BERTHOLD TECHNOLOGIES LB 3602, Руководство по эксплуатации

Страница: 22 / 43

LB 379
22
6 Radiation Protection
Radioactive isotopes used for density measurements emit gamma radiation. Gamma radi-
ation consists of high-energy electromagnetic waves, i.e. a type of radiation which resem-
bles light, but has a much higher energy, so that it can pass through matter having a
higher density. This high-energy radiation is hazardous to living beings; it can damage
cells and cause mutations. To minimize this hazard, one must be extremely careful when
handling radioactive substances.
Radioactive sources which are used for density measurements are enclosed radioactive
materials, i.e. the actual radioactive substance is surrounded by at least one, often several
sealed layers made of stainless steel, each of which is checked individually for leaks. An-
other check ensures that no radioactive particles are deposited on the surface of the cap-
sule. The user will receive an official certificate specifying these features of the radioactive
source.
Technical terms
In radiation measuring technique, just as in other fields, the units of measurement have
been converted into SI units. The old units are also included in the following explanations.
1. Activity
Radiation is emitted as a result of nuclear disintegration. The higher the number of these
nuclear transformations, the higher the activity. Unit of measure is the Becquerel (Bq), 1
Bq being equal to 1 decay per second. The old unit Curie (Ci) is sometimes still being used.
The following correlation can be established between both units of measure:
3.7 *10
10
Bq = 37 GBq = 1 Ci
37 * 10
6
Bq = 37 MBq = 1 mCi
2.
Dose and dose rate
Various energies of individual isotopes have different effects on living beings. To allow a
comparison, the so-called RBE-factor was introduced; it specifies the relative biological
effects of radiation. This dose equivalent is measured in Sievert (Sv); it can be converted
into the old unit rem as follows:
10
-2
Sv = 1 rem
10 µSv = 1 mrem
Sv (or rem) specifies the dose incorporated over a period of undefined length. To get an
indication of the intensity of the radiation, the dose rate is specified as dose per unit of
time. It is measured in Sv/h or rem/h. More common are the smaller units mSv/h or
mrem/h.
To calculate the dose rate generated by a source, you need to know the gamma radiation
constant (k) in order to take into account the different energies of the various isotopes.
The following table lists the constants for the radioactive sources most frequently used in
industrial applications: