Radiation hazards and safety

The ability of radiation to destroy cells can be useful in treating cancer, but healthy cells can be damaged too. This is why exposure must be carefully controlled.

Reducing exposure: time, distance and shielding

Radiation dose measures exposure in terms of its potential biological harm. It is measured in sieverts (Sv). Safety precautions aim to keep the dose as low as possible.

Three approaches reduce irradiation:

• Reduce the exposure time. Spending less time near a source reduces the radiation received.
• Increase the distance. Using tongs rather than holding a source keeps it farther from the body and reduces exposure.
• Use shielding. Suitable shielding absorbs radiation before it reaches a person. For example, a lead-lined container is used to store a source when it is not needed.

These precautions work together. In a school experiment, a source should remain in its shielded container until needed, be moved using tongs and be returned promptly after use.

Gloves and suitable protective clothing serve a different purpose: they help keep radioactive material off the skin and clothing. They should not be confused with shielding against penetrating radiation.

Keeping patients and medical personnel safe

A medical procedure may offer an important benefit, but the patient's radiation dose must still be limited. Exposure should be no greater than needed for the procedure. When radiation is directed at a particular area, careful targeting and appropriate shielding help protect healthy tissue.

For an investigation using a radioactive tracer, the isotope should have a half-life short enough for its activity to fall quickly after the test. However, its half-life must also be long enough for the tracer to reach the area being investigated and remain detectable while measurements are made. Choosing the shortest possible half-life without considering the investigation would not necessarily work.

Medical personnel may carry out many procedures, so repeated exposure can build up over time. They leave the room or work behind shielding during exposures where possible, increasing their distance from the source and reducing the radiation reaching them. A dosimeter, often worn as a badge, monitors their accumulated dose. It records exposure; it does not itself shield the wearer.

Irradiation and contamination: radiation or radioactive material?

The key distinction is what reaches the person or object.

Irradiation occurs when radiation reaches an object from a source. For example, radiation from nearby radioactive dust may irradiate someone's skin even though no dust lands on them. Irradiation does not make the skin radioactive. Once the source is removed or the radiation is blocked, that exposure stops, although any damage already caused may remain.

Contamination occurs when radioactive material itself gets onto or inside something. Radioactive dust settling on skin contaminates it. The dust continues emitting radiation while it remains there, so the contaminated skin is also being irradiated. Radioactive material may enter the body by being inhaled or swallowed, exposing internal tissues as it decays.

Comparing the hazards and choosing precautions

Both irradiation and contamination can damage tissue or cause mutations. Contamination can produce prolonged exposure because the source remains on or inside the person. Internal contamination is particularly concerning because the source is close to internal tissues and may be difficult to remove. Contamination can also spread when radioactive material is transferred elsewhere.

However, a strong external source can deliver a dangerous dose without causing contamination. The hazard depends on the radiation emitted, the dose received and how long exposure continues—not just the label given to the exposure.

For irradiation, the main protections are time, distance and shielding. Preventing contamination means preventing radioactive material from reaching the body: gloves and protective clothing protect surfaces, while suitable sealed protective equipment can prevent radioactive dust from being inhaled. Removing contamination removes the material responsible for continuing exposure.

• Reduce time, increase distance, use shielding.
• Store sources in shielded containers; handle them with tongs.
• Gloves and protective clothing help prevent contamination.
• Patients: limit dose and protect healthy tissue. Tracer half-life must be short enough to reduce prolonged exposure but long enough to complete the investigation.
• Medical staff: leave the room or use shielding; monitor accumulated dose with a dosimeter.

Compare exposure

Both can cause harm. Contamination may cause prolonged internal exposure and can spread; external irradiation can also deliver a dangerous dose.