Let me introduce my darling - Scintillix gamma spectrometer. As I mentioned in the "Introduction" section of this forum, it took me rather longer time to develop it (you know ... job, family, other hobbies ...). The first thoughts about gamma spectrometry came on my mind after Fukushima NPP accident and the final working prototype registered very first gamma quanta during late summer of 2016.



Spectrometer is based on a 9-stage high PHR 3" photomultiplier tube operated up to 1 kV and optically coupled to a 2.5" NaI(Tl) crystal. Pulses coming from the PMT are amplified and shaped directly in the probe housing, thus sound card unit is fed with amplified pulses, which are less prone to EMI. Only drawback of this solution is, that two cables are needed to interconnect a driver and the probe. In this setup, one cable is for HV and second one for signal and low power supply voltage needed for amplifier and shaper. Signal is processed with a sound card incorporated into the driver unit. With the acquisition card, there was little problem, I spent lot of time to find suitable one, which will not deteriorate resolution. Despite the fact, that at first glance the sound cards looked exactly the same (blue USB stick), external circuitry was fairly different and some of them was really sloppy. Difference between the best and the worst was up to 3% FWHM @662 keV of Cs-137. There was piece to piece variability as well.
When I checked my spectrometer in a laboratory with properly chosen and tweaked sound card, I obtained fairly good value of resolution 6.9% FWHM @662 keV of Cs-137, which is not far from physical limit of the used system.

Stability of the system is very good as well, if the spectrometer is left to warm up few minutes. In a following image is the result of a stability test done in course of 8 hours with uranium bearing mineral as a sample. Spectra were collected for 10 minutes every two hours. Upper spectrum is average of bottom four spectra.

Now I use my spectrometer for different kinds of measurements, covering mainly low level activities of naturally occurring radioactive materials (NORM) in the environment, everyday items, some special chemicals and in food.
Milos