by measuring the values of I and Q simultaneously which has all the information contained about the original RF signal in it.

Direct Conversion Software Defined Receiver

SDRs have become increasingly popular in recent years due to their relative low cost; the ubiquitous availably of high speed computers and they are significant flexible in terms of bandwidth and demodulation in comparison with traditional superheterodyne receivers. So I thought I might be good to build a few different units to gain an understanding of these receivers and see if these low cost radios can be employed in a Radio Telescope project at least in the latter IF and Detector stages.

Examples of software used include:

 

174Mhz Receiver with 10.7Mhz SDR IF Detector

I've always thought a low-cost single band Software Defined Radio (SDR) might be used to convert a VHF or UHF FM Radio into an "All Mode" Receiver. Recently I came a across a low cost PLL VHF 174Mhz FM 0.2uV telemetry receiver card on ebay. So I have removed a few component to disconnect the 455khz down converter and FM limiter and then wired in the software defined radio tuned 10.7Mhz into the IF. I'm pleased to report this actually works.

Direct Conversion Software Defined Receiver

VHF SDR 173Mhz

Using a 48Khz USB Sound card wired in directly and the WRplus SDR Software and a Signal Generator tuned to 173.308Mhz

SDR 173.308Mhz

Signal Generator tuned to 173.328Mhz giving this reciver a bandwidth or tuning range of 24khz

SDR 173.328Mhz

10.7Mhz Crystal Oscillator

10.7Mhz Local Oscillator on the SDR PCB

Electric Go-Cart built from roadside junk.

This electric Go-Cart was built completely from roadside junk over a year period and was completed in 2001 as the result of a challenge I had with the young man in the photo. He didn't believe anything was really fun or cool unless it was new and cost money, so after some discussion the challenge was to help him build a go-cart entirely out of road-side junk.

One of my most fond childhood memories is the rumble as a dozens of kids racing down the road on billy-carts, made from a hodge-podge of road side junk in the 70's. The junk in those days was not much different to what we see today, but we always found ways to cobble something mobile together and role down a hill on it.

Unfortunately, today flocks of kids riding down the middle of Suburban Streets without a helmet and breaks is very much frowned upon.

Electric Go-Cart built from roadside junk.

Specifications

  • No electronics, this same cart could have been built 50 years ago
  • Three wheeler with rear wheel drive
  • 4 x 12V SLA Batteries of dubious quality from an old UPS
  • Frame made from cut up furniture and other scrap metal found about.
  • Single gear drive made from two washing machine pulleys and a car fan belt.
  • Two tyres found on a broken sack-truck, the other on a wheel barrow.
  • Seats where used from two different chairs.
  • Contactors, wire and switches found in a factory yard being demolished (permission given)
  • Motor is a 24V truck starter-motor of unknown origin, also found in factory yard
  • Left button on the H steering for full forward
  • Right button on the H steering for full backward
  • Braking is achieved by going in reverse (doesn't work when batteries are flat)

Horrifyingly bad steering and stability, wheel spins when taking off from a stand-still and very dubious braking, batteries went flat in 15 minutes and took 12 hours to charge - all in all, a great success!

10 Years latter

An old electric go-cart I built about 11 years ago, Charlie (my son) was asking about it, so we got it out of the shed and dusted it off. Still runs just needs batteries.

10years latter
My son Charlie and daughter Eva 2011

Electron particle accelerator

Experimenting with speeding electrons (draft)

When a sufficient high voltage is applied across two electrodes inside a vacuum chamber, electrons are liberated from the negative charged electrode (cathode) and stream across the vacuum to the positively charged electrode (anode) this stream of electrons is commonly called cathode rays.

Vacuum Chamber

This high voltage accelerates electrons to a high velocity (about 59,000 km/s, or about 20 percent of the speed of light at a voltage of 10 kV) due to their low-mass. When they get to the anode at the other end of the chamber, they have so much momentum many fly past the anode and strike the wall of the chamber. When they strike the wall of chamber they knock the orbital electrons of the atoms in the wall into a higher energy level. When the electrons fall back to their original energy level, it emits a photon (light) such as a green glow in the case of a glass vacuum chamber.

If a few atoms of gas remain in the chamber this will cause the cavity between the electros to glow. Although this useful in cold cathode applications, too much gas has the an unwanted affect as electrons will only travel a short distance before hitting a gas molecule. So the current of electrons is moved in a slow diffusion process, constantly colliding with gas molecules and never gaining much energy.</p>

Vacuum Chamber with traces of gas

If the cathode is heated, electrons will flow more really, at lower voltages at increased current, in much higher vacuum because the added thermal energy overcomes the binding potential of the atoms in the metal cathode this is called thermionic emmission.

thermionic emission

With a reliable stream of electrons it is possible to focus the electrons into a beam, accelerate it and even bend the beam using an electrostatic or magnetic field.

Electron Gun Electrostatic Deflection                  Electron Gun Magnetic Deflection

Fluorescent Tube Oscillator

This project is yet another spin-off from my Cosmic Ray Detector Project. I recently stumbled across this as an unwanted artefact in the detector and so I thought I'd let people know as it might make an interesting project for electronic music people.

(Yes I know the same thing can be made very cheaply with other components, it is just a kooky oddity)

When exploring into this artefact in detail, I found I could make a very effective relaxation oscillator using only a fluorescent tube and a couple of components, which will resonate at a specific frequency and with few additional components the frequency and distortion could also be adjusted.

I imagine it would make a very strange looking electric instrument indeed arranged with a number of tubes in front of a keyboard and a panel of control knobs. Where the tubes would glow and flicker as they where activated.

Here is a bench top test, the filament voltage is set between 7 to 9V in this example it is set at 8V just a very faint glow, the capacitive trigger is set at -350VDC (copper tap around the tube). the Cathode to Anode Voltage is being adjusted from 2V to 100V and oscillation begins at 47VDC up to 100 and down to about 33V where it ceases in the video (Note the distortion begins around 45V and down).

The circuit is basically a Thyratron Valve driven relaxation oscillator and emits a Sawtooth waveform. R1 is 10K ohms and C2 is 10nF (note voltages are estimates and will vary from one fluorescent tube manufacturer to another). The foil tube coupling could be replaced with wire mesh to allow the light to be seen easily.

Fluorescent tube oscillator

High Voltage DC Supply

Warning High Voltage

SAFETY NOTE: Please do not attempt to recreate the experiments shown on this page unless you are familiar with High Voltage Safety Techniques! Direct Current even above 60V maybe lethal even when the AC supply voltage has been disconnected due to the stored energy in the capacitors.

I wanted to build a reliable high voltage DC supply for some cathode ray and simple particle accelerator experiments I am planning and here is where I'm up to so far.  A voltage multiplier also sometimes called a Cockcroft–Walton Generator or Villard Cascade is a circuit that converts AC or RF power from a lower voltage to a higher DC voltage using a network of capacitors and diodes.

A single secondary winding HV transformer is the most easily accessible and so I experimented with a few different variations finding that using two cascades of opposite polarity at the same time gave better results than a single long cascade.

Stacked Villard Cascade Voltage Multiplier

This is the result of an actual 16 stage voltage multiplier using a low current ~1.5kv AC input:

However by stacking the two cascades we can not only double the output voltage but also improve ripple and capacitor charging characteristics than could be achieved using a single long cascade for the same input voltage.  Here is the result of two 8 stage cascads stacked together using the same 1.5kv input supply in the previous video above:

The next challenge has been the high voltage AC Supply to drive the voltage multiplier and the best candidate for this seemed to be a resonate fly-back inverter the type that many people use for Plasma balls and Kirlian photography as the circuit is quite simple and doesn't require a very heavy mains transformer due to the high frequency used.

After some experimentation with different circuits I found that the impedance of the Flyback Transformer, the load and the value of CR where critical and I am now thinking resonate fly-back inverter disign is not the best, but the below circuit does work to give me approximately 140kv at 20V DC in.

Flyback Inverter Circuit

 

The next circuit I tried was a Mosfet resonate based design called the Vladimro Mazzilli Inverter this circuit is very effective and can easily burn out your secondary HV winding if not well insulated.

Vladimro Mazzilli Inverter

 

 

High Voltage Power Supply 0-15KV DC

This is a basic unregulated 100VA 5KV Transformer with a Voltage Multiplier, which can be adjusted using a Variac.

Used with a variac it provides a simple high voltage DC supply for experiments.

Jacob's ladder (traveling arc generator)

Travelling Arc

A Jacob's ladder is a wonderful exotic-looking display of electric white, yellow, blue or purple arcs, which is often seen in films about mad scientists. As a boy I was always fascinated by these in science displays, and as they were often powered from mains electricity it also gave off a wonderful 100hz v,v,voop! busts of sound as well.

Please note: A traveling-arc device is very dangerous. The spark can burn through paper and plastic and start fires. Contact with the high-voltage conductors can be lethal even if the high voltage power supply originates from a battery.

Jacob's ladder (travelling arc generator)

A Jacob's ladder (more formally a travelling arc generator) is a device for producing a continuous train of large sparks that rise upwards. The spark gap is formed by two wires, approximately vertical but gradually diverging from each other towards the top in a narrow V shape.

When a high voltage approximately above 10,000v is applied to the gap, a spark forms across the bottom of the wires where they are nearest to each other, rapidly changing to an electric arc. Air breaks down at about 30kV/cm depending on humidity and temperature.

When an arc forms it is virtually a short circuit and so the voltage drops and the current rapidly raises and will draw as much current as the power supply can deliver. Consequently some form of current limiting is required to sustain the arc without destroying the power supply.

An electric arc is essentially hot ionized air and so it will rise carrying the current path with it. As the trail of ionization gets longer, it becomes more and more unstable and finally breaks. The voltage across the electrodes then rises and the spark re-forms at the bottom of the device.

Requirements

  1. High Voltage Transformer or Inverter greater than 8kv with current regulation (neon transformers are ideal)
  2. Electrodes that can support their weight and be shaped into a V.  Stainless steel rod is good, the resistance of the metal provides more current regulation, it is strong and dissipates heat well.
  3. Insulators to mount electrodes that  both insulate a High Voltage and heat (Ceramic is best)
  4. Ventilated metal enclosure for the transformer to avoide fire risk
  5. Ventilated glass case to enclose the whole display, this device is dangerous not only electrically it is also a fire risk, plastic burns.  Ventilated as it can produce fumes of ozonecarbon monoxidenitrous oxide and other compounds.
  6. The glass case needs a firm base to avoid tipping, lockable to avoide people opening it and more than one emergancy off switch. 

My entry into the 2015 Hackaday Prize

My #2015HackadayPrize entry more details here - http://hackaday.io/project/5103-smart-dew-point-water-harvester

Harvesting clean water from air, using the cold storage of coolant when the sun shines, then using it at optimum dew-point conditions.

Dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air. The condensed water is called dew when it forms on a solid surface. 

Harvesting water from air is not a new idea however many systems rely on environmental conditions or large amounts of energy. This system uses what is known about dew point water harvesting and tries to optimize the conditions in the most "energy convenient" way. 

The system would be powered by a solar/battery system, however rather that just relying on storage batteries most of the solar power would be used to cool liquid coolant in an insulated tank. This cooling process would only run while the sun shines. A controller logs daily barometric pressure, humidity and temperature to calculate when to run the dew point water harvesting at the most optimum time.

Overview Flow Diagram

Project Conclusion

This was a crude prototype for testing and proof of concept. Which has demonstrated there is significant energy available from a solar panel to cool over 20 litres of liquid well below -4C in less than 6 hours using off-the-shelf peltier coolers. Further that liquids can be stored over 48 hours and used later to dehumidify air when conditions are best and collect water for drinking. Cooling could be significantly improved using a compressor refrigerator unit with better energy efficiency but at a greater cost. Dehumidifying the air could be significantly improved with better vessel and distillation coil design. The system could be scaled up or scaled down. Coolant storage is not required if batteries are used but this also comes at greater cost. The system could be run while the sun shines if sufficient humidity is available and the dehumidifer vessel is appropriately insulated.

Parallel Port Robot Control Pin-Out

This is very much a work in progress, just to keep me thinking about it.

I have used Parallel Port controllers as a very simple switch and sensor, this project is to develop a very low-cost simple computer controller for robot of a reasonable size.

Basic circuit
The basic circuit above only shows one relay, but this chip will support up to 7 relatively large 12V relays.

Previous Prototype
Above are two examples of previous projects, one is made inside a D Connector, and the other is a test unit with LEDs and terminal block.

Output

Pin

State = 0

State = 1

D0

2

Left motor power off

Left motor power on

D1

3

Right motor power off

Right motor power on

D2

4

Left motor forward

Left motor reverse

D3

5

Right motor forward

Right motor reverse

D4

6

Left motor slow

Left motor fast

D5

7

Right motor slow

Right motor fast

D6

8

Light On - OK

Sound Alarm - Not OK

D7

9

Regenerative Brake Off

Regenerative Brake On

Input

 

This is a very simple circuit.

0V=State 0, +5V=State 1

Acknowledge

10

Motor power is Off

Motor power is On

Busy

11

No Obstruction

Obstruction Rear

Paper Out

12

No Obstruction

Obstruction  Left Front

Select

13

No Obstruction

Obstruction Right Front

Error

15

Distance Pulse Off

Distance Pulse On

Notes:
1. Main motor controls are not powered up until system in right state (so it does not matter if PC data pins change state at boot-up).
2. Start control software to sets parallel ports to the right state
3. Find someone to help write code ;-P

Simple 3 Amp Step Down Switchmode Regulator

Although this example is 5V, there are also 3.3V, 12V, 15V, and adjustable output versions of the LM2576 (see attached datasheet).

The board layout here is using a simple Vero Board which are available from just about any electronics store

Except for the Adjustable output version the same layout can be used for each.

Note: Pin 5 (which is grounded below) can also be used to switch the external loads on/off via a logic input e.g. 0v or 5V, for example an LPT port.

The boards below where built for projects in the Air-Stream Wireless Network as the circuit is ideal for Power over Ethernet (PoE) applications where a Wireless Access Point is mounted up on the mast.

Solar Cooker

January in Australia is summer, and it is then we have our summer holidays. In Adelaide where I live it is also the hottest time of the year, sometimes reaching temperatures of 45 Degrees Centigrade (113F) with clear blue skies and weeks without rain. 

Ideal weather for solar experiments with the kids, as they tend to become a little crazy staying inside out of the sun.

Attach cast-iron pot

On 5th January 2013 I was trying to clean my workshop when I came across a big roll of self-adhesive foil tape and just at the same time my daughter Eva (4yo) decided she wanted me to do something with her and it was then I had an idea. "We can make a solar cooker with this" I said, "can we cook sausages on it?" said Eva, "yes maybe lets see."  

I also got out an old off-set parabolic satellite dish I'd been keeping in the shed and so Eva set about peeling the backing of the foil tape while I stuck it on the dish reflector.

120cm offset dish Eva peal

After about 30 minutes we had a big mess and had covered the whole reflector with foil tape.Pealed tape

Stick on the Tape

I also soon learned very quickly that you must wear protective eye covering if you want to keep you're eyesight. Gas welding goggles I found are ideal to align the dish, as even a brief flash from the reflector can cause you to see spots for some minutes after.

Welding goggles

I sat a cast-iron pot in a loop of wire tied to where the LNA is usually mounted and I adjusted the focal point balancing on a base of bricks. The temperature measured inside the pot was averaging between 165 to 220C (329 to 428F) at 11:30am, (this was difficult to measure without burning my fingers).

Attach cast-iron pot

Ok so we didn't cook sausages, as Eva's mother loves baked potatoes, it was an easy first try not requiring turning.

Baked Potatoes

I pre-heated the pot first by pointing solar reflector on it for about 30 minutes, wrapping some potatoes in foil and popped them into the pot with the lid on. The reflector required reposition every 15 minutes for 1.5 hours and voilà baked potatoes! Both potatoes where soft and cooked through, so I reckon 1 hour would have easily done the job.

Baked Potatoes

While I was testing, I also tried boiling water, this took about an easy 30 minutes.

                  

 

           

 

 

 

 

Solid State Gamma Ray Detector

Current project areas I've been experimenting with such as: cosmic ray detectors and x ray crystallography have relied heavily on Geiger–Müller tubes or photomultipliers and Scintillators as the detector. The issue with using these deectors are a limited life and high voltages between 300 to 1600V DC which must also be low noise and regulated. Further without going into detail here, there are significant cost issues when using new components and even more so when needing to measure the energy level of the radiation being detected.

Solid state devices particularly Si Pin Photodiodes are capable of measuring both gamma rays and their energy level but also come with their own issues and compromises such as: more complexity, noise, cost and small aperture size. But also have the benefit of low voltage, power and greater longevity. The aim of this project is to develop a relatively cost effective detector that can measure gamma rays and also offer some usable energy resolution.

There are low-cost of-the-shelf Pin Photo diodes such as the BPW34F which have been featured in many DIY projects over the years. However these require significant amplification, very noisy and very susceptible to RFI. So can only be practically used as a simple gamma counter, with no energy resolution and has very low sensitivity having a very small aperture.

There are also specialist Photodiodes designed specifically for gamma ray and xray detection, but these are very expensive and difficult to source in small quantities. So the next best candidate are the medium range detectors usually with a 10mm x 10mm aperture, which come with and without a light shield. Current detectors I am testing include:

  • Manufacture First Sensor Part # 5014450 - has visible light filter
  • Manufacture First Sensor Part # PS100B-7-CERPINE - has visible light filter
  • Hamamatsu Part # S3590 - no visible light filter

Basic Circuit:

Gamma Detector Circuit

Check Source:

The check source I'm using in these experiments is on the side of an old CD V-700 Geiger Counter which uses an isotope of radium 226Ra and has a half-life of 1,600 years. During decay it mostly emits alpha particles with an energy of 4.7843 MeV followed by 4.601 MeV which are not detectable by a solid-state detector. Fortunately the decay products go on to futher decay and emit a gamma ray at an energy of 186 keV which can be detected. 

Check Source 226Ra

Thomson's jumping ring experiment

This project is being designed for SciWorld a South Australian not-for-profit organisation full of people who are passionate about science. They provide science outreach programs in various locations around Adelaide and South Australia. 

The jumping ring experiment demonstrates how a conducting non-magnetic ring can be thrown into the air using an alternating magnetic field. The well-known experiment was originally discovered by Elihu Thomson an English engineer and inventor (March 29, 1853 – March 13, 1937).

An aluminium, copper or brass (non-magnetic) ring is placed over an iron core with a coil at the base. The coil is connected to an alternating current (AC) supply and when switched on the observer(s) will see the ring jump quickly into the air reaching a height of about 1 meter.

The height of this jump can be dramatically increased by cooling the ring to the temperature of liquid nitrogen (-196 °C). The ring may easily jump to a height well over 6 meters!

The coil, the ring and the core act as a transformer. The ring in this case can be considered as the secondary coil. The induced current in the ring produces a magnetic field in such a way that the ring is repelled. A stronger magnetic field is produced when the ring is cooled, so it will jump to a greater height.  At low temperatures, metals will have lower electric resistance and so electric currents can reach higher values, and so the repelling force will be stronger.

Draft design in planning stages - 07/12/2104

Jumping Ring

 

Wire Cut and Straightening Machine Upgrade

At SA Group Enterprise, where I do real work, one of our businesses SA Wire Ware had just purchased an old 1960s Wire Cut and Straightening Machine, from NSW. Which we have done before with other equipment like spot welders and break presses and other machines. Although many of these machines can be purchased new, they are very expensive and not generally available in Australia. Also the fact is many of these machines haven't changed much in 40 years except for running a little faster and other control electronics. With a little effort fixing they are well worth considering as they are usually over engineered, build like a truck and so last for many more years.


Wire Cut and Straightening MachineWire Cut and Straightening Machine
Before and After

Here is the machine operating after the upgrade.

Sequence of construction Remove all the old and dubious wiring clean the machine.

Wire Cut and Straightening Machine Wire Cut and Straightening Machine

Wire Cut and Straightening Machine Wire Cut and Straightening Machine Wire Cut and Straightening Machine
Then a new controller and termination box was built and installed.

Wire Cut and Straightening Machine Wire Cut and Straightening Machine Wire Cut and Straightening Machine
Wire Cut and Straightening Machine Wire Cut and Straightening Machine

X-Ray Crystallography

The aim of this project is to use a narrow beam of X-Rays to produce an image/data that reflects the atomic and molecular structure of atoms in a crystal. The method used is called X-Ray crystallography where a narrow beam of X-rays is fired at a crystal, although most will pass straight through some of the x-rays are diffract by the lattice of atoms arranged in a crystal which sum and subtract to create an interference patterns at an angle to the main beam.

Braggs Law

Crystals are regular arrays of atoms, and X-rays can be considered waves of electromagnetic radiation.  Atoms scatter X-ray waves, primarily through the atoms' electrons. Just as an ocean wave striking a lighthouse produces secondary circular waves emanating from the lighthouse, so an X-ray striking an electron produces secondary spherical waves emanating from the electron. This phenomenon is known as elastic scattering, and the electron (or lighthouse) is known as the scatterer. A regular array of scatterers produces a regular array of spherical waves. Although these waves cancel one another out in most directions through destructive interference, they add constructively in a few specific directions, determined by Bragg 's law:  2d \sin \theta = n \lambda

I bought an X-ray tube for this project, to provide a narrow beam of x-rays. It's called a diffraction transmitting target x-ray tube made in Soviet Russian times during the 1990s type BS7-W. As it turned out the design of this tube is quite unusual, but nevertheless it works quite well and produces a fine beam of soft x-rays and a little more safer than other tubes to work with.  

More details about this here:   X-ray tube - diffraction transmitting target (Russian BS7-W)

As the tube requires a modest operating voltage of 15Kv and current for the Anode and a small voltage of 1.5V for the filament the power supply t was relatively easy to construct using commonly available components. 

Dual Power Supply

 

Here is the first test of the tube in operation. The Geiger Counter is first checked against other radioactive sources to gauge roughly relative output levels. 

 

 

Power Supply and X ray Tube

X-ray tube - diffraction transmitting target (Russian BS7-W)

X-ray tube  Diffraction  transmitting target BS7-W

I bought the above X-ray tube for a  X-Ray crystallography project I'm currently working on - It's called a diffraction transmitting target x-ray tube made in Soviet Russian times during the 1990s type BS7-W. They are available from a store in the Ukraine called Soviet Radio Components.

Unfortunatly the english translated datasheet isn't that helpful other than some operating numbers.

  • Operating voltage is 10kV max 15kV
  • Filament voltage is 1.2V max 1.5V
  • Beam is 5 degrees

As there is no pin out information either, my first attempts to use the tube had mixed results. Nevertheless I was able to able to produce quite a nice fine beam of x-rays before blowing the filament.

Although blowing the filament wasn’t really the best result, it did give me the opportunity to break open the tube and find out how it ticked.  As it turned out this was a very worthwhile and interesting process, because it was not built in a way I expect almost the reverse. I was also left with a Beryllium x-ray window which I can use for the light screen in an x-ray detector.

How it works

The design of this x-ray tube is quite the reverse of most x-ray tubes I've seen, nevertheless it does produce a fine beam of
x-rays.  But how it does this is a bit mysterious.

X Ray tube pin out

 

Typical x-ray tube
In a typical x-ray tube, X-rays are produced when a beam of electrons emitted by a filament in the Cathode are accelerated by a high voltage potential between the Cathode and Anode.  The beam of electrons produced hit the Anode and are suddenly decelerated upon collision with the atoms in the metal Anode. 

Typical Xray Tube

These x-rays are commonly called brehmsstrahlung or "braking radiation". If the bombarding electrons have sufficient energy, they can knock an electron out of an inner shell of the Anodes metal atoms. Then electrons from higher states drop down to fill the vacancy, emitting x-ray photons with precise energies determined by the electron energy levels.

X-Ray Source using Vacuum Tubes

This X-Ray project is a spin-off of the Cosmic Ray Detector Project to find a suitable radioactive source for testing. So with a little googling I've found its quite simple to produce x-rays if you have a high voltage DC source in excess of 45Kv and a suitable vacuum tube.

X-Rays and High Voltages are very dangerous always be careful and use a Geiger Counter.

Only for people experienced in working with high voltages

Here are some useful links I found:

Dangerous Laboratories

The Bell Jar

High Voltage and X-Ray Experiments

The X-ray page

Jochen's High Voltage Page

So it is quite lucky I've held onto those TV rectifiers and beam triodes that I had in the shed.

My first tests where very limited using a 50hz hv supply and half wave voltage multiplier. This is because you must use a higher frequency ac supply to archive any level of current, when using low value capacitors. I achieved ~55kv with a ten stage multiplier with a ~5kv 2khz ac supply using affordable 10nf 6kv capacitors.

Achieving an increase in the rate of clicks on a Geiger Counter above normal background levels which has been just enough to test the cosmic ray detector elements.


xray prototype one

Community Wireless Networks

My involvement in Community Wireless Networks came about, as a result of experiences and challenges establishing a wireless network between different office locations in order to reduce IT costs within my organisation in 2001. From this experience I realised that Community Wireless Networks offer many benefits for the broader community and other non-profit organisations like my own.

I have been a member of a group called Air Stream Wireless since 2002, and involved in the establishment of a number of key sites in the network and was voted onto the committee in 2004 holding the position of Secretary till October 2008. I have recently retired from committee due to extra commitments at work and home with the birth our second child (daughter). However, I intend to continued my participation as an active member and strong advocate for Air-Stream Wireless.

It also happens to be quite good fun making stuff and you meet many people with similar interests.

CWN Projects

Shawn Robert and Chris

Projects I have been involved at Air Stream Wireless can be seen on their website, some of these sites include:

  • Highgate Park
  • Carrick Hill
  • Bedford Park
  • MOB
  • O'Halloran Hill
  • Mawson Centre
  • Melrose Park
  • North Terrace
  • Northfield
  • Skye1,2 & 3
  • Pasadena
  • Elizabeth Water Tower
  • Parkside
  • Ridleyton

My own home wireless set-up

I run a OpenWRT customised router connected to Air-Stream network using a 25dbi grid dish antenna, the router provides multihomed services with a firewall between the Air-Stream network, my local network. It also runs a VPN between my local network and my work network which is also connected to Air Stream Wireless, providing easy access to work files, email and other services.

Another web server, which is located in the shed with the router for sharing files and information with other Air Stream Wireless members over the network.

What is a Community Wireless Network (CWN)

CWN's are a true phenomena of the 21st century and is now found in thousands of countries around the world. Although there are differences, between countries and groups most have common characteristics:

1) They are non-commercial entities established and maintained by groups of individuals.

2) They use wireless LAN to form a network that:

  • Spans across property boundaries and/or public spaces
  • Allow TCP/IP network devices and computers to communicate and share/stream data

3) They grow by:

  • Interconnecting smaller networks together to form larger networks and so overcome topographical boundaries.
  • Developing a group identity designed to focus efforts and facilitates cooperation between people of different backgrounds, skills and interests.

4) Their popularity has grown due to:

  • The relative low cost of wireless LAN equipment.
  • The ability of individuals to connect a network across property boundaries without need of a commercial carrier or special licence.
  • Public familiarity with wireless and networking/internet applications.

5) They use one or more combinations of network models:

  • WLAN – Wireless local area network
  • Mesh - Self organising adhoc wireless network
  • WAN – Wide Area Networks using wireless for user connections and backhaul
  • Hybrid – Any combination of the above including wire or fibre, in networks there are really no boundaries.

Line Of Sight (LOS), a motivator for shared networks
One of the major hurdles faced by many people setting up a wireless network over distance is the problem of establishing good LOS between two sites. Without LOS it is highly unlikely or impossible to establish a reliable network over a few hundred metres. This is because of the high frequency and low power used by most standard wireless LAN devices 802.11(a/b/g) has difficulty passing through a solid object without a significant reduction and dissipation of the signal.

With good LOS however, it is not uncommon to see links over 10kms sustained at relatively high data rates using low cost off-the-shelf equipment. But in the real world good LOS between different locations is often rare for an individual working on their own and this is the main reason many CWN groups have formed. By coordinating a group people who can share and combine their networks between those with good LOS and others without, they can overcome many of the topographical barriers that an individual would find difficult on their own.

Network Systems
To achieve the aim of building a large network and joining smaller networks together there becomes a need to develop some form of network management to allow significant numbers of nodes and users to be joined together. This is because a simple Layer 2 WLAN would not be effective and would soon congest, just as a basic wired LAN, as they do not have the ability to route or shape traffic if network congestion or failures occur.

As a result two main routing protocols have become predominantly used by CWN Groups. These are either self organizing routing systems, often termed Mesh using OLSR or Autonomous Systems similar to that used by the Internet typically BGP or in some cases OSPF.