CsI(Tl) + SiPM audio CODEC based spectroscopy gadget

[madexp]

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).

Let me know what you think!


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 reflector


Reflector in place


And 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!!!).


Uranium ore gamma spectrum


Cs137 FWHM test


6.5-6.6% FWHM as expected. Now, let's do some more or less calculations : 30x30x30mm CsI(Tl) I pay 160€, 4x 6x6mm SiPM 200€ and now my custom electronics are worth 50€. Total project cost: 410€ for me to make it. If I've used a PMT in place of SiPM I could have saved at least 150€.
Now for me is time to add an enclosure. I will turn on my lathe a cylindrical aluminum enclosure and I will 3D-print an inner frame in PTFE to hold the parts together inside the enclosure. Last thing, I will fill the empty space with atoxic soft silicone rubber resin to be sure that moisture will stay outside.

[DL8BCN]

Nice project!
Well done

[NuclearPhoenix]

With over 50€ of cost per SiPM it's definitely not the case.

Are you aware that there is a listing for these SiPMs on Mouser that only costs 30€ (excl. VAT) per piece? There are two listings for the same part, one is cheap and one is more than double the cost. Should bring your cost for the SiPMs down by like 50€.

[madexp]

I've bought a stock in 2020... anyway my source is Mouser.
29€ < 10pc + VAT 22% in Italy = 35€. Yes the price dropped since 2020.