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LostCosmonaut

Let's Talk About Radiation Exposure Thresholds

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Excessive amounts of radiation will kill you. Even over long terms, small amounts of radiation can do damage. But how much radiation causes health risks?

 

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Since exposing people to radiation for *science* is frowned upon, there's not enough data to make a unified theory. Right now, the US government uses the linear no threshold (LNT) model for determining acceptable limits of radiation exposure. Hippies use the supralinear no threshold model, because they hate anything vaguely related to nuclear stuff. There's some data that indicates that both these models overestimate the health risks from radiation. Many nuclear fans like the hormesis threshold model, which asserts that limited exposure to radiation is not harmful, and could actually be beneficial. There's a bit of data which supports this hypothesis.

 

Which model do you feel most accurately represents reality and should be used when determining exposure limits and such (bearing in mind that we can't stick people next to reactors to see what happens)?

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I'm familiar with the controversy, but not versed enough in the literature to have a strong opinion.  It would seem to me that the body's natural self-repair mechanisms would provide some sort of buffer at lower radiation exposure levels.  After all, we're getting smacked by UV from the sun, encountering small amounts of teratogenic chemicals in our food, drinking small amounts of radioactive minerals in well water, et cetera.

 

The Atomic Podcast has a show where they discuss this.  They come down heavily against LNT.

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I managed to find a few papers talking about hormesis;

 

http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/36/113/36113744.pdf

http://www.radiationhormesis.com/RadiationHormesis/Radiation%20Hormesis.pdf (to be fair, "radiationhormesis.com" doesn't scream unbiased source)

 

It looks interesting, but definitely not enough to make a consensus.

 

Also, a blurb about how the hypothesis fell out of favor; http://www.belleonline.com/newsletters/volume8/vol8-2/n3v82.html

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I'd honestly be as surprised if it wasn't an exponential increase in danger with increasing exposure as I would be if some amount was actively beneficial to a measurable degree, but that's a moderately informed guess based on not being able to come up with a mechanism by which totally isolating a person from radiation would increase the incidence of cancer. Linear Quadratic (or a higher power curve) Threshold wouldn't surprise me in the slightest. There's got to be some mechanisms to deal with radiation, and I'd expect a faster than linear scaling as they progressively get overwhelmed, and overwhelmed sufficiently that errors start overlapping.

 

(These guesses are as much guided by analogy to keeping data safe in other disciplines as anything else)

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I'm PMed a guy on AH.com who's pretty knowledgeable on this topic about hormesis, and this is what he had to say;

 

 


This is a very interesting, and very complicated, topic. My personal opinion is that we just don't know, and probably can't know. Because the hypothesized effects are so weak, they're essentially impossible to detect statistically. The only way we'll ever be able to figure it out conclusively is with a better understanding of the mechanics of the cell itself, rather then with epidemiology. In the meantime, I think we should stick with LNT on the grounds of better-safe-then-sorry, but I wouldn't be surprised at all if it was wrong. There's certainly plenty we don't know about radiation - for example, theory predicts that there should have been a significant increase in birth defects among children conceived by Hiroshima citizens after the bomb, but there wasn't.

In terms of sources: Biological Effects of Ionizing Radiation is the go-to source for the "official" opinion. IIRC, they don't really give any space to hormesis, but it's the go-to summary for mainstream opinion. The French Academy of Sciences published an equivalent volume that ended up coming down on the side of hormesis, but unfortunately I don't remember the title. Elements of Controversy by Barton Hacker is an excellent, even-handed summary of the AEC's radiation safety program as it relates to weapons testing. For hormesis, Dr. Edward Calabrese is the go-to guy, and he's written several papers about the history of LNT and hormesis, e.g. "Radiation Hormesis: The Demise of a Legitimate Hypothesis", in Human & Experimental Toxicology, Vol. 19, pp. 76-84. Though I think he's a bit biased.

Hope this helps,

asnys

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More evidence that LNT is garbage; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2477708/

 

tl;dr Cobalt-60 sources get mixed into scrap steel recycled and used in apartments in Taiwan, a shitload of people get exposed to low level radiation for years, but cancer rates are significantly (p<.001) lower than for the general population.

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On 10/20/2017 at 4:46 PM, Sturgeon said:

Is there any evidence that LNT predicts "safe" levels of exposure that are actually dangerous?

 

Not that I'm aware of. LNT might underpredict the effects of really high radiation doses (reasoning: LNT was derived from effects of high radiation doses, so if actual effects are sublinear and go up to linear higher, actual effects could have a greater than linear dose at very high levels), although at those points (500+ rem) the effects go from "how bad are you hurt" to "which if your body's systems catastrophically shutting down will kill you first". The highest doses I can think of off the top of my head are ~5,000 rem at some of the crit accidents back in the 50s/60s, and those guys died very fast.

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22 minutes ago, LostCosmonaut said:

 

Not that I'm aware of. LNT might underpredict the effects of really high radiation doses (reasoning: LNT was derived from effects of high radiation doses, so if actual effects are sublinear and go up to linear higher, actual effects could have a greater than linear dose at very high levels), although at those points (500+ rem) the effects go from "how bad are you hurt" to "which if your body's systems catastrophically shutting down will kill you first". The highest doses I can think of off the top of my head are ~5,000 rem at some of the crit accidents back in the 50s/60s, and those guys died very fast.

 

So LNT is probably not hurting anyone at least.

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24 minutes ago, Sturgeon said:

 

So LNT is probably not hurting anyone at least.

 

Correct, although if you got rid of LNT you could save a lot of money/time on radiation protection (since it will no longer be the end of the world if somebody gets a couple hundred millirem a year). I was going to say that it's also contributed to the general hysteria around radiation in general that prevents wider adoption of nuclear, but hippies are dumb enough that different models for how radiation affects the human body aren't even on their radar.

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