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CERN at Home: Building a Particle Detector (clanhouse.com)
154 points by kasbah on Sept 1, 2020 | hide | past | favorite | 25 comments

Cool stuff! Here are a few interesting resources:

http://www.techlib.com/science/ion.html - old and gold. A friend tried building these ion chambers, but apparently getting high enough isolation between the container and the electrode was very hard.

http://physicsopenlab.org/2016/04/24/diy-cherenkov-detector/ - one for detecting muons (a PMT taped inside a thermos)

And a fun little application note from Maxim to build a gamma detector from a photodiode : https://www.maximintegrated.com/en/design/technical-document...

Great followup info!

Looking for the datasheets for the pin diodes I've got in the parts drawer to see if I can make the Maxim circuit. I know there's some very low noise op-amps down there.

The circuit used in the blog article is a very much simplified version of the Maxim one. And probably not so much worse in terms of signal to noise ratio: https://github.com/ozel/DIY_particle_detector/

The ion chambers are impressive because even lower-cost. But they also detect the presence of people, touches and what not. :) My favourite aspect of silicon sensors like those PIN diodes is that you get the absorbed particle energy as well. In particular with alpha particles that gets quite interesting when measuring for example old ceramics painted with uranium glaze ('Fiestaware').

Speaking of CERN at home, the Fusor Forum [0] is a good place to visit. It's a community for fusor experimenters - a fusor is basically a glow discharge tube, but capable of achieving nuclear fusion. It's not an easy project, but has been extensively documented, and it's potentially doable by anyone with dedication.

A class of more difficult projects is particle accelerators. Many people built fusors, but fewer people had built electrostatic and linear accelerators. In addition to technical difficulties, X-ray hazards from an accelerator is much greater than a fusor.

Cyclotrons are the hardest, a successful build is extremely rare. Experimenters reported that there were still considerable difficulties even with access to a college lab. In 2010, there was a "Small Cyclotron Conference" [1] - a meetup event for experimenters to share experience. It featured many fascinating presentations, make sure to see [2][3][4].

[0] https://fusor.net/board/

[1] https://web.archive.org/web/20110725214245/http://cyclotronc...

[2] https://web.archive.org/web/20110725214959/http://cyclotronc...

[3] https://web.archive.org/web/20110725214353/http://cyclotronc...

[4] https://web.archive.org/web/20110725220048/http://cyclotronc...

Fusors make neutrons and can cause activation of nearby materials which can lead to all sorts of decay chains and radioactive products.

Particle accelerators are cool though, despite the obvious danger. If you're dealing with just electrons, IIRC you need to get to about 6MeV to overcome the nuclear binding forces and initiate a decay. You can make a hell of a lot of X-rays below that of course, but personally one of my life's goals is to cause an atom to split :) No time for that now, but that's what retirement is for. As a bonus, radiation is a lot less damaging when you're past 50, so unless you get high enough to induce acute radiation poisoning you'll probably be fine.

You can actually make a fairly low-tech accelerator with just a large Van De Graaff generator. There are even designs which replace the belt with a chain(https://en.wikipedia.org/wiki/Pelletron) and reach fairly high energies(for a home unit anyway).

Here is a much simpler detector: A bottle of Corona (or any other beer in a long-necked, clear bottle) makes a workable cloud chamber. Chill well in the freezer, and watch the neck closely as you open it. You may see the streak of a cosmic ray passing through just as the cloud of condensation forms. Of course, as a bonus, it may take more than one try…. It's not an ideal project to do with your teen-aged child—a soda doesn't get cold enough, it has to be a beer. And yes, it really does work.

Will need some source for this. This sounds virtually impossible to pull off in practice even if it'd work in theory.

Parts required for particle detector:

Glass container

Alcohol vapor

Super-cold bottom (-26c or colder)

Technically all of the above would be present in a neck of a really cold beer, as it is being opened. But I don't think my fridge can make the beer cold enough. Soda obviously doesn't work because it contains no alcohol vapor. Also soda is solid at -26 c, unable to release vapors whereas beer will still be a liquid (I think probably depends on the beer).

I'm pretty sure I saw beer bottles break in my freezer due to content freezing. Don't know about a corona specifically thought

I managed to freeze a bottle of beer the other week when I put some in the freezer to cool down and forgot about the last one.

Bottle didn't break though the contents were sadly inaccessible - seemed to be an opaque white viscous slurry.

Charles Stross had an interesting short story about hobbiest particle accelerators called "Dechlorinating the Moderator": http://www.antipope.org/charlie/fiction/moderator.html

I was hoping this article would cover building a particle accelerator in a pool, but it only covers the detection part of the system.

> The problem seems to be that sound cards (or chips) in modern PCs are too clever for their own good. They are designed to optimise microphone input for Skype and Zoom and that means removing the noise and extraneous clicks that are exactly the signal that the detector puts out.

Ugh! I wonder what other hidden features are lurking on my laptop hardware. I am conflicted because while I understand perfectly well why market forces compel hardware manufacturers to add these "features", I don't like the idea of not being able to trust my primary computing hardware.

A 10-bit ADC chip and a Raspi zero together cost under $10 on Adafruit. You would sidestep the audio card altogether.

or one of those even cheaper 16bit USB soundcards https://github.com/ozel/DIY_particle_detector/wiki/Soundcard... I believe Steve (who wrote the blog) might have had the wrong cable for his other computer (3-pin vs. 4-pin 3.5 mm jack)

I've used the audio i/o hardware on mainstream notebook computers, and cheap USB audio adapters, for years, to perform audio signal analysis. This includes hardware purchased fairly recently.

The audio subsystems contain the basic DC blocking and anti-aliasing features that you'd expect, but do not seem to add any other processing unless you ask for it (e.g., equalization). At least, nothing that would be noticeable in either steady state or transient analysis.

So far as I know, apps like Skype and Zoom do their own processing.

Probably worth remembering that the sound card is generally designed to put out sound (or take in sound) for human perception.

These "features" are features because they better map the physically raw input to the actual desired input for the most common use case. Sound is only sound because of human perception; if the hardware is sensitive to EM interference that the human ear isn't sensitive to, that's noise (literally).

Quick tip for pulling these types of signals out of noise: use a trapezoidal filter. It's just the difference between two offset moving averages. The length of the average (peak time) serves as an integration that removes high frequency noise. The offset (gap time) provides differentiation of the integrated signal, which removes low frequency changes in baseline. Timing precision is improved by using the trap filter output rather than the raw signal compared to a threshold, as it effectively acts like a constant fraction discriminator. It also makes it easier to deal with pile-up events where multiple waveforms lie on top of each other, though that's improbable unless you measure a source that's really hot or pulsed.

In principle that is a good idea and nice digital version of analog pulse shaping. However, the pulses have a very distinctive shape (not visible in the blog post picture, but here in figure 7/9: https://www.mdpi.com/1424-8220/19/19/4264). My programs use the trigger level just to select which waveform snippets are recorded. The peaks themselves are then identified by their steep slopes which shows up nicely in the derivatives: https://github.com/ozel/DIY_particle_detector/blob/90c180207...

That is a typical kind of shape for a particle detector, though the time constants are very long which is a good thing because it's the result of the preamp doing some shaping to remove high frequency noise, which helps make the numerical integration less essential. However, I think you will find a trap filter will allow you to push to lower trigger thresholds more reliably. Calculating the slope from one sample to the next is equivalent to the output of a trap filter with peak time of 1 and gap time of 1. Once you enter the regime where the signal amplitude at each recorded sample is comparable to the magnitude of noise, especially for slow signals and fast background, the derivitive without any integration will start going crazy. What should matter most is recovering the area under the signal peak independent of noise on top of it, which will ultimately average to 0. An alternative method is to just integrate the entire signal over a window and then do baseline subtraction, but this still requires a robust trigger signal to indicate when to start integrating, which brings things back to the trap filter.

The pulse detection works really quite satisfactory with the current method and for beta-decay electrons and alphas. I also prefer that the derivative is easy to understand for students since this is still mainly an educational project. For detecting lower energy particles like fluorescence x-rays, your proposal would be certainly something to investigate. However, for improving the SNR I would in general first redesign the amplifier. It's really optimized for super low part count and costs at the moment. That said, I will definitely keep you suggestion in mind. Thanks!

Awesome to see an original EEE Pc still being used in 2020!

While not the original one, my 1215B is still working with the latest XUbuntu, upgraded to 8MB/SSD HD. :)

I missed the ATLAS/TDAQ HLT/Alice references, though. :)

A very interesting home experiment. I'm glad it worked. But "Clanhouse.com" is just ... so many red flags.

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