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DIY Particle Detector (cern.ch)
226 points by homarp 8 months ago | hide | past | favorite | 42 comments

The parts list includes 9 resistors, 8 capacitors, a photodiode, a dual op amp chip, a switch, and a BNC connector.

The op amp chip is in an 8 pin DIP. The capacitors, the photodiode, and 8 of the 9 resistors are all in packages with leads. The switch and BNC connector can easily have leads soldered to them

Then there is R3, a 40 M resistor that the parts list calls for getting as in SMD. In fact, the parts overview link specifically calls for a black SMD.

As far as I can see, R3 is the only thing that needs a PCB. Everything else would work fine with a solderless breadboard, or any other common non-PCB hobbyist electronics construction method.

Is there some reason R3 has to be black and has to be an SMD resistor for this thing to work? Looking at the schematic it appears to just be part of the feedback loop to control the gain of the op amp in the first stage amplifier, which should work no matter how one decides to get 40 M of resistance.

Hey, project owner here. Glad you all enjoy this! :-) I've never built my particle detectors on a breadboard. It is extremely likely that they will oscillate or frustrate in another way. You have to keep in mind that the amplification is enormously large, per particle only a few thousands of charges are being generated and turned into a still tiny voltage. The lower 10M-feedback electron-detector version works if _soldered_ on a prototyping/veroboard. Those with regular hole patterns - if the parts are put really close together.

Please don't be put off by the circuit board requirement, I have listed it on kitspace such that it is really easy and cheap to get one: https://kitspace.org/boards/github.com/ozel/diy_particle_det... Even if you have never ordered a PCB, it should be straight forward using kitspace as a proxy to get it right.

For beginners, I would propose soldering the electron-detector first (on the plus side, it has 4 times more the sensitivity) and if that works swap few parts and upgrade to the alpha-spectrometer variant since that is a bit more tricky to operate and get running. I've commented on the through-hole/SMD choice and similar questions in this twitter thread https://twitter.com/0zelot/status/1260931205676990466.

In short, I choose leaded components over SMD where possible such that it is easy to solder. But analog signal integrity and low noise vs. signal require a circuit board.

Presumably this would be suitable for soldering Dead Bug or no circuit board style - component to component.

even the alpha-spectrometer might work if soldered wisely on a regular prototyping grid. in any case, thoroughly cleaning after soldering with alcohol will help. but considering the really cheap and fast PCB productions nowadays, the hassle is most likely not worth it.

The short answer is that you can put it on a breadboard, but it will require attention be paid to the first op-amp circuit.

The first op-amp is used as a charge amplifier. A high energy charged particle will deposit a charge Q on un-grounded node of the reverse biased diode. The voltage on the output of the amplifier is V_out = -Q/C_feedback + V_bias, where v_bias is made with the voltage divider on the non-inverting input. The resistor R3 is only used to adjust the frequency response (and I assume stability) of the amplifier. It will low pass the signal at ~800 Hz.

The problem and the reason they want you to use small low capacitance components is that in order to get a large charge to voltage conversion factor, C_feedback is small (5 pf). If you build the circuit on a breadboard and place the op-amp output and input on consecutive lanes then parasitic capacitance can easily add another ~10 pF to that and drop your amplification.

To get around this, you'd have to lift up that leg of the capacitor and solder your connections to it instead. This will avoid stray capacitance from lowering your gain.

There seem to be builds using a through hole resistor for R3:


The opamp appears to be configured as a transimpediance amplifier. 40M is a lot of gain. Probably keeping traces short and the resistor away from the board helps. That’s probably why they mount the resistor vertically when they use a through hole in the pic above (my guess anyway). Using a SMD keeps the traces short, which might be why they use it in the current version.

Another option could be just to air wire the resistor. Sometimes people bend up the legs on the opamp and wire the resistor/input directly to the IC pin.

I think you might have issues on a breadboard. Air wiring the whole thing would probably work. Or using protoboard, trying to keep the traces short.

> There seem to be builds using a through hole resistor for R3

That's the "electron-detector" version, which uses a 10M feedback resistor. The alpha-spectrometer version is the one that uses the 40M SMD resistor.

I don’t think that makes much of a difference to the part selection (it’s the same board). If you look at the schematics they say you can use either through hole or SMD. SMD is preferred:


I created a cloud chamber a few years ago to test out a piece of uranium ore I bought on Amazon. It's a pretty simple design, cooled with a Peltier (thermoelectric) device instead of dry ice. I got the idea from an Instructable article[1] and the whole thing was pretty awesome actually. I have a video[2] if you're interested in what it looked like. It's a few minutes long and unedited, so heads up on that. If you watch any 10-20 second portion of it you'll get the general idea.

[1] https://www.instructables.com/id/Make-a-Cloud-Chamber-using-...

[2] https://youtu.be/vaRyXmMGJdk

The GitHub project page has a better and more comprehensive introduction than the CERN page:

* https://github.com/ozel/DIY_particle_detector/

Paper (Open Access, click "Download PDF"):

* Smartphone and Tablet-Based Sensing of Environmental Radioactivity: Mobile Low-Cost Measurements for Monitoring, Citizen Science, and Educational Purposes


Thank you, this diy particle detector looks pretty neat. Love more reading material on the subject.

If you want another fun particle detector project, you can build a cloud chamber with some dry ice and an old fish tank: https://www.symmetrymagazine.org/article/january-2015/how-to...

I made a really crude one of these a long time ago. Seeing the trails live is really strange and cool. If you can only get weak isopropyl you can remove water pretty easily by salting it [0]. Drawing the alcohol off the top with a turkey baster or similar is probably the best way with typical household equipment. If you don’t have one of those, you can do it in a water bottle, let the water settle out with a bottle upside down, poke a small hole in the base of the bottle then just partially open the lid over sink and let it drain until you get to the alcohol. Just remember that this stuff is now super flammable so be careful. (Salting doesn’t really work with ethyl alcohol so save your vodka)

Dry ice is pretty easy to get at Graeter‘s if you have one of those local. Just don’t store it in a closed container. Gloves are a great idea of course but I also advise wearing thick socks or slippers when you’re using it. Stepping on even a very small piece of dry ice in bare feet is experience you will remember.

Dry ice is a lot of fun but doesn’t last long. If you go through this, check youtube for other experiments and things to do, and buy a little extra. Just remember never put it in a closed container, it will almost certainly explode. Physics doesn’t care about you, respect the material. (edit: I just checked, heat of sublimation of CO2 is approximately 570 kJ per kilogram. A stick of dynamite has approximately 1 MJ. There’s a lot of energy cached in those blocks.)

Have fun!

[0] https://youtu.be/CtwQ2aEBur4

Jumping in to remind folks: If you notice an increasing level of panic-like feelings when working with dry ice, seek fresh air immediately.

Great point. There have definitely been some tragedies when people play with dry ice without understanding the dangers. Don’t throw it in the pool and go swimming or try to cover yourself with fog, etc etc. Study up.

The link says 90% isopropyl alcohol but I've seen many instructions that suggest using a high percentage methyl alcohol is better. But methyl alcohol is quite toxic if you get it on your skin it can be absorbed and cause many problems (blindness for one).

I've never built one but it's always something I plan on building.

Isopropyl alcohol works well if it is of high purity (we use 96% I think). Methyl alcohol would be a really dangerous choice.

Yes I'd certainly use isopropyl alcohol. I'm pretty sure I can get it with a purity of 95% or more at my local pharmacy.

Dry ice is the other problem it's not something readily available in my town. I don't think regular ice is cold enough especially when using isopropyl alcohol which isn't as volatile as methyl alcohol (methanol).

Let me just point here again to the project entries on Kitspace.org:



Yes, this project is very much doable for electronic beginners with a knack for science (16-year olds who have never soldered manage it well if guided a little bit). The parts are easy to solder and ordering the circuit board will make your life much easier in order to get it working. BTW, no one earns money with the kitspace website above. This is community-run and intended to make open hardware projects easier to build by simplifying the ordering procedures. The parts and board suppliers linked on kitspace should cover most of the world.

Here's another "kitchen-table" project, it's a muon detector.

This one uses plastic scintillating material in front of the detector.


github: https://github.com/spenceraxani/Desktop-Muon-Detector

also its website: http://www.cosmicwatch.lns.mit.edu

In terms of difficulty to build and operate it, I would rate the discussed projects such: cloud chamber < DIY particle detector (electron-detector variant) < DIY particle detector (alpha-spectrometer variant) < desktop muon detector

Even DIY cloud chambers can be a bit tricky to get running for the first time (especially with too high humidity like in summer). Just don't give up! ;-) A few tips can be found in this manual: https://scoollab.web.cern.ch/cloud-chamber

It's amazing how accessible some of these detectors can be. I wonder if you could perform some of the classic physics lab experiments with them like muon lifetime measurement.

Very cool -- one thing I don't understand though. I know that alpha radiation is stopped by a piece of paper thickness. How does this then detect such radiation through the metal of a box if the detector has to be inside?

Actually alpha radiation can get through a piece of paper. Check out thought emporiums videos on it on YouTube. I remember he did a video about the different types and had a detector between the sources and some thickness of stuff and they seemed to go through paper just fine. I think it's his video about those healing bracelets that actually emit radiation.

Unfortunately, that video contained some flawed conclusions. I had left a comment back then. Alpha particles from natural sources like an uranium stone penetrate 50 micrometers of solid hard material at most. Let's give it maybe 100 micrometers of soft paper, but that's about it. What was most likely observed in that video is radon, which is a radioactive gas, slowly diffusing out of uranium or thorium stones. Since it's gaseous, it can circumvent the paper and then do its alpha decay just behind it. I wrote a few lines on those aspects in this article https://www.mdpi.com/1424-8220/19/19/4264

Oh that's pretty cool! I guess the best way to check would have been to have it in a paper box then?

Yes, radon is pretty hilarious and spreads in very unexpected ways. Completely wrapping sources of radon like uranium or thorium minerals (or these bracelets containing some of that), only holds back the diffusion process for some time unless the shielding is really thick and very dense. That's why radon accumulates so well in household cellars, it penetrates concrete walls easily.

If you look closely in thought emporiums video (link below), the thick clouds - representing each the full paths of individual alpha particles (from the point of decay until full absorption in the air) - don't originate right at the surface of his shielding materials (paper, chicken skin... whatever). Instead, the alpha particle clouds stand by themselves in free space and can only really stem from radon that decided to decay at those positions somewhere outside of the shielding (transforming to "solid" polonium in that process and sticking itself to the next closest lump of molecules/dust). If the alpha particles would penetrate the shieldings (which they can't because of too much material/density), we would see clouds stemming directly from the shielding surfaces which I don't see happening:

https://www.youtube.com/watch?v=C7TwBUxxIC0&feature=youtu.be... You may find and like my comment there, maybe it helps to fight some misconceptions about natural radioactivity. ;-)

Awesome thanks!

I once did an experiment with a rock containing uranium and a Geiger counter. The noise stopped immediately after putting printing paper between them and resumed after taking it off.

This device does not detect radiation outside the box. You have to put the object you want to measure radiation from inside the box, close to the sensor.

Oh, well that is a big, big, caveat.

It's fine for what it is. But I think a particle detector that most people imagine is really something you want to be able to hold portably in the air and detect ambient/impinging radiation from unknown sources, rather than have to put samples in a closed container.

If there were some modification that made that possible (getting around the light-tight requirement), that would make this incredibly more useful.

this is possible! you can use a thin foil made from e.g. mylar, for example taken from a cracked-open old large foil capacitor and superglue one layer on the rim of the diode's metal case. It can then point through a hole into the outside of the tin box if not held into direct sunlight (some additional foam ring can be used to help block more light). Using one of the sturdy aluminum die-cast cases I've listed in the schematic should be favored in a mobile scenario. Much less affected by vibrations/microphonic effect.

Interesting, thanks!

If i understand correctly, the sensor hast to be inside the metal box, as well as the item to be measured. Both shilded from light.

Even the glas covering the diode has to be broken away / removed

This is great. I am very curious what other common diodes can be used in place of the $3000 PIN diode detectors typically used in XRF setups.

Alot of big power diodes can also be used, and they should have a larger volume of silicon available. Presumably the snr will be worse. Maybe start by filtering for diodes with low reverse bias current but high forward current on digikey?

I wonder whether those common, $10 PIN diodes for UHF/microwave can be used.

Could this be used to create HW RNG?

yes totally. There is a great DIY project for doing that https://www.fourmilab.ch/hotbits/ It's not required to have the particle energy measured for making random numbers, detecting precisely the arrival time of particles is more important plus having a high hit rate is usually desired. My DIY detectors are not optimized in that way but it would work in principle. Timestamps are already recorded by the python scripts on github, it would be just a matter of evaluating them.

Would be interesting with an article describing how this works

Just place an order. Will read after it comes.

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