# Nuclear decay

The emission of radiation from an unstable may cause changes to the nucleus, including:

• an increase or decrease in its and/or
• a change in its

Changes due to radioactive decay can be represented by balanced nuclear equations. The changes that happen depend on the type of radiation emitted.

## Alpha decay

consist of two and two . Protons are positively charged. When a nucleus emits an alpha particle, these changes happen:

• the mass number decreases by 4
• the atomic number decreases by 2
• the nuclear charge decreases by 2

### Example

Radon-219 decays into polonium-215 by emitting an alpha particle. This is the balanced equation for the reaction:

$_{86}^{219}Rn \rightarrow _{84}^{215}Po + _{2}^{4}\alpha$

Notice that:

• the mass number of the nucleus decreases by 4, from 219 to 215
• the atomic number of the nucleus decreases by 2, from 86 to 84
• the numbers at the top and bottom give the same totals on both sides

Polonium have 84 protons, so their nuclear charge is +84. They have two fewer protons than radon nuclei, which have 86 protons and so a nuclear charge of +86.

## Beta decay

A beta particle forms when a neutron changes into a proton and a high-energy . The proton stays in the nucleus but the electron leaves the atom as a beta particle. When a nucleus emits a beta particle, these changes happen:

• the mass number stays the same
• the atomic number increases by 1
• the nuclear charge increases by 1

### Example

Carbon-14 decays into nitrogen-14 by emitting a beta particle. This is the balanced equation for the reaction:

$_{6}^{14}C \rightarrow _{7}^{14}N + _{-1}^{~0}\beta$

Notice that:

• the mass number of the nucleus stays the same, 14
• the atomic number of the nucleus increases by 1, from 6 to 7
• the numbers at the top and bottom give the same totals on both sides, as (7 - 1) = 6

Nitrogen nuclei have 7 protons, so their nuclear charge is +7. They have one more proton than carbon nuclei, which have 6 protons and so a nuclear charge of +6.

## Gamma decay

are a type of . There is no change in mass or charge for this type of decay.

Gamma radiation transfers energy from the nucleus, so the symbol $$_{0}^{0}\gamma$$ may appear in some balanced equations.