|
Technological Hazard >>
Radiation hazard >> Radiation detection |
|
|
Nature of radioactivity, types of radiation Interaction
radiation with matter Radiation sources,
natural and artificial radiation Nuclear and
radiological accidents, protection measures |
Radiation is difficult to measure; we cannot detect
it through any of our senses though we can measure it by indirect means. We
can make the measurements 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 on photographic film.
An ionization chamber collects the charge produced by radiation in a gas. Film-badge dosimeters enclose a piece of
photographic film, which will become exposed as radiation passes through
it.
|
