2.4 Instrument Description
20
2.4.6 Rod Source with Rod Detector
Rod sources with rod detectors allows measurement at very low
source activities and can be used for wide conveyor systems.
2.4.7 Point Source Shielding
Depending on the activity or isotope, we distinguish between three
different shielding sizes. Each of these shieldings offers radiation
exit angles of 54° and 72°. Selection of the exit angle is dependent
on the measurement geometry.
See drawing for Point Source Shielding on page 142.
2.4.8 Detector
Scintillation counters are used as detectors, since only these detec-
tors provide the required high sensitivity to Gamma radiation and
their service life is not limited by the radiation field.
The detector comprises
a) sodium iodide crystal doped with Thallium
b) photomultiplier
c) electronics unit.
The built-in microprocessor defines the configuration, counts the
pulse rates, controls the high voltage, measures the temperature
of the probe, transfers data and performs calibration and control
functions. Supply and communication with the evaluation unit LB
442 take place via two-wire cable.
The detector material consists of a special crystal which generates
flashes of light when absorbing Gamma radiation. The number of
light flashes per unit of time is a measure for the intensity of the
measured radiation field. The individual flashes of light are very
short, so that a high resolution is achieved and this detector can be
used for high count rates.
+
−
AmplifierRadiation
Light flash
Scintillator Dynodes
Photo cathode
.
.
.
Figure 12: Scintillation counter
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