Geiger counters are a popular hacker project, and may yet prove useful if and when the nuclear apocalypse comes to pass. They’re not the only technology out there for detecting radiation however. Scintillation detectors are an alternative method of getting the job done, and [Alex Lungu] has built one of his own.
Scintillation detectors have several benefits over the more common Geiger-Muller counter. They work by employing crystals which emit light, or scintillate, in the presence of ionizing radiation. This light is then passed to a photomultiplier tube, which emits a cascade of electrons in response. This signal represents the level of radioactivity detected. They can be much more sensitive to small amounts of radiation, and are more sensitive to gamma radiation than Geiger-Muller tubes. However, they’re typically considered harder to use and more expensive to build.
[Alex]’s build uses a 2-inch sodium iodide scintillator, in combination with a cheap photomultiplier tube he scored at a flea market for a song. [Jim Williams]’s High Voltage, Low Noise power supply is used to run the tube, and it’s all wrapped up in a tidy 3D printed enclosure. Output is via BNC connectors on the rear of the device.
Testing shows that the design works, and is significantly more sensitive than [Alex]’s Geiger-Muller counter, as expected. If you’re interested in measuring small amounts of radiation accurately, this could be the build for you. We’ve seen this technology used to do gamma ray spectroscopy too.
I picked up a photomultiplier tube from a skip. It looks like it was unused (still in original box).
I am not sure how to test it (don’t want to ruin it in the process).
Please use caution when testing high voltage devices! I would recommend that you look up a data sheet for your specific device. You need to properly bias each dynode, so the you need to build a restive voltage divider. Then you need proper amplification of the signal that comes out. It’ll take some learning. Again, high voltage can kill/injure, so spend the time to educate yourself first.
He might luck out and have one of the more modern tubes that have the dynode resistor chain built in. Much easier to play with unless you have a handy source of really big R values.
The photomultiplier tube will need less than 1mA, so its supply will not be very dangerous. I think you are more likely to hurt yourself from the shock reaction than the current itself.
This is probably useful for you, Ren.
https://www.hamamatsu.com/resources/pdf/etd/PMT_handbook_v3aE.pdf
A good reference, thanks
Umm, just a comment, high voltage doesn’t kill, AC current running thru your heart does. I f high voltage kills, I’d a been dead 30 years ago from leaky TV focus dividers
DC across your heart will kill you, too, it’s just that the threshold is higher.
Power supplies that are designed for driving scintillator PMTs usually only deliver a few hundred microamps at most. They’re dangerous, but not THAT dangerous. It’s also really hard to shock yourself if you are using the proper connectors.
The real danger is if you are driving them with some kind of DIY HVPS that is able to deliver more current and/or is not properly enclosed etc.
Actually what hurts most people is being bit and reacting violently. yanking their arms back or jumping up, and hurting themselves in the process. The shock is much less painful and easier on our body than yanking your arm back into a wall. The nice thing is most radiation monitoring devices use ultra low current. When you get into playing with ham linear amps, or high powered commercial transmitters, x ray machines, or things of that ilk, you can get into a heap of trouble. The kind of trouble you get get into once.
Keep the frequency nice and high and the amps nice and low… Let the skin effect save you :D
Umm, that’s an ignorant dangerous meme, because it ignore the roles voltage plays in driving lethal currents. The reason Andy is still around is because they have yet to encounter a condition where high voltage can drive lethal current trough their body. This meme has cause at least two YouTube channels to produce videos, that teach the facts rather than belching out a phrase that should have been discounted when it was first created.
I stand corrected somewhat, someday comment authors will be able to redact them, themselves…
The field of study of electrocutions is most likely a whole bunch of non talking victims
https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html
Pardon my ignorance, but why is a photomultiplier tube used as opposed to an avalanche Photodiode?
1) you will not easily find an APD in the trash or in an auction for a few dollars
2) APDs can’t do spectrum
3) at this time and age, “silicon photomultiplers” (yes, I know it’s just an array of APDs) are the way to go, the cost is coming down to a point where normal people can afford buying them and you can buy them in single quantities (provided your country is not on the ITAR nono list)
Does anyone else notice this article has a huge blank space between the sponsor logos and category/tags, or do I just need a photomultiplier tube to see what’s there?
Nope, it’s the same way for me. If you drag select, you can see there are a bunch of blank spaces on new lines.
Photomultipliers are a pain in the rear. They require not just HV but also magnetic shielding, which gets expensive in a hurry. Not exactly a hacker’s dream. Now, figuring out how to do this with an avalanche photodiode might be interesting, but I remain unimpressed.
ditch the single APDs and get with the times… https://en.wikipedia.org/wiki/Silicon_photomultiplier
an example use case: http://cosmicpi.org/uploads/Cosmic-Pi-Orconf-2015-final.pdf
technically you can use them without shielding, but you have to keep them stationary and even then the sensitivity will drift…
btw this is a thing and amateurs can buy it… https://en.wikipedia.org/wiki/Silicon_photomultiplier
In radiology for a long time now film has been increasingly replaced by digital detector panels that are an XY array of phototransistors or photodiodes joined to a large thin scintillation crystal.
For JUST a simple single photodiode scintillation detector which can discriminate between various isotopes by way of the photopeak, it should be easy to grow a salt crystal around the photodiode. This is entirely within the reach of any hacker, albeit a task requiring some patience.
IMHO having the patience would be the greater part of the task.
Doubt you could market anything like this as it’s all been covered by multiple patents.
Growing single, (relatively) large, optically nearly perfect crystals of hygroscopic salts, while quite DIY-able, is NOT easy!
Traditionally NaI:Tl crystals are grown from a molten pool using a carefully maintained temperature gradient, you (reeeeally) slowly move the growing crystal to keep it growing. A newer and more interesting method is keep everything in place and move the temperature gradient instead.
I have a project on the long “want” list, to try and make a computer controlled kiln with multiple, individually controlled heating elements, that could repeatably slowly move the temperature gradient through the kiln, so a large crystal could be easily grown…(and to automatically do the controlled cooldown once finished, because the entire growing and cooling operation takes literal days and cannot be interrupted)
BTW the resultant crystal is very sensitive to temperature changes (will crack if you hurry too much with the cooling) and very hygroscopic when cold – once it absorbs water, the crystal structure is irreversibly damaged, then you have to start over.
There are non-gyroscopic inorganic scintillators, but those typically require stupidly high temperatures to grow from a melt.
If you want to coat the sensing elements, organic scintillators might be a better choice.
Scintillation counters can have their surprises: When I was a kid ,my father was working with isotopes in medical research, and fallout from nuclear tests in Nevada would blow through once in a while and everyone would just have to go home for the day because the scintillation counters would just go berserk.
Size. Recovery time. HV supply.
Blog post presenting OpenSPAD: http://www.gaudi.ch/GaudiLabs/?page_id=718