<P> Ionization smoke detectors are usually cheaper to manufacture than optical detectors . They may be more prone to false alarms triggered by non-hazardous events than photoelectric detectors, and have been found to be much slower to respond to typical house fires . </P> <P> Americium - 241 is an alpha emitter with a half - life of 432.6 years . Alpha particle radiation, as opposed to beta (electron) and gamma (electromagnetic) radiation, is used for two additional reasons: alpha particles have high ionization, so sufficient air particles will be ionized for the current to exist, and they have low penetrative power, meaning they will be stopped, safely, by the plastic of the smoke detector or the air . About one percent of the emitted radioactive energy of Am is gamma radiation . The amount of elemental americium - 241 is small enough to be exempt from the regulations applied to larger sources . It includes about 37 kBq or 1 μCi of radioactive element americium - 241 (Am), corresponding to about 0.3 μg of the isotope . This provides sufficient ion current to detect smoke, while producing a very low level of radiation outside the device . </P> <P> The americium - 241 in ionizing smoke detectors poses a potential environmental hazard, albeit a very small one . Disposal regulations and recommendations for smoke detectors vary from region to region . The amount of radioactive material contained in ionizing smoke detectors is very small and thus doesn't represent a significant radiological hazard . If the americium is left in the ionization chamber of the alarm the radiological risk is insignificant because the chamber acts as a shield to the alpha radiation . A person would have to open the sealed chamber and ingest or inhale the americium for the risk to be significant . The radiation risk of exposure to an ionic smoke detector is much smaller than natural background radiation under normal operation . </P> <P> Some European countries, like France, and some US states and municipalities have banned the use of domestic ionic smoke alarms because of concerns that they are not reliable enough as compared other technologies . Where an ionizing smoke detector has been the only detector, fires in the early stages have not always been effectively detected . </P>

What is the name of the source of alpha radiation in a smoke alarm