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A multiple pulse display system
NUCLEAR
INSTRUMENTS
AND
METHODS
21 (1963) 5 3 - 5 5 , N O R T H - n O L L / k N D
PUBLISHING
CO.
A MULTIPLE PULSE. DISPLAY SYSTEM L. CUCAN~Id # CE.RN, Geneva, Switzerland Received 27 J u n e 1962
A method for simultaneous pulse height analysis of m a n y coincident pulses is described. The pulses obtained from several scintillation a n d ~erenkov counters are shaped in fast linear gates, a n d fed as current pulses into a delay line a t different
points. The t r a i n of pulses in the delay line is fed to a n oscilloscope a n d photographed. I t is possible to display simultaneously u p t o 20 pulses.
1. The Principle of Operation I n high-energy particle experiments many counters are often used simultaneously. This is the case, for instance, in experiments where the detector is surrounded by anticoincidence counters in order to suppress charged particle background 1'2). It cart be important to know through which counters the observed particle did penetrate in order to get more data about the nature either of the events wanted, or of the background. The amplitude of the pulse is of interest because it depends on the nature, the energy; the path length inside the counter, and sometimes on the direction of the transversing particle. Therefore a visual display of the counter pulses is often desirable, particularly in low counting-rate experiments. The simplest possibility is to feed the counter pulses directly through separate delay lines of different length to an adder, and to display the train of pulses obtained on an oscilloscope. This method has the advantage that pulses of both polarities cau be displayed. But in order to distinguish one pulse from another it is necessary to provide a sufficient time difference between two successive pulses, say a few hundred nsec. There~ fore every delay line should be a few hundred nsec longer than the previous one requiring a large amount of cable. Also, reflections due to incorrect matching may be confusing. Most important, with high single counting rates in some of the counters,
the problem of having uncorrelated pulses displayed becomes serious. To overcome these difficulties the following electronic system was designed. A separate linear gate was introduced for every channel. It cuts out by means of a suitable master pulse only that part of the inspected pulse which is around its maximum. Correct timing with respect to the master pulse ensures that the amplitude information is preserved. The master pulse generator is a slightly modified fast trigger unit 3) able to generate pulses 30 nsec long, which can be triggered by any combination of pulses characterizing interesting events. This requires a minimum time difference of ~ 60 nsec between two successive channels. The pulse obtained are completely free of jitter.
2. Description of the Apparatus and Results A circuit diagram is shown in fig. 1. Amplified counter pulses are applied to the bases of the transistor T2 with a collector current nearly proportional to the input voltage. In the absence of the master pulse the current flows through the diode D1, because the transistor T1 is cut off by a proper bias setting. I n all the channels simultaneously, the master pulse switches the current from the diode D 1 to the transistor T 1. This yields a train 1) H. Faissner, CERN, N P i n t e r n a l Report 61-6 (not published). ~) H. Faissner, F. Ferrero a n d M. Reinharz, CERN, N P I n t e r n a l R e p o r t 61-11 (not published). 3) H. XCerweij, CERN, N P Electronic Group Note 60-3 (not published).
~-Present address: Institute " R u d e r Bo§kovid", Zagreb, Yugoslavia. 53
s4
z. CUCAN~I~
of pulses in the delay line, the amplitude of each being proportional to the respective input amplitude. The pulses propagate in both directions and are absorbed by matching resistors R o at both ends. A fast oscilloscope probe can be applied on one end of the delay line. ro the oscilloscope_
The apparatus constructed has been made as a unit containing ten identical channels, each wired on a separate 12-contact plug-in card. Some cards and delay lines can be taken out ff not in use. Also, for the display of more than l0 pulses several units can be connected in series.
Delay line (coaxial came 125z~.')
I
m
! L=,,~fl
,.
"
I 22nF U / ' ~ ~ ~ +Input ~ ~
i.,np
2N50
t
.~OA 126/9
Ot
t i i
1.2 k~ 22 F
I
~47 k~ i
220Zz 220n/ ~ Chann¢i
!L2kn 56n
l
l.2k.n 56~
Channel B
I [ I
- Master Pulse
Input
8.2k~
I
+20V
Fig. 1. Circuit d i a g r a m .
As shown on the circuit diagram, transistors of type 2N501 are introduced as T 1 and T2 because of their excellent switching properties. The operating point of T 2 is chosen at low d.c., therefore, no high collector dissipation is required. This low d.c. offers a good linearity and contributes a small pedestal on the trace, which indicates the position where a pulse in this channel would appear. The effective load impedance of T, is twice 125t2 in parallel, hence the value of resistor in the emitter of T 2 is chosen to be 56~/in order to obtain a gain of the gate roughly equal to 1. By introducing a one-stage pulse amplifier (the n-p-n silicon transistor 2N706) the sensitivity is improved roughly three times. By variable load resistors of the amplifiers it is possible to adjust the total gain of all the channels to the same value, and to compensate for the difference in delay Iine attenuation for different channds.
Fig. 2. Coincidence b e t w e e n pulses of t w o counters.
As an example, a photograph taken under real conditions during one of the neutrino background runs 2) is shown in fig° 2. i t shows coincident pulses in two counters. Display was photographed on the Tektronix 517 scope. 3. Limitations Tile maxim~ number of simultaneously displayed pulses is limited by the distortion of the pulse shape in the delay line. For the cable used, 4) F. Ferrero, p r i v a t e c o m m u n i c a t i o n .
A MULTIPLE
PULSE
type SUHNER RG 63 B/U, this number i s about 20. Another important source of distortion is the rise-time of the oscilloscope. With the Tektronix 581 oscilloscope (3.5 nsec rise-time) and repetitive pulses, significantly better results have been obtained. Unfortunately, because of a poor spot brightness, this scope is not useful for a single-shot operation under these conditions. The smallest measureable positive input pulses are of 40 mV amplitude. The upper limit of the input pulses amplitude is 1 V for linear response. The number of displayed pulses can be increased
DISPLAY
SYSTEM
55
b y use of a multi-gun scope and several display systems working in parallel. The distortion appearing ill the delay line can be somewhat compensated by connecting a clipping delay line at the input of the oscilloscope, and terminated with an adjustable resistor (of value less than cable impedance; length of clipping line ¼ of channel separation).
Acknowledgements I would like to express my gratitude to Drs. H. Faissner, F. Ferrero and M. Reinharz for stimulating discussions and for their co-operation during the runs.
INSTRUMENTS
AND
METHODS
21 (1963) 5 3 - 5 5 , N O R T H - n O L L / k N D
PUBLISHING
CO.
A MULTIPLE PULSE. DISPLAY SYSTEM L. CUCAN~Id # CE.RN, Geneva, Switzerland Received 27 J u n e 1962
A method for simultaneous pulse height analysis of m a n y coincident pulses is described. The pulses obtained from several scintillation a n d ~erenkov counters are shaped in fast linear gates, a n d fed as current pulses into a delay line a t different
points. The t r a i n of pulses in the delay line is fed to a n oscilloscope a n d photographed. I t is possible to display simultaneously u p t o 20 pulses.
1. The Principle of Operation I n high-energy particle experiments many counters are often used simultaneously. This is the case, for instance, in experiments where the detector is surrounded by anticoincidence counters in order to suppress charged particle background 1'2). It cart be important to know through which counters the observed particle did penetrate in order to get more data about the nature either of the events wanted, or of the background. The amplitude of the pulse is of interest because it depends on the nature, the energy; the path length inside the counter, and sometimes on the direction of the transversing particle. Therefore a visual display of the counter pulses is often desirable, particularly in low counting-rate experiments. The simplest possibility is to feed the counter pulses directly through separate delay lines of different length to an adder, and to display the train of pulses obtained on an oscilloscope. This method has the advantage that pulses of both polarities cau be displayed. But in order to distinguish one pulse from another it is necessary to provide a sufficient time difference between two successive pulses, say a few hundred nsec. There~ fore every delay line should be a few hundred nsec longer than the previous one requiring a large amount of cable. Also, reflections due to incorrect matching may be confusing. Most important, with high single counting rates in some of the counters,
the problem of having uncorrelated pulses displayed becomes serious. To overcome these difficulties the following electronic system was designed. A separate linear gate was introduced for every channel. It cuts out by means of a suitable master pulse only that part of the inspected pulse which is around its maximum. Correct timing with respect to the master pulse ensures that the amplitude information is preserved. The master pulse generator is a slightly modified fast trigger unit 3) able to generate pulses 30 nsec long, which can be triggered by any combination of pulses characterizing interesting events. This requires a minimum time difference of ~ 60 nsec between two successive channels. The pulse obtained are completely free of jitter.
2. Description of the Apparatus and Results A circuit diagram is shown in fig. 1. Amplified counter pulses are applied to the bases of the transistor T2 with a collector current nearly proportional to the input voltage. In the absence of the master pulse the current flows through the diode D1, because the transistor T1 is cut off by a proper bias setting. I n all the channels simultaneously, the master pulse switches the current from the diode D 1 to the transistor T 1. This yields a train 1) H. Faissner, CERN, N P i n t e r n a l Report 61-6 (not published). ~) H. Faissner, F. Ferrero a n d M. Reinharz, CERN, N P I n t e r n a l R e p o r t 61-11 (not published). 3) H. XCerweij, CERN, N P Electronic Group Note 60-3 (not published).
~-Present address: Institute " R u d e r Bo§kovid", Zagreb, Yugoslavia. 53
s4
z. CUCAN~I~
of pulses in the delay line, the amplitude of each being proportional to the respective input amplitude. The pulses propagate in both directions and are absorbed by matching resistors R o at both ends. A fast oscilloscope probe can be applied on one end of the delay line. ro the oscilloscope_
The apparatus constructed has been made as a unit containing ten identical channels, each wired on a separate 12-contact plug-in card. Some cards and delay lines can be taken out ff not in use. Also, for the display of more than l0 pulses several units can be connected in series.
Delay line (coaxial came 125z~.')
I
m
! L=,,~fl
,.
"
I 22nF U / ' ~ ~ ~ +Input ~ ~
i.,np
2N50
t
.~OA 126/9
Ot
t i i
1.2 k~ 22 F
I
~47 k~ i
220Zz 220n/ ~ Chann¢i
!L2kn 56n
l
l.2k.n 56~
Channel B
I [ I
- Master Pulse
Input
8.2k~
I
+20V
Fig. 1. Circuit d i a g r a m .
As shown on the circuit diagram, transistors of type 2N501 are introduced as T 1 and T2 because of their excellent switching properties. The operating point of T 2 is chosen at low d.c., therefore, no high collector dissipation is required. This low d.c. offers a good linearity and contributes a small pedestal on the trace, which indicates the position where a pulse in this channel would appear. The effective load impedance of T, is twice 125t2 in parallel, hence the value of resistor in the emitter of T 2 is chosen to be 56~/in order to obtain a gain of the gate roughly equal to 1. By introducing a one-stage pulse amplifier (the n-p-n silicon transistor 2N706) the sensitivity is improved roughly three times. By variable load resistors of the amplifiers it is possible to adjust the total gain of all the channels to the same value, and to compensate for the difference in delay Iine attenuation for different channds.
Fig. 2. Coincidence b e t w e e n pulses of t w o counters.
As an example, a photograph taken under real conditions during one of the neutrino background runs 2) is shown in fig° 2. i t shows coincident pulses in two counters. Display was photographed on the Tektronix 517 scope. 3. Limitations Tile maxim~ number of simultaneously displayed pulses is limited by the distortion of the pulse shape in the delay line. For the cable used, 4) F. Ferrero, p r i v a t e c o m m u n i c a t i o n .
A MULTIPLE
PULSE
type SUHNER RG 63 B/U, this number i s about 20. Another important source of distortion is the rise-time of the oscilloscope. With the Tektronix 581 oscilloscope (3.5 nsec rise-time) and repetitive pulses, significantly better results have been obtained. Unfortunately, because of a poor spot brightness, this scope is not useful for a single-shot operation under these conditions. The smallest measureable positive input pulses are of 40 mV amplitude. The upper limit of the input pulses amplitude is 1 V for linear response. The number of displayed pulses can be increased
DISPLAY
SYSTEM
55
b y use of a multi-gun scope and several display systems working in parallel. The distortion appearing ill the delay line can be somewhat compensated by connecting a clipping delay line at the input of the oscilloscope, and terminated with an adjustable resistor (of value less than cable impedance; length of clipping line ¼ of channel separation).
Acknowledgements I would like to express my gratitude to Drs. H. Faissner, F. Ferrero and M. Reinharz for stimulating discussions and for their co-operation during the runs.