Answer to Question #11701 Submitted to "Ask the Experts"

I have noticed recently there is an ionization smoke detector in my apartment. There is some radioactive material inside the smoke detector. From the Health Physics Society's Ask the Experts answers, I know some smoke detectors use radioactive material but they are safe.

I opened the smoke detector to change the battery, and I also saw the chamber for holding the americium-241 (²⁴¹Am) ionizing radiation source. The chamber is intact, and I never touched it. When I opened the detector to change the battery, was I exposed to excessive radiation? If not, how much of a radiation exposure or dose did I get?

Another question I have is whether there is any possibility that the ²⁴¹Am in the chamber could fall out of the detector with time. This is my biggest concern, because I have a child with me, and I'm concerned that she may accidentally pick up the ²⁴¹Am source and eat it.

I also noticed that the smoke detector in my room may be several years old. Could the ²⁴¹Am be leaching out with the time? I know that the small particles (i.e., less than 1 micrometer [µm]) may be more harmful to us when eaten or inhaled. I worry about my child that she may inhale or ingest the possible falling particles.

Is there is any method that I could use to measure the radiation from the smoke detector?

First I am very glad you have a smoke detector in your apartment and that you keep the battery up to date. You are improving your family's safety and life expectancy tremendously by this simple act.

Changing the battery will not give you any radiation exposure. The ²⁴¹Am is an alpha-radiation emitter. Alpha radiation is completely shielded by a sheet of paper, by 2.5 centimeters (cm) of air, and even more so, by the steel chamber that houses the radioactive ²⁴¹Am. In fact, most common radiation detectors cannot detect the ²⁴¹Am source while it remains in the steel chamber that it is sealed in.

Smoke detectors are designed, built, and tested to assure that the americium disk will not fall out of the chamber. See the Health Physics Society's fact sheet titled "Consumer Products Containing Radioactive Materials."

However, even if someone intentionally pried the americium disk out of the chamber and ate it, the person's radiation dose would be nil. There is a documented case where someone at a smoke detector company slipped two americium disks into a coworker's sandwich. It took 16 to 24 days for the disks to pass through the worker's digestive system. The worker's dose was "not significant from the point of view of radiological protection" and was most likely less than the dose from the x rays taken to try to find the two disks in the worker's intestinal system.

It is impossible for the ²⁴¹Am to leach out over time while in your home. Not even small particles of it will flake off. The americium is electroplated onto the metal disk, just like chrome is plated on a car bumper or door handle. It could be removed only by grinding or by using very strong chemical acids. Additionally, the americium is protected by a thin, gold-metal layer that is very chemical resistant. So, the ²⁴¹Am on the disk of a smoke detector can be removed only if it is done intentionally and by using very aggressive methods. This was proven by the two disks sitting for 16 to 24 days in a bath of hydrochloric acid (digestive juices) in the stomach of the worker at the smoke detector company, from which only a tiny fraction of the americium plated on the disks was removed.

John P. Hageman, MS, CHP