We continue the series of posts about PSoC describing the application of the coincidence detection circuit to the case of cosmic rays. These have been treated in numerous articles and so here we simply expose the results we obtained using the PSoC-based coincidence detector. The system has been connected to two SiPM detectors coupled to plastic scintillators, as described in the figures below :
The plastic scintillators are particularly sensitive to charged particles and therefore they are suitable for the detection of β rays and cosmic radiation, which are composed for the most part by muons.
The pulses detected by the individual sensors are for the most part due to the passage of the muon through the plastic scintillator. Positioning the two sensors one above the other, as shown in the figure below, we select the muons which go through both plastic crystals, thus with direction and suitable energy.
Placing instead the two sensors side by side we obtain the coincidences due to distinct particles that have originated from the same primary cosmic ray, that is, they belong to the same cosmic shower.
The experimental setup is shown in the images below :
Detectors Side by Side in Contact
Time = 27088 s
Coincidence Rate = 0,137 ± 0,01 CPM – Pulses 62
Detector 1 Rate = 12,4 ± 0,2 CPM – Pulses 5609
Detector 2 Rate = 14,7 ± 0,2 CPM – Pulses 6631
Detectors at 50 cm distance
Time = 25622 s
Coincidence Rate = Pulses 1
Detector 1 Rate = 11,4 ± 0,2 CPM – Pulses 4849
Detector 2 Rate = 12,7 ± 0,2 CPM – Pulses 5431
Detectors Stacked in Contact
Time = 17492 s
Coincidence Rate = 5,68 ± 0,14 CPM – Pulses 1655
Detector 1 Rate = 16,5 ± 0,2 CPM – Pulses 4801
Detector 2 Rate = 16,2 ± 0,2 CPM – Pulses 4719
Detectors above one another at 65 cm distance
Time = 20959 s
Coincidence Rate = 0,03 ± 0,01 CPM – Pulses 11
Detector 1 Rate = 16,4 ± 0,2 CPM – Pulses 5736
Detector 2 Rate = 17,6 ± 0,2 CPM – Pulses 6133
Muon Flux Calculation
Muon Flux slm = 0,6 part/cm2 min sterad
Detector Area = 32,5 cm2
Detector Muon Flux = 19,5 part/min sterad
The values measured by the individual detectors vary from 12 to 17 CPM, so rather close to the “theoretical” value of 19 CPM. It must take into account that the quantum yeld of detectors is probably less than one, especially for the muons that pass away from SiPM : for these muons the probability of being detected is lower.
In case of stacked detectors the value of coincidences is a bit lower, being about CPM 5,68 : in this case it must be taken into account that the useful solid angle is reduced, also due to the lateral position of the SiPM. Increasing the distance between the detectors causes a diminishing count because the solid angle is reduced very much, by placing the detectors at 65 cm of vertical distance the value is reduced to 0.03 CPM.
With the detectors positioned side by side the coincidence value is 0.14 CPM, low but not zero, demonstrating the existence of cosmic showers. Increasing the distance between the detectors the value is practically reduced to zero, at 50 cm distance, in different hours of measure, there has been only one pulse in coincidence.