To date, many of my Cosmic Ray experiments and projects have relied on Geiger–Müller tubes or photomultipliers and Scintillators as the detector. The issue with using these detectors is 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 measuring the energy levels of ionizing particles.

Solid state devices, particularly Si Pin Photodiodes, can measure gamma rays and their energy level. They also come with issues and compromises, such as more complexity, noise, cost and small aperture size. But also have their benefits with low voltage, low power and greater longevity. This project aims to develop a relatively cost-effective detector to measure muons and offer usable energy resolution.

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

There are also specialist Photodiodes designed specifically for gamma-ray and x-ray detection, but these are expensive and difficult to source in small quantities. So the next best candidate is 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 a visible light filter
  • Manufacture First Sensor Part # PS100B-7-CERPINE – has a 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 further decay and emit a gamma ray at an energy of 186 keV, which can be detected. 

Check Source 226Ra