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A 200 DOLLAR OPEN-SOURCE GAMMA SPECTROMETER THAT IDENTIFIES WHICH ISOTOPE IS IN FRONT OF IT

A Geiger counter only beeps. This measures photon energy and therefore tells you which isotope is in front of it.

by OpenGammaProject

FULL CAD BOM FIRMWARE DOCS

ScienceOpen-hardware

difficulty
●●●●○
time
a weekend-plus
license
GPL-3.0
repo
repo ACTIVE359 stars

WHAT YOU’LL NEED

  • 3D printer + filament — printable parts — files are in the repo
  • Electronic parts — full list with part numbers in the repo BOM
  • Dev board / microcontroller — runs the project firmware

Partner

Show off your build — Record and edit your build video by editing the transcript, not the timeline.Try Descript
1

COMPAREE VERDICT

This is a gamma spectrometer — a device that measures photon energy and therefore identifies radioactive isotopes — built around a NaI(Tl) scintillator crystal, a silicon photomultiplier and a Raspberry Pi Pico, with a bill of materials of roughly two hundred dollars. A professional setup with an ORTEC digiBASE-E detector base and Maestro software costs around eight thousand, so the price is real. The detector gives 4096 channels and about seven percent energy resolution at 662 keV, enough to separate caesium-137, americium-241, sodium-22 and the other common isotopes cleanly. The board files, firmware and a printable enclosure are all published. What is missing is an assembly guide and a calibration procedure. You have a schematic, a few repository photos and example spectra to match against. If you have built and debugged mixed-signal boards before, that is enough. If you have not, this will be the project where you learn, and it will take longer than a weekend. The scintillator crystal and the photomultiplier are specialist parts — the repo links suppliers but availability moves around, and a counterfeit or damaged crystal will give you a spectrum full of noise with no way to know why. The board carries up to 36 volts for the photomultiplier bias, so it is not something to probe while powered. The single biggest trap is assuming this will work like a kit: it will not. It is a reference design for someone who can read a schematic and chase down a signal.

NOT IN THE REPO

  • —GPL-3.0 licence, non-commercial use permitted but derivative works must remain GPL.
  • —Board Gerbers, schematic, firmware, example spectra and a printable enclosure are all in the repo.
  • —No assembly guide — you work from the schematic and a few photos.
  • —The NaI(Tl) scintillator crystal and the silicon photomultiplier must be sourced separately; the repo links some suppliers but availability shifts.
  • —No calibration procedure is documented — you match your peaks to known isotopes by hand.
  • —Example spectra are provided for caesium-137, americium-241, sodium-22 and lutetium-176.

Can I build this?

Printan enclosure (STL files provided)
Buya PCB (Gerbers provided), a NaI(Tl) scintillator crystal, a silicon photomultiplier, a Raspberry Pi Pico, an OLED display, passives and a handful of ICs per the BOM
Toolsa soldering iron, a multimeter, a way to order a PCB (JLCPCB, PCBWay or equivalent), and ideally an oscilloscope for debugging the photomultiplier output
Skillsintermediate to advanced electronics — you are building a mixed-signal board with a high-voltage bias supply and debugging it from a schematic
Timea weekend to assemble and another few evenings to calibrate and match spectra, longer if the photomultiplier or crystal arrives faulty
Cost$$, dominated by the scintillator crystal and the silicon photomultiplier, together around 80–120 dollars depending on source and size
SafetyThe board carries up to 36 volts for the photomultiplier bias — do not probe it while powered. The device only detects radiation and emits none. Do not handle radioactive sources unless you know what you are doing; example spectra in the repo come from the author's own measurements.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

A desktop 3D printer that prints in full colorPartner · Kickstarter
A desktop 3D printer that prints in full color

HeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.

See how it prints

Gallery

https://github.com/OpenGammaProject/Open-Gamma-Detector
https://github.com/OpenGammaProject/Open-Gamma-Detector
https://github.com/OpenGammaProject/Open-Gamma-Detector
https://github.com/OpenGammaProject/Open-Gamma-Detector
https://github.com/OpenGammaProject/Open-Gamma-Detector

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the hardware documentation (Schematic, Gerbers and a component list. No assembly guide.)
  2. 2.Order the PCB and source the scintillator and photomultiplier(The repo links some suppliers but availability changes. Verify the photomultiplier matches the board footprint.)
  3. 3.Flash the firmware to the Pico (Precompiled UF2 provided. Drag and drop.)
  4. 4.Assemble the board and test the photomultiplier output(An oscilloscope helps. If you see no pulses, check the bias voltage and the scintillator coupling.)
  5. 5.Match your spectrum to the example files(Caesium-137, americium-241, sodium-22 and lutetium-176 spectra provided. Calibration is manual.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

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KNOWN ISSUES

  • The scintillator crystal and the silicon photomultiplier are specialist parts — a counterfeit or damaged crystal will give you noise and no clear way to know why.
  • There is no assembly guide. You work from the schematic, a BOM and a few photos. If that sentence makes you nervous, pick a different project.
  • No calibration procedure is documented. You match peaks to known isotopes by hand using the example spectra.
  • The photomultiplier bias runs up to 36 volts. Do not probe the board while it is powered.
  • If you have never debugged a mixed-signal board before, expect this to take longer than a weekend — possibly much longer if something is wrong with the photomultiplier or the crystal.
  • The GPL-3.0 licence means derivative works must also be GPL. If you plan to sell a modified version, read the licence first.

What is the difference between this and a Geiger counter?

A Geiger counter registers that radiation is present. A gamma spectrometer measures the energy of each photon, and because every isotope emits at its own signature energies, the shape of the spectrum identifies it. Caesium-137 peaks at 662 keV, americium-241 at 26 and 60, sodium-22 at 511 and 1275.

Is seven percent resolution good?

Good enough to separate the common isotopes cleanly. Professional scintillator-based systems achieve around six to eight percent at 662 keV. High-purity germanium detectors do better — under one percent — but cost tens of thousands and require liquid nitrogen cooling.

Where do I get radioactive sources to test it?

Do not. The example spectra in the repo come from the author's own measurements. Some smoke detectors contain americium-241, some old camera lenses contain thorium, and potassium-40 is in bananas and salt substitutes, but if you do not already know how to handle radioactive materials safely, this is not the project to learn on.

Can I use this to measure dose or check if something is safe?

No. It measures energy spectra, not dose rate, and it is not calibrated for survey work. If you need to know whether something is safe, you need a professional survey meter.

What is the biggest single thing that will go wrong?

A faulty or counterfeit scintillator crystal or photomultiplier. If either is bad, you will see noise and nothing else, and distinguishing a bad part from a bad solder joint or a firmware bug is hard without an oscilloscope and experience.

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Discussion1

FROM THE COMPAREE TEAM

Four thousand channels of resolution, for two hundred dollars. What isotope would you point it at first?

CompareeTEAM15d ago

Practical notes from our verification: the repository contains Gerbers, firmware, example spectra and a printable enclosure, but no assembly guide — you work from the schematic and a few photos. The single biggest variable is the scintillator crystal and the silicon photomultiplier: both are specialist parts, availability shifts, and a faulty or counterfeit part will give you noise with no easy way to diagnose it. If you have debugged mixed-signal boards before, that is a known risk. If you have not, this is the project where you will learn, and it will take longer than a weekend. The board carries up to 36 volts for the photomultiplier bias, so do not probe it while powered.

OpenGammaProject

An open hardware project to make gamma spectroscopy accessible outside professional laboratories. The design is built around widely available components and a Raspberry Pi Pico.

GitHub

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
GitHub repo