YOU CAN BUILD A PARTICLE DETECTOR THAT COUNTS PIECES OF SPACE PASSING THROUGH YOUR DESK
A particle detector you can assemble in an evening that counts muons from space as they pass through your desk.
by Spencer Axani, Katarzyna Frankiewicz, Janet Conrad
ScienceOpen-hardware
- difficulty
- ●●●○○
- time
- an evening
- license
- license not specified
- repo
- repo ACTIVE72 stars
●●●○○ · an evening · license not specified · 72 stars · repo ACTIVE
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
COMPAREE VERDICT
This is a real particle physics instrument scaled down to a desktop build, designed by MIT physicists who wanted students to assemble their own detectors. The engineering is careful: a block of plastic scintillator emits a faint light pulse when a muon passes through, a silicon photomultiplier catches it, and an Arduino-based board counts and displays the rate on an OLED. The published paper claims under 100 dollars in parts and four hours for a beginner, which feels honest for someone following the illustrated guide — most of the time is careful soldering of the SiPM and checking the high-voltage bias is set correctly. The single biggest trap is that two key components, the scintillator and the SiPM, are not general electronics parts; you are buying from physics suppliers or specific distributors, and if you order the wrong SiPM model the detector will not work. The second trap is that the repository carries no licence file, so the legal status for any use beyond personal build is undefined. If you want to see coincidence detection (two stacked detectors firing together), you need to build two complete units. What you get is an instrument that genuinely detects cosmic ray muons at the rate physics says you should see them, and people have flown them to watch the count climb with altitude. If you want to hold something in your hand that shows particles from space in real time, and you are comfortable with specialist components and no-licence risk, this is the project.
IN THE REPO
NOT IN THE REPO
- —Complete PCB Gerbers, Eagle files, Arduino firmware, illustrated assembly guide and full BOM are in the v3X repository.
- —No licence file in the repository — the files are published but there is no SPDX identifier or stated terms, so commercial use status is unclear.
- —The paper (linked in the repo README) states material cost under $100 and ~4 hours assembly time for a novice student; those are the authors' claims, not ours.
- —The silicon photomultiplier (SiPM) and plastic scintillator are specialist items — you will not find them at a general electronics supplier.
- —Two-detector coincidence mode requires building two complete units and running the coincidence firmware; the repos contain the code but you need both sets of hardware.
- —Active repository with recent commits; Spencer Axani responds to issues.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Videos
CosmicWatch: The Desktop Muon Detector4:23
Official tutorial video from the CosmicWatch team, shows the detector working and explains the physics; used as source footage for the reel
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the assembly guide PDF in the Documentation folder(Illustrated step-by-step with photos; follow the SiPM soldering and bias adjustment sections carefully)
- 2.Order the PCB using the Gerber files in the PCB folder (Upload the Gerbers to JLCPCB or similar; minimum order is usually 5 boards)
- 3.Source the SiPM and scintillator from the BOM links(These are the two hardest parts to find; the BOM has supplier links but check stock and lead time before ordering the rest)
- 4.Flash the Arduino firmware from the GUI folder (Standard Arduino IDE upload; the GUI software runs on your computer to log and plot the muon rate)
KNOWN ISSUES
- The SensL MicroFC-60035-SMT SiPM is a specific model; ordering a different SiPM or a used/counterfeit part will result in a non-working detector or wrong count rates.
- The plastic scintillator is EJ-200 in a specific size; generic acrylic will not scintillate and the detector will see nothing.
- The repository has no licence file, so you cannot legally sell a built detector or modified design without clarifying terms with the authors first.
- The SiPM is static-sensitive; ground yourself and use ESD precautions during soldering or a single touch can kill it before you power up.
- Setting the SiPM bias voltage correctly is critical; too low and sensitivity drops, too high and noise dominates — follow the calibration procedure in the docs.
- For coincidence detection you need two complete detectors, two Arduinos, and the coincidence firmware; the parts cost doubles and the setup is more complex.
Is this safe? Am I detecting dangerous radiation?
You are detecting cosmic ray muons, which are a natural background particle that has always been passing through you. The detector does not emit radiation and the muon rate it measures is normal environmental levels, not a hazard. It is not a dosimeter and does not replace radiation safety equipment.
Can I use a different SiPM or scintillator to save money?
Not reliably. The firmware and bias voltage are tuned for the SensL MicroFC-60035-SMT SiPM and EJ-200 scintillator. A different SiPM may have a different gain or breakdown voltage, and a different scintillator may emit at the wrong wavelength or with the wrong decay time. You would need to re-tune the entire detector, which requires equipment most people do not have.
What does coincidence mode actually give me?
Two detectors stacked with coincidence firmware count only particles that pass through both scintillators within a narrow time window (nanoseconds). This cuts out noise and ensures you are counting real muons, not electronic glitches or background light. It is the same technique used in large physics experiments. You need two full builds to do it.
Why is there no licence in the repository?
The files are published openly and the authors clearly intend educational and research use, but there is no SPDX licence or explicit terms. For personal builds this is fine, but if you want to sell kits, modify and distribute, or use it commercially, contact the authors first to clarify.
Will I actually see muons, or is this theoretical?
You will see them. At sea level the expected rate is roughly one muon per square centimetre per minute, and the detector's active area gives a count rate of a few per minute, which you will see ticking up on the OLED. People have published data from these detectors showing the rate increasing with altitude on flights, exactly as predicted by physics.
Community builds
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Discussion1
FROM THE COMPAREE TEAM
At sea level you should see a few muons per minute ticking up on the OLED — people have flown these detectors and logged the rate climbing with altitude. If you built one, what would you measure first?
Spencer Axani, Katarzyna Frankiewicz, Janet Conrad
Spencer Axani, Katarzyna Frankiewicz and Janet Conrad are physicists at MIT who designed CosmicWatch as an instrument students could build themselves to learn particle detection hands-on. The project grew out of the question: can a real muon detector cost less than a textbook? The answer was yes, and detectors built from these plans have been used in classrooms, taken on planes, and contributed to citizen science experiments.
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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.
CompareeTEAM11d ago
Practical notes from our verification: the repository is active with recent commits and Spencer Axani responds to issues, so the project is maintained. The official tutorial video (e4IXzNiNxgU) is clear and the illustrated assembly guide in the Documentation folder is thorough, but there is no licence file in the repo — the files are published but legal terms for modification or commercial use are undefined. The arxiv paper (1606.01196) is where the under-$100 and ~4-hour claims come from; those are the authors' numbers for a student build, not independently verified. The single biggest practical hurdle is sourcing the SiPM and scintillator — these are not general electronics parts, and the BOM links are helpful but stock and lead times vary. If you order the wrong SiPM model, the detector will not work and there is no easy substitute.