54733-10BA2L
2 – 236 02.2017
4 Repair, Maintenance and Upkeep Volume 2
4.5.1 Checking the NaI Point Detector (CrystalSENS)
Malfunctions of the scintillation counter are not always indicated by
a missing pulse rate; it is also possible that the specific Gamma sen-
sitivity appears to have changed or obvious instabilities are appar-
ent. These errors can be detected only by means of a plateau check.
The detectors of the SENSseries include a function for automatic
plateau recording. The check can be performed using the source at
the measuring site or better a test source. Plot the measurement
results in a curve (Fig. 4-3). The detector works perfect when you
get a clearly visible plateau; the position of the plateau within the
high voltage range does not matter. The plateau is recorded auto-
matically. See also page 3-406.
Fig. 4-3 Plateau curve of NaI detector
If the count rate changes by more than 5% per 100 V high voltage,
or if the plateau is shorter than 50V, the scintillation counter will be
unstable. In this case the complete detector or the crystal-multiplier
assembly should be replaced.
The radiation conditions must be constant while recording the pla-
teau!
100
200
300
400
500
600
700
800
900
1000
1100
I/s
HIGH VOLTAGE (V)
600
900 1200 1500
Plateau
To Next Page
Loading...
