The $100 muon detector | Hacker News Reader

The $100 muon detector

symmetrymagazine.org

75 pointsjonbaer27 comments

Imagine outfitting a datacenter with these, and using them to understand the rate of bit flips in your processors. Maybe we'll find some parts of the Earth have fewer cosmic rays hitting there, and are thus are more naturally suited to being datacenters.

If you could find some undiscovered pattern in cosmic rays distributions, you'd be discovering something much more interesting than where to site your datacenter. If you could explain such an undiscovered pattern, you may be discovering what it's like to win a Nobel prize :-)

The basements of large buildings made from concrete spring to mind, then geographical areas that are at or below sea level.

Random thought: anti-coincidence detector? A detector above the RAM chips and one below with data processing set so that if the detector above gets a count and the one below does not or sees a count with significantly lower energy, you know some energy has been absorbed somewhere near the RAM.

This won't work because all particle detectors are noisy. Pretty much all tracking detectors need to use multiple coincidences to determine that a muon has indeed passed by. Individual counts by themselves are not reliable. My past life as a particle physicist included design and build of muon detectors using scintillating plastic and (much more expensive) multi-anode photomultipliers to look at nuclear composition of volumes. Something like an underfunded British version of decision sciences http://www.decisionsciences.com/ :-)

> The basements of large buildings made from concrete spring to mind

What is concrete made out of? Rocks? What do rocks contain? Radioactive elements.

So that's not actually the best way to protect against radiation.

The energy involved in radioactive decay is far less than that of cosmic rays. If the goal is to protect ICs from bit flips then indeed putting them under concrete or natural rock will reduce them.

You don't have a background in nuclear spectroscopy, and I claim my £5.

The irony of this: what is typically used for nuclear spectroscopy? Semiconductor detectors? If you get one out -- albeit probably a geranium^Wgermanium detector rather than silicon, if you do gamma rays -- potassium-40 products stand out in a typical environment. (I've mostly done that over sandstone -- why the lab was there; it may be different somewhere like Edinburgh.) Concentrated in a calibration source rather than a concrete block, it would be controlled.

IC vendors do terrestrial radiation testing on their parts and get upset rates. For example: http://www.koszek.com/papers/zynq_protons_r7.pdf

The paper: https://arxiv.org/abs/1606.01196

The paper contains the following link to the supplementary material which contains BOM, PCB drawings and some code:

https://dspace.mit.edu/handle/1721.1/102942

Edit: spelling and a little more info.

Given muons can catalyse the nuclear fusion of deuterium and tritium I wonder if you could extend this to your own very low power fusion reactor? Not quite sure where you get the deuterium and tritium.

https://en.wikipedia.org/wiki/Muon-catalyzed_fusion

Tritium from firearms optics or iron sight paint and you'd need to make the deuterium. Both quite expensive and still very doable.

Interesting, I was just looking at the SiPM (its $132 qty 1 (http://sensl.com/estore/microfc-60035-smt/)), nice to see it in use.

Any practical use?

It's a great educational project for a physics class, from what I can tell. The article (http://arxiv.org/abs/1606.01196) is nicely detailed and accessible to undergraduates. Good introduction to instrument design and construction, especially if (as the author suggests) the students are asked to write their own analysis software for it.

As far as applications go, the article offers a few ideas:

1. Measure the relative depths of subway stations across the city, using the measured muon rates.

2. Test relativistic time dilation on the cosmic ray flux by measuring the flux at various elevations, such as in an airplane or on a mountain, compared to sea level.

3. Investigate correlations between the atmospheric temperature/pressure/humidity and the count rate.

4. Investigate seasonal variations in muon rates.

5. Using multiple detectors, measure the angular muon rate by looking at the coincidence rate.

6. Lower the gain of the circuit to look at high-energy stopping muon events. Investigate whether or not one can see the Michel electron from the muon decay.

Tempted to build one, but I don't immediately understand how it discriminates between muons and other forms of ionizing radiation that an ordinary Geiger counter will pick up.

Scintillators are able to resolve particle energy, and can be used to measure a spectrum. Muons have very high energy, which can be used to identify them.

For extra certainty, you can use two stacked scintillators and only count a signal if it occurs in both of them within nanoseconds. This also allows determining the rough direction the particle came from since a particle that comes in at a low angle will not hit both detectors. Changing the distance between the scintillators will change the solid angle the instrument can 'see'. (as given by 5 in your list)

This guide for a student experiment has more background than the paper you linked:

http://home.fnal.gov/~group/WORK/muonDetection.pdf

> Scintillators are able to resolve particle energy

No, scintillators only detect a particle going through.

The amount of photons in the scintillator is proportional to the energy deposited. This is described by the Bethe-Bloch equation [1]. Pages 3-6 of this guide [2] have some plots and explanations on what that looks like for different particles.

How good that works in practice depends on the energy- and time resolution of the scintillator. Energy resolution depends on how different the light emission is for different energy depositions. Time resolution depends on how quickly the scintillator is back to a dark state (there are cascading effects from the deposited energy and there is a corresponding decay time). Anorganic material (eg NaI) is better in energy resolution, organic material (eg. plastic/polystyrene) is better in time resolution.

High energy resolution is good if you eg. want to look at a spectrum of nuclear fission products to find details of the fission process. High time resolution is good because it is easier to resolve different particles and you have a higher probability of a 'pure' signal.

[1] https://en.wikipedia.org/wiki/Bethe_formula

[2] http://home.fnal.gov/~group/WORK/muonDetection.pdf

> The amount of photons in the scintillator is proportional to the energy deposited.

Exactly: it is proportional to the energy deposited in the scintillator! Which, for a cosmic ray, can be a tiny fraction of the total energy. In order to measure the kinetic energy of a particle, you need to stop it. In that case, your detector is called a calorimeter.

My (NaI based) gamma spectrometer disagrees.

I suspect that this is a question of energy. At high energies, it's difficult/impossible to stop a particle, so you place a row of scintillators out, bend the charged particle path using a magnetic field and measure its displacement (and thus velocity and thus energy).

At lower energies, you can stop the particle in, e.g. an NaI detector which is known as calorimetry. Typically, of course, cosmic rays are quite high energy and given the low rate of muon interaction calorimetry is difficult/impossible. A HEP physicist may use both techniques, e.g. by using heavy-metal plates to cause an EM cascade and measure the resultant shower in a crystalline detector. But typically when one talks of scintillator devices (and almost certainly in the case of cosmic rays) one talks of tracking and measuring deflection in magnetic fields if wanting to measure the energy.

Your NaI detector is rubbish for spectroscopy because of the lousy resolution. High resolution studies in the UK in the 80s corrected several misapprehensions about the physics from attempted spectroscopy with NaI. It was only useful for Compton suppression as far as we were concerned, and soon replaced for that.

Not disputing that, but in undergraduate labs you're likely to find research cast-offs, though the only plastic scintillator experiment I've known (albeit 35 years ago) was purpose-built. There was also a Ge(Li) "jelly" counter, and demonstrators who didn't understand pile-up...

"Conrad and Axani have taken the detector down into the Boston subway, using the changes in the muon count to calculate the depth of the train tunnels."

The main point, though, is to expose younger students to undergraduate-level physics concepts cheaply and easily.

Why, does it need any?

Put it into a usb stick, or a keychain, and we could all be collecting data. The internet of things

The next sensor for phones?

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