Учебное пособие Казань-2016 Сайфуллина М. Н., Хабирова Н. М. English for Physicists
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Posobie dlya fizikov Habirova Sajfullina ispravv
| In the background
There is a natural level of radiation all around us, which comes from several sources. Some gamma radiation comes from space as cosmic rays. Other radiation comes from sources in the atmosphere, such as radon gas and some of its decay products. There are also natural radioactive materials in the ground – and as well as the obvious elements such as uranium there are also radioactive isotopes of common substances such as potassium and carbon. To understand how 96 much background radiation is around, it helps to distinguish between effects on normal matter and on the human body. The amount of radiation absorbed by non-biological matter is measured in grays, a unit equivalent to a joule of energy per kilogram of mass. For biological tissue, a dose equivalent is measured in sieverts (Sv) depending on the type of radiation involved and how much damage that radiation does to the particular cells affected. The average amount of radiation received from background sources in the UK is around 2–2.5 mSv per year. Because of the preponderance of granite, which contains higher than average levels of uranium, in areas such as Cornwall or Aberdeenshire it can be twice this level – not high enough to cause any concern, but high enough that nuclear facilities can’t be built there as the background level already exceeds the maximum allowed radiation limit. In some parts of the world, such as northern Iran, the background radiation is as high as 50 mSv per year. There are a variety of other natural and routine artificial causes of low doses of radiation. A dental x-ray will give you a dose of under 1 mSv; a full-body CT scan, 10 mSv. As fewer cosmic rays are stopped by the atmosphere the higher you go, the crew of a passenger jet flying between the US and Japan once a week for a year would receive an additional a dose of around 9 mSv. Under normal conditions, the dose limit for workers in the nuclear industry is 50 mSv per year. жүктеу/скачать 1,1 Mb. Достарыңызбен бөлісу:
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