A student asked me what the effect would be of swallowing a small amount of a radioactive substance like Am-141 in terms of biological effect and the equivalent dose in sievert. I started looking into it, but couldn’t find any good sources that allowed me to calculate it, so I’m hoping someone here has a good answer.
During the six hours it takes to pass through the digestive system, a gram of Americum-241 (not 141) loses about a microgram due to radioactive decay. If all that mass is converted to radiation energy, and fully absorbed by your 90-kg-body, you take in a megasievert. That seems like a weak upper bound though.
241 of course. Slip of the fingers from me as I composed the post while the students’ mid-lesson break was ending.
And that’s a really weak upper bound if you mean plugging a microgram into E=mc^2, but helped me think about it in a useful way. The nearly 1.1 microgram “lost” to Am-241 is nearly all there in the resulting Np-237 and alpha particle. Only 25 millionths of the “lost” mass is converted into energy. But that helps me calculate that the converted mass is about 2.76*10^-11 grams, or 2,48 MJ …
Maybe that’s what you meant all along?
Similar question in If I put this uranium ore down my underpants what would happen?. Good sources there on health and dosing. Tell the kid to PM me if he wants.
Nothing on what level of radiation an amount of Am-241 will emit though.
Note that alpha sources, while relatively safe outside of the body, are the absolute worst sort to ingest in any way (eating, inhaling, etc.). Alpha particles are really easy to stop by almost anything. When the “almost anything” is your clothing, or the dead layer on the surface of your skin, there’s no problem. When the “almost anything” is the living portion of your body, though, it’s very bad.
1 gram is not exactly a “small amount” of Am-241. It’s about 3.5 Curie (cite) or 127 GBq of activity. An average smoke detector has 0.29 microgram of Am-241 (cite), so that’s enough Am-241 to make 3 million smoke detectors.
127GBq means 127 billion decays per second. If we over-simplify and say each decay produces one 5.5 MeV alpha particle, the dose is about 0.1 Joule per second. If that were distributed over the entire body (and assume 80kg body weight) for one hour (and then removed), that’s an absorbed dose of about 5 Gy, which has a 5-50% chance of killing you via acute radiation poisoning (cite).
Of course the reality is much more complicated - most of it will pass through the body and only irradiate the tissue in the digestive tract. But some of it will be absorbed by the body, and alpha emitters are the most dangerous for ingestion. The annual occupational limit for ingestion of Am-241 is 37 kBq (cite), or 0.3 microgram. So if you swallowed 1 gram, you’d be ingesting 30 million times more than the annual allowable limit.
Nice cites. The root url of the last one is fascinating.