Question:
Americium Smoke Detector

FYI, Am241 emits alphas, gammas, and betas. The beta particles are emitted via Auger emission or internal conversion. Nonetheless, at the given particle energies, a small Am241 source is not an external hazard. As an internal hazard, even if the source was moderately damaged, only a small fraction could become respirable (probably 1E-04 to 1E-06). If inhaled, this would lead to a dose of only 0.5 to 52 millirem over 50 years (assuming a 1 uCi source). However, even this is an insignificant dose.

Answer: Look, your thinking process is in error. Considering certain facts, it is certainly NOT insignificant and you shouldn't be glossing over the facts. When considering cancer caused by radioactive substances, since cancer occurs at a cellular level, it is NOT the whole-body dose which is important, but both the cellular dose and the cellular dose rate. Makes sense, eh? Talking about the whole-body dose is **misleading**.

If that dose were spread out over the whole body then you would be right in saying that it is insignificant. But in the case of causing mutations and cancer, it is the repeated hits from ionizing radiation in one tiny spot that will more likely damage the local cells' DNA permanenttly. The dose you speak of (and I didn't do your calculations) is concentrated on one little spot wherever the flecks land and lodge in the lungs. DNA damage at that spot is concentrated and occurs at the same cellular dose rate as if your whole body were up close to such an isotope, inside and out. How would **that** be for a dose rate? Therefore, it may over-whelm the body's local protection/repair mechanisms and eventually lead to cancer at that location, and then cancer will likely develop and spread. This is why radon causes lung cancer, because its decay particles, though extremely tiny, are quite radio active and stay in the body for life. Radon isn't good to breath in, and neither is Americium 241.

Now lets do some figures. If 1 curie is 3.7 x 10**10 disintegrations per second, then 1 microcurie is 37000 disintegrations per second. One thousandth of this (the upper limit of your suggested inhaled particle) is only 37 disintegrations per second. But I wouldn't consider that to be insignificant.

There are 3600 seconds per hour and 86640 seconds per day. In fifty years this is approximately 59 BILLION disintegrations in a tiny volume, any one of which could cause the fatal DNA error.

Do you like those odds? Actually, the body's repair mechanisms are indeed pretty marvellous, and possibly the victim may not develop a cancer. But even so, there's no way I want some tiny little fleck in my lungs giving 37 disintegrations per second for life, of highly ionizing radiation, alpha particles being 20 times more damaging to tissue it is in contact with than gamma rays. Nothing natural in the body is that active in such a small spot.

You shouldn't be so minimizing. And not even 1 pico curie should be absorbed if it is not necessary. Remember the ALARA (as low as reasonably achievable) principle. In this case, pretty well zero is achievable. The licensing procedure is to assure that the one possessing the isotopes is both educated and qualified to act responsibly. I can see the agencies' wisdom in this.

I had a thought about disposing of these in the landfills. What if some CAT operator was, as they usually do, digging up or pushing the garbage in the landfills around and the operator happened to catch one of these smoke detectors and crushed it to powder? The americium would certainly leak out and the operator, or anyone nearby, would likely be contaminated unknowingly. It would seem to me likely that they could ingest these tiny particles accidentally without their knowledge. So in Canada, we are supposed to return these smoke detectors to their manufacturers.

Just remember that possessing a scheduled quantity of a radioactive substance without a license is against the law, which law is meant to protect both the ignorant and the knowledgeable. You break the law and you can go directly to jail. For most, I think, this latter reason will have to be the bottom line.