USES OF RADIOACTIVE MATERIALS

 

Radioisotopes in Medicine

There are many uses of radioisotopes in medicine. One already mentioned (on the Radiation and You page) is the sterilisation of surgical equipment using high-energy gamma rays.

In the same way food may be sterilised using gamma radiation in order to increase its shelf-life. The gamma rays kill micro-organisms, such as bacteria, that may be harmful to humans.

The picture below shows food and surgical equipment being sterilised with gamma rays.

Radioisotopes (tracers) can be injected into humans in order to locate cancerous tumours and other medical problems. An example is the use of Iodine-131: a radioisotope of Iodine-127.

Iodine-131 is used to detect thyroid (a gland that absorbs Iodine) problems. If the thyroid is not absorbing Iodine properly the gamma rays emitted by Iodine-131 would reveal a problem.

Another common tracer is Technetium-99. This emits gamma rays and has half-life six hours. It is used to find tumours in the body. The gamma rays are detected with a 'gamma camera'. The image of the tumour shows up as a coloured glow after a few hours.

The picture on the left shows the image from a 'gamma camera' immediately after a human has been injected with Technetium-99. The picture on the right shows an image six hours later. You can see cancerous cells as a yellow glow (lung cancer).

The important factors to consider when choosing a radioisotope for medical use are:

1.

It must emit gamma rays only. Gamma rays pass through the body, which means they can be detected with a 'gamma camera'. Alpha particles would not be able to penetrate through the skin so they could not be detected.

Gamma rays do not ionise cells inside the body so no damage is caused. Alpha particles and beta particles would ionise cells, which could lead to the formation of cancer cells.

2.

It must have a short half-life (typically around a few hours). A short half-life ensures that all the radiation inside the patient leaves the body quickly and does not accumulate.

3.

It must be able to be easily administered to the patient. Injections and tablets are used.

Radioisotopes in Industry

Radioactive tracers can be used to locate leaks in pipes in much the same way they are used to find tumours in medicine. The radioisotope is injected into the pipe and a detector outside is used to find the leak. The reading on the detector increases when near a leak as the radiation can escape through the hole in the pipe more easily.

Radioisotopes used to find leaks are ones that emit gamma radiation with a short half-life. Gamma rays can easily penetrate pipes (even if they are underground) and reach the detector. Both alpha and beta particles would not pass through pipes so could not be used.

Another use of radioisotopes in industry is in the thickness control of materials such as paper, cardboard and metal (e.g. tin foil).

The picture below shows how beta radiation is used to monitor paper thickness.

A source of beta radiation is used to pass beta particles through the paper.

A detector on the other side of the paper detects the beta particles that pass through.

The detector is connected to a hydraulic control via a processor unit.

If the radiation level detected drops it means the paper is too thick so the hydraulic control pushes rollers closer together in order to reduce the paper thickness.

If the radiation level detected increases it means the paper is too thin so the hydraulic control pulls the rollers apart so the paper thickness can be increased.

The radioactive source must be a beta emitter for paper or cardboard thickness testing and a gamma emitter for metal testing. This ensures that the radiation can pass through the material. An alpha source cannot be used as paper and metal absorbs alpha particles.

In each case the beta or gamma emitters must have a long half-life (approximately a few years). This means the equipment will have a long lifetime and not require regular maintenance.

Smoke Detectors

Smoke alarms in homes and in industry use the radioisotope Americium-241 with a half-life of around 460 years.

Americium-241 emits alpha particles that ionise the air molecules around the alarm.

The charged air molecules conduct electricity so a small current flows inside the alarm.

When smoke enters the alarm alpha particles are absorbed. This makes the current inside the alarm fall and set off a ringing sound.

Alpha emitters must be used for smoke detectors since only alpha particles ionise air.

Gamma rays and beta particles easily pass through air without causing ionisation.

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