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.
The video above is the first operational test of the detector and the the audio track is achieved by a passive parallel voltage summing circuit below. The clicking sounds are the result of 1 millisecond pules coming from all 18 Geiger–Müller tubes as they detect an ionising particle. When an ionising particle passes through the brass plate and into a tube in the top layer, then through another brass plate into a tube in the bottom layer the LED flashes. The LEDs are arranged to corresponds with the X and Y coordinates of tubes in the top and bottom layers see figure 1.
Final PCB design of the 9 Channel Geiger–Müller Tube Detector to 5V TTL
The audio output was a little hard on the ears so to make this more pleasant, I've 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 keybord.
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.
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 С