[BetterGeiger]

I think the core of the explanation given is correct but some of the adjacent details need adjustment. The important part is:

"Clothes dryers are very effective at making statically charged surfaces. (Dryer sheets help.) So when radon and its temporary decay products are blown through the dryer, electrically-polarized molecules tend to be attracted to the charged surfaces"

What that commenter misses is that nearly all hobbyist grade detectors (Geiger tubes) are not sensitive to alpha but they are highly sensitive to beta and a little sensitivity to gamma. However, any thin solid will block beta, so they would need the Geiger tube to be very near the radiation emitting material to pick up the beta. In other words, if they're just waving the detector around they're probably just catching the gamma.

The radon in the air decays into various progeny, and by the time it reaches the dryer that will be to some extent in equilibrium, so several isotopes, including gamma emitters, will be present in the mix. Therefore I'm not surprised the detector reads a tiny bit of that.

Why it dissipates is probably not a decay thing but rather the accumulated material gradually diffusing away from the filter or whatever after the dryer is turned off and no longer actively accumulating radon.

This could be tested by putting a detector right next to the filter to see how much beta it picks up. I've basically done that with a home air filter:

https://twitter.com/BetterGeiger/status/1605639346865901570?...

That's with the detector I make and sell which is primarily sensitive to gamma, which is why I could register a reading through the plastic container, even a couple days after preparing the test. When I used a pancake style detector sensitive to alpha and beta, directly against the exposed filter, the detector reacted much more strongly... But the Better Geiger S-1 gives an accurate dose reading, the Geiger tube or pancake probe will dramatically overestimate dose in that scenario, which can cause undue concern... In reality it's pretty harmless levels of radiation. :)

[antognini]

> hobbyist grade detectors (Geiger tubes) are not sensitive to alpha but they are highly sensitive to beta and a little sensitivity to gamma.

This was part of the reason why it took so long to discover the cause of Alexander Litvinenko's death by Polonium-210 poisoning. Doctors (and later detectives) had suspected some form of radiation poisoning, but the early tests used Geiger counters and came back negative. But Po-210 decays almost exclusively by emitting an alpha particle which is not detectable by Geiger counters. (And it also means it's not very dangerous outside the body but becomes extremely toxic if ingested.)

[BetterGeiger]

Yes, and even if you have a high-end alpha detector, ingested radioactive material cannot be detected externally if it's only emitting alpha. One would need to take a blood sample or something like that and do more complicated tests.

[jojobas]

Polonium-210 is a very rare example of near pure alpha-decay chain, radon decay products are short-lived and emit both beta and gamma particles.

[antognini]

Yes, this is why the idea to use Po-210 was a stroke of (evil) genius. Because of its unique decay profile it is extremely hard to detect. The FSB agents who did this could obtain a small but lethal dose of Po-210 in Russia and then carry it across borders dissolved in a vial of water. In that state it is not dangerous, so the agents had little risk to themselves by carrying it. And it is also undetectable by border security, even if they were monitoring for radiation.

[misja111]

Thanks for all the great insights! But why was the Po-210 not dangerous in that vial of water? It seems many people who got in touch with it got ill: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767288/

[FormFollowsFunc]

According to another article the glass wall of the vial stops the radiation.

https://www.argonelectronics.com/blog/litvinenko-and-the-per...

[Gare]

That was after they opened it.

Also, from the article:

> The UK Health Protection Agency, which is advising authorities on technical aspects of the case, characterises the contamination in all 12 cases as “not significant enough to result in any illness in the short term,” while “any increased risk in the long term is likely to be very small.”

[jojobas]

When alpha particles are stopped by anything, secondary x-rays are created. I wonder if airport x-ray machines are sensitive enough to pick that up.

[brippalcharrid]

It would probably just appear as faint noise, and then only if it happened to be at wavelengths that the sensors were tuned to detect, and which the machine's signal processors weren't trying to ignore, and if the image processing was designed to draw attention to it.

[simmo9000]

Reading more on Po-210, apparently it is used in anti-static objects.

"An antistatic fan made by NRD, of Grand Island, N.Y., contains 31,500 microcuries of polonium 210 — or, in theory, more than 10 lethal doses."

Source: https://www.nytimes.com/2006/12/03/weekinreview/03broad.html

[jxf]

How did it get detected?

[antognini]

His symptoms were consistent with radiation poisoning and because he was a high profile dissident his case attracted enough attention that the Atomic Weapons Establishment tested his blood and urine.

They performed gamma ray spectroscopy but did not discover any strong signals, except for a very small spike at 803 keV. Some of the scientists were talking about the case and they were overheard by an older scientist who had worked on the UK's atomic weapons program back in the 50s. The early bombs relied on Po-210 and he recognized that 803 keV line as being characteristic of Po-210. Although the decay is almost exclusively via alpha particles, a very small fraction of decays happen via emission of a gamma ray at 803 keV.

Once they had the connection to Po-210 it was straightforward to test for its presence in his body.

[codethief]

> except for a very small spike at 803 keV. Some of the scientists were talking about the case and they were overheard by an older scientist who had worked on the UK's atomic weapons program back in the 50s. The early bombs relied on Po-210 and he recognized that 803 keV line as being characteristic of Po-210

I don't understand. So professionals from the AWE tried to identify the measured radiation lines from memory(?!), instead of consulting a publicly available database of spectral & decay lines? It's been a while since I've done any spectral analysis but I used to use ie.lbl.gov a lot (seems offline unfortunately) and they had a search function[0] that allowed you to filter their entire database of isotopes and decay chains by whatever line you were looking for.

[0]: https://web.archive.org/web/20150408041531/http://ie.lbl.gov...

[nocoiner]

Man, so glad I decided to finally click on the comments after seeing the article at the top of hn most the day - we don’t have radon where I live (I don’t think?) so I figured the dryer thing wasn’t applicable to me.

But for the vast majority of my life, I’ve always wanted a Geiger counter, and once they were cheap and readily available on Amazon, I was just about to pull the trigger. And then Fukushima happened a week later and sent prices into the stratosphere.

A few times recently I idly looked at the ones on Amazon but never got around to it because I couldn’t tell which were junky crap and which were somewhat more expensive junky crap.

But very cool to see a knowledgeable manufacturer explaining his product in a highly relevant comment thread. Finally, the radiation detector for me!

There’s a former 12 year old kid out there who still remembers the Geiger counter exhibit from taking a pre-9/11 NPP tour who’s going to be very excited for something coming in the mail in the next week or two.

[BetterGeiger]

Fantastic! Let me know if you have any questions... and be sure to find a current 12 year old kid to plant the seed of interest in radiation. :)

[hermitdev]

What's NPP here?

[S3rM5Y5]

Nuclear Power Plant

[thewanderer1983]

>What that commenter misses is that nearly all hobbyist grade detectors (Geiger tubes) are not sensitive to alpha

from the original post: "If your Geiger counter is actually detecting radiation, it's almost certainly the half-hour lead and bismuth. " If you look at the table he provided lead and bismuth are beta decay. It is likely he is specifying that on the fact that most home geiger counters only detect beta and gamma not alpha.

[Turskarama]

Could also be a happy accident though. Half an hour is short enough that the amount of radiation emitted is pretty high, but long enough that it hasn't pretty much all decayed by the time you try to measure it.

[BetterGeiger]

You are right, the commenter implied that.

[K2h]

$149 for https://www.bettergeiger.com/product-list/p/better-geiger-ra...

[ilyt]

I'm mildly disappointed that banana is not listed as option for test material

[Turskarama]

Even though bananas are famously radioactive, it's very low activity and I don't know that a regular detector could pick up the emissions from a single banana. You'd probably need a truck full of them.

[kneebonian]

For those curious about the radioactivity of bananas. https://what-if-origin.sciesnet.net/158/

[BetterGeiger]

haha, yes... unfortunately they emit such an extremely tiny amount you can't measure it with ordinary means, I tried:

https://twitter.com/BetterGeiger/status/1523769482602196992

[dogben]

My geiger counter activity goes up when air conditioner is working. Never figured out why. This could be a good explanation.

[detrites]

Does your AC include a negative ion generator for cleaning the air? I wonder if that could be affecting it?

[dogben]

I don't think it has negative ion generator. I guess the fan itself can generate ions, that's why aircraft have static dischargers.

[Cerium]

Is your interior AC unit or its ducting in a basement or crawlspace?

[dogben]

It's interior. No ventilation. I guess it's ionizing the air and bringing radioactive dust particles to the whole room. The radiation level is still very low so I'm not worried.

[ZeroCool2u]

I have absolutely no need for your product, but I do want one and fully intend to gift them to others now. Great little device, awesome work.

[BetterGeiger]

Thank you! Most people don't need one (and hopefully it stays that way) but I still think it's a fun and educational device. If nothing else it's a conversation piece. :)

[thadt]

Hey, that's a pretty slick package (and price point). I looked through bettergeiger.com and read the discussion about the difference between GM tubes vs scintillators, but never saw an indication of what material you're using. Would be useful information for those of us thinking of upgrading from an SBM-20.

[BetterGeiger]

I'm sorry to say that some of the sensor design details, including material and geometry, are not shared. That was a critical optimization process during the design phase (tricky balancing act between cost and performance) and I want to slow down any copy-cat devices. However in terms of performance I am pretty open and detailed about how the device actually behaves:

https://twitter.com/BetterGeiger/status/1475480971050901511

Another metric some people like is CPM/[uSv/hr] when exposed to Cs-137 (662 keV). That number is about 415, whereas cheapo Geigers can be as low as 10, and decent consumer-grade Geiger counters are usually around 120. This number gives a decent idea about relative X-ray/gamma sensitivity of those devices.

[kloch]

> but they are highly sensitive to beta

I’m not familiar with Geiger counter design/specs but would the considerable static electricity send some electrons into the detector and cause a false positive beta hit?

[BetterGeiger]

Beta particles are basically energetic electrons flying around, yes, but for a Geiger counter to detect them they have to be quite energetic in order to penetrate the Geiger tube itself (detection occurs essentially inside the tube, in the gas)... So I doubt that static field is generating electrons anywhere near that energy needed to be detected by a Geiger tube.

[kloch]

Dryer static charges are probably a few keV at most so yeah that shouldn't make it through a metal envelope.

However, I wonder how well shielded the electronics are. In a poor quality design even the static charge fields themselves might trigger a false hit.

[jve]

What's the difference between alpha/beta/gamma and which is of concern?

[_Algernon_]

Alpha has the shortest range and can be blocked by a piece of paper. Alpha radiation consists of protons.

Gamma goes through most things and has the highest range. Gamma consists of electro magnetic radiation.

Beta is somewhere in the middle. It consists of electrons.

All are of concern, but Alfa is mainly of concern if ingested or inhaled. This is because all the radiation will be absorbed by your body, while most gamma would just escape. Gamma is of more concern outside the body, due to its reach.

I may remember some details wrong. I last learned about this in school a decade ago.

[EntropicHeaven]

> Alpha radiation consists of protons.

Alpha radiation is helium-4 nucleus - two protons and two neutrons.

> Beta is somewhere in the middle. It consists of electrons.

Beta is either electron (β− decay) or positron (β+ decay)