O Level Physics Chapter :25: Use of Radioactivity Prepared By: Shakil Raiman

25.1: The Use of Radioactivity:

25.1: The Use of Radioactivity in Medicine: As tracers in diagnosis: Radioactive isotopes are used as tracers to help doctors identify diseased organs. A radioactive tracer is a chemical compound that emits gamma radiation. The tracer is taken orally by the patient (swallowed) or injected. Its passage the body can then be traced using a gamma ray camera.

25.1: The Use of Radioactivity in Medicine: Tracer Isotope used in diagnosis: Different compounds are chosen for different diagnostics tasks. For example, the isotope iodine- 123 is absorbed by the thyroid gland in the same way as the stable form of iodine. The half-life of iodine-123 is about 13 hours. A short half-life is important as this means that the activity of the tracer decreases to a very low level in a few days.

25.1: The Use of Radioactivity in Medicine: Tracer Isotopes: Technetium-99: Technetium-99 is the most widely used isotope in medical imaging. It is used to help identify medical problems that affect many parts of the body. Imaging techniques enable doctors to produce three-dimensional computer images of the parts of a patient’s body. These are of great value in diagnosis.

25.1: The Use of Radioactivity in Medicine Equipment used for 3D Imaging:

25.2: Use of radioactivity in Treatment: Treating Cancer: A way of treating cancer is to kill the cancer cells inside the body. Very high doses of radiation will kill the living cells. This can be done with chemicals containing radioactive isotopes. The radiation kills diseased cells as well as healthy ones. To reduce the damage to healthy tissue, chemicals are used to target the location of the cancer in the body. They may emit either alpha or beta radiation. Both these types of radiation have a short range in the body, so they will affect only a small volume of tissue close to the target. The radioisotope iodine-131 is used in the treatment of various diseases of the thyroid gland. It has a half-life of about eight days and decays by beta particle emission.

25.3: Use of radioactivity in Sterilisation: Ionising radiation can kill living cells. It is therefore micro-organisms on surgical instruments and other medical equipment. The technique is called irradiation. Gamma radiation is used to sterialise.

25.3: Use of radioactivity in Sterilisation Medical Equipment: Ionising radiation can kill living cells. It is therefore used to kill micro-organisms on surgical instruments and other medical equipment. The technique is called irradiation. Gamma radiation is used to sterialise.

25.4: Use of radioactivity in Sterilisation of Food: Radiation is used to kill bacteria in food which does not destroy vitamins in the food like other means of killing bacteria such as high temperature treatment.

25.5.1: Use of radioactivity in Industry: Gamma Radiography: A gamma ray camera is like the X-ray camera used to examine the content of your luggage at airport. A source of gamma radiation is placed on one side of the object to be scanned and a gamma camera is placed on the other. Gamma rays are more penetrating than X-ray. Gamma radiography is used to check for imperfection in welded joints and for flaws in metal casting. Two advantages of Gamma Radiography: More penetrating Gamma sources is small and do not require power source.

25.5.2: Use of radioactivity in Industry: Gauging Quantity: In industrial processes raw materials and fuel are stored in large tanks or hoppers. Radioactive isotopes are used to gauge, or measure, how much material there is in a storage vessel. Advantages: No direct contact Dust or fog will not affect the measurement.

25.5.3: Use of radioactivity in Industry: Gauging Thickness and Finding Leaks:

25.5.4: Use of radioactivity in Industry: Tracing and Measuring the flow of liquids and gases: Radioisotopes are used to track the flow of liquids in industrial processes. Very tiny amounts of radiation can easily be detected. Complex piping systems, like heat exchangers in power stations, can be monitored for leaks. Radioactive tracers are even used to measure the rate of dispersal of sewage.

25.6.1: Radioactive Dating: A variety of different methods involving radioisotopes are used to date minerals and organic matter. The most widely known method is radiocarbon dating. Radiocarbon Dating: Carbon-14 is an isotope of carbon which is produced in the atmosphere due to sun. The proportion of Carbon-14 is constant for living organism or plants as it is replaced by the food. When a living organism dies, the replacement process stops. As time passes, the radioactive carbon decays and the proportion of radioactive carbon in the remains of the plant or animal, compared with the stable carbon isotope, decreases. Carbon-14 has a half-life of approximately 5600 years. The amount of carbon-14 in dead plant or animal material is found by measuring the activity of the sample. This is compared with the amount of carbon-14 that would have been present when the sample was part of a living organism. From this it is possible to estimate when the source of the sample died. Sample older than 50000-60000 years are not measured in this method because the amount of remaining carbon-14 in the sample is too small to measure accurately.

25.6.2: Radioactive Dating:

25.6.3: Radioactive Dating: Rocks: When a radioactive substance decays it transforms into a different isotope, sometimes of the same element, sometimes of a different element. The original isotope is called the parent nuclide and the product is called the daughter nuclide. For rocks containing such radioactive isotopes, the proportion of parent to stable daughter nuclide gives a measure of the age of the rock.

25.7: Health Hazards of Ionising Radiation: Ionising radiation can damage the molecules that make up the cells of living tissue. If the cell start to behave unexpected way because it has been damages we call this cell mutation. Some types of cancer happen because damaged cells start to divide uncontrollably. Different types of ionizing radiation present different risks. Alpha particles have the greatest ionizing effect, but they have little penetrating power. This means that an alpha source presents little risk, as alpha particles do not penetrate the skin. If the source of alpha particles is taken into the body or breathed in or taken in through eating food it will be a real risk to health and might cause cancer.

25.7: Health Hazards of Ionising Radiation: Beta and gamma radiation can penetrate skin and flesh and can cause cell damage by ionization. Beta and gamma emitters that are absorbed by the body present less risk than alpha emitter, because of their lower ionizing power.

25.8: Safe Handling of Radioactive Materials: Samples of radioactive isotopes used in school and colleges are very small. This is to limit the risk to users. Precautions to reduce risk: Store in lead container Labelled as a radiation hazard Handle using tongs Nuclear waste must be stored in sealed container that must be capable of containing the radioactivity for enormously long periods of time.

Thank You All Wish you all very good luck and excellent result.