[Michael Thayne]

Originally Posted by Anthony

For those who are curious: if you have purified U-235, something like 92% of total decay energy will be alpha decay from U-235 to Th-231, another 8% will be Th-231 to Pa-231, and unless you leave it for thousands of years, everything else is negligible (Th-231 has a half-life of 25.5 hours so it reaches equilibrium quickly, but Pa-231 has a half-life of 32,000 years). Decay rate is 4.5e-16/sec with a decay energy of 2e+9J/g for an energy output of 9e-7W/g. 1J/kg is 100 rads, so for a 70 kg person that works out to 1.3e-6 rad/sec (about 1 rad per 9 days) if you absorb it all, which pretty much means swallowing powdered uranium.

Now, for nuclear fuel that has been used in a reactor, radiation output starts at around 6.5% of the total thermal power output of the reactor (so probably more like 20% of electrical power output), which will kill people impressively fast.

This is really helpful. What's the equivalent math look like for the plutonium-238 in an RTG?