Radioactive decay

Alpha decay

An alpha particle consists of two protons and two neutrons and is often described as a helium nucleus. It is not the same as a helium atom as it does not contain any electrons but it is written with the same chemical nomenclature as a helium atom:

\(_{2}^{4}\textrm{He}\)

When a radioactive atom emits an alpha particle the mass number decreases by four and the atomic number drops by two.

Here is the equation for the alpha decay of radon-219 into polonium.

\(_{86}^{219}\textrm{Rn}\rightarrow\, _{84}^{215}\textrm{Po}\,+\,_{2}^{4}\textrm{He}\)

Beta decay

Beta decay involves the conversion of a down quark to an up quark. This changes a neutron into a proton plus an electron.

The proton stays in the nucleus and the electron leaves the atom with high energy - we call it a beta particle. This is written as:

\(_{-1}^{\,\,\,\,0}\textrm{e}\)

The mass number remains unchanged as the total of protons and neutrons is the same. The atomic number increases by one as there is one new proton.

Here is the equation for the beta decay of carbon-14.

\(_{6}^{14}\textrm{C}\rightarrow\, _{7}^{14}\textrm{N}\,+\,_{-1}^{\,\,\,\,0}\textrm{e}\)

Carbon-14 is a radioactive isotope of carbon. Each atom has six protons and eight neutrons.

It decays to form nitrogen, which has seven protons and seven neutrons.

Revise: Nuclear reactionsRadioactive decay