Using radioactivity safely

	Using radioactivity safely Ionising radiations are hazardous and it is best to avoid being exposed to them. However, some exposure is unavoidable (from natural as well as man-made sources) so an understanding of the hazards is essential. It means we can put them to good use and maintain safety. Radiation hazards Ionising radiations cause damage when they pass through a cell. The most direct method is if the radiation ionises the DNA in a cell. This may alter the function of the cell or kill it. There are also indirect methods in which water molecules are ionised producing free radicals (such as H+ and OH-). These can then react with and damage parts of the cell. For low doses, the damage can and might cause physiological problems at a later date (even years later) such as cancer or genetic diseases. These can be caused by even the smallest dose – there is no such thing as a safe dose. However, although the outcome doesn't change as the dose decreases, the chances are reduced. It's similar to smoking-related diseases – lung cancer is no better or worse if you smoked 5 or 40 cigarettes a day. But the chance of contracting it increases with your intake. For high doses, the effects are more predictable. The unit for dose is the gray. Doses above 1 gray cause burns and other skin problems. A whole body dose of 5 grays can be fatal and 20 grays is always fatal. However, whilst we are all exposed to small doses, you won't be exposed to these higher doses in normal circumstances. Are all radiations equally hazardous? Low doses of the different types of ionising radiations are hazardous in different ways. Alpha radiation is almost harmless from the outside. It is absorbed by the outer layer of dead skin and doesn't reach any living cells. However, if an alpha emitter is ingested (either by inhaling it or eating something containing a radioactive substance), then there is a chance that an alpha particle will be emitted inside your body. It will then cause lots of ionisation within living cells. The equivalent dose from alpha radiation is reckonned to be twenty times that of beta and gamma because of the amount of ionisation it causes. To protect ourselves from alpha radiation, we need to ensure that no sources of alpha radiation contaminate our food, water or air supply. Beta radiation can cause skin problems but is, again, more of a hazard if a beta emitter is ingested. Gamma radiation has similar effects whether its source is inside or outside the body. In each case, we need to consider the source of radiation rather than the radiation itself. For example, the isotope radon-222 gives out alpha radiation. Where possible, we should avoid radon gas because this isotope will be passing in and out with each breath.
Picture 2.8 A smoke detector uses a small source of alpha radiation.	Uses of alpha Smoke detectors The most effective smoke detectors use a source of alpha radiation – americium-241. The alpha radiation is aimed into a gap between two electrodes. There is a voltage across these electrodes. The alpha radiation ionises the air in the gap and allows a current to flow between the electrodes. When smoke finds its way between the electrodes, the air ions attract the smoke particles and stop flowing so freely. The resulting drop in current is detected by the circuitry and sets off the alarm. Luminous paint The old stye luminous paint is no longer used. However, you can still get second-hand watches that have luminous numerals painted on them. This paint is a mixture of radium salt and a fluorescing substance. The radium emits alpha particles which cause the fluorescent material to glow. Although this is perfectly safe for owners of the watches, the factory workers (who used to lick their paint brushes to get a good point) ingested the radium and suffered badly. Hence it was banned in the 1950s.

	Uses of beta Therapeutic Isotopes The main use of beta radiation is in the treatment of cancers. The radiation kills the cancer cells. It is sufficiently penetrating to allow it to be held in a container (if necessary) and to penetrate a number of cells. Yet it is sufficiently short range to limit its action to a local area, like a tumour. The beta radiation penetrates a few millimetres of tissue.Basic radio-therapy involves sealing a radioactive isotope, such as technetium-99, into a catheter or a probe. This is inserted into the patient and left in the area of the tumour. Technetium has a half life of six hours. This means it releases a lot of beta radiation in a short time. Another version is to put the radioactive istope in tiny metal spheres which are injected into a tumour. New systemic methods of radiotherapy are being developed. These involve modifying monoclonal antibodies so that they are carrying a radioactive isotope - often yttrium-90. These antibodies attach themselves to the cells of specific tissues, including tumours. In this way, the radiotherpay (in this case called radioimmunotherapy) is extremely accurate in the tissue that it treats.
	Uses of gamma Medical investigations Sources of gamma radiation are used to see inside the body. Unlike X-rays, which have to go through the body, a gamma source can be injected into the body and its radiation produces pictures of specific areas. For example, technetium methylene diphosphonate is a chemical that will build up in bones. This can be made with radioactive technetium-99, which emits gamma radiation. The radiation can be used to expose photographic plates or be picked up by a scanner outside the body giving a very detaile picture of the bone structure. Thallium-201 is a potassium analogue that is taken up by tumours and emits gamma radiation. Again, using photographic plates, radiologists can get very accurate pictures of tumours – because they effectively emit their own radiation. Thallium-201 is also used to evaluate how well regions of the heart are pumping after a coronary artery bypass surgery. The thallium acts as a tracer, giving out gamma radiation. The radiation is captured in special detectors and an image is built up. By using 3 detectors placed around a body, it is possible to create a 3D image. This technique is called Emission Computed Tomography (ECT). In the case of the heart, the method is refined and is known as Single Photon ECT (SPECT). Industrial tracers Gamma sources can be used to detect leaks in pipes and to trace pollution. Scientists can label possible sources of the leak or pollution by introducing a short lived gamma emitter. If they detect gamma radiation later on, they can work out the source of the leak. Similarly if they're not sure where a leak is in a buried pipe, they can add a gamma source to the inflow and search for a build up of radiation. Sterilisation Gamma-emitting radioisotopes, such as cobalt-60, can be used to sterilise pharmaceuticals and cosmetics. Their gamma radiation kills bacteria without needing to heat up these heat-sensitive products. This technique can also be used in hospitals for medical equipment and is useful because instruments can be sterilised without opening the packages. Crack detection Gamma radiation can be used to search for cracks in welds and pipes and give an early warning of failure where they are wearing thin – useful for aeroplane safety checks. This works in a similar way to X-rays – the gamma radiation penetrates the metal a little but will show up as hot spots where there is a fault. However, unlike X-rays, the gamma source can be put in awkward places – it doesn't involve carrying around a high energy piece of machinery.
	Question 7 Ionising radiations can cause cancer. However, they can also cure cancer. Explain this apparent paradox and why people are willing to have radiotherapy.