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The word radiation covers a lot of ground but in the nuclear context we’re talking about ‘ionising radiation’, which basically means streams of invisible waves or particles with sufficient energy to knock electrons out of atoms, creating ions, resulting in chemical changes to materials at the molecular level.


There are  three different types of naturally occurring radiation, designated Alpha, Beta and Gamma.


Alpha particles are the biggest and composed of two protons and two neutrons but they are also the weakest and cannot penetrate more than a few centimetres of air and even have trouble getting through a few sheets of paper. However, that actually makes Alpha radiation quite dangerous -- at close quarters and in very high doses -- because the particles are so big  they are more likely to interact with and cause chemical and biological changes to whatver they happen to smash into


Beta particles are essentially loose electrons or positrons,  they have more energy and penetrating power than Alpha particles and can punch through a few millimetres of wood or metal. Like all radiation, if there’s enough of it, it will change or damage whatever it comes into contact with.


Gamma particles (or waves) are essentially high-energy photons -- the same stuff as light and the gamma radiation family also includes X-Rays. Gamma radiation has no charge but it packs a lot of energy. However, because the particles are so small they can pass right through matter without hitting anything, but once again if there’s enough of it then it can and will cause chemical and biological changes


Ionising radiation  sounds like a bad thing but the fact is we are being constantly bombarded with natural radiation, from the food we eat (Brazil nuts are notoriously radioactive),  rocks and minerals, water, air, cosmic rays from outer space and a wide range of consumer products in and around the home, from smoke alarms and flourescent lamps to old clocks and watches with luminous hands. Even our own bodies are naturally radioactive, and it's not just the nicotine and tar in tobacco that can kill you. In the past sixty years there has been a small but measurable increase in the background radiation from such things as nuclear power generation, fallout from nuclear weapons, moreover your exposure to ionising radiation is significantly increased if you have an X-Ray, travel regularly by air or undergo radiological treatment.


The point is the human race has been exposed to low level doses of radioactivity since the year dot. We have evolved to deal with it, it may even have had a part to play in the evolutionary process, it’s when we get too much of it that things can go wrong.


Scientists can say with some certainty how much radiation will kill you outright, and the sort of exposure that will make you sick but these tend to massively large doses that we are never likely to encounter in our normal day-to-day lives. When it comes to very low levels exposure no one can say exactly how much is bad for you.


Unfortunately  no-one knows. It depends on a multitude of factors including age, gender, genetic makeup, where you live, what you eat and needless to say, which experts you talk to. There are clear beneficial effects and controlled exposure to high doses of ionising radiation is a cornerstone of modern Nuclear Medicine; some even suggest that small doses can be good for you, therapies, like those offered in this Radon Mine are claimed to date back 6000 years.


Nevertheless it is generally accepted that most of us, on average, receive a dose of between 100 and 200 millirem (1- 2 millisievert) of radiation per year (the millirem is a measurement of absorbed radiation dosage and 100 mrem = 1 millisievert). We live to tell the tale because almost all of it comes from natural sources and it is a part of our normal environment.


Around 70 to 80 mrem comes from purely natural sources, as much as 11% of that from naturally-occuring materials in our own bodies. Apparently you will receive an 0.05 microsievert dose sleeping next to someone for 8 hours, even porcelain crowns and living within 50 miles of a coal plant produces a measurabe dose ...  The rest is man-made with the bulk of it coming from hospital and dental X-Rays and medical treatments, 4 - 6 mrem comes from nuclear power plant emissions and leakage and fallout from nuclear weapons plus 1 to 2 mrem from consumer products, such as smoke detectors and so on.


The internationally agreed limits for exposure to radiation for those working in the nuclear industry is a maximum whole body dose of 5,000 mrem (or 5 rem) per year. For the rest of us exposure levels are significantly lower. A chest X-Ray, for example typically gives a surface dose of 50 to 80 mrem, abdominal X-rays can be up to 600mrem whilst a full body CT Scan can be as high as 1000 mrems. For the record a whole body dose of 500 rem will be enough to kill you, usually within one to two weeks whilst a dose of 100 rem will cause severe radiation sickness.




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