BERTHOLD TECHNOLOGIES Uni-Probe LB 490 - Page 243

Uni-Probe LB 490
BERTHOLD TECHNOLOGIES GmbH & Co. KG
2 – 243
Volume 2 4 Repair, Maintenance and Service
2
position of the plateau does not matter. The plateau is recorded
automatically. Please refer to the respective software description.
Figure 4-11 Plateau curve of NaI detector
If the count rate changes by more than 5% per 100Volt high volt-
age, 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.
IMPORTANT
Radiation conditions must be constant while recording the plateau!
4.14.2 Checking the Crystal-Multiplier Assembly
The plateau becoming too small or too steep indicates faults in the
crystal-multiplier assembly. They can often be detected through
visual inspection. To do this, take the crystal-multiplier assembly
apart. To separate both parts, remove the Mu-metal shielding and
carefully detach the crystal from the multiplier window by gently
sliding the crystal sideways. Wipe silicon oil traces off the mating
faces of crystal and multiplier using a soft cloth. While you are
doing this, make sure that the multiplier is not exposed to bright
sunlight.
Figure 4-12 Crystal-multiplier assembly
100
200
300
400
500
600
700
800
900
1000
1100
I/s
HIGH VOLTAGE (V)
600
900 1200 1500
Plateau
Magnetic shielding (Mu metal)
Optical connection
Multiplier
Crystal