Irradiation and contamination

In a nutshell

Radiation can have harmful effects on anything in its surroundings. Irradiation is exposure to radiation. Contamination is when radioactive material is deposited on or in an object. Background radiation is the low-level radiation present in the environment.

Irradiation

Definition

Irradiation is exposure to radiation from a nearby radioactive source.

This can be prevented or reduced by keeping sources in appropriate storage boxes made from materials that they cannot penetrate.

Example

Sources that undergo gamma decay should be kept in thick lead boxes. 

Contamination

Definition

Contamination is when radioactive material is deposited on or in an object. This can be dangerous as it could be on or in the body. The radioactive material may continue to decay which would release more radiation.

To prevent contamination, gloves and tongs should be used when handling sources. A hazardous materials (hazmat) suit is used to prevent contamination from highly radioactive materials. 

Example

In $$1986$$​, the nuclear reactor in Chernobyl exploded. Even today, the Chernobyl nuclear power plant's control room can only be visited by people wearing hazmat suits!

Background radiation

Background radiation is low-level radiation that is constantly present in the environment. The radiation can come from naturally occurring sources or from artificial (man-made) sources. 

Naturally occurring sources include rocks and cosmic rays from space.  Artificial sources involve radiation due to human activity (e.g. nuclear waste, x-rays, etc.).

Background radiation sources

1. Radon gas (produced when uranium in rocks decays) 2. Rocks and building materials 3. Medical (e.g. x-rays) 4. Food  5. Cosmic rays 6. Other

Tip: When taking measurements of the count rate of a source, make sure to always subtract the background radiation.

Radiation dose

Radiation dose shows the risk of irradiation doing harm to the human body. It is measured in sieverts ($$Sz$$). 

The radiation dose varies depending on the location. Background radiation usually has a small risk of harm and therefore a low radiation dose.

Effects of radiation

The different types of radiation cause different amounts of harm.

Beta and gamma sources are the most harmful outside the body. This is because they can penetrate the skin and cause damage to organs. Alpha particles cannot penetrate the skin so can't do much damage when the source is outside the body. 

Irradiation is most dangerous outside the body.

Alpha sources are the most harmful inside the body. This is because they cannot pass out of the body so do damage within a localised area. Beta and gamma sources can pass straight out, or do a smaller amount of damage in a wider area. 

Contamination is most dangerous inside the body.