KATA DGM-1500 Turva, Manual

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6.5 Gamma radiation measurement in foodstuffs
The DGM-
1500’s precision measurement function enables the measurement of
extremely low dose rates, and therefore extends the area of application of the
meter considerably.
When a nuclear disaster occurs radioactive substances may be carried in the
atmosphere for thousands of kilometres. Radioactive dust is deposited on the
earth’s surface by rain and other precipita
tion to form an uneven radiation field.
Radionuclides become part of the natural food cycle and eventually reach the
dinner table via plants and animals. A large number of radioactive substances are
released in a nuclear accident, a high proportion of these are gamma radiators. By
screening foodstuffs before they are used excessive gamma radiation can be
detected and the food cleansed. For example, Cesium-137 can be removed by
soaking the food in purified water. Cesium is soluble in water so slivers of meat,
for example, can be cleansed in this way. By monitoring the radiation level the
effectiveness of the decontaminating process can be assessed and, if necessary,
the cleansing process repeated with fresh purified water.
It should be noted that the authorities may impose limitations on the consumption
of foodstuffs in situations in which there is no necessity for shelter against external
radiation.
The rate at which radioactivity decreases is determined only by the half-life of the
radionuclide in question. The half-life of Cs-137 is 30 years, which means it takes
30 years for the level of radioactivity of Cs-137 to decrease by one half. Because
Cs-137 is soluble in water its so-called biological half-life is often quite short. This
means that most of the Cesium in animals will be removed within a few weeks if
they are fed uncontaminated food. The same applies to human beings.
To perform the measurement you will need
- a DGM-1500 radiation meter
- a 2-litre minigrip plastic bag
- a table
- a non-slip support for the meter
- some packing tape
Preparation
Position the table against a wall (not stone or brick). Place the meter on the
table, with a suitable non-slip support (e.g. foam rubber, rubber, styrox etc.)
underneath it, and lean it upright against the wall.