| What is Irradiation? | Irradiation - Exposing objects to beams of radiation. Irradiation from radioactive decay can damage living cells. This can be useful and hazardous. |
| Uses of Irradiation | Irradiation for Sterilisation:
To preserve fruit in supermarkets, exposed to a radioactive source (cobalt-60). The gamma rays emitted destroy any bacteria on the fruit, but don't change it in any significant way. This process doesn't cause the object to become radioactive
Medical Irradiation:
- Sterilisation of surgical instruments
- beams of gamma rays (called gamma knife), can be used to kill cancerous tumours deep inside body
Beams are aimed at tissue from many directions to maximise dose on tumour and minimise dose surrounding soft tissue. Healthy tissue can be damaged, so calculations are done to get the best dose - enough to kill tumour, but not so much that healthy tissue is damaged. |
| In Medical Applications that use Radioactive sources, How are long-term effects avoided? | Considering:
1) The nature of the decay (alpha, beta, gamma)
2) The half-life (long enough for the isotope to produce useful measurements, but short enough for the radioactive sources to decay to safe levels soon after use)
3) Toxicity
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 |
| Advantages and disadvantages of irradiation | Advantages:
-sterilisation can be done without high temperatures
-it can be used to kill bacteria on things that would melt
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 irradiation could expose people’s cells to damage and mutation |
| Medical Contamination | Medical Contamination:
1) Radioactive source (technetium-99) injected, used as tracers to make softer tissue (blood vessels, kidney) show up through medical imaging processes. An isotope that emits gamma rays, which easily pass through body to a detector (e.g. x-ray/gamma camera). The radioactive isotope can be followed as it flows through a particular process in the body.
2) Changes in amount of gamma emitted from different parts, indicate how well isotopes are flowing or if there's a block.
3) Isotopes chosen must:
- 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 |
| Contamination to check for leaks | 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 which can be found using a Geiger-Muller tube. This makes it easier to decide where to dig to find the leak
Isotopes chosen must:
- Emit gamma
- 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 and Disadvantages of Contamination | Image: |
| Irradiation Versus Contamination | Image: |
| Effects of Radiation on the Body | Radioactive materials are hazardous. Nuclear radiation can ionise chemicals within a body, which changes the way the cells behave. It can also deposit large amounts of energy into the body, which can damage or destroy cells completely |
| Precautions taken to Reduce Risk of Using Radioactive Sources | 1) keep radioactive sources like technetium-99 shielded (preferably in a lead-lined box) when not in use
2) wear protective clothing to prevent the body becoming contaminated should radioactive isotopes leak out
3) avoid contact with bare skin and do not attempt to taste the sources
4) wear face masks to avoid breathing in materials
5) limit exposure time - so less time is spent around radioactive materials
handle radioactive materials with tongs in order to keep a safer distance from sources
6) monitor exposure using detector badges, etc |
| Background Radiation | Radioactive materials occur naturally and, as a result, everyone is exposed to a low-level of radiation every day. This exposure comes from a mixture of natural and man-made sources
- Amount of radiation your exposed to depends on where you live, your job...
- Scientist must consider amount of BGR when working/experimenting with radioactive sources
- BGR mainly effects people by irradiation, but small amount is from contamination by radioisotopes in food/drink consumed |
| Measuring Radiation | Simplest measure of radioactivity - Becquerel(Bq). Measures activity of nucleus. Activity - no. of decays per second from an unstable nucleus. However this particle could be alpha/beta ∴ have a different effect on the body:
- Beta particle has lot of energy but may not cause lots of damage due to its low ionisation power
- Alpha has less energy but cause more damage in a shorter distance as its bigger
Sievert (Sv) is the unit to measure radiation dose and is the amount of damage that would be caused by the absorption of 1 joule of energy per kilogram of body mass. Usually absorption is less than 1 Sv, so milliSieverts (mSv) are often used instead. 1,000 mSv = 1 Sv. |
