Smoke Detector Radiation Danger

[AgentofEvil]

I was reading the editorial section of today’s paper (New Zealand Sunday Star Times) and I came across a letter about the use of radioactive material in smoke detectors.
The letter had an almost conspiricy theory tone about, with a claim that information about smoke detectos was "being withheld from the public world-wide.
I was aware that very small quantities of Americium were used in most smoke detectors, but this letter implied (without actually saying, mind you) that this was dangerous and quoted that an (unnamed) test of 200 smoke detectors had shown that “all emmited between 300-400 counts of radition per second”
Now, I don’t have a clue as to how to interpret that figure, so two questions.

1. What does that mean?
2. How dangerous is that much radiation?

[Desmostylus]

From here

The risk of harm from radiation exposure from smoke detectors is considered to be miniscule. Alpha radiation, which is emitted by the radioactive source used to make the detector operate, will not even penetrate through air for more than a few centimetres and is therefore contained within the chamber of the detector. Gamma radiation emitted by the source is of low intensity (penetrating ability) and is substantially shielded by the detector housing. Gamma radiation intensity decreases rapidly with increasing distance from the source.

The gamma radiation at 1 metre from an unshielded Americium-241 source of the typical activity found in domestic smoke detectors would expose a person to about 3,000 times less than the dose they would receive from natural background radiation1. Everyone is exposed to natural background radiation. Natural background radiation includes radiation from rocks and soil and cosmic rays from the sun.

It should be noted that the actual dose received from the detector would be much less than this since the Americium-241 source is shielded by the metal chamber and a person would not normally be at a distance of 1 metre from the smoke detector for any length of time. The radiation dose that an individual receives from smoke detectors installed in their house is therefore miniscule.

The probability of the source being removed from the tamper proof chamber and then swallowed is extremely remote. The internal radiation hazard is therefore minimal. A case has been documented where a worker in a factory making smoke detectors swallowed two of the radioactive sources. Even in this case the radiation exposure was small as the the sources passed through his body with very little leakage.

[Ice_Wolf]

From the American EPA site.

Smoke detectors containing Am-241 also provide some radiation exposure. However, the radiation exposure people receive from a smoke detector is very low. The health risk reduction from the fire protection vastly outweighs the health risk from the radiation. That said, you should still handle smoke detectors containing americium with care.

It seems you stand more risk if you tamper with the detector, and actually swallow or inhale Americium, than anything else.

[scr4]

“Counts per second” is the number of photons detector by an instrument every second. Unless they tell you the size and efficiency of the detector as well as the distance from the source, it’s a meaningless number.

[Polycarp]

The Master speaks.

[Desmostylus]

Whoops. Should have referred to what This Guy had to say.

[AgentofEvil]

Wow, thanks for the quick and detailed responses.

[scr4]

*Originally posted by scr4 *
**“Counts per second” is the number of photons detector by an instrument every second. **

That should be “detected by”, of course. Sorry…

[hobbes730]

We handled Alpha-emitting radiation sources all the time in high-school chemistry, with hardly any special equipment. Like Desmostylus said, Alpha rays (aka Helium nuclei) can be completely blocked by a single sheet of paper, and make up most of the radiation in a detector. Gamma rays, although much more dangerous, are emitted in such low quantity as to be negligible compared to background radiation. Even if you were to remove the radioactive source, I think your dosage would still be negligible, unless you decided to sleep with it close to your head on a regular basis or something