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Alpha Decay



Example of alpha decay:


Radium-226 will alpha-decay to radon-22





ð In general, alpha decay can be written as as shown on the right


ð Alpha decay occurs when the strong nuclear force cannot hold a large nucleus together.


ð The mass of the parent nucleus is greater than the sum of the masses of the daughter nucleus and the alpha particle;

         this difference is called the disintegration energy.


ð Alpha decay is so much more likely than other forms of nuclear disintegration because the alpha particle itself is quite stable





An Application

ð One type of smoke detector uses alpha radiation

ð The presence of smoke is enough to absorb the alpha rays and keep them from striking the collector plate.

Ionization detectors have an ionization chamber and a source of ionizing radiation. The source of ionizing radiation is a minute quantity of americium-241 (perhaps 1/5000th of a gram), which is a source of alpha particles (helium nuclei). The ionization chamber consists of two plates separated by about a centimeter. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the americium knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively-charged oxygen and nitrogen atoms are attracted to the negative plate and the electrons are attracted to the positive plate, generating a small, continuous electric current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The drop in current between the plates triggers the alarm.