A small amount of americium - 241 is used in smoke detectors. A stream of radiation flows between two electrodes. If smoke interrupts the stream, the alarm goes off. What feature of the radioisotope americium - 241 would be most helpful for the smoke detector to work?

Americium-241 needs to keep emitting radiation steadily for the detector to work over many years. A long half-life means it decays slowly, so its radiation output remains useful for a long time. Therefore, the helpful feature is a long half-life, choice B.

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