Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a radioactive source - typically cobalt-60. The gamma rays emitted by the cobalt will destroy any bacteria on the fruit but will not change the fruit in any significant way. The process of irradiation does not cause the irradiated object to become radioactive.
Doctors also use radioactive sources for a number of reasons, eg:
A gamma knife is a specific type of gamma irradiation used to kill cancerous cells in the brain. The head is clamped into a special helmet to make sure it stays perfectly still during the irradiation.
In medical applications that involve using radioactive sources, efforts are made to ensure that irradiation does not cause any long-term effects. This is done by considering:
If the half-life chosen is too long, the damaging effects of the radiation would last for too long and the dose received would continue to rise.
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 an X-ray machine or a 'gamma camera'. In this way, the radioactive isotope can be followed as it flows through a particular process in the body.
Changes in the amount of gamma radiation emitted from different parts would indicate how well the isotopes are flowing, or if there is a blockage.
In medical applications that involve injecting radioactive sources, efforts are made to ensure that contamination does not cause any long-term effects. This is done by choosing isotopes that:
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-Müller tube. This makes it easier to decide where to dig to find the leak.
The isotope used for this purpose must:
|Advantages of contamination||Disadvantages of contamination|
|Radioactive isotopes can be used as medical and industrial tracers||Radioactive isotopes may not go where they are wanted|
|Use of isotopes with a short half-life means exposure can be limited||It can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind|
|Imaging processes can replace some invasive surgical procedures||Exposure to radioactive materials can potentially damage healthy cells|