Scintillocartography | Hacker News Reader

Scintillocartography

ivan.sanchezortega.es

49 pointsjdelacueva21 comments

One line in the piece says "Observing the direct effects of radiation, although possible, requires extraordinary circumstances.". While this is mostly true, you can actually observe radiation directly, with your own eyeballs, without any extraordinary methods. Basically all you need is a radioactive source, scintillator and a very dark room. That's how scintillation counting was done back in the day. This sort of device is called a Spinthariscope, you can find examples of them on youtube and what you see is a lot like the map in the OP. So I'd say the author did a good job.

The author probably counts these as indirect effects, as it is the collision of the α particles with zinc sulfide, and not a direct effect of radiation like Cherenkov.

isnt cherenkov also caused by interaction with water molecules?

edit: the article goes into a little more detail and talks about how its due to the different speeds of light in water and vaccuum, and I don't know enough about semantics or physics to say what this means about my original question :)

It's kinda a complicated question. Cherenkov radiation can be produced in any medium that has index of refraction greater than 1, that's what allows the charged particle radiation to go faster than the light it produces, which ultimate is what causes the Cherenkov light. The process is not reliant on the specific molecular/chemical/whatever properties of the medium, only dependent on the index of refraction. But, the index of refraction in turn comes from polarizabilty and magnetic susceptibility of the medium. Those factors depend on both what atoms & molecules exist in the medium, but also the structure of those molecules. For example, ice and water have the some chemical composition, but slightly different indices of refraction.

Well, for the purposes of observing the Cherenkov light it is fairly important the material is transparent at blue wavelengths :)

To be a bit nit-picky, Cherenkov light typically has a wide spectrum. For water it spans the entire optical range, peaking around 350nm and dying off at longer wavelengths. So you could, for example, put dye in water such that it absorbed more blue light, but you'd still be able to observe some red light from the Cherenkov radiation escaping. But the signal would be much fainter.

Although, one further caveat, changing a materials absorption spectrum will also change it's refractive index as a function of wavelength, which will in turn effect how much Cherenkov light is emitted at each wavelength. So the situation is more complicated still.

Agreed the classical electrodynamic approach lets us derive this relationship in terms of electric fields (Ampere-Maxwell and Gauss given a suitable gauge), a change in permittivity /varepsilon lets us change the region of this effect

Interesting read, it culminates in making a sparkly twinkly map to graphically convey radon location and strength which seems a bit 1980s to my mind.

    For the work in Nuclear Sessions I’ve used a 2017 dataset of radon potential, published by the Spanish Nuclear Safety Council. 

    This dataset was selected purely on the basis of availability: it was the easiest (and first) geographic dataset regarding radiation to be found.

They could have gone for the full Australian 256 channel raw (or post processed full spectrum or "artifical colour" U-K-Th 3-channel) dataset covering the bulk of the continent.

https://www.ga.gov.au/scientific-topics/disciplines/geophysi...

The usual practice is to accumulate one second sample windows of the gamma spectrum while travelling at 70 m/s, normalise the data to remove various wobble factors, and extract three significant channels to form an RGB image - you can always add fiddle layers to indicate radon or out of band features (such as uncommon trace elements from atomic tests).

That said when reading the title I though this might be about the new trend in radiometric sampling - using a scintallation source surround by layered spinning masks - when you get a gamma spark you can better guess to some degree the direction of the source, when many gamma interactions accumulate you can build up a pretty decent 3-D image of gamma sources surrounding your instrument.

One of these was recently trialed in the HN infamous Western Australia Mining Company loses Radiactive Source! stories from earlier this year.

I suppose this is as good place as any to ask: What is a good scintillating detector for DIY use? Geiger tubes are relatively easy to find, but all scintillators I could find were "ask for pricing" scientific equipment or some dubious old russian military stock (which I don't want even if it works).

Geiger tubes are click counters - number of gamma ray events within a large window, but was that click from Potassium by products, Uranium decaying, or Thorium falling apart?? Or, shock, horror, something "radioactive" from atomic fallout!! You'll never know.

If you want to identify stuff, you'll be looking for an energy spectrum.

If you're after an actual spectrum and you're thinking DIY then a starting point is a thalium doped sodium iodine cyrstal and electronics

https://alphaspectra.com/scintillation-detector-manufacturin...

https://www.alibaba.com/product-detail/2-inches-NaI-Scintill...

Alibaba is listing a single 50mm round x 50mm thick crystal plus electronics at 3K USD each (less than 10) which seems steep to me given years back we used 42 litre crystal packs (with CSIRO grown crystals and in house PhD electronics engineers, etc - so YMMV).

Now your problem is sampling the output levels several thousand times a second, binning the counts, and having a calibration source and compensating for tempreture drift.

You can buy a box that'll do that for you or you can <cough> DIY that with reference to radiometric survey field guides (there's one from AGSO - probably Bob Minty has his name on it).

A good all in one handheld is probably something like https://www.radiationsolutions.ca/wp-content/uploads/2020/03...

which is one of those "contact us and get a quote" jobs from a Canadian company of good repute with Jens Hovgaard, a Finn, as the Tech CEO | President.

He knows his stuff and has an industry algorithm named after him .. although others did similar work elsewhere about the globe.

I've had my eye on this one. Not affiliated, just looks fun.

https://www.radiacode.com/

Ok. This is very cool.

It is very neat for the price - the spectral resolution from Cesium Iodide is less than Sodium Iodide by more than half and it's a small crystal .. but it does pack a lot of fun into a small package.

If you're in the earth sciences, I linked a data sheet for the crystal: https://www.gammadata.se/assets/Uploads/CsITl-and-Na-data-sh...

There's a reddit community: https://old.reddit.com/r/Radiacode/

and a desktop interface: https://downloads.radiacode.com/EN/RC-101_Windows.pdf

with a few OS choices.

For semi serious use I'd want to continuously download full spectra with a (?) 2 to five second window (subject to understanding how well it counts, subsamples, saturates) and pool those spectra with GPS data to build up NASVD type "typical background" fingerprints to differentiate against to boost outlying signals.

I'd like to see the gadget user groups pooling their data also.

First thoughts on browsing the manual is that spectra export is a UI interface driven one at a time operation so someone would want to get into the guts of that and determine how to continuosly transfer to a server | home PC | nearby phone to retransmit, etc.

This, of course, might be in the reddit forum or Telegram group.

I might get a few of these as Xmas presents for a few folk I know that work with the bigger geophysical survey toys to get some cross over happening.

That is a fantastic pocket sized super fun gadget.

A relevant spec sheet to compare against what was outlined above is:

https://www.gammadata.se/assets/Uploads/CsITl-and-Na-data-sh...

The actual map animated map: https://ivan.sanchezortega.es/2023-02-radonmap/radonmap.html

> One of those circumstances is being close to a nuclear reactor submerged in water, which allows Cherenkov radiation to be observed. In layman’s terms: gamma radiation exits the reactor at the speed of light in a vaccuum, but the speed of light in water is lower, and photons have to slow down somehow. The direct, observable effect is that water glows blue.

Almost but not quite. The speed of light is always the speed of light. There's nothing wrong with gamma rays.

It's charged particles such as beta and alpha rays that generate the blue Cherenkov radiation. The writer's link to Wikipedia already reflects that.

The speed of light in a vacuum is always the same, but not through dielectric media such as water or glass. In diamond it is less than half the speed.

You're right, but I knew that. I should've worded my statement in such a way to prevent criticism.

Gamma rays always follow the speed of light in the medium that they travel through, because they are light. They cannot exceed the local speed of light, thus they cannot generate Cherenkov radiation. It must be particles with charge and non-zero mass that are capable of generating Cherenkov radiation.

> Cloud chambers seem to be a thing of the past

I saw one at the German Museum of Technology (Deutsches Technikmuseum) in Berlin: https://technikmuseum.berlin/en/spectrum/world-of-experiment...

> This blue glow has barely entered popular culture. The only two examples I’m aware of are the cinematographic depictions of the Chernobyl disaster, and the ficticious Nuka-Cola Quantum non-alcoholic beverage in the Fallout videogame series.

Don't forget Dr Manhattan from Watchmen!

At least in Brazil, because of this pretty infamous accident, people now know to be aware of blue light sources.

* https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident

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