Radioactivity 5

1. Radioactivity 5 Uses of radioactive sources

2. Using Gamma Rays • A patient is injected with a radioactive tracer that emits gamma rays. • The gamma ray is electromagnetic radiation of very high penetration power.

3. Using Gamma Rays • Therefore more rays exit the body and are available for detection than interact with the patient's tissue. • These can be detected by a gamma camera and the concentration of radioactive tracer in various parts of the body can be ascertained.

5. Radiotherapy • Smoking kills – in a terrible way sometimes - the image on the next slide shows a smoking related oral cancer emerging from the throat of the patient in its late stage

6. Radiotherapy • High doses of ionizing radiation can kill cells; • They are used to kill cancer cells and harmful microorganisms.

7. Radiotherapy • Tumours can be treated using gamma rays (nuclear radiation) or high energy X-rays (which can have the same wavelength as gamma rays – but are not from the nucleus). Definition: tumour n. (US tumor) a swelling, especially from an abnormal growth of tissue, whether benign or malignant. It comes from the Latin tumor from tumere ‘ to swell’

8. Radiotherapy • Cells that divide rapidly are more prone to damage by high-energy electromagnetic radiation. • This means that tumour cells are more radiosensitive than their normal counterparts. Definition: tumour n. (US tumor) a swelling, especially from an abnormal growth of tissue, whether benign or malignant. It comes from the Latin tumor from tumere ‘ to swell’

9. Radiotherapy • By carefully aiming the rays at the tumour (gamma-ray beams directed from a multitude of angles that result in the maximum gamma ray intensity within the tumour) the harmful effect of the ionising radiation is kept to a minimum in the surrounding tissue.

10. Radiotherapy • This kind of treatment is most hazardous when a brain tumour is being irradiated and the surrounding tissue is vital for normal brain function.

11. Radiotherapy • Several treatments are usually given over a time period of several weeks to minimise the unpleasant side effects (most commonly nausea, sickness, and tiredness).

12. Radiotherapy • New methods of delivering radiation treatment have been developed • Interstitial radiationinvolves implanting radioactive chemicals (termed seeds) directly into a tumour. • Stereotactic radiosurgerydelivers a high, single dose of radiation to a small, well-defined area.

13. Sterilisation of Food and Surgical Instruments • Food and surgical instruments can be irradiated with gamma rays to sterilize them • Gamma rays kill bacteria. Therefore irradiating food or surgical instruments is a good way of ensuring they are sterile.

14. Sterilisation of Food and Surgical Instruments • The gamma rays penetrate packaging, so the food or instrument can be sealed and then sterilized so that re-contamination cannot occur. • No radioactive source particles are allowed to get in touch with the irradiated substance. • The source is sealed so that only gamma rays get out. Therefore the irradiated substance is sterile but NOT radioactive.

15. As radiation passes through a material it can be absorbed. • The greater the thickness of a material the greater the absorption. • The absorption of radiation can be used to monitor/control the thickness of materials.

16. The absorption of radiation can be used to monitor/control the thickness of materials • The more radiation that gets through, the thicker the barrier must be. • Circuitry can automatically adjust the roller settings so that a constant count is attained.

17. Alpha Uses Long half life: • Dating of rocks using Uranium-238/lead ratios  • Smoke detectors  • Gas lamp mantles  • Nuclear batteries  

18. Beta Uses Short half life • Tracers in industry - detecting leaks in pipes  Long half life • Thickness control of very thin metal sheets, paper or cardboard in manufacturing and industry  • C-14 dating  • Emergency sign lighting 

19. Gamma Uses Short half life • Medical tracer - used with gamma camera   • Tracers in industry - detecting routes of underground rivers and streams 

20. Gamma Uses Long half life • High activity - radiotherapy   • High activity - sterilization of medical surgical instruments  • High activity - irradiation of food to kill bacteria and prolong shelf life  • Thickness control of metal sheets (when too thick for beta) in manufacturing and industry  • Checking welds 

21. Other Uses • Leaks from a pipeline can be traced by adding a radioactive isotope into what ever it is carrying. The source must have a short half-life (a few hours) so that it can be detected as it passes through but not stay radioactive long enough to pose a health hazard.

22. Other Uses • Wear of moving parts can be tested by making the part radioactive and monitoring the proportion of worn parts in the lubricating oil by looking for the level of radioactivity in it. • A gamma source can be used to check welds in metal parts. It is used in a similar way to X-rays on a human body. A photographic plate is placed behind the weld. It is exposed more where the weld is weak.

23. Nuclear Batteries • The Apollo Moon missions used a radioisotope thermal generator (RTG). • A rod of plutonium-238 weighing approximately 2.5 kilograms provides a thermal power of approximately 1250W. Plutonium-238 is a non-fissile isotope of plutonium that decays by alpha particle emission with essentially zero associated gamma emissions.

24. Smoke Detectors • Some smoke detectors contain a small amount of Americium-241, an alpha emitter (an low energy gamma emitter) with a half life of 460 years. • They consist of an ionization chamber linked to a simple electronic alarm circuit.

25. Smoke Detectors • The Americium ionizes the air between the plates, causing a current to flow. • Smoke entering the detector absorbs some extra alpha particles than the air would , lowering the current, and triggering the alarm.