Detection of radioactivity

Background radiation is the natural radiation present in our environment all the time. It comes from various sources, both natural and man-made, and is always around us. In this section, we will learn about what background radiation is, its sources, and how it is measured.

What is background radiation

Background radiation is the low level of ionising radiation that is always present in the environment. It comes from natural sources like cosmic rays from space and radon gas from the ground, as well as from human activities like medical procedures and industrial processes.

• Background radiation is natural and unavoidable. It is part of our daily life and contributes to the radiation dose we receive.

Sources of background radiation

The main sources that contribute to background radiation are:

Radon Gas (in the air):

• • Radon is a naturally occurring radioactive gas that comes from the decay of uranium in the Earth's crust. It seeps out of the ground and accumulates in the air, particularly in buildings that are poorly ventilated.

  • Radon gas is one of the largest contributors to background radiation.

Rocks and Buildings:

• • Certain rocks, such as granite, contain radioactive elements that release radiation. Buildings made of such materials also emit small amounts of radiation.

  • Areas with lots of granite rock, like parts of Cornwall in the UK, tend to have higher levels of background radiation.

Food and Drink:

• • Many foods and drinks naturally contain small amounts of radioactive elements. For example, bananas contain potassium-40, which is a radioactive isotope.

  • These radioactive elements enter the food chain from the soil and water, meaning we consume a tiny amount of radiation through our diet.

Cosmic Rays:

• • Cosmic rays are high-energy radiation that originates from outer space and interacts with the Earth's atmosphere. They contribute to background radiation levels, especially at high altitudes where there is less atmospheric shielding.

  • Pilots and people living in high-altitude areas receive higher doses of cosmic radiation compared to those living at sea level.

Measuring radiation

Ionising radiation can be measured using a radiation detector connected to a counter. There are different types of detectors, but one of the most common is the Geiger-Müller (GM) tube.

• The detector senses radiation, and the counter records the number of radioactive particles detected over time.

Count rate

The count rate is the number of radioactive events detected per second or minute. It is a measure of how much radiation is present.

• Count Rate Units:

  • Counts per second (counts/s).

  • Counts per minute (counts/min).

The count rate tells us how active a radioactive source is, or how much radiation is present in a particular area.

Corrected count rate