Most common smoke detectors (Fig. 13-2) contain a small amount
of 241Am, a radioactive isotope. 241Am is produced and recovered
from nuclear reactors. Alpha particles emitted by the decays of
241Am ionize the air (split the air molecules into electrons and
positive ions) and generate a small current of electricity that
is measured by a current-sensitive circuit. When smoke enters
the detector, ions become attached to the smoke particles, which
causes a decrease in the detector current. When this happens, an
alarm sounds. These detectors provide warning for people to
leave burning homes safely. Many lives have been saved by the
their use. Because the distance alpha particles travel in air is
so short, there is no risk of being exposed to radiation by
having a smoke detector in the house. Since ionization-type
smoke detectors contain radioactive materials, they should be
recycled or disposed of as radioactive waste. It is important to
follow the instructions that come with the smoke alarm when they
need to be d