Density Meter LB 444 SECTION 2. SYSTEM DESCRIPTION
11
Detector
Scintillation counters are used as detectors, since only these detector systems
provide the required high sensitivity to Gamma radiation and the radiation field
does not limit their service life.
The detector comprises
• a sodium iodide crystal doped with Thallium
• a photomultiplier
• an electronics unit.
The built-in microprocessor tracks the configuration, counts the pulse rates,
controls the high voltage, measures the temperature of the probe and an exter-
nal Pt 100, transfers data and performs calibration and control functions.
+
−
AMPLIFIERRADIATION
LIGHT FLASH
SCINTILLATOR DYNODES
PHOTO CATHODE
.
.
.
Figure 7: Scintillation counter
The scintillator converts the incidence of Gamma into light flashes.
The flashes of light are converted into electrical signals in a photomultiplier,
which is optically coupled, to the detector. To achieve a very high accuracy and
a high long-term stability, the integrated processor automatically adjusts the op-
timum operating point of the photomultiplier, monitors the limit values, and
stores all detector-specific data. Power is supplied via 2-wire technique; all
measured data and information is transmitted between detector and the evalua-
tion unit at the same time.
The detector probe is mounted in a sturdy stainless steel housing which pro-
tects the instrument against normal environmental stress.
To ensure reliable operation and a long service life, the detector probe
must not be subject to heavy mechanical stress or vibrations.
Cooling must be provided for ambient temperatures above 50°C. (see sec-
tion 3.3 Installation of Water Cooling).
For more information see: Technical Information LB 444.
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