And the muons produce two pulses in your detector, one when they are scattered to a stop and another when they decay. By measuring the time between the pulses you can fit the probability distribution and determine the half life of the mupn which is about 2.2 microseconds [1] And of course you can take measurements over time, at different altitudes and in different positions. If it wasn't for relativistic time dilation, muons would mostly decay high up in the atmosphere and not reach the ground.
This was one of the most popular experiments in the Physics 510 lab, which was the only class you had to take to get a Physics PhD at Cornell because it was so easy. It's also popular for high school physics for the same reason.
Simpler and cheaper and much more visual, build yourself a cloud chamber [1] and actually see the particle zip through it. A transparent container, a flash light, some isopropanol, and some dry ice and you are good to go. Maybe one could even replace the dry ice with really cold ice cube, then many people would have everything required at home, but I have only done it with dry ice so far.
It's things like this that remind me there's always a little more to discover. I've built a number of those SBM20 geiger counters but I've never come across this muon detector design before. Seems to be a pretty well known design:
Pro tip - not all the SBM-20 tubes on Ebay are created equal! Some sellers will happily sell you tubes that are shorted, open, or just don't work. The better ones test their tubes.
My new favorite sciencey DIY site. It reminds me of the early Popular Mechanics and Scientific American projects. Now all I need is lots more time (or less responsibility). These are the sorts of things that should be available in middle and high schools everywhere.
edit: Adding a link to a page with a list of projects on the site.
I'm the editor of Spectrum's "Hands On" DIY column: thank you so much! The general goal is to have projects that can be done in a weekend or three for less than roughly $300 and which point to something interesting beyond just the build itself. A lot of credit has to go to David Schneider who is the author of this piece, and has contributed many of Spectrum's citizen science projects.
BTW, If you want to see just the DIY projects instead of all our DIY-related coverage (which can include e.g. interviews or news articles) another handy link is:
Worth noting that IEEE is the professional society for electrical engineers. Spectrum seems to be their kind of pop-sci outreach magazine. But, being under IEEE’s umbrella makes it quite special, pop-sci magazines are always pulled toward the bombastic and over-dramatic. Spectrum, because of their origins in a research/professional EE society seems to remain more… grounded.
My good friend convinced another friend to do this for a "small" uni project.
They showed it worked to a very impressed professor, only to shortly after discover (and not reveal to the professor) that it was disconnected and they were just seeing noise.
He passed away a few months after, but this sparked a smile in me.
This is common in early stage research. And, should the students reveal the error to the professor, the reaction should have been along the lines "thank you for the update! It was a great idea. Ideas can at first appear to work due to luck or a methodology error, then fail. This is normal. Great job self-discovering the failure. Keep trying ideas, this is how the research is done!"
But it is important to eventually do more rigorous checks before going for a public announcement. See Robert Wood's debunking of N-rays for what happens when one does not.
Well, I have 2 experiences of discovering this to be the case in others' setups (one that they reported noise instead of results, or maybe even went further. They reported a massive success, and yes, better "results" than I did. They were always reporting zero + some noise as opposed to measurement + noise. Given that it was always reporting zero I might be convinced this was a mistake rather than cheating, but ... they certainly didn't correct anything. Their method just didn't work, so they measured small values, which made the noise on their sensor actually close to the correct value (they "corrected" negative values by ignoring the minus sign). Another was a case of dissolved metals suddenly appearing out of nowhere in test tubes, changing the results (where only 3 people, not including me, but including the professor, has access to them) and in one case I was ignored, in the other case punished (essentially fired).
When I have the time, I'd like to build an antenna to try to pick up the hydrogen line from space.
Just that simple thing is so strange to me, that with a handful of components you can listen to the cosmos. I really wish science classes would have included that sort of thing.
Sounds a bit like Lofar. Stick a few hundred antennas into a field, collect all the raw data, and then do some herculean signal processing and you end up with a fantastic radio telescope that you can "point" retrospectively, e.g. to look at something that just happened in the gamma, before it happened (on a scale of seconds).
The title here is incorrect; this is not tomography (and the OP doesn't claim it is). The article mentions tomography but what's happening here is individual measurements.
Tomography is also pretty cool, although the math is pretty painful (Terry Tao has papers on it)
True. That said, I'll also mention that tomography is a very rich, interesting field that's still open to new innovations. I work in the area and unfortunately needed to pass on a muon tomography contract some years ago. By the way, you may know this, but the following is for the broader audience.
---
If anyone is interested, the book Parameter Estimation and Inverse Problems by Aster, Borchers, and Thurber give an easy introduction to simple tomography problems in their book. Example 1.12 in their second edition has a very basic setup. More broadly, tomography intersects with an area of study called PDE constrained optimization. Commonly, tomography problems are setup as a large optimization problem where the difference between experimental data and the output of a simulation are minimized. Generally, the simulation is parameterized on the material properties of whatever is under study and are the optimization variables. The idea is that whatever material property that produces a simulation that matches the experimental data is probably what's there. This material property could be something simple like density or something more complicated like a full elasticity tensor.
What makes this difficult, is that most good simulations come from a system of differential equations, which are infinite dimensional and not suitable for running directly in an optimization algorithm. As such, care must be taken into discretizing the system carefully, so that the optimization tool produces something reasonable and physical. Words you'll see are things like discretize-then-optimize or optimize-then-discretize. Generally speaking, the whole system works very, very poorly if one just takes an existing simulator and slaps an optimizer on it. Care must be taken to do it right.
As far as the optimizer, the scale is pretty huge. It's common to see hundreds of millions of variables if not more. In addition, the models normally need to be bounded, so there are inequalities that must be respected. For example, if something like a density isn't bounded to be positive (which is physical), then the simulator itself may diverge (a simulator here may be something like a Runge-Kutta method.)
Anyway, it's a big combination of numerical PDEs, optimization, HPC, and other tools just to get a chance to run something. Something like the detector in the article is very cool because it may be a realistic way to get data to test against for super cheap.
I saw a wonderful demonstration of a supper simple interactive tomographic reconstruction (in a web page explaining what a CAT scan is). I cannot find it anywhere now. It produced pretty good results with the simple algorithm and was easily understood. It just drew stripes across the reconstruction image of the value of the average measurement of each row of the sample image and then rotated both images and did it again (maybe someone can explain it better).
Sure. But nowhere does the article claim to be combining measurements, or doing tomography. He's making his inferences directly from the values of the individual measurements. Tomography is a mathematical way to combine measurements to get more information than by just looking at the individual results.
Back when I was a physics student, I helped engineer exactly this experiment as a off-the-shelf solution for schools as a classroom experiment! We used PMTs mounted on top of coffee cans:
The FTL muons produce Cherenkov radiation in the water in the coffee cans, which is picked up by the PMTs.
Using this setup gives a much higher rate, as the surface is much larger compared to geiger tubes. Thus it's possible to quickly capture a sufficient amount of muons.
Weird coincidence...I live roughly 2-miles from Reed Gold Mine. This sounds like a lot of fun, I look forward to trying this out. I also have family who are geologists, we spend a lot of time vacationing near abandoned mica mines, and our hiking is frequently scored by the chip-tuned sounds of my uncle's hacked Geiger counter (he rigged it up with an ADC and micro-controller so he can hear not only counts-per-second, but also some other metrics he has mapped to the tone's pitch).
I've wanted to make such a thing, but that got me thinking about a 6 tube design, three tubes on each layer in a # pattern, to get some angular resolution.
It also got me down the path of making a scintillation detector. However I've yet to find a hardware store source of scintillating material.
I kinda wanted something that didn't rely on a one-off source like asking my local uni for some scraps.
Plastic scintillator from Eljen isn't very expensive, especially if you only need a few cubic inches.
You can do very well with optically isolated pixels stacked together, followed by a common diffuser, followed by a drift gap, then 4 pmts or a position sensitive pmt with 4 cathodes. This will let you identify the struck pixel with less instrumentation. You can passively couple the outputs with resistors to get a horizontal and vertical position signals so you only need 2 data acquisition channels.
> Plastic scintillator from Eljen isn't very expensive
Do they sell directly to private individuals? If not, where would I get some? There are some listings on eBay but not exactly the place I prefer to shop such stuff.
I order stuff from them all the time in small quantities to a university, and a normal person's credit card should be much more convenient for them than dealing with procurement beurocracy, net90, etc.
The plastic scintillator is chemically just plastic so there are no safety complications shipping or receiving it. You might have more trouble getting large amounts of liquid scintillator because of the solvents.
Another thing you might consider is scintillating fiber with wavelength shifter. If you read out from both ends you can estimate position within the fiber by timing and possibly amplitude weighting.
This may be a stupid question, but is this thing emitting anything or is it simply a passive detector? I’m mainly worried about any potential health risks.
In the most pedantic sense, yes: electrons, magnetic fields, infrared light, etc. It's not designed to, nor is it likely to, emit any sort of ionizing radiation
> simply a passive detector
Yes, it is a passive detector
> I’m mainly worried about any potential health risks
You are bombarded with radiation constantly. If you've flown on a plane, you are exposed to several times ionizing radiation levels that you experience on the ground. If you've stepped outside and witnessed a lightning storm you have exposed yourself to high energy gamma rays and neutrons. If you've ever eaten a banana, spent the night in a strangers bed, strayed near clay river beds, entered a basement of a house, or stepped outside in sunlight you have exposed yourself to substantial increase of ionizing radiation compared to baseline.
Humans brains have an extraordinarily hard team comprehending logarithmic scales. "Safe" radiation exposure isn't "None", as that's pretty much impossible. Your body has also long ago evolved to deal with these problems and can easily handle 100x times what occurs naturally at the ground without even a single health effect.
If you want zero exposure, the only real option is to move to an undersea bubble thousands of feet below the sea, but even seawater contains radioactive ions from the metal salts dissolved in it.
The most dangerous thing about this is that the geiger tubes run at about 400V, backed by a small capacitor. If you touch it, it will feel about like getting hit by a bug zapper.
You may be extremely lucky, but these detectors come from everywhere, even could be from exactly some nuclear facility like Chernobyl, so contaminated with radioactive dust.
But, for Russian electronics exists good rule - handle in gloves and wipe with alcohol before use (sure than properly utilize used swabs).
So you will clear all dust from surface, and if you will not used to suck or crunch radio components you are in safety as from my own experience these detectors are really durable.
This might be the easiest "particle physics without a particle accelerator" experiments you can do. This is your accelerator:
https://en.wikipedia.org/wiki/Air_shower_(physics)
And the muons produce two pulses in your detector, one when they are scattered to a stop and another when they decay. By measuring the time between the pulses you can fit the probability distribution and determine the half life of the mupn which is about 2.2 microseconds [1] And of course you can take measurements over time, at different altitudes and in different positions. If it wasn't for relativistic time dilation, muons would mostly decay high up in the atmosphere and not reach the ground.
This was one of the most popular experiments in the Physics 510 lab, which was the only class you had to take to get a Physics PhD at Cornell because it was so easy. It's also popular for high school physics for the same reason.
[1] https://en.wikipedia.org/wiki/Muon
Simpler and cheaper and much more visual, build yourself a cloud chamber [1] and actually see the particle zip through it. A transparent container, a flash light, some isopropanol, and some dry ice and you are good to go. Maybe one could even replace the dry ice with really cold ice cube, then many people would have everything required at home, but I have only done it with dry ice so far.
[1] https://en.wikipedia.org/wiki/Cloud_chamber
[dead]
It's things like this that remind me there's always a little more to discover. I've built a number of those SBM20 geiger counters but I've never come across this muon detector design before. Seems to be a pretty well known design:
* https://www.hackster.io/jdpetrey/muon-detector-23bb72 * https://www.madexp.it/2024/11/19/muon-and-geiger-counter/ * https://iopscience.iop.org/article/10.1088/0031-9120/50/3/31...
Pro tip - not all the SBM-20 tubes on Ebay are created equal! Some sellers will happily sell you tubes that are shorted, open, or just don't work. The better ones test their tubes.
The cosmic watch detector is cheaper, more reliable (due to above shenanigans), and uses only 1 piece of plastic scintillator.
It might take more work though. They don't say it but I believe you should try to see if other scintillator materials work. (Including PET,PSU,PES).
http://cosmicwatch.lns.mit.edu/
My new favorite sciencey DIY site. It reminds me of the early Popular Mechanics and Scientific American projects. Now all I need is lots more time (or less responsibility). These are the sorts of things that should be available in middle and high schools everywhere.
edit: Adding a link to a page with a list of projects on the site.
https://spectrum.ieee.org/topic/diy/
I'm the editor of Spectrum's "Hands On" DIY column: thank you so much! The general goal is to have projects that can be done in a weekend or three for less than roughly $300 and which point to something interesting beyond just the build itself. A lot of credit has to go to David Schneider who is the author of this piece, and has contributed many of Spectrum's citizen science projects.
BTW, If you want to see just the DIY projects instead of all our DIY-related coverage (which can include e.g. interviews or news articles) another handy link is:
https://spectrum.ieee.org/type/hands-on/
Worth noting that IEEE is the professional society for electrical engineers. Spectrum seems to be their kind of pop-sci outreach magazine. But, being under IEEE’s umbrella makes it quite special, pop-sci magazines are always pulled toward the bombastic and over-dramatic. Spectrum, because of their origins in a research/professional EE society seems to remain more… grounded.
My good friend convinced another friend to do this for a "small" uni project. They showed it worked to a very impressed professor, only to shortly after discover (and not reveal to the professor) that it was disconnected and they were just seeing noise.
He passed away a few months after, but this sparked a smile in me.
This is common in early stage research. And, should the students reveal the error to the professor, the reaction should have been along the lines "thank you for the update! It was a great idea. Ideas can at first appear to work due to luck or a methodology error, then fail. This is normal. Great job self-discovering the failure. Keep trying ideas, this is how the research is done!"
But it is important to eventually do more rigorous checks before going for a public announcement. See Robert Wood's debunking of N-rays for what happens when one does not.
Well, I have 2 experiences of discovering this to be the case in others' setups (one that they reported noise instead of results, or maybe even went further. They reported a massive success, and yes, better "results" than I did. They were always reporting zero + some noise as opposed to measurement + noise. Given that it was always reporting zero I might be convinced this was a mistake rather than cheating, but ... they certainly didn't correct anything. Their method just didn't work, so they measured small values, which made the noise on their sensor actually close to the correct value (they "corrected" negative values by ignoring the minus sign). Another was a case of dissolved metals suddenly appearing out of nowhere in test tubes, changing the results (where only 3 people, not including me, but including the professor, has access to them) and in one case I was ignored, in the other case punished (essentially fired).
I would say much of my career in science consisted of getting results, showing them to smarter people, and being told I was just looking at noise.
(most of the time, that was true)
When I have the time, I'd like to build an antenna to try to pick up the hydrogen line from space.
Just that simple thing is so strange to me, that with a handful of components you can listen to the cosmos. I really wish science classes would have included that sort of thing.
You're in luck! David Schneider, the author of this piece, also built a $150 hydrogen line antenna for us, based on a TV tuner SDR:
https://spectrum.ieee.org/track-the-movement-of-the-milky-wa...
:)
Unfortunately I'm in the middle of moving, but once I'm done with that, I'll give this a try :)
FYI, an antenna for the 21 cm line can be extremely low effort:
https://spaceaustralia.com/news/diy-radio-telescope-sees-fir...
Unfortunately I'm in the middle of moving, but once I'm done with that, I'll give this a try :)
> that with a handful of components you can listen to the cosmos
Tuning an analog radio or TV between stations also accomplishes this in a more abstract way.
Could tuning several analog radio receivers between station be used in some sort of synthetic aperture telescope?
Sounds a bit like Lofar. Stick a few hundred antennas into a field, collect all the raw data, and then do some herculean signal processing and you end up with a fantastic radio telescope that you can "point" retrospectively, e.g. to look at something that just happened in the gamma, before it happened (on a scale of seconds).
https://www.astron.nl/telescopes/lofar/
yes, but in an inefficient way, similar to how large clusters with ECC are weak cosmic ray detectors.
This is pretty cool.
The title here is incorrect; this is not tomography (and the OP doesn't claim it is). The article mentions tomography but what's happening here is individual measurements.
Tomography is also pretty cool, although the math is pretty painful (Terry Tao has papers on it)
True. That said, I'll also mention that tomography is a very rich, interesting field that's still open to new innovations. I work in the area and unfortunately needed to pass on a muon tomography contract some years ago. By the way, you may know this, but the following is for the broader audience.
---
If anyone is interested, the book Parameter Estimation and Inverse Problems by Aster, Borchers, and Thurber give an easy introduction to simple tomography problems in their book. Example 1.12 in their second edition has a very basic setup. More broadly, tomography intersects with an area of study called PDE constrained optimization. Commonly, tomography problems are setup as a large optimization problem where the difference between experimental data and the output of a simulation are minimized. Generally, the simulation is parameterized on the material properties of whatever is under study and are the optimization variables. The idea is that whatever material property that produces a simulation that matches the experimental data is probably what's there. This material property could be something simple like density or something more complicated like a full elasticity tensor.
What makes this difficult, is that most good simulations come from a system of differential equations, which are infinite dimensional and not suitable for running directly in an optimization algorithm. As such, care must be taken into discretizing the system carefully, so that the optimization tool produces something reasonable and physical. Words you'll see are things like discretize-then-optimize or optimize-then-discretize. Generally speaking, the whole system works very, very poorly if one just takes an existing simulator and slaps an optimizer on it. Care must be taken to do it right.
As far as the optimizer, the scale is pretty huge. It's common to see hundreds of millions of variables if not more. In addition, the models normally need to be bounded, so there are inequalities that must be respected. For example, if something like a density isn't bounded to be positive (which is physical), then the simulator itself may diverge (a simulator here may be something like a Runge-Kutta method.)
Anyway, it's a big combination of numerical PDEs, optimization, HPC, and other tools just to get a chance to run something. Something like the detector in the article is very cool because it may be a realistic way to get data to test against for super cheap.
I saw a wonderful demonstration of a supper simple interactive tomographic reconstruction (in a web page explaining what a CAT scan is). I cannot find it anywhere now. It produced pretty good results with the simple algorithm and was easily understood. It just drew stripes across the reconstruction image of the value of the average measurement of each row of the sample image and then rotated both images and did it again (maybe someone can explain it better).
The "individual measurements" add up to tomography, there's no need to them to be fast or simultaneous if you are imaging caves or pyramids.
Sure. But nowhere does the article claim to be combining measurements, or doing tomography. He's making his inferences directly from the values of the individual measurements. Tomography is a mathematical way to combine measurements to get more information than by just looking at the individual results.
Back when I was a physics student, I helped engineer exactly this experiment as a off-the-shelf solution for schools as a classroom experiment! We used PMTs mounted on top of coffee cans:
http://kamiokanne.uni-goettingen.de/gb/kamiokanne.htm
The FTL muons produce Cherenkov radiation in the water in the coffee cans, which is picked up by the PMTs.
Using this setup gives a much higher rate, as the surface is much larger compared to geiger tubes. Thus it's possible to quickly capture a sufficient amount of muons.
Weird coincidence...I live roughly 2-miles from Reed Gold Mine. This sounds like a lot of fun, I look forward to trying this out. I also have family who are geologists, we spend a lot of time vacationing near abandoned mica mines, and our hiking is frequently scored by the chip-tuned sounds of my uncle's hacked Geiger counter (he rigged it up with an ADC and micro-controller so he can hear not only counts-per-second, but also some other metrics he has mapped to the tone's pitch).
I've wanted to make such a thing, but that got me thinking about a 6 tube design, three tubes on each layer in a # pattern, to get some angular resolution.
It also got me down the path of making a scintillation detector. However I've yet to find a hardware store source of scintillating material.
I kinda wanted something that didn't rely on a one-off source like asking my local uni for some scraps.
Plastic scintillator from Eljen isn't very expensive, especially if you only need a few cubic inches.
You can do very well with optically isolated pixels stacked together, followed by a common diffuser, followed by a drift gap, then 4 pmts or a position sensitive pmt with 4 cathodes. This will let you identify the struck pixel with less instrumentation. You can passively couple the outputs with resistors to get a horizontal and vertical position signals so you only need 2 data acquisition channels.
> Plastic scintillator from Eljen isn't very expensive
Do they sell directly to private individuals? If not, where would I get some? There are some listings on eBay but not exactly the place I prefer to shop such stuff.
I order stuff from them all the time in small quantities to a university, and a normal person's credit card should be much more convenient for them than dealing with procurement beurocracy, net90, etc.
The plastic scintillator is chemically just plastic so there are no safety complications shipping or receiving it. You might have more trouble getting large amounts of liquid scintillator because of the solvents.
Another thing you might consider is scintillating fiber with wavelength shifter. If you read out from both ends you can estimate position within the fiber by timing and possibly amplitude weighting.
This may be a stupid question, but is this thing emitting anything or is it simply a passive detector? I’m mainly worried about any potential health risks.
> is this thing emitting anything
In the most pedantic sense, yes: electrons, magnetic fields, infrared light, etc. It's not designed to, nor is it likely to, emit any sort of ionizing radiation
> simply a passive detector
Yes, it is a passive detector
> I’m mainly worried about any potential health risks
You are bombarded with radiation constantly. If you've flown on a plane, you are exposed to several times ionizing radiation levels that you experience on the ground. If you've stepped outside and witnessed a lightning storm you have exposed yourself to high energy gamma rays and neutrons. If you've ever eaten a banana, spent the night in a strangers bed, strayed near clay river beds, entered a basement of a house, or stepped outside in sunlight you have exposed yourself to substantial increase of ionizing radiation compared to baseline.
Humans brains have an extraordinarily hard team comprehending logarithmic scales. "Safe" radiation exposure isn't "None", as that's pretty much impossible. Your body has also long ago evolved to deal with these problems and can easily handle 100x times what occurs naturally at the ground without even a single health effect.
If you want zero exposure, the only real option is to move to an undersea bubble thousands of feet below the sea, but even seawater contains radioactive ions from the metal salts dissolved in it.
The most dangerous thing about this is that the geiger tubes run at about 400V, backed by a small capacitor. If you touch it, it will feel about like getting hit by a bug zapper.
Apart from that, yes, they are passive detectors.
You may be extremely lucky, but these detectors come from everywhere, even could be from exactly some nuclear facility like Chernobyl, so contaminated with radioactive dust.
But, for Russian electronics exists good rule - handle in gloves and wipe with alcohol before use (sure than properly utilize used swabs). So you will clear all dust from surface, and if you will not used to suck or crunch radio components you are in safety as from my own experience these detectors are really durable.
It uses the muons that you are naturally being bombarded with!
No, it is safe. It is not emitting anything, just detecting.
Could this be of consequence to, say, a treasure hunting operation? Perhaps in the North Atlantic?
A treasure hunt? On Oak Island? Could it be...?
Is it a Spanish galleon? Or, perhaps, the Knights Templar?
Tomography or tombography :)