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All-In-One Gamma-Ray Spectrometer

More sensitive to gamma radiation than a Geiger counter with the added bonus of telling exactly what's inside your samples!

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Using a small custom PCB, a Raspberry Pi Pico microcontroller and a scintillator (typically NaI(Tl)) you can build your own gamma spectrometer! The needed processing and multi-channel analyzer are all on-board so no external parts are needed, except something to look at the data (with a screen, obviously).

This detector uses a silicon photomultiplier (SiPM) instead of the usual photomultiplier tubes that are more common with these types of DIY projects. This means that the whole assembly is much smaller and also safer, because no high voltages are needed! Also in contrast to projects like theremino you don't strictly need a computer or even an external sound card -- everything is self-contained. You can do standalone measurements using only a USB power cable and save the spectra to the Pico's flash storage or connect to your PC via the Serial-over-USB connection.

The principle of operation for the detector looks like this:

Here are some of the most important key facts:

  • Compact design: Only 60 x 60 mm (not including scintillator).
  • All-in-one detector: No external parts (e.g. sound card) required to record gamma spectra.
  • Micro-USB serial connection and power.
  • Easily programmable using the standard Arduino IDE.
  • Low-voltage device: No HV needed for a photomultiplier tube.
  • Low power consumption: ~25 mA @ 5 V.
  • Default Mode: Capable of up to around 40,000 cps while also measuring energy.
  • Geiger Mode: Capable of up to around 100,000 cps without energy measurement.
  • 4096 ADC channels for the energy range of about 30 keV to 1300 keV.

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main_schematic.pdf

Schematic of the main detector board

Adobe Portable Document Format - 97.55 kB - 05/02/2022 at 11:29

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main_BOM.csv

BOM for the main detector board

ms-excel - 3.58 kB - 05/02/2022 at 11:29

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sipm_schematic.pdf

Schematic of the SiPM carrier board

Adobe Portable Document Format - 26.73 kB - 05/19/2022 at 15:34

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sipm_BOM.csv

BOM for the SiPM carrier board

ms-excel - 964.00 bytes - 05/19/2022 at 15:34

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  • 1 × Raspberry Pi Pico Microcontroller and heart of this detector
  • 1 × MicroFC-60035 SiPM The silicon photomultiplier used with the scintillator
  • 1 × SiPM carrier PCB Production-ready gerber file in GitHub repo
  • 7 × SMD components SiPM board See BOM for exact parts
  • 1 × Main detector PCB Production-ready gerber file in GitHub repo

View all 6 components

  • New detector revision coming soon!

    NuclearPhoenix3 days ago 0 comments

    Firstly, welcome to all the numerous newcomers to this project that came here from some of the articles released in the last couple of days! I'm glad that so many other people are interested in this kind of (arguably) pretty exotic topic :)

    As you might have noticed, some parts are currently becoming Unoptanium. This includes the OPA2354 OpAmp that's used and most importantly the MicroFC-60035-SMT silicon photomultiplier itself. To try and fix these issues, I'm working hard on replacing these parts in the mean time, until they eventually get in stock again (which will probably not happen too soon unfortunately).

    Like I said before, I also want to improve some other things with the new boards that I didn't consider yet with the current design. The most important parts are as follows:

    • Custom preamp gain so that you can use different scintillator sizes, SiPMs and of course, change the energy resolution and range.
    • Custom PSU voltage! The new SiPM power supply will include some potentiometers so that you can set the voltage anywhere from 28 V - 33 V. This will also enable you to use many more different SiPMs like the (still-in-stock!) Broadcom AFBR-S4N66C013, which is mostly identical to the "old" SiPM except in supply voltage and price (it's much cheaper).
    • Entirely new SiPM PSU tuned to be used with these kinds of applications including very low noise applications (~5mVpp @ 30V).
    • Changing all the OpAmps for parts that are still in stock and mostly identical as well (not that easy with the current supply issues).
    • Improved PCB layout which includes a better mechanical structure and getting rid of the dodgy pin connectors.
    • Custom I2C header for the Pico so that you can use it to expand it's use case to your own likings, e.g. connect it to a display, etc.
    The Broadcom AFBR-S4N66C013 SiPM

    By the way, the Raspberry Pi Pico W was released today which is very exciting news! In the future I might use it on this detector as well, enabling wireless communication and more. However, we need to wait for enough stock and full software support.

    I hope to get finished in the next couple of days, so stay tuned for more project logs!

  • New SiPM carrier board

    NuclearPhoenix05/19/2022 at 10:52 0 comments

    I'm currently working on a new detector board that makes this whole thing more modular and usable. It is going to include variable SiPM bias voltage and preamp gain this time. There will also be a better option for mounting than just the pin header now. And last but not least, I'll change the preamp and SiPM DC/DC converter to fit better parts!

    In the mean time there is a new SiPM carrier board design! It's way smaller with 18 x 18 mm and also less stupid with the holes in the PCB, because there are no more holes (well, except for two tiny vias) that could make it harder to isolate the sensor from light. Enjoy!

    Link to the GitHub repo

View all 2 project logs

  • 1
    Solder SiPM carrier board components

    All the SMD parts, the pin header and the SiPM itself. Orient yourself with the schematic and BOM.

  • 2
    Couple SiPM with scintillator

    Center the SiPM on the scintillator crystal and put some silicon grease between the two parts to optimize the coupling (and minimize reflections)

  • 3
    Wrap scintillator assembly

    Use black electrical insulation tape to wrap the whole assembly except for the pin header, of course. This will reduce light passing to the SiPM to an absolute minimum, otherwise it won't work properly. You should use multiple layers of tape just to be sure.

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Discussions

Wesley Ellis wrote 05/19/2022 at 00:36 point

Neat project, but I think there's a typo in "a USB power cable and safe the spectra to the Pico's flash storage" where safe should be save

  Are you sure? yes | no

NuclearPhoenix wrote 05/19/2022 at 09:17 point

Yes, thank you!

  Are you sure? yes | no

yahyabangash2004 wrote 05/06/2022 at 16:06 point

Good initial

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