How is radioactivity measured?

Radioactivity is measured in disintegrations per second and its unit of measure is the Becquerel (Bq), in honour of the physicist Henry Becquerel who discovered the spontaneous emission of radiation from uranium in 1896.  As mentioned above, the radiation produced by the disintegration of radioisotopes interacts with matter, transferring energy. The magnitude and the gravity of the effects depend on the dose and the type of radiation received. For example, small doses of ultraviolet radiation from the Sun are harmless to man, but an excessive exposure can cause sun burns. The unit of measure of the absorbed dose is the gray (1 Gy = 1 joule absorbed by 1 kg of matter). To give a measure of the biological effects caused by radiation the concept of equivalent dose has been introduced. This allows the evaluation of the damage caused by the same dose of different types of ionising radiation. In this case, the unit of measure is the sievert (Sv). For a chest X-ray, 0.14 mSv are administered (mSv = millisievert, i.e. one thousandth of a Sv), for a mammography, 1mSv.

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