Explain what happens to the nucleus of an atom when it undergoes alpha decay.

Eduqas A-Level Physics — 3.5 Nuclear decay · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Radioactive nuclei can become more stable by emitting different types of radiation. One of these processes is alpha decay.

Model answer (5 marks)

An alpha particle is emitted from the nucleus.
The alpha particle consists of 2 protons and 2 neutrons.
The proton number (atomic number) of the nucleus decreases by 2.
The mass number (nucleon number) of the nucleus decreases by 4.
A new (different) element is formed because the proton number has changed.

Examiner tips

Use the word "emitted" to show the process. Show the change in Z and A explicitly. Mention that the new element has a different chemical identity.
Include the composition of the alpha particle (2p+2n).

Common mistakes

Forgetting to state that the alpha particle is 2p+2n. Not recognising that the element changes. Mixing up the changes in Z and A (e.g., saying Z increases).

Mark scheme (5 marks)

An alpha particle is emitted from the nucleus
An alpha particle consists of 2 protons and 2 neutrons
The proton number (atomic number) of the nucleus decreases by 2
The mass number (nucleon number) of the nucleus decreases by 4
A new (different) element is formed because the proton number has changed

Key terms in this question

alpha decay · nucleus