Ionizing smoke detectors contain approximately 1 microcurie of Americium 241. This is an alpha emitter and the flux of alpha particles is measured by the unit to determine if smoke is present between the Am-241 source and the detector. Am-241 also emits low energy gamma-rays which were measured here. The smoke detector used is shown in the image below.
As with the other spectra, four 0.093" sheets of Plexiglass were used to block any beta particles that could swamp the spectrum. The alpha particles emitted by the Am-241 are absorbed within the smoke detector itself as the smoke detector was not modified in any way for obvious safety reasons. The gamma-ray spectrum obtained is shown in the following plot.
The two prominent gamma rays from Am-241 can be easily seen.
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