Answer to Question #13930 Submitted to "Ask the Experts"

Category: Consumer Products

The following question was answered by an expert in the appropriate field:

Q

I read an internet post that said, "The physical properties (specifically particle size) are of concern if the sealed source leaks and americium-241 (241Am) particles are released into the air." My question is in relation to my home smoke detector. I would like your advice on whether or not I should get my smoke detector tested for radiation leaks.

I saw online that a 1970s Sears smoke detector contained 5 microcuries (µCi) of 241Am and there was caked yellow dust on the vents of their ionization chamber to which someone replied was due to "the alpha recoil reaction that can destroy the thin coating over the source and allow source material to recoil out of the source."

My home smoke detector was bought in the early 1990s and may have suffered a few bangs over the years. It is a 0.9 µCi detector. Would it have been possible for the alpha recoil, or simply due to age, to have caused the seal over the radiation to break down? The inside lid of my smoke detector is covered in dust and some fell off when opening it. Is there any way the dust could be contaminated with 241Am or its decay products and I might have inhaled it?

A

There is no chance the 241Am source could be leaking particles outside the sealed source under any household conditions. 

According to the Nuclear Regulatory Commission document, NUREG/CR-156 titled Environmental Assessment of Ionization Chamber Smoke Detectors Containing Am-241, the 241Am alpha sources are essentially a rolled foil with the 241Am contained in a gold matrix sealed between a silver backing and a thin gold alloy cover. The radioactive americium is in an oxide form, AmO2. The manufactures of the alpha sources start with AmO2 being uniformly mixed with gold and formed into a briquette. The briquette is sintered at above 8,000?. The briquette is then mounted between a backing of silver and a front cover of gold and sealed by hot forging. The composite briquette is then cold rolled in several steps until the required active area is achieved. The resulting gold cover ends up about 0.002–0.003 mm in thickness and the total piece thickness is 0.2 mm.

Results of high temperature (1,200?) tests performed on 241Am sources indicate that between 0.01% and 0.2% of the source activity (with an average value of 0.05%) may be released as airborne contamination. Tests involving whole smoke detectors at the same temperature resulted in the release of less than 0.06 %.

John Hageman, MS, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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