Alpha particles are made of 2 protons with
This means that when a nucleus emits an alpha
particle, it loses 2 protons and so its atomic
number decreases by 2.
Also, when a nucleus emits an alpha particle,
its atomic mass decreases by 4
(that's 2 protons plus 2 neutrons)
So Americium-241 (an -source
used in smoke detectors), which has an atomic number of 95 and an
atomic mass of 241, will decay to Neptunium-237 (which has an atomic
number of 93 and an atomic mass of 237).
The equation would look like this:-
Note that an alpha particle is the same as the nucleus
of a Helium atom (2 protons and 2 neutrons).
Thus we can write
Alpha-decay occurs in very heavy elements, for example, Uranium
These heavy elements have too many protons to be stable. They can
become more stable by emitting an alpha particle.
Alpha particles have a large charge(+2), so they easily
ionise other atoms that they pass. Ionising atoms requires energy,
so alpha particles lose energy rapidly as they travel. Thus they
have a range of only a few centimetres in air.
Remember, in Alpha decay:-
- atomic number decreases
- atomic mass decreases by