Every time you eat a banana or take a flight, you are exposed to a tiny amount of radiation. This constant, low-level ionizing radiation present around us at all times is called background radiation.
Because radioactive decay is governed by the random nature of decay, you cannot predict which nucleus will decay next. This means that if you measure background radiation over short periods, the count rate will constantly fluctuate. To measure it, scientists use a Geiger-Müller (GM) tube connected to a counter.
When measuring a radioactive source in an experiment, the counter detects both the source and the background radiation. To find the true activity of the source, you must subtract the background count.
Worked Example:
Step 1: Measure the background count with no source present (e.g., cpm).
Step 2: Measure the total count with the radioactive rock present (e.g., cpm).
Step 3: Subtract the background count from the total count.
Final Answer: cpm.
Most background radiation comes from naturally occurring sources in our environment:
Human activities also contribute to background radiation, though usually in much smaller amounts than natural sources:
Radiation dose is a measure of the risk of harm to your body resulting from exposure to ionizing radiation. It depends on the type of radiation, the intensity, and the duration of exposure.
While low doses of radiation can cause mutations in DNA (increasing the risk of cancer), very high doses can cause rapid cell death, leading to radiation sickness.
Your geographical location significantly impacts your annual radiation dose:
Certain jobs expose workers to higher levels of radiation:
To manage their risk, these workers use shielding (like standing behind lead-lined screens or wearing lead aprons) and wear a dosimeter (or film badge). The dosimeter does not protect them from radiation; rather, it measures and records their cumulative dose over time to ensure it stays below safe legal limits.
Students often confuse Background Radiation with CMBR (Cosmic Microwave Background Radiation). CMBR is evidence for the Big Bang, whereas background radiation is the ionizing radiation in our local environment.
When asked why three separate background radiation readings are different, you must explicitly state that radioactive decay is a random process.
For questions about radiation exposure in aeroplanes or high-altitude locations, the key mark-earning explanation is that the atmosphere is thinner, providing less shielding from cosmic rays.
Never describe radiation simply as 'dangerous' or 'harmful'. Always use specific biological terminology, stating that it 'increases the risk of harm' or 'causes mutations in DNA'.
You do not need to memorize the definition of a Sievert, but you must be able to recognize it in data tables and convert between Sv and mSv ().
Background radiation
The constant, low-level ionizing radiation that is present around us at all times from both natural and man-made sources.
Ionizing radiation
Radiation with enough energy to remove electrons from atoms, creating ions which can damage living cells and DNA.
Random nature of decay
The unpredictable process of nuclear decay; it is impossible to know when a specific nucleus will decay or which one will decay next.
Geiger-Müller (GM) tube
A device used to detect and measure ionizing radiation, often connected to a counter to provide a count rate.
Counter
An electronic device attached to a GM tube that records the number of radioactive decay events detected.
Radon gas
A naturally occurring radioactive gas produced by the decay of uranium in rocks and soil, acting as a highly ionizing alpha emitter.
Cosmic rays
High-energy radiation and particles originating from outer space and the Sun that strike the Earth.
Nuclear fallout
Radioactive material dispersed into the atmosphere following a nuclear explosion that eventually settles back to Earth.
Radiation dose
A measure of the risk of harm to the body resulting from exposure to ionizing radiation.
Sieverts (Sv)
The standard unit of radiation dose.
Millisieverts (mSv)
A smaller unit of radiation dose commonly used for everyday exposure levels, equal to one-thousandth of a Sievert.
Shielding
Materials (like lead or concrete) placed between a person and a radioactive source to absorb radiation and reduce exposure.
Dosimeter
A wearable badge used to monitor and measure the cumulative radiation dose a person receives over time.
Put your knowledge into practice — try past paper questions for Physics
Background radiation
The constant, low-level ionizing radiation that is present around us at all times from both natural and man-made sources.
Ionizing radiation
Radiation with enough energy to remove electrons from atoms, creating ions which can damage living cells and DNA.
Random nature of decay
The unpredictable process of nuclear decay; it is impossible to know when a specific nucleus will decay or which one will decay next.
Geiger-Müller (GM) tube
A device used to detect and measure ionizing radiation, often connected to a counter to provide a count rate.
Counter
An electronic device attached to a GM tube that records the number of radioactive decay events detected.
Radon gas
A naturally occurring radioactive gas produced by the decay of uranium in rocks and soil, acting as a highly ionizing alpha emitter.
Cosmic rays
High-energy radiation and particles originating from outer space and the Sun that strike the Earth.
Nuclear fallout
Radioactive material dispersed into the atmosphere following a nuclear explosion that eventually settles back to Earth.
Radiation dose
A measure of the risk of harm to the body resulting from exposure to ionizing radiation.
Sieverts (Sv)
The standard unit of radiation dose.
Millisieverts (mSv)
A smaller unit of radiation dose commonly used for everyday exposure levels, equal to one-thousandth of a Sievert.
Shielding
Materials (like lead or concrete) placed between a person and a radioactive source to absorb radiation and reduce exposure.
Dosimeter
A wearable badge used to monitor and measure the cumulative radiation dose a person receives over time.