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3. Instrument Description
3.1 Radioactive Source
Radioactive sources for industrial applications are always “encapsulated radioactive sub-
stances” which are tightly welded into a sturdy stainless steel capsule, so that the radio-
active substance cannot leak out. Contamination is therefore ruled out. Moreover, any
activation of the product being measured by the sources used is not possible for physical
reasons.
The following sources can be used for these measuring configurations.
241
Am,
60
Co,
137
Cs.
The following isotopes are primarily used for density measurements:
60
Co has a relatively high energy of 1.17 and 1.33 MeV, respectively. It is used for den-
sity measurements over very long distances and/or if the radiation has to pass through
very thick pipe or vessel walls. Its half-life period is 5.27 years.
137
Cs is the isotope most frequently used for density measurements. Its energy of 0.660
MeV is sufficient to penetrate commonly used pipe and container walls. Due to the lower
energy, the measuring effect is better than with Co-60. Also, the shielding costs for a Cs-
137 source are lower than for a Co-60 source. The half-life period of Cs-137 is approx.
30 years.
Am-241 is ideally suited for measurement of the concentration of components with high
atomic order (iron, nickel, HCl, etc.) in a carrier medium with low atomic order. Its en-
ergy is 60 keV and its half-life period 433 years.
*
Please note the Radiation Protection Guidelines in Chapter 11!
*
According to NBS, half-life is defined as: Time for the activity of any particular radioisotope to be reduced to
half its initial value.
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