Genuinely fascinating. ~ 1c proton beam doesn't explode guy's head because they're too powerful.

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@waxwing Radiation works that way in general. The *more* penetrating radiation is less harmful to get inside your body, because the energy is spread over a larger area. So contamination that produces alpha particles is safer externally, because almost anything can stop it. But more deadly internally, because what stops the particles is your own tissues.

...and bullets work that way too, just at a bigger scale...

@pete yes but this case is pretty unusual! Usually alpha is less dangerous (as you say, strictly if external) because of short stopping distance,, here the stopping distance was too *large* to inflict (as much) damage.

Also as explained in vid it's not just a case of spreading out, actually the biggest part of the "deposit" of energy is pretty concentrated in the last chunk of distance as in the idea of non-invasive tumor destroying treatment.

@waxwing Re-read what I wrote; I think we're saying exactly the same thing. :)

@waxwing Oh, actually I do see your point re: the Bragg peak effect. Alpha particles actually do that too. But it doesn't make a practical difference re: health because they're stopped so quickly.

@waxwing IIUC it can however make the relative danger of certain beta emitters and alpha particles emitters complex to compare, as there are some very low energy beta emitters, and some very high energy alpha emitters. Eg Tritium is a common example of a low energy beta emitter that acts more like an alpha emitter in many circumstances.

@pete yes, iirc it's indeed very complex and difficult to measure this stuff, *especially* at low dose, but even at higher doses. I used to work in this field (nuclear reactor engineering), but it was so long ago I couldn't tell you much useful :)

@waxwing Well, you can tell me something useful: don't go swimming in the spent fuel pool. You might die of lead poisoning. :D #xkcd

@waxwing Though seriously, the complexity of measuring any of this stuff is still way less than so many chemical contaminants. Chemical contaminants don't come with the handy feature of regularly shooting off easily detected energy packets. :)

@pete Yes, true, the complexity comes almost all from the biology and biochemistry, not the physics, as I understand it. Heck even the materials science part of nuclear reactor safety is in many ways much more difficult than the neutron physics stuff.

@waxwing For sure. Materials do rweird things when you inject energy into them constantly from radiation. Not to mention the complexity of predicting how alloys will behave in environments with enough radiation to have a non-trivial amount of the materials transmuted; it's common for alloys to have parts-per-million tolerances. Reactors also tend to require much longer maintenance free time periods than is typical, making understanding that degradation even more important.

@waxwing Speaking of, a surprising amount of plastic is actually radiation crosslinked. Usually with electron beams.

@waxwing IIUC the bragg peak effect isn't a huge difference. Significant. But we're talking about maybe 5x, not orders of magnitude.

@pete That is interesting. The nonlinearity here may mean that the 500MeV I saw quoted in the video changes that estimate a lot, but perhaps more important is that with the tissue material there are going to be thresholds, such that a 5x increase could be easily enough to decide lethality or just repairable damage (the guy lived to old age, apparently).

Or more likely, it's just way more complex and I have no clue :)

@pete He did have permanent nerve damage that semi paralyzed the left side of his face though, plus problems in the USSR due to the sensitivity of his case, that were really quite sad.

@waxwing Something that people may be discounting in this story is that the beam he was hit with was iiuc quite narrow. People often survive deep, penetrating, head wounds, and a narrow deeply penetrating beam may very well be _less_ harmful than an equivalent thickness bullet.

@pete right, unless the alpha particles were really "alpha" :) (like these protons), then it'd be the same story presumably :)

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