Contamination & Irradiation

Definition of Contamination

Contamination occurs when radioactive material is deposited on or inside an object or living tissue, such as skin. This radioactive material itself is the source of radiation exposure because it continues to emit radiation until it decays or is removed.

Contamination can spread radiation to other surfaces or people if not handled carefully. For example, if radioactive dust settles on a workbench, anyone touching the bench can become contaminated. This is why contamination requires strict safety procedures to prevent the spread of radioactive substances.

Definition of Irradiation

Irradiation is the exposure of an object or person to radiation without the object itself becoming contaminated. In other words, the radiation passes through or hits the object but does not leave any radioactive material behind.

Unlike contamination, irradiation does not make objects radioactive. The exposure is temporary and only lasts while the radiation source is nearby. For example, a patient receiving an X-ray is irradiated but not contaminated.

Types of Radiation

There are three main types of radiation relevant to contamination and irradiation: alpha particles, beta particles, and gamma rays. Alpha particles can be stopped by skin but are dangerous if ingested or inhaled. Beta particles can penetrate skin but are stopped by materials like plastic or glass. Gamma rays are highly penetrating and require dense materials like lead or concrete for shielding.

Hazards of Contamination and Irradiation

Both contamination and irradiation can damage living cells, which increases the risk of cancer. The radiation can ionise atoms in cells, causing mutations or cell death.

Contamination is generally more dangerous if radioactive material enters the body (e.g., through a cut or by inhalation) because it continues to expose cells internally over time. Internal contamination is harder to remove and can cause prolonged damage.

Irradiation risk depends on the length of exposure and the intensity of the radiation. The longer the exposure or the stronger the source, the greater the potential harm. However, once the source is removed, the risk stops immediately.

For instance, if a worker is exposed to a radiation source for 10 minutes, their risk is less than if they were exposed for an hour. This is why controlling exposure time is crucial in radiation safety.

Background Radiation

Background radiation is the low-level radiation that is always present in the environment from natural sources such as cosmic rays and radioactive materials in the earth. This contributes to natural irradiation but is usually at low levels that do not cause harm.

Protection Methods

To protect against contamination and irradiation, several safety methods are used:

• Shielding: Using materials like lead, concrete, or thick barriers to absorb or block radiation and reduce exposure.
• Limiting exposure time: Minimising the time spent near radioactive sources to reduce the dose received.
• Maintaining distance: Increasing the distance from a radiation source reduces exposure because radiation intensity decreases with distance, following the inverse square law (intensity halves each time distance doubles).
• Proper disposal: Contaminated materials must be safely contained and disposed of to prevent spreading radioactive contamination.

For example, workers handling radioactive materials wear protective clothing and use tongs to keep a safe distance, reducing contamination risk.

Example: If a radiation source emits 0.2 mSv per minute, spending 5 minutes near it results in a dose of 1.0 mSv.