Detection of radioactivity
Cambridge IGCSE Physics (0625) · Unit 5: Nuclear physics · 10 flashcards
Detection of radioactivity is topic 5.2.1 in the Cambridge IGCSE Physics (0625) syllabus , positioned in Unit 5 — Nuclear physics , alongside The atom, The nucleus and The three types of nuclear emission. In one line: Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).
The deck below contains 10 flashcards — 1 definition — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
State what is meant by background radiation
Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.
What the Cambridge 0625 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Know Know what is meant by background radiation
- Know Know the sources that make a significant contribution to background radiation including: (a) radon gas (in the air) (b) rocks and buildings (c) food and drink (d) cosmic rays
- Know Know that ionising nuclear radiation can be measured using a detector connected to a counter
- Use Use count rate measured in counts/s or counts/minute
- Use Use measurements of background radiation to determine a corrected count rate Supplement
State what is meant by background radiation.
Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.
A radiation detector records a count rate of 24 counts per minute in a laboratory. Suggest two possible sources of this background radiation.
Possible sources include:
1. Radioactive materials in the surrounding rocks/soil (
State four significant sources of background radiation.
1. Radon gas (in the air)
2. Rocks and buildings
3. Food and drink
4. Cosmic rays
(Each correct source is worth 0.5 marks)
A student measures background radiation using a Geiger-Muller tube. The initial reading is 10.0 counts per minute. She then places a lead sheet in front of the tube. Suggest why the measured count rate might be slightly lower, but not zero.
The lead sheet absorbs some, but not all, of the background radiation. Background radiation originates from multiple sources (radon gas, rocks, cosmic rays, food/drink) and some of these sources are not blocked by the lead sheet.
A detector connected to a counter records 20 counts per minute due to background radiation. A radioactive source is then placed near the detector, and the counter now reads 110 counts per minute. Calculate the count rate due to the radioactive source alone.
Count rate from source = Total count rate - Background count rate
Count rate from source = 110 counts/minute - 20 counts/minute
Count rate from source = 90 counts/minute
Explanation: The background radiation must be subtracted from the total count rate to determine the radiation emitted by the source only.
A student measures the background radiation in a laboratory. Suggest two sources that contribute to this background radiation.
1. Cosmic rays from space: High-energy particles from space constantly bombard the Earth.
2. Radioactive materials in the ground or buildings: Small amounts of radioactive isotopes are naturally present in rocks, soil and building materials.
A Geiger-Muller (GM) tube detects 3960 counts in 3 minutes. Calculate the count rate in counts/second.
Count rate = Total counts / Time
Count rate = 3960 counts / (3 minutes * 60 seconds/minute)
Count rate = 3960 counts / 180 seconds
Count rate = 22 counts/s
The count rate is calculated by dividing the total number of counts by the time interval in seconds.
A radioactive source is measured to have a count rate of 10 counts/s using a Geiger-Muller tube. State what a 'count rate' is.
Count rate is the number of radioactive decays detected per unit of time, typically measured in counts per second (counts/s) or counts per minute (counts/minute). It indicates the activity of the radioactive source.
A Geiger-Muller (GM) tube detects 32 counts per minute in a laboratory. A radioactive source is then placed near the GM tube, and the count rate increases to 198 counts per minute. Determine the corrected count rate of the radioactive source.
Answer:
Corrected count rate = Total count rate - Background count rate
Corrected count rate = 198 counts/min - 32 counts/min
Corrected count rate = 166 counts/min
Explanation: The background radiation must be subtracted from the total count rate to find the count rate due only to the radioactive source.
A student measures a background radiation count of 10 counts per minute. They then place a radioactive sample near the detector and measure a total count rate of 24 counts per minute. Explain why it is important to measure the background radiation when determining the activity of a radioactive source.
Answer:
Background radiation is present from sources other than the radioactive sample (
Key Questions: Detection of radioactivity
State what is meant by background radiation.
Background radiation is the low-level radiation that is present in the environment at all times. It originates from natural sources, such as radioactive materials in the Earth and cosmic radiation from space, as well as artificial sources like nuclear weapons testing and medical procedures.
More topics in Unit 5 — Nuclear physics
Detection of radioactivity sits alongside these Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Detection of radioactivity deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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