Recall that alpha, β– (beta minus), β+ (positron), gamma rays and neutron…

The idea

An unstable nucleus can shed energy or particles to become more stable, and the emissions are alpha particles, β– (beta minus) particles, β+ (positron) particles, gamma rays and neutrons. Each type comes from the nucleus itself, not from the electron shells. The process is random: you cannot predict which nucleus will decay next or exactly when it will happen, even though large samples show a steady average rate. For example, a sample of many unstable nuclei will emit radiation at an unpredictable moment for any single nucleus, yet the count rate over time follows a smooth decay curve. Recognising the five named emissions and the random nature of decay is the recall target here.

What earns the marks

• Lists alpha, β– (beta minus), β+ (positron), gamma and neutron radiation as emissions from unstable nuclei.
• States that these emissions originate from the nucleus.
• Explains that decay is random because the timing and identity of the next decaying nucleus cannot be predicted.
• Distinguishes random decay of individual nuclei from the predictable average behaviour of a large sample.

Common mistakes and how to put them right

• Says gamma rays come from the electron shells.

  Put it right by stating that gamma radiation is emitted from the excited nucleus.

• Claims decay is predictable for a single nucleus.

  Put it right by explaining that only large samples show a predictable average rate.

• Omits neutron radiation or β+ (positron) emission from the list.

  Put it right by naming all five emissions in the specification.

Exam tips

• Learn all five emissions as a set so none is missed in a recall question.
• Use the word random to mean unpredictable for an individual nucleus, not that the rate changes without pattern.
• Link each emission to the nucleus as its source.