Re: taking apart smoke detectors

[Stan Dodds <dodds@RICE.EDU>]

Disclaimer: Dismantling a smoke detector is probably
illegal. Depending on the isotope and activity the resulting source
may well require NRC and/or state license for possession.

The source foil will probably be on a metal post or stud in the ion
chamber, which is just a small metal box sitting on the circuit board
in the ones I have seen. A small amount of alpha-emitter, usually
Americium, is plated or otherwise placed on the foil. The covering
material, if any, must be thin so that the alphas can escape. This
means that there is some risk of spreading active material if the
source foil is rubbed in any way, although there should be no
possibility of significant contamination leaking out of the intact
unit. The exact compromise between letting alphas get out and
preventing contamination is dependent on the manufacturing technique,
and will probably not be evident on simple inspection.

Given the potential problems, real and legal, I would certainly not
use a source extracted from a smoke detector in a student lab. The
Nucleus and other suppliers mentioned here recently would privide
better choices. In a research situation, with appropriate monitoring,
it could be a convenient, if still illegal, alpha source.

Stan


> I've been thinking about using a smoke detector as a radiation
> source.  Does anybody know how far I can safely open it up?  If
> I take the circuit board out of the case and set it next to my
> detector, I get about 4x background.  I'm a long way from where
> it looks like the source sits.  Can I remove the plastic cage?
> Is the source sealed up or would it smear onto anything it
> touches?  (I really don't want to find out the hard way.)
>
> Carmen