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A simple photomultiplier performance monitor
NUCLEAR
INSTRUMENTS
AND
METHODS
60 0968)
A SIMPLE PHOTOMULTIPLIER
I23-124;
© NORTH-HOLLAND
PERFORMANCE
PUBLISHING
CO.
MONITOR t
L. LAVOIE and R. NORTON The Enrico Fermi Institute for Nuclear Studies, The University of Chicago, Chicago, lllinois, U.S.A.
Received 14 December 1967 A PMT noise rate monitor is described which gives a continuous indication of the proper operation of phototube, base, power supply, and logic first discriminator. W e have developed a relatively simple* way to keep a p p r a i s e d o f the p r o p e r o p e r a t i o n o f p h o t o m u l t i p l i e r tubes used in scintillation and C e r e n k o v counters. This m e t h o d uses the n o r m a l noise o u t p u t as a sensitive
relative measure o f the P M T ' s gain in a d d i t i o n to directly displaying the noise rate which can m a r k aging, i m p r o p e r t u b e installation, slowly developing light leaks, g r a d u a l electrical b r e a k d o w n within the tube or its container, a n d the effects o f i n a d e q u a t e m a g n e t i c shielding. All this is possible because the noise rate is relatively stable in p r o p e r l y functioning P M T s after a c o o k - i n time has allowed rate changes due to glass p h o s p h o r e s c e n c e and d y n o d e fatigue to stabilize. The p a r t i a l t e m p e r a t u r e dependence o f P M T noise can be easily a c c o u n t e d for when n o t i n g the noise rate, m o r e over the reduced t h e r m i o n i c c o m p o n e n t in low noise tubes tends to minimize this factor as t e m p e r a t u r e i n d e p e n d e n t noise sources b e c o m e d o m i n a n t . By t a k i n g the P M T noise signal f r o m an o u t p u t o f the first d i s c r i m i n a t o r + in the c o u n t e r ' s subsequent electronic
t Research supported on U.S. Atomic Energy Commission Reprint no. C00-1701-2. * A considerably more complicated and expensive system has been described in Nanonotes 1, no. 1 (Nov. 1963) publ. by the Nuclear Instrumentation Division of Edgerton, Germeshausen and Grief Inc. of Salem, Mass. + PMT gain and discriminator sensitivity made the counting threshold equivalent to about 1 photoelectron at the photocathode. PPS •
.
.
.
.
.
.
.
.
.
.
q
E i
i
5Ko 20K o 50Ko All pvots
SIGNAL I N P U T -2.5V
+4v-+lOV GATE TRIGGER ~
RY I
•
5
~
' i
-¢w--~ IK IOK T-
,z
3.3K
r
IO0/J. f -I1÷ QZ
,
3
RIO
I
Q4 c
2 2K
2K R9
I , r-I-s-161
~
22K
EAR
lu i'~
.v
RESET
INPUT
I. All Fixed Resistors ~ 4W,5"/o Z T I ( T 2 pri ( s e c , 5 T u r n s Eoch Of,'= 3 0 Wire On Smell Fertile Toroid 3. All Intergroted Circuils Fairchild p.L- 914 4. All Tronsistors 2 N 5 1 5 3 5. MRI Meter Relay, A s s e m b l y Products Co. M o d e l 2 2 5 , IO0/zA
Fig. 1. Circuit diagram for photomultiplier performance monitor. 123
124
L. L A V O I E A N D R. N O R T O N
logic, one also monitors the discriminator's operation. By bringing the signals from these discriminators into a suitable switching and fan-in unit, individual or summed monitoring can be accomplished for the appropriate counter(s) with the operation of a switch. Fig. 1 shows a circuit we have used quite successfully for two years. It is entirely straightforward. The input is shaped by the one shot, QI, where the scale factor is also controlled. The input signal amplitudes, polarities, and impedances can be properly interfaced to Q1 and Q2 by suitably modifying T1 and T2. Q2 and Q3 take an external trigger and generate a gate which blocks
the circuit from counting either individual "real" events from CW accelerators or the beam spill from pulsed accelerators. The output of the gate is then mechanically integrated by the ballistics of the indicating meter movement. In our case we used a self-latching meter relay which turns on a warning light and a buzzer alarm whenever the rate exceeds a preset value. Zero and full scale adjustments are R9 and R10 respectively, and Q4 and 5 are amplifiers to drive the alarm relay, RY-1. Linearity and accuracy are between 5 and 10% for both repetitive and random rates for all ranges from 200-50000 pps full scale.
INSTRUMENTS
AND
METHODS
60 0968)
A SIMPLE PHOTOMULTIPLIER
I23-124;
© NORTH-HOLLAND
PERFORMANCE
PUBLISHING
CO.
MONITOR t
L. LAVOIE and R. NORTON The Enrico Fermi Institute for Nuclear Studies, The University of Chicago, Chicago, lllinois, U.S.A.
Received 14 December 1967 A PMT noise rate monitor is described which gives a continuous indication of the proper operation of phototube, base, power supply, and logic first discriminator. W e have developed a relatively simple* way to keep a p p r a i s e d o f the p r o p e r o p e r a t i o n o f p h o t o m u l t i p l i e r tubes used in scintillation and C e r e n k o v counters. This m e t h o d uses the n o r m a l noise o u t p u t as a sensitive
relative measure o f the P M T ' s gain in a d d i t i o n to directly displaying the noise rate which can m a r k aging, i m p r o p e r t u b e installation, slowly developing light leaks, g r a d u a l electrical b r e a k d o w n within the tube or its container, a n d the effects o f i n a d e q u a t e m a g n e t i c shielding. All this is possible because the noise rate is relatively stable in p r o p e r l y functioning P M T s after a c o o k - i n time has allowed rate changes due to glass p h o s p h o r e s c e n c e and d y n o d e fatigue to stabilize. The p a r t i a l t e m p e r a t u r e dependence o f P M T noise can be easily a c c o u n t e d for when n o t i n g the noise rate, m o r e over the reduced t h e r m i o n i c c o m p o n e n t in low noise tubes tends to minimize this factor as t e m p e r a t u r e i n d e p e n d e n t noise sources b e c o m e d o m i n a n t . By t a k i n g the P M T noise signal f r o m an o u t p u t o f the first d i s c r i m i n a t o r + in the c o u n t e r ' s subsequent electronic
t Research supported on U.S. Atomic Energy Commission Reprint no. C00-1701-2. * A considerably more complicated and expensive system has been described in Nanonotes 1, no. 1 (Nov. 1963) publ. by the Nuclear Instrumentation Division of Edgerton, Germeshausen and Grief Inc. of Salem, Mass. + PMT gain and discriminator sensitivity made the counting threshold equivalent to about 1 photoelectron at the photocathode. PPS •
.
.
.
.
.
.
.
.
.
.
q
E i
i
5Ko 20K o 50Ko All pvots
SIGNAL I N P U T -2.5V
+4v-+lOV GATE TRIGGER ~
RY I
•
5
~
' i
-¢w--~ IK IOK T-
,z
3.3K
r
IO0/J. f -I1÷ QZ
,
3
RIO
I
Q4 c
2 2K
2K R9
I , r-I-s-161
~
22K
EAR
lu i'~
.v
RESET
INPUT
I. All Fixed Resistors ~ 4W,5"/o Z T I ( T 2 pri ( s e c , 5 T u r n s Eoch Of,'= 3 0 Wire On Smell Fertile Toroid 3. All Intergroted Circuils Fairchild p.L- 914 4. All Tronsistors 2 N 5 1 5 3 5. MRI Meter Relay, A s s e m b l y Products Co. M o d e l 2 2 5 , IO0/zA
Fig. 1. Circuit diagram for photomultiplier performance monitor. 123
124
L. L A V O I E A N D R. N O R T O N
logic, one also monitors the discriminator's operation. By bringing the signals from these discriminators into a suitable switching and fan-in unit, individual or summed monitoring can be accomplished for the appropriate counter(s) with the operation of a switch. Fig. 1 shows a circuit we have used quite successfully for two years. It is entirely straightforward. The input is shaped by the one shot, QI, where the scale factor is also controlled. The input signal amplitudes, polarities, and impedances can be properly interfaced to Q1 and Q2 by suitably modifying T1 and T2. Q2 and Q3 take an external trigger and generate a gate which blocks
the circuit from counting either individual "real" events from CW accelerators or the beam spill from pulsed accelerators. The output of the gate is then mechanically integrated by the ballistics of the indicating meter movement. In our case we used a self-latching meter relay which turns on a warning light and a buzzer alarm whenever the rate exceeds a preset value. Zero and full scale adjustments are R9 and R10 respectively, and Q4 and 5 are amplifiers to drive the alarm relay, RY-1. Linearity and accuracy are between 5 and 10% for both repetitive and random rates for all ranges from 200-50000 pps full scale.