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Technological Hazard >> Radiation hazard >> Radiation detection
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Nature of radioactivity, types of radiation Interaction radiation with matter Radiation sources, natural and artificial radiation |
Radiation
is difficult to measure; we cannot detect it through any of our senses though
we can measure it by indirect means. We can interpret the measurements we make
in terms of the energy deposited by the radiation. The amount of energy
deposited per unit mass in a material is called the 'absorbed dose'. The unit
of absorbed dose is the gray (Gy), which is one joule per
kilogram. Ionising
radiations differ in the way in which they interact with biological materials,
so that equal absorbed doses do not always have equal biological effects.
Equivalent dose is the absorbed dose multiplied by a factor that takes account
of the relative effectiveness in causing biological harm. The unit of
equivalent dose is the sievert (Sv), which is one joule per kilogram. For
beta, gamma and X-rays, 1 Gy is the same as 1 Sv, but neutrons and alpha rays
are more damaging and, for these, 1 Gy is worth between 5 Sv and 20 Sv. There are a wide variety of instruments used to measure different types of radiation, different energy ranges and different accuracies. Here are a few examples. In radiography such as a chest X-ray, the variation of the penetrating power of X-rays in bone and tissue gives rise to an image. It is natural to use an ion chamber to measure ionising radiation. An ionisation chamber collects the charge normally from ions in a gas. Film-badge dosimeters enclose a piece of photographic film, which will become exposed as radiation passes through it. Geiger counters and scintillometers measure the dose rate of ionizing radiation directly.
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