Industrial tracers - Finding leaks and blockages

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1 Cancer Treatment Alpha radiation is used to treat various forms of cancer. This process, called unsealed source radiotherapy, involves inserting tiny amounts of radium-226 into cancerous organs. The alpha particles destroy cancer cells but lack the penetrating ability to damage the surrounding healthy cells.

2 Static Eliminator Alpha radiation from polonium-210 is used to eliminate static electricity in industrial applications. The positive charge of the alpha particles attracts free electrons, thus reducing the potential for local static electricity. This process is common in paper mills, for example. Smoke particles disrupt this current, triggering an alarm.

3 Pacemaker Battery Alpha radiation is used as an energy source to power heart pacemakers. Plutonium-238 is used as the fuel source for such batteries; with a half-life of 88 years, this source of power provides a long lifespan for pacemakers.

4 Industrial tracers - Finding leaks and blockages A leak or blockage in a pipe may be difficult to find, particularly if the pipe is buried underground. Substances that emit gamma radiation are often used as tracers because the radiation easily passes through many substances. To find a leak or blockage, the radioactive material is put into one end of the pipe. A radiation detector outside the pipe or above ground is used to track its progress through the pipe. The leak or blockage is discovered by finding where amount of radiation detected decreases.

5 Dating rocks Radioactivity can be used to date rocks. Rocks often contain traces of uranium. This is unstable and eventually decays to lead, which is stable. The age of a rock can be calculated if its ratio of uranium to lead is known. The older the rock, the lower its uranium to lead ratio: Young rocks have a high uranium to lead ratio Very old rocks have a low uranium to lead ratio The table shows how this works. Time Percent of uranium Percent of Uranium:lead ratio lead :0 After 1 half-life :1 After 2 half-life :3 After 3 half-life :7 The half-life of uranium is 4.46 billion years. If a rock has a uranium to lead ratio of 1:1, one half-life must have passed since it formed. This would make it 4.46 billion years old.

6 Smoke Detector Alpha radiation is used in some smoke detectors. The alpha particles from americium-241 bombard air molecules, knocking electrons free. These electrons are then used to create an electrical current.

7 Carbon dating Materials that originally came from living things, such as wood and natural fibres, can be dated by measuring the amount of carbon-14 they contain. For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain. Later called Ötzi the Iceman, small samples from his body were carbon dated by scientists. The results showed that Ötzi died over 5000 years ago, sometime between 3350 and 3100 BC. Carbon-14 is a radioactive isotope. It is found in the air in carbon dioxide molecules. The amount of carbon-14 in the air has stayed the same for thousands of years. There is a small amount of radioactive carbon-14 in all living organisms because it enters the food chain. Once an organism dies, it stops taking in carbon-14. The carbon- 14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases. The approximate time since the organism died can be worked out by measuring the amount of carbon-14 left in its remains compared to the amount in living organisms.

8 Metal Thickness monitoring Most Beta particles are stopped by a few mm or cm of solid materials. The thicker the layer the more beta radiation is absorbed. A beta source is placed on one side of a sheet of material. A detector (e.g. a Geiger counter) is put on the other side and can monitor how much radiation gets through. The signal size depends on thickness of the sheet and it gets smaller as the sheet gets thicker. Therefore the signal can be used to monitor the sheet thickness. The half-life must be quite long so that change in the signal does not result from rapid decay. This idea is used to control production lines of paper, plastic or steel sheeting. Before the sheet material passes through 'flattening' rollers, it passes between a beta source and detector. The detector signal is checked against that for a preset thickness. If the signal is too big the sheet is too thin and the rollers are moved apart to thicken the sheet. If the signal is too small the sheet is too thick and the rollers are moved closer together.

9 Medical tracers Technetium-99 is a gamma emitter (half-life 6 hours) and is used in medicine as a tracer. In medical applications, in a suitable chemical form, the radioisotope is injected into the body and its 'movement' can be followed. Time is allowed for the radioactive tracer to spread and its progress tracked with a detector outside the body. The patient can be placed next to a 'detection screen' that shows where the radioactive tracer is. The effective function of organs like the liver and digestion system can be checked. Similarly, a patient can breathe in air with a gaseous gamma emitter in it, and the effectiveness and structure of the lungs can be checked. The half-life must be relatively short so it does not linger in the body increasing the harmful effects of cell damage. Technetium atoms can be incorporated into many organic chemicals called radiopharmaceuticals which can be used to monitor biochemical aspects of the bodies chemistry e.g. the functioning and performance of a particular organ.

10 Radiotherapy It seems ironic that the very radiation which causes cancer, can also be used to treat it. A beam of gamma radiation is directed onto the tumour site to kill the cancer cells. Unfortunately the radiation passes through the 'good' tissue too and kills or damages 'good' cells. Modern techniques use multiple rotating gamma sources that are focused on to the tumour. This means the surrounding 'good cells' are less frequently hit and minimises potential harmful side-effects on the rest of the body (e.g. sickness or other mutations). Radiotherapy also avoids the need for intrusive surgery which has its own risk factors. The gamma emitters used have relatively long half-lives to give the instrument a good working life.

11 Non-destructive testing (NDT) In a sense it is an alternative to X-ray photography for more dense materials e.g. It is used test the structure and quality of pipe welds. A gamma source is placed inside the pipe and photographic paper wrapped around the weld. If there is any gap or flaw in the weld, more gamma radiation gets through and shows up as increased exposure on the 'gamma-ray picture'. It s better to find out the fault now, rather than later when it fractures, and has to be 'dug up' or retrieved from the bottom of the sea!

12 Sterlisation Because gamma radiation is so deadly and penetrating it can be used to sterilise surgical equipment or packaged food: The radiation is deadly for bacteria even in the most microscopic pockets of apparently smooth and shiny stainless steel of surgical instruments. It is very convenient for 'convenience' food!. After cooking and sealing in a plastic packet, you don't need to reopen to complete the sterilization to give it a long shelf-life!

13 Thyroid function Iodine-131, another gamma emitter (half-life = 8 days), can be used to check on the functioning of a thyroid gland. The body needs iodine to make the hormone thyroxine and so the take up of iodine can be monitored by measuring the gamma radiation from the thyroid gland. Gamma radiation, being the most penetrating, it passes out through the body and so readily be detected outside the body by some suitable detector e.g. with a special camera or fluorescent screen. The half-life should be long enough to allow good detection BUT NOT too long to be dangerous to the body over a period of time!

14 Thyroid cancer treatment One method of treating thyroid cancer is to inject Iodine-131 into the body in a soluble salt form e.g. potassium iodide, so that it deliberately concentrates in the thyroid gland and the gamma radiation kills the thyroid cancer cells. This is another example of 'medical physics' and important diagnostic technique in clinical medicine. Beta sources can be used, though not as penetrating as gamma and have an increased risk of cell damage.. Alpha sources are too readily absorbed to show up with a Geiger counter or other detector and so are not suitable for these 'tracer' applications. However, an alpha particle emitting isotope of radium can be directly injected in tiny quantities into tumourous tissue to directly irradiate and kill cancer cells.

15 Maintenance of Stents Radioisotopes -- chemicals that emit radiation -- are widely used in medicine. In a process known as brachytherapy, beta radioisotopes can be used to irradiate areas inside a patient to prevent the growth of certain tissues. This approach has been used successfully to prevent the clogging of arterial inserts called stents. Beta particles are also used in some forms of therapy to kill cancer cells. In addition, the emission of beta particles is used indirectly in the medical scanning technique known as positron emission tomography (PET).

16 Biological Tracers Radioisotopes are commonly used as tracers in chemical and biological research. By synthesizing molecules containing a radioactive atom, the path and fate of that type of molecule in a particular reaction or metabolic process can be followed by tracking the radioactive signal of the isotope. One radioisotope used for this process is carbon-14 which can be inserted into organic or biological molecules and followed by its beta radiation signal.

17 Measuring thickness Beta rays have a number of important uses in industrial processes. Since they can pass through some materials, they are used to gauge the thickness of films of material coming off production lines such as paper and plastic film. A similar process checks the integrity of sewn seams in textiles. In another application, the thickness of various coatings, such as paints, can be deduced from the activity of beta particles scattered back from that surface. In the paper industry, promethium-147, which is a beta emitter, is used as a source for measuring the thickness of paper. The paper can pass freely between the units in such apparatuses and measurements may be made continually.