When a nucleus decays, we can write down an equation that describes the decay. The mass number, and the atomic number must balance in this equation.
Alpha decay
Alpha particles are helium nuclei, written
During alpha decay, a part of the nucleus consisting of two protons and two neutrons is emitted. The remaining fragment will be a different element.
The equation describing the decay is
For example
The mass and atomic numbers balance on both sides of the equation: 241=237 +4 and 95=93+2.
Beta Decay
Beta particles,
are fast moving electrons emitted from the nucleus. The electron is emitted when a neutron decays into a proton, resulting also in the emission of a particle called an anti neutrino, labelled
An antineutrino has no charge and probably no mass, (we believe it is massless). The full decay is given by the equation
for example
Gamma Ray Emission
When a gamma ray,
is emitted, the element does not change. The gamma ray is emitted because the nucleus is in an excited state. The gamma ray carries away excess energy, leaving behind a more stable nucleus in a lower energy state. The equation describing gamma ray emission is
