Berthold LB 444 K-40 - Page 57

01/10 347 LB 444 K-40
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2
The multiplier window is coated with a vapor-deposited layer acting as photocathode.
This layer gives the window a brownish tint similar to smoked glass. If this layer is no
longer present or if it is stained, then the photocathode has been destroyed (e.g. by
overheating, glass breakage, or incident light), and the multiplier must be replaced.
Faults caused by damage to the dynode systems (e.g. by excessive vibration) cannot be
identified by appearance. If in doubt, replace the multiplier.
The glass pane at the mating face to the photo multiplier must not show any cracks.
Before re-assembly, apply a drop of clean silicon oil between crystal and multiplier and
distribute it evenly by gentle rubbing to ensure sound optical connection between both
components. Attach the Mu-metal screen and fix it with screws, making sure that the
Mu-metal screen is only under light tension.
Re-assembly:
Set the crystal again onto the front face of the photo multiplier and twist both compo-
nents several times counter-clockwise. If you have to replace a component, apply 1 or 2
drops of silicone oil on the mating faces of the new and old component. It may also
suffice to press the new component against the mating face of the old one and to turn it
several times. Reassemble parts properly.
Just as after replacement of a complete detector, the calibration should be checked
immediately.
10.3.2 Testing and replacement of the photomultipliers in the
detector LB 5430
Fig-
ure
17:
As-
sembly of the scintillation
counter
The organic scintillator is in the front housing part of the detector LB 5430 (1 in Fig. 17 ).
This housing should only be opened by the service staff from Berthold.
The detector electronics and the photomultiplier are located in the rear housing part (2 in
Fig. 17 )..
The same rules and criteria apply as for the detector LB 5430 regarding dismantling and
inspection.
The detector must stand upright on the flange for dismantling and installation of the
detector electronics. An installation of the electronics in horizontal position of the
detector is very difficult. The multiplier can get damaged.
1. Dismantle electronics with photomultiplier (see above)
2. Check photomultiplier and replace if necessary.
3. Put 1-2 drops of silicone oil on the frontal area of the photomultipliers before assembly