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Home · IGCSE 0625 · Nuclear physics · Radioactive decay equations · Practice
Core · Practice questions · Radioactive decay equations

Make it balance.

Six original Cambridge-style questions on decay equations: completing alpha and beta decays, how the element changes, gamma emission, and the random nature of decay.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

Balance top and bottom.

01
Recall
[2 marks]

State what is meant by saying that radioactive decay is random and spontaneous.

  • Random: you cannot predict when a particular nucleus will decay. ✓
  • Spontaneous: it is not affected by outside conditions such as temperature or pressure. ✓
02
Calculation
[2 marks]

Polonium-210 (proton number 84) decays by emitting an alpha particle. State the nucleon number and proton number of the daughter nucleus.

nucleon: 210 - 4 = 206 ; proton: 84 - 2 = 82

daughter: nucleon number 206, proton number 82 (lead-206)

03
Calculation
[2 marks]

Carbon-14 (proton number 6) decays by emitting a beta particle. State the nucleon number and proton number of the daughter nucleus.

nucleon: stays 14 ; proton: 6 + 1 = 7

daughter: nucleon number 14, proton number 7 (nitrogen-14)

04
Analysis
[2 marks]

Explain why a nucleus becomes a different element when it emits a beta particle.

  • A neutron changes into a proton, so the proton number increases by 1. ✓
  • The element is decided by the proton number, so it becomes the next element. ✓
05
Recall
[2 marks]

A nucleus emits a gamma ray only. State what happens to its nucleon number and proton number, and explain why.

  • Both stay the same. ✓
  • Gamma is energy only; no protons or neutrons leave the nucleus. ✓
06
Calculation
[3 marks]

In the decay below, find the missing nucleon number a and proton number b, and state whether it is alpha or beta decay.

uranium (238, 92) → thorium (a, b) + alpha (4, 2)

a = 238 - 4 = 234 ; b = 92 - 2 = 90
  • a = 234, b = 90. ✓
  • It is alpha decay (a helium nucleus is emitted). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.