[Jacques]

Hi
In the decay of U238 -> Th234 + He4 why He come out ionized ?
The nucleus of U is surrounded by 92 electrons and when the alpha particule is emitted by the nucleus it must goes through this cloud of electrons. Why doesn't the alpha particule doesn't capture the two electron it is missing to get electricaly neutral ? What happen to the 2 excess electrons left on the Th atom ?

[swansont]

A few MeV of energy is liberated in the reaction, which is well above the ionization energy of He. The excess electrons will be lost from the Th, and some electrons will eventually find their way to the He, once it has deposited its KE along its path, mostly by ionizing atoms. So there will be a lot of jumbling around of the electrons. Everything will eventually recombine and form neutral atoms.

[Jacques]

Thanks

[Gilded]

Yeah, that pretty much answered it. :) Btw, I recall it being quite many air (N, O etc.) molecules one single 2MeV alpha particle hits on its way - about 60 000 or so? That makes you think how badly you actually want to eat those delicious alpha decayers you have lying about.

[swansont]

Gilded said:

Yeah, that pretty much answered it. :) Btw, I recall it being quite many air (N, O etc.) molecules one single 2MeV alpha particle hits on its way - about 60 000 or so? That makes you think how badly you actually want to eat those delicious alpha decayers you have lying about.

That would be 3.3 eV per reaction, so that's reasonable. Yeah, alpha as an internal dose is pretty bad, since much of that energy is deposited in a small volume.

[jdurg]

Alpha radiation is actually the most damaging form of radiation, but it's also the least penetrating form. If alpha particles had the penetrating power of gamma rays, we'd all be mighty dead and/or cancerous. But as long as your alpha source is properly stored inside a glass container, at the minimum, you really don't have to worry. Gamma rays aare pretty low in terms of damaging power. They are neutral in charge so they have a rough time ionizing things unless they get a perfect hit. That is also why their penetrating power is so high. Sure you don't want to be putting them near yer genitals, but having a gamma emitter around isn't the end of the world. Like everything in life, it's all about moderation.