Know that a β-particle is a high-speed electron emitted from the nucleus, formed when a neutron changes into a proton and an electron and a reduction in the number of excess neutrons; the following change in the nucleus occurs during β-emission neutr

5.2.3 Radioactive Decay – β‑Particle Emission

What is a β‑particle?

A β‑particle is a high‑speed electron that is emitted from the nucleus of an unstable atom. It is produced when a neutron in the nucleus transforms into a proton and an electron (the β‑particle) together with an antineutrino.

The nuclear reaction

The fundamental change that occurs during β‑emission can be written as:

\$n \;\rightarrow\; p^{+} + e^{-} + \bar{\nu}_e\$

where:

• \$n\$ = neutron
• \$p^{+}\$ = proton
• \$e^{-}\$ = electron (β‑particle)
• \$\bar{\nu}_e\$ = antineutrino (carrying away excess energy and momentum)

Changes in the nucleus

Because a neutron is converted into a proton, the atomic number (\$Z\$) of the nucleus increases by 1, while the mass number (\$A\$) remains unchanged.

For a generic nucleus \$^{A}_{Z}\!X\$, the β‑decay can be expressed as:

\$^{A}{Z}\!X \;\rightarrow\; ^{A}{Z+1}\!Y + e^{-} + \bar{\nu}_e\$

Resulting changes

Example of β‑decay

Carbon‑14 decays to nitrogen‑14:

\$^{14}{6}\!C \;\rightarrow\; ^{14}{7}\!N + e^{-} + \bar{\nu}_e\$

Here, a neutron in the carbon nucleus becomes a proton, turning the element from carbon (\$Z=6\$) into nitrogen (\$Z=7\$) while the mass number stays at 14.

Comparison with other types of radiation

Key points to remember

• A β‑particle is a high‑speed electron emitted from the nucleus.
• β‑decay occurs when a neutron changes into a proton, an electron, and an antineutrino.
• The atomic number increases by one; the mass number does not change.
• β‑particles have moderate penetrating ability and can be stopped by a few millimetres of aluminium.
• Because the nucleus loses a neutron, the number of excess neutrons is reduced, moving the nucleus toward a more stable configuration.

Suggested classroom activity

1. Provide students with a list of common β‑emitters (e.g., \$^{14}{6}\!C\$, \$^{32}{15}\!P\$, \$^{90}_{38}\!Sr\$).
2. Ask them to write the nuclear equation for each decay, showing the change in \$Z\$ and \$A\$.
3. Discuss how the emitted β‑particle can be detected using a Geiger‑Müller tube.
4. Compare the shielding requirements for α, β, and γ radiation.