Analogue Gamma Spectrometer
Also called sound card spectrometer, Gammaspectacular or Theremino adaptor, these have been around since around 2010, and typically provide high voltage bias to a scintillation detector via a coupling. The electronic pulse from the PMT in the detector is fed into to an audio sound card like a microphone signal and transmitted to a PC or Mac where the pulse height analysis and histogram is done by a software MCA on the PC side. Free open source programs like PRA, Impulse, Theremino and Becqmoni have been written for this purpose and all work great. Audio sound cards typically sample at 48,000 Hz, but most computers these days can oversample at 384 kHz with great results, this means a gap of 2.6 µs between samples (1 sec/384,000), and for best results we need to integrate around 60 samples for a good pulse height measurement, which takes around 150 µs., this in turn limits the count rate to around 2500 counts per second. Once the count rate exceeds this limit we get pulse overlap which the software filters out and we start getting loss of counts. For most users working with low activity sources this is not a problem, and for borderline cases it usually suffices to move the detector a bit further away.
Digital Gamma Spectrometer (MCA)
Digital gamma spectrometers have been around since the 1950's but have recently become a lot faster and smaller. Unlike analogue spectrometers, the digital spectrometer may also provide high voltage bias to the detector via a coupling, but instead of sending the pulse data to a PC for processing, it has a built in microprocessor which digitises, integrates and sorts the pulses into a histogram list which is then transmitted to the PC at regular intervals. In this case the PC serves no other function than to display the histogram data it receives. Historically digital spectrometers have been very expensive and only operate with propriety software, but now we have open source software like Impulse and Becqmoni and probably more to come. The advantage of the digital spectrometer is speed, unlike a PC sound card, the built in microprocessor samples at several MHz, which means the pulse from the detector can be made much shorter, and now it is possible to reliably count pulses from an NaI detector at speeds up to 100,000 cps. (faster for some other crystals).
GS-PRO-V5 vs GS-MAX-8000
I now make both analogue and digital versions the GS, both are built into a similar high quality CNC machined enclosure, but are indeed very different.
- Compare Specs
GS-MAX-8000 https://www.gammaspectacular.com/blue/g ... s-max-8000
