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Biology Essay

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GM tube

The GM tube is a hollow cylinder filled with a gas at low pressure. The tube has a thin window made of mica at one end. There is a central electrode inside the GM tube. A voltage supply is connected across the casing of the tube and the central electrode as shown in the following diagram.
When an alpha or beta or gamma radiation enters the tube it produces ions in the gas. The ions created in the gas enable the tube to conduct. A current is produced in the tube for a short time. The current produces a voltage pulse. Each voltage pulse corresponds to one ionising radiation entering the GM tube. The voltage pulse is amplified and counted.
Sources of background radiation
Background radiation is all around us. Some of it comes from natural sources and some comes from artificial sources.
Natural sources
Natural sources of background radiation include: * Cosmic rays - radiation that reaches the Earth from space * Rocks and soil - some rocks are radioactive and give off radioactive radon gas * Living things - plants absorb radioactive materials from the soil and these pass up the food chain

For most people, natural sources contribute the most to their background radiation dose.

Average contribution of different sources to natural background radiation

Artificial sources
There is little we can do about natural background radiation. After all, we cannot stop eating, drinking or breathing to avoid it!
However, human activity has added to background radiation by creating and using artificial sources of radiation. These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical x-rays.
Artificial sources account for about 15 per cent of the average background radiation dose. Nearly all artificial background radiation comes from medical procedures such as receiving x-rays for x-ray photographs.

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