The three most common kinds of radiation given off when a radionuclide decays are alpha, beta, and gamma radiations.

In terms of modern-day scientific knowledge, Rutherford’s three types of “radiation” are characterized as follows:

An alpha particle is a particle in which two protons and two neutrons are present that are emitted by certain radioactive nuclei. The notation used to represent an alpha particle is _-1⁰α. The numerical superscript indicates a mass of 4 amu.

Alpha particles are identical to the nuclei of helium atoms -4 (⁴₂He); because of this, an alternative designation for an alpha particle is ⁴₂He.

Equations for radioactive decay

The terms parent nuclide and daughter nuclide are often used in descriptions of radioactive decay processes.

A parent nuclide is the nuclide that undergoes decay in a radioactive decay process.

A daughter nuclide is the nuclide that is produced in a radioactive decay process.

Alpha particle decay

Alpha particle decay is the radioactive decay process in which an alpha particle is emitted from an unstable nucleus. It always results in the formation of a nuclide of a different element. The product nucleus has an atomic number that is 2 less than that of the original nucleus and a mass number that is 4 less than that of the original nucleus. We can represent alpha particle decay in general terms by the equation

where X is the chemical symbol for the nucleus of the original element undergoing decay and Y is the chemical symbol of the nucleus formed as a result of the decay.

Nuclear equations differ from ordinary chemical equations in three important ways:

1. The symbols in nuclear equations stand for nuclei rather than atoms. (We do not worry about electrons when writing nuclear equations.)
2. Mass numbers and atomic numbers (nuclear charge) are always specifically included in nuclear equations.
3. The elemental symbols on both sides of the equation frequently are not the same in nuclear equations.

Beta particle decay

Beta particle decay is the radioactive decay process in which a beta particle is emitted from an unstable nucleus. Beta particle decay, like alpha particle decay, always produces a nuclide of a different element. The mass number of the new nuclide is the same as that of the parent nuclide. However, the atomic number is increased by 1 unit. The general equation for beta decay is

Specific examples of beta particle decay are

Both of these nuclear equations are balanced; superscripts and subscripts add to the same sums on both sides of the equation.

Gamma ray emission

Gamma ray emission is the radioactive decay process in which a gamma ray is emitted from an unstable nucleus. For naturally occurring radionuclides, gamma ray emission always takes place in conjunction with an alpha or a beta decay process; it never occurs independently. These gamma rays are often not included in the nuclear equation because they do not affect the balancing of the equation or the identity of the daughter nuclide.