Re: Radioactive Boy Scouts and Smoke Detectors

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Tim Sullivan x5830 wrote:

> ....A photo of the source in a smoke detector is given at:
>
> howstuffworks.com/inside-smoke.htm
>
> and a fact sheet on americium in smoke detectors is given at:
>
> www.uic.com.au/nip35.htm
>
> The fact sheet says that the americium is in the form of AmO_2 and that 1
> gram of the oxide makes about 5000 detectors. The sheet says that since it
> is in the oxide form and ....

Thanks for sharing, Tim. If this is true then each smoke detector
contains 176 micrograms of Am-241 (or 4.4*10^17 atoms). From
the half-life (458 years--> lambda=4.8*10^-11 per second) one can
calculate the rate of 21,000,000 decays per second. In Am-241, if I
recall correctly, each decay produces essentially one alpha particle.
About half of them escape into air. If each alpha particle produces
200,000 pairs of ions, then in each second about 2.1*10^12 positive
and negative carriers are created. The current of 2.1*10^12 electrons
per second is 0.34 microamps. Double this to obtain the total current
in air,  when the rate of recombination is negligible.

Nothing serious, just playing with numbers. A good problem for
students of radioactivity. I hope I did not make an error.

Ludwik Kowalski