CsI(Tl) + SiPM audio CODEC based spectroscopy gadget
Excited to share my latest gadget for spectroscopy!
It’s a device built around a PCM2902 USB audio codec chip. The circuit is surprisingly simple just follow the PCM2902 application note to design the schematic.
Of course, the audio input must be connected to a signal conditioning network that processes pulses from a SiPM (yes, a SiPM!). This means a BIAS generator is also needed to power it.
The signal conditioning circuit uses three operational amplifiers:
An inverting amplifier with a gain of 2.
A Sallen-Key filter with an RC network (22 kOhm and 1 nF).
Another inverting amplifier with a gain of approximately 4.
Check out the photos below—hopefully you’ll find them interesting! They showcase how I prepared the 30x30x30mm CsI(Tl) crystal (6.6% FWHM).
Crystal + SiPM MicroFC 6x6mm on the background… Crystal is not encapsulated. CsI(Tl) is moisture insensitive.Applying special thick optical coupling tape.The crystal + tape + SiPM placed in order to avoid crystal imperfections. The crystal is sanded with 220 size sandpaper it works ang gives best FWHM!Applying special thick PTFE optical reflectorReflector in placeAnd now the most crytical task: solder the wire-wrap wires on SiPM pads. It should be as quick and precisely done as possible to don’t overheath and consequently damage the SiPM. With over 50€ of cost per SiPM it’s definitely not the case.Applying aluminium tape to avoid light ingress. The back of SiPMs is insulated with 4 layers of PTFE to avoid short-circuiting the solder on the soldering pads with the aluminium tape.All the SiPM terminals are soldered together in parallel. Good!Final assembly, ready for testing
Now the results, I’ve used BecqMoni software (the original one!!!).
