B15.3 – Radioactive Decay

State the meaning of radioactive decay.

When a nucleus is unstable, it will disintegrate (break up). This shoots out tiny particles and a burst of energy. These materials are radioactive, so the breaking up of the nucleus is called radioactive decay. Each unstable nucleus changes into an isotope of a different element after radioactive decay.

Use equations (involving words or symbols) to represent changes in the composition of the nucleus when particles are emitted.

When a nucleus emits an alpha (α) particle, it loses 2 protons and 2 neutrons. This is denoted by the symbol ⁴₂α. 4 denotes the total number of nucleons (protons and neutrons) emitted and 2 denotes the number of protons emitted. Example:

alpha decay
The radon isotope with 219 nucleons and 86 protons has given out an alpha particle of 4 nucleons and 2 protons to become an isotope of Polonium with a nucleon number of 215 and proton number of 84. (You can find out what element’s isotope it becomes by looking at which element has a proton number that is two times lesser than the original element, in the periodic table).

When a nucleus emits a beta (β) particle, an electron are emitted and a neutron in the nucleus changes into a proton. This is denoted by the symbol ⁰_-1β. 0 denotes that there is no emission of any nucleon. -1 denotes the electron emitted (as well as the proton gained instead of emitted). Example:

The Carbon isotope with 14 nucleons and 6 protons has given out a beta particle of 1 electron to become an isotope of Nitrogen with 14 nucleons and 7 protons. (You can find out the new element formed by looking at the periodic table to find out which element has a proton number that is one greater than the original element)