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Home · IGCSE 0625 · Nuclear physics · Background radiation · Practice
Core · Practice questions · Background radiation

Sources, counting, correcting.

Six original Cambridge-style questions on background radiation: where it comes from, how it is detected, and how to correct a measurement for it.

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

Name it, detect it, subtract it.

01
Recall
[1 mark]

State what is meant by background radiation.

  • The low level of radiation that is present around us all the time, from natural and man-made sources. ✓
02
Recall
[3 marks]

State three natural sources of background radiation.

  • Radon gas from rocks and soil. ✓
  • Cosmic rays from space. ✓
  • Radioactive substances in food and drink (also rocks and building materials). ✓
03
Recall
[2 marks]

Name the instrument used to detect radioactivity, and state what quantity it measures.

  • A Geiger-Muller tube connected to a counter. ✓
  • It measures the count rate (counts per second or per minute). ✓
04
Calculation
[2 marks]

The background count rate is 18 counts per minute. With a source present, the counter reads 96 counts per minute. Calculate the count rate due to the source.

corrected = measured - background = 96 - 18

corrected count rate = 78 counts per minute

05
Application
[2 marks]

A student measures the count rate from a source but forgets to subtract the background. Explain what is wrong with their value for the source.

  • Their value is too high. ✓
  • The counter also detects background radiation, which has not been taken away. ✓
06
Analysis
[2 marks]

A student takes several one-minute background readings and gets slightly different values each time. Explain why, and suggest how to get a more reliable background value.

  • Radioactive decay is random, so the count varies from minute to minute. ✓
  • Take several readings and find the average (or count over a longer time). ✓

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.