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.

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.

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.

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.

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.

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.

 

Second Prototype still more work to do 24th March 2012, but getting there.
 

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 400V and 5 V power supply

 

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.  

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

20 wired GMTs installed between two plastic brackets which was changed to 18 for practical reasons.

Drilled completed bracket for holding GMTs

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

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.

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

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

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 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

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

Assembled with shielding

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.

 

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

Draft PCB of Pin Diode amplifier section

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

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

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

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. Moderator - 20mm 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

Boron Coated Cathode Corona Pulse Neutron Tube 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

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.

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)

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.

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.

Proposed layout of Prototype Version 2

More information soon...

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.

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.

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.

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 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 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.

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 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.

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.

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.

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

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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)

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.

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.

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.

My son Charlie and daughter Eva 2011

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.

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.

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.

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. 

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.

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

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.

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.