Originally Posted by
Jiri Vasina
I'll take it from the last:
Ole, there is a Thorium 238 isotope, but the only info I found about it is that it has a half-life of 9.4minutes. Not it's decay chain. (wikipedia).
Further calculations might be wrong (I might have a mistake somewhere), but I believe they are not fundamentally wrong:
The amount of radioactivity in thorium 232 is negligible - if it has a halflife on the order of 10^10 years, that means that in 1kg of pure Thorium 232 one radioactive decay every 1010 minutes - that is almost every 17hours between that. At that moment a Radium 228 is created, which is a beta emitter with half-life of 6.7 years - again, that means that every minute it has a 0.0000197% chance of decaying - a chance you would in other situations consider negligible.
And that is only speaking of time. If you also consider the aspect of space and all the possible directions the generated particle can travel in, the chance of the particle hitting your body is even less (by orders).
The long half-life of the mother isotope also means (and short half-life of the dangerous isotopes like all the beta emitters (there are no gama) 228Ra, 228Ac), that the equilibrium state achieved is one with very low amount of those dangerous particles. And the resulting radioactivity is very low.
Tomorrow I'll take my 305mm Repro-Claron (S/N 8,xxx,xxx) to work and measure if any radiation is detectable (not-alpha. Have no means to detect that).
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