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.
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.
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