Page 562 - Instrumentation Reference Book 3E
P. 562
544 Nuclear instrumentation technology
4,
I
-
-
Photomultiplier (PM)
I -
L -HV I
PM = MULLARD XP1040
R1 -R13=27kS2 50 S2
HV = 2250-2850 V at 4.3-5.5 mA output
Figure 22.28 Dynode resistor chain for high counting rates - 1 O6 cs.
22.3.6.2 Addeuslmixers 22.3.6.3 Balancing units
When a number of detector signals have to be These units are, in effect, potentiometer units
combined into a single output, a mixer (or fan-in) which allow the outputs from a number of
unit is used. This sums the signals from up to eight separate detectors, often scintillation counters
preamplifiers or amplifiers to give a common out- with multiple-photomultiplier assemblies on
put. This is used, for example, when the outputs each large crystal, to be balanced before enter-
from several photomultipliers mounted on one ing the main amplifier of a system. This is
large scintillator must be combined. Such a unit especially necessary when pulse-height analysis
is also used in whole-body counters, where a num- is to be performed, as otherwise the variations
ber of separate detectors are distributed around in output would prevent equal pulse heights
the subject being monitored. Figure 22.29 shows being obtained for given energy of a spectrum
the circuit of such a unit. line.
t
Input
Input 2
Input 3
Figure 22.29 Fastsignal mixer/adder.
