Dangers of Ionising Radiation

When this happens inside the human body, it triggers a dangerous chain of events. To fully describe this process in an exam, you must follow this specific sequence:

• First, radiation enters a living cell and collides with atoms inside DNA molecules.
• Then, these atoms are ionised, causing the chemical bonds that hold the DNA strand together to break or chemically alter.
• Next, if the cell repairs this damage incorrectly, it results in a mutation (a permanent change in the genetic base sequence).
• Finally, these mutated cells can divide and multiply uncontrollably via mitosis, leading to the formation of tumours and cancer.

At low doses, the primary risk is this slow development of mutations. However, at high doses, radiation kills massive numbers of cells simultaneously. This acute cell death results in severe tissue damage, radiation burns, and radiation sickness, where major organs fail to function.

The overall risk of harm to the body is measured as a radiation dose, recorded in Sieverts (Sv) or millisieverts (mSv) (where $1\text{ Sv} = 1000\text{ mSv}$). To validate findings about these health effects, scientists must ensure their studies undergo peer review before publication.

Internal vs External Hazards

Swallowing a radioactive source is a completely different hazard to standing next to one. The danger a specific type of radiation poses depends entirely on whether it is outside the body or inside the body.

External Hazards (Outside the Body):

• Gamma and beta are the most dangerous externally because they are highly penetrating. They can pass straight through the skin to reach internal organs.
• Alpha is the least dangerous externally. It has extremely low penetrating power and is easily absorbed by a few centimetres of air or the outer layer of dead skin.

Internal Hazards (Inside the Body):

• Alpha is the most dangerous internally. Because it is strongly ionising, once it is inhaled or swallowed, it causes intense, localised damage to DNA and cannot escape the body.
• Gamma is the least dangerous internally. It is weakly ionising and highly penetrating, meaning it is likely to pass straight out of the body without interacting with any cells.

Additionally, the hazard depends on the source's half-life. Sources with a short half-life have very high initial activity, posing severe short-term risks. Sources with a long half-life pose long-term risks because they remain radioactive for thousands of years.

Safety Precautions (Time, Distance, and Shielding)

How do workers in nuclear power plants stay safe around radioactive materials every single day? To prevent DNA mutation and tissue damage, they minimise their exposure using three main protocols: distance, shielding, and time.

• Distance: Keeping as far away from the source as possible rapidly decreases the intensity of radiation reaching the user. In laboratory settings, this means always using long tongs or forceps to handle sources and keeping them at arm's length.
• Shielding: Dense materials can be placed between the user and the source to absorb radiation. Radioactive sources must be stored in lead-lined boxes. Medical staff use lead aprons, stand behind lead-glass screens, or work behind thick concrete walls.
• Time and Monitoring: The duration a source is out of its container must be strictly minimised. To track this exposure, workers wear dosemeters (radiation badges) containing photographic film. The film darkens when exposed to radiation, allowing the total cumulative dose to be constantly monitored.

Irradiation vs Contamination

Why do hospital staff wear disposable gloves when handling radioactive liquids, but just step behind a lead screen when operating an X-ray machine? This comes down to the critical difference between irradiation and contamination.

Irradiation occurs when an object is exposed to radiation from an external source. Crucially, an irradiated object does not become radioactive.

The hazard vanishes the exact moment the source is removed or shielded. You protect against irradiation using distance (tongs) and lead shielding.

Contamination, however, is the unwanted presence of radioactive atoms on or inside a person or object. A contaminated object does become radioactive and will continuously emit radiation until the atoms naturally decay or are physically washed away. You protect against contamination by wearing gloves, lab coats, and face masks to prevent inhalation or physical transfer.