Contamination
Contamination occurs if an object has a When unstable atoms give off particles that can be harmful to humans. material introduced into it. An apple exposed to the Energy carried by particles from a radioactive substance, or spreading out from a source. from cobalt-60 is irradiated but an apple with cobalt-60 injected into it is A substance is contaminated if another substance is mixed or dispersed within it..
As with Process of exposing an object to a source of radiation. Eg fruit exposed to gamma rays in order to destroy bacteria is said to have been irradiated., contamination can be very useful as well as being potentially harmful.
Medical contamination
Cancer tumours can be treated by injecting them with a radioactive material. The cancer cells absorb radiation from the material and receive a high dose of energy. Doctors must work out the danger to nearby healthy tissue before giving this treatment.
In some cases, injected radioactive sources (such as technetium-99) can be used as A radioisotope used to trace, eg the flow of blood through an organ. to make soft tissues, such as blood vessels or the kidneys show up through medical imaging processes. An Atoms of an element with the same number of protons and electrons but different numbers of neutrons. emits A type of ionising radiation that is also part of the EM spectrum. It has no mass. rays that easily pass through the body to a detector outside the body, for example an x-ray machine or a 鈥榞amma camera鈥. 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 Energy is 'given-out' by the material and the internal energy of the material will decrease. For example, infrared radiation from the Sun is emitted into space. from different parts would indicate how well the isotopes are flowing, or if there is a blockage, perhaps caused by a cancer.
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:
- have very short The time it takes for the number of nuclei of a radioactive isotope in a sample to halve. Also defined as the time it takes for the count rate from a sample containing a radioactive isotope to fall to half its starting level. - 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鈥檚 body
- are not poisonous
PET scanners
Positron emission tomography (PET) scans use a positron emitter as the contamination tracer. These tracer materials, such as fluorine-18, have very short half-lives, and need to be manufactured in the hospital and injected into the patient鈥檚 blood soon after manufacture.
The positrons emitted will react with electrons in the patient鈥檚 body and produce gamma rays which can be detected outside the body. Multiple detections can build up a picture of the movement of the tracer inside the body.
Contamination to check for leaks
Water supplies can be A substance is contaminated if another substance is mixed or dispersed within it. with a gamma-emitting radioactive Atoms of an element with the same number of protons and electrons but different numbers of neutrons. 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.
The isotope used for this purpose must:
- be a gamma emitter
- have a half-life of at least several days to allow the emissions to build up in the soil
- not be poisonous to humans as it will form part of the water supply
| 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 |
| Advantages of contamination | Radioactive isotopes can be used as medical and industrial tracers |
|---|---|
| Disadvantages of contamination | Radioactive isotopes may not go where they are wanted |
| Advantages of contamination | Use of isotopes with a short half-life means exposure can be limited |
|---|---|
| Disadvantages of contamination | It can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind |
| Advantages of contamination | Imaging processes can replace some invasive surgical procedures |
|---|---|
| Disadvantages of contamination | Exposure to radioactive materials can potentially damage healthy cells |
Irradiation versus contamination
The two processes of irradiation and contamination are often confused. However they are very different and useful in their own right.
| Irradiation | Contamination |
| Occurs when an object is exposed to a source of radiation outside the object | Occurs if the radioactive source is on or in the object |
| Doesn鈥檛 cause the object to become radioactive | A contaminated object will be radioactive for as long as the source is on or in it |
| Can be blocked with suitable shielding | Once an object is contaminated, the radiation cannot be blocked |
| Stops as soon as the source is removed | It can be very difficult to remove all of the contamination |
| Irradiation | Occurs when an object is exposed to a source of radiation outside the object |
|---|---|
| Contamination | Occurs if the radioactive source is on or in the object |
| Irradiation | Doesn鈥檛 cause the object to become radioactive |
|---|---|
| Contamination | A contaminated object will be radioactive for as long as the source is on or in it |
| Irradiation | Can be blocked with suitable shielding |
|---|---|
| Contamination | Once an object is contaminated, the radiation cannot be blocked |
| Irradiation | Stops as soon as the source is removed |
|---|---|
| Contamination | It can be very difficult to remove all of the contamination |