Background Radiation

Background radiation is the low-level ionising radiation that is always present in the environment. It arises from the decay of unstable atomic nuclei in natural and artificial sources, emitting particles or electromagnetic radiation.

Sources of Background Radiation

Background radiation comes from both natural and artificial sources.

Natural Sources

• Rocks and Soil: Some rocks contain radioactive elements like uranium and thorium. These naturally emit radiation over time.
• Cosmic Rays: High-energy particles from space constantly bombard the Earth’s atmosphere, producing radiation that reaches the surface.
• Radon Gas: Radon is a radioactive gas produced by the decay of uranium in rocks and soil. It can accumulate in buildings, especially in poorly ventilated areas.

Artificial Sources

• Medical Sources: X-rays and some treatments use radiation, which adds to background levels.
• Nuclear Industry: Nuclear power plants and nuclear weapons testing have increased background radiation in some areas.

Background radiation levels vary depending on location. For example, areas with granite rocks tend to have higher natural radiation, and cosmic radiation increases at higher altitudes.

Measurement of Background Radiation

Background radiation is measured using a Geiger-Müller (GM) tube, a device that detects and counts radioactive particles.

• The GM tube clicks or gives a reading each time it detects a radioactive particle.
• The number of clicks per second is called the counting rate.
• Because background radiation is always present, the counting rate includes background counts.

The unit for measuring radioactive activity is the becquerel (Bq), which means one radioactive decay per second. Note that the counting rate from a detector approximates the activity but may differ due to detector efficiency.

For example, if a GM tube detects 20 counts in one second, the activity is approximately 20 Bq.

To measure radiation from a specific source, you subtract the background count rate from the total count rate.

Example: If the total count rate near a source is 150 counts per second and the background count rate is 30 counts per second, the source’s radiation is:

$150 - 30 = 120 \text{ counts per second (Bq)}$

For instance, if a GM tube counts 50 clicks in 5 seconds, the counting rate is $\frac{50}{5} = 10$ counts per second.

Hazards of Background Radiation

Even though background radiation is low-level, it can still pose some risks because it is ionising radiation. Ionising radiation can damage living cells by ionising atoms inside them.

• Cell Damage: Ionising radiation can cause mutations in DNA, potentially leading to cancer.
• Low-Level Exposure: Most people are exposed to low levels daily without immediate harm, but long-term exposure increases the risk of health problems.
• Long-Term Concerns: Continuous exposure to slightly higher background radiation (e.g., in certain workplaces or homes with radon) can increase the chance of developing illnesses over many years.

The risk depends on the dose and duration of exposure. Background radiation is usually too low to cause immediate effects but is important to monitor and control where possible.

Protection from Background Radiation

To reduce exposure to background radiation, three main methods are used:

• Reducing Exposure Time: Spend less time near sources of radiation to lower the total dose received.
• Increasing Distance: Radiation intensity decreases with distance, so staying further away from sources reduces exposure.
• Using Shielding: Materials like lead, concrete, or thick walls can absorb or block radiation, protecting people behind them.

For example, radon gas levels can be reduced in homes by improving ventilation, which lowers the amount of radioactive gas indoors.

Example: If a person spends 2 hours near a source emitting 50 Bq and then moves to a place where the source is twice as far away, the radiation exposure will be reduced by about four times (due to the inverse square law of distance).