The dangers and uses of radiation - CCEA

• To identify and understand the dangers of exposure to radioactive sources.

• To state ways to reduce the risk when using radioactive sources.

• To identify the correct radioactive source for different applications.

Radioactive materials are hazardous.

Radioactive emissions cause dangerous ionisation by removing electrons from atoms.

When this happens with molecules in living cells, the genetic material of a cell (the DNA) is damaged.

This can lead to cancer.

Radiation can also deposit large amounts of energy into the body, which can damage or destroy cells completely.

Key points

• Alpha radiation is not as dangerous if the radioactive source is outside the body, because it cannot pass through the skin and is unlikely to reach cells inside the body.

• Alpha radiation will damage cells if the radioactive source has been breathed in as a gas or dust or if it is swallowed.

• Beta and gamma radiation can penetrate the skin and cause damage to cells inside the body.

The risk associated with radioactive materials depends on the amount of exposure.

Being exposed to highly radioactive materials or being exposed to radioactive materials for long periods of time or on a regular basis increases the dose received which, in turn, increases the risk.

Given that radioactive materials are hazardous, certain precautions need to be taken to reduce the risk when using radioactive sources.

These precautions fall under three main headings:

1. Time: being exposed to the source for as short a time as possible.

2. Distance: keeping the source as far away from the body as possible by using tongs.

3. Shielding: wearing protective clothing to prevent the body becoming contaminated should radioactive isotopes leak out and also to protect against absorbing radiation e.g. using a lead apron, face masks, etc.

Radioactive materials should be kept in lead-lined containers when not in use.

Background radiation is the radiation detected when there are no known radioactive sources present.

Background radiation released by soil, rocks and cosmic rays is always in the environment.

Most of it comes from natural sources but some also comes from artificial sources.

Radioactive sources are found all around us and in our bodies.

Most radioactive background activity comes from natural sources such as:

• Soils and rocks containing uranium which is radioactive. These may be used for building materials. When uranium decays radon, a radioactive gas, is released.

• Cosmic rays - radiation reaching the Earth from outer space.

Human behaviour adds slightly to the background activity that we are exposed to through medical X-rays, radioactive waste from nuclear power plants and the radioactive fallout from nuclear weapons testing.

As a result, gas, living things and plants absorb radioactive materials from the soil, which are then passed along the food chain.

For example, by eating a banana which contains radioactive potassium.

As it passes along the food chain the concentration of radioactivity will increase.

The actual amount of radiation that a person is exposed to depends on where they live, what job they do and many other things.

There is little we can do about natural background radiation, although people who live in areas with a high background radiation due to radon gas require homes to be well ventilated to remove the gas.

A radiation barrier (thick concrete based) should also be built into the foundation of the house.

Sterilisation of surgical instruments

Gamma rays are high energy electromagnetic waves which are only stopped by thick lead or concrete.

This means they can easily pass through medical equipment, such as syringes.

As gamma rays pass through the packaging and syringe, they will kill viruses and bacteria which contaminate the syringe.

As long as the equipment remains in a sealed plastic pack, it will remain free of viruses and bacteria and be safe for use with patients.

The gamma ray source used should have a long half-life so that the hospital does not have to replace it too frequently.

Advantages:

• Sterilisation can be done without high temperatures.

• It can be used to kill bacteria on things that would melt e.g. plastic syringes.

Disadvantages:

• It may not kill all bacteria on an object.

• It can be very harmful - standing in the environment where objects are being treated by radiation could expose people’s cells to damage and possibly cancer.

Although ionising radiation can cause cancer, high doses can be directed at cancerous cells to kill them.

This is called radiotherapy.

About 40 per cent of people with cancer undergo radiotherapy as part of their treatment.

It is administered in two main ways:

• From outside the body using X-rays or gamma rays from radioactive cobalt.

• From inside the body by putting radioactive materials into the tumour or close to it.

Beams of gamma rays, called a gamma knife, can be used to kill the cancerous tumour deep inside the body.

These beams are aimed at the tumour from many different directions to maximise the dose on the tumour but to minimise the dose on the surrounding soft tissue.

This technique can damage healthy tissue, so careful calculations are done to establish the best dose enough to kill the tumour, but not so much so that the healthy tissue is damaged.

The gamma ray source used should have a long half-life so that the hospital does not have to replace it too frequently.

In some cases, injected radioactive sources (such as technetium-99) can be used as tracers to make soft tissues, such as blood vessels or the kidneys, show up through medical imaging processes.

An isotope emits gamma rays that easily pass through the body to a detector outside the body, for example a ‘gamma camera’.

In this way, the radioactive isotope can be followed as it flows through a particular organ in the body.

Changes in the amount of gamma emitted from different parts would indicate how well the isotope is flowing, or if there is a blockage.

The isotope used must:

• Be a source of gamma rays so that they pass out through the body to be detected by the gamma camera or GM tube.

• Have very short half-lives - sources used typically have half-lives of hours so after a couple of days there will hardly be any radioactive material left in a person’s body.

• Not be poisonous.

To control the thickness of metal or paper

To check for leaks in water pipes

Water supplies can be contaminated with a gamma-emitting radioactive isotope to find leaks in pipes.

Where there is a leak, contaminated water seeps into the ground, causing a build-up of gamma emissions in that area.

The build-up of gamma emissions can be found using a Geiger-Muller tube.

This makes it easier to decide where to dig to find the leak without having to dig along the whole length of the pipe.

The isotope used for this purpose must:

• Be a gamma emitter to penetrate the ground and road surface.

• Have a half-life of at least several days to allow the emissions to build up in the soil but not too long so that exposure is limited and will not be poisonous to humans as it will form part of the water supply.

Smoke detectors

One type of smoke detector uses Americium-241, an alpha particle source, to detect smoke.

When smoke enters between the plates, some of the alpha particles are absorbed.

An alpha source is used because alpha radiation does not penetrate very far.

It is absorbed by a few cm of air.

This means that as long as the detector is high up on a wall, or the ceiling, it is safe for humans to be in the same room.

The source should have a long half-life so that the smoke detector does not have to be replaced too frequently, and so that the count rate remains almost constant each day.

Gamma rays are used in agriculture to kill the bacteria on food, prolonging its shelf life.

While the use of gamma radiation on food has many opponents it would be valuable in hot climates where refrigeration is not always possible.

The radioisotopes used in food processing plants should have a long half-life so that it is a long time before they need to be replaced.