ORTEC 264 User manual

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INSTRUCTION
MANUAL
264
PHOTOMULTIPLIER
TIMING
DISCRIMINATOR
AND
PREAMPLIFIER

1 i
INSTRUCTION MANUAL
MODEL 264
PHOTOMULTIPLIER TIMING DISCRIMINATOR
AND PREAMPLIFIER
Serial No.
33
Purchaser
Date Issued
P. 0. BOX C
OAK RIDGE, TENNESSEE 37830
Telephone [phone]
TWX 810-572-1078
) ORTEC Incorporated 1966
Printed in U*S*A«

TABLE OF CONTENTS
Page
WARRANTY
PHOTOGRAPH
1. DESCRIPTION 1-1
2. SPECIFICATIONS 2-1
3. INSTALLATION INSTRUCTIONS 3-1
3.1 Det-ector Mounting 3-1
3.2 Photomultlplier Insertion 3-1
3.3 System Connection and Initial Adjustment 3-1
4. OPERATING INSTRUCTIONS 4-1
4.1 Timing with Photomultipliers 4-1
4.2 Applications 4-2
5. CIRCUIT DESCRIPTIONS 5-1
5.1 Voltage Divider Network 5-1
5.2 Linear Preamplifier 5-1
5.3 Discriminator Circuit 5-1
6. MAINTENANCE INSTRUCTIONS 6-1
6.1 Divider Network 6-1
6.2 Preamplifier 6-1
6.3 Fast Crossover Discriminator 6-1
BLOCK DIAGRAM AND SCHEMATICS
264-0101-Bl ORTEC 264 Block Diagram
264-0101-Sl ORTEC 264 Schematic
264-0201-Sl ORTEC 264 Schematic
264-0301-Sl ORTEC 264 Schematic

LIST OF FIGURES
Page
Figure 1. Suggested Cutaway Drawing of PM — Scinti I lator Mounting 2-3
Figure 2. Incorrect Adjustment of R-26 4-2
Figures. Correct Adjustment of R-26 4-2
Figure 4. Incorrect Adjustment of Crossover Zero R6 4-3
Figures. Correct Adjustment of Crossover Zero R6 4-3
Figure 6. Simple Sub-Nanosecond Coincidence System 4-6
Figure 7. Wide Dynamic Range Timing Spectrum Using "Fast"
Crossover 4-7
Figure 8. Narrow Dynamic Range Timing Spectrum Using
"Fast" Crossover 4-8
Figure 9. Timing Resolution (Leading Edge vs. "Fast" Crossover) 4-9
Figure 10. Open Unit Showing Picture of Controls 6-2
SYSTEM BLOCK DIAGRAMS
200058 Gamma-Ray Pair Spectrometer 4-10
200057 Fast Timing System for (Semiconductor Detector-Photo-
multiplier Tube) Coincidence Using Two Crossover Pickoff
Techniques 4-11
200067 Associated - Particle Neutron Time of Flight System with
Energy Selecting Side Channels 4-11
200068 Pulse Shape Discrimination System 4-12
200056 Fast-Fast Coincidence (Photomultiplier Tube) with Pulse
Shape Discrimination 4-12
200060 Sub-Nanosecond Timing System (Semiconductor-Photomultiplier
Tube) 4-13

STANDARD WARRANTY FOR ORTEC ELECTRONIC INSTRUMENTS
DAMAGE IN TRANSIT
Shipments should be examined immediately upon receipt for evidence of external or con
cealed damage. The carrier making delivery should be notified immediately of any such damage,
since the carrier is normally liable for damage in shipment. Packing materials, waybills, and other
such documentation should be preserved in order to establish claims. After such notification to the
carrier, notify ORTEC of the circumstances so that we may assist in damage claims and in providing
replacement equipment when necessary.
WARRANTY
ORTEC warrants its electronic products to be free from defects in workmanship and materials,
other than vacuum tubes and semiconductors, for a period of twelve months from date of ship
ment, provided that the equipment has been used in a proper manner and not subjected to abuse.
Repairs or replacement, at ORTEC option, wil l be made without charge at the ORTEC factory.
Shipping expense will be to the account of the customer except in cases of defects discovered upon
initial operation. Warranties of vacuum tubes and semiconductors, as made by their manufacturers,
will be extended to our customers only to the extent of the manufacturers' liabi lity to ORTEC.
Specially selected vacuum tubes or semiconductors cannot be warranted. ORTEC reserves the right
to modify the design of its products without incurring responsibility for modification of previously
manufactured units. Since instal lation conditions are beyond our control, ORTEC does not assume
any risks or liabilities associated with the methods of installation, or instal lation results.
QUALITY CONTROL
Before being approved for shipment, each ORTEC instrument must pass a stringent set of
quality control tests designed to expose any flaws in materials or workmanship. Permanent records
of these tests are maintained for use in warranty repair and as a source of statistical information
for design improvements.
REPAIR SERVICE
ORTEC instruments not in warranty may be returned to the factory for repairs or checkout at
modest expense to the customer. Standard procedure requires that returned instruments pass the
same qual ity control tests as those used for new production instruments. Please contact the factory
for instructions before shipping equipment.

P3Z H"®"

1-1
ORTEC 264
PHOTOMULTIPLIER TIMING DISCRIMINATOR AND PREAMPLIFIER
1. DESCRIPTION
The ORTEC 264 Photomultiplier Timing Discriminator and Preamplifier consists of:
1) a base structure providing a mechanical assembly and resistive voltage divider
network with appropriate capacity decoupling for the operation of the RCA 8575
photomultiplier tube; 2) a linear preamplifier providing integration and line drive
capability for the linear dynode signal; and 3) a walk-free timing discriminator
that is remotely controlled. This complex is designed to operate with fast organic
phosphors, e.g., plastic and fast decay liquid phosphors. It may be readily altered
to accommodate phosphors having a fast decay component time constant that is rel
atively long, i.e., 5 to 20 nsec. It is not meant for use with Nal(TI) or Csl(TI).
I

J

2- 1
2. SPECIFICATIONS
(NOTE: All photomultiplier specifications ore given by monufocturer.)
Base Structure:
Hi-Voltage: Negative, 3 kV maximum
Bleeder Current: 2 mA maximum (last 4 dynodes available externally for added
stabilization when desired)
Controls: Focus electrode, 2nd Dynode (D2)
Connectors:
Discriminator Output: BNC
Preamplifier Output; BNC
Auxiliary; MS 3112E12-10S or Bendix PT02E12-10S
Hi-Voltage: Kings KV-79-13; mating connector KV-59-22, compatible with
RG-59/U coaxial cable, available as an accessory.
Preamplifier:
Input: Signal current from 9th dynode
Input Impedance: 2.2M shunted by 100 pF
Voltage Gain (Ay): 2
Output Signal Dynamic Range: lOV open circuit, 5V on 100 ohms
Integral Nonlinearity: =±0.1%
Output Rise Time (Tp): =50 nsec
Temperature Stability: ±0.015%/°C
Output Impedance (Z^): 100 ohms
Power: Dc from 403*or 403A Time Pickoff Control Unit, via power and bias
cable supplied.
Walk-Free Timing Discriminator:
Input Signals: Anode Signal, Dynode 12 signal
Output Signal: 12 mA on 50 ohms, Tp, <2 nsec, width»ilO nsec
*Refer to modification note on 403 to 403A.

2-2
Discriminator Control Range: 1 mA to 10 mA of anode current (Specified with
403A Time Pickoff Control)
Pulse Pair Resolving Time: Threshold discriminator recovers to =5% error in
25 nsec
Discriminator Temperature Stability: =±0.01 m^°C (Anode Current)
Walk (Time Shift vs. Pulsje Height): Typically ^±0.1 nsec for 100:1 dynamic
range
Power: Dc from 403* or 403A Time Pickoff Control, via 15 foot cable, 264-Cl,
supplied with base.
The timing or logic signal from the discriminator output will normally connect to the
input of the 403A which provides fan-out capabilities. The linear signal from the
preamplifier will normally connect to a shaping amplifier such as the 410 or 435.
The ORTEC 216 (for 56 AVP, etc.) or 217 (for 58 AVP or XP 1040) Magnetic Shield
is a recommended accessory to reduce the effect of the earth's magnetic field and of
stray fields from other equipment.
Power Required: (From 403A): +24V - 15 mA + 12V - 30 mA
-24V-20 mA -12V-40 mA
*Refer to modification note on 403 to 403A.
L

2-3
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Figure 1. Suggested Cutaway Drawing of PM — Scinti I later Mounting

3-1
3. INSTALLATION INSTRUCTIONS
3.1 Detector Mounting
The 264 is designed for the best in pulse fidelity and requires that the anode be
operated at ground potential. This means that the photocathode is at negative
high voltage. Care must then be taken to assure that this high voltage is not
dropped across the glass envelope of the photomultiplier. Care should be taken
to prevent the scintiMotor also from imposing a ground at the front surface of the
photocathode to cause the above. A drawing of a suggested method of mount
ing a simple detector is shown in Fig. 1 (Drawing 264-0000).
3.2 Photomultiplier Insertion
The 218 Magnetic Shield, if used, should be removed. The tube may now be
inserted directly into the socket. CAUTION: The socket end of this photo
multiplier tube should be made light tight with the boot furnished by RCA or by
ORTEC. Place the felt washers around the photomultiplier and re-mount the
magnetic shield.
3.3 System Connection and Initial Adjustment
This unit is tuned up with a specific photomultiplier at the factory. The design
of the photomultiplier ensures that there is little variation from unit to unit so
that it may not be necessary to readjust even when changing from one photo
multiplier to another as long as the high voltage for which the tube is operated
is in the region of -2200 volts ±200 volts. One may assume that this is the case
and skip Section 3.3.2 in the initial adjustments procedure.
3.3.1 System Connection
1. Connect the power and bias control cable, 264-Cl, from the assoc
iated 403A to the auxiliary connector of the 264.
2. Connect the signal from the discriminator out connector by way of
a 50-ohm coaxial cable to the input CN-1 of the 403A.
3. Connect the preamp output signal to the input of a linear shaping
amplifier (if side channel energy selection is to be used).
4. Connect a high voltage power supply to the high voltage input con
nector and ENSURE that the power supply is set to deliver negative

3-2
voltage.
5. Turn on dc power to 403A and linear amplifier.
6. Turn on high voltage power supply and set the power supply to
-2200 volts (or to the voltage at which the tube is to be operated).
7. For operating instructions see Section 4.0 of this manual.
3.3.2 Initial Adjustments (Perform when necessary)
Before connecting into the system, remove the high voltage divider
cover to obtain access to the controls. WARNING: The voltages
used in this network are dangerous, so caution in adjusting the controls
should be exercised. The controls for this unit are trimmed for optimum
operation with a specific photomultiplier at the factory; however, if
when inserting a new photomultiplier, the unit may need trimming, the
following steps are given as a guideline for performing this operation:
1. Connect the power and bias control cable, 264-Cl, from the assoc
iated 403A to the auxiliary connector of the 264.
2. Connect the signal from the discriminator out connector by way of
50-ohm coaxial cable to the input CN-1 of the 403A.
3. Connect the preamp output signal to the input of a linear amplifier
such as the 410 or 435 with 100 ohm coaxial cable.
4. Turn on dc power to 403A and amplifier.
5. Connect a high voltage power supply to the high voltage input con
nector and ENSURE that the power supply is set to deliver negative
voltage.
6. Turn on high voltage power supply and set the power supply to
-2200 volts (or the voltage at which the tube is to be operated).
7. Place a radiation source appropriate to the chosen scintiMotor near
the detector.
8. Observe the output waveform from the shaping amplifier associated
with the linear output signal and adjust the two bleeder string controls.

3-3
i.e., the FOCUS (R17) and DEFLECTOR 2 adjustment (R15) for
maximum output signal (see Fig. 10). This assures that the input
optics are adjusted properly for that specific photomultiplier used.
3.3.3 Adjustment of the Time Derivation Circuit
This adjustment has been performed at the factory and will not be affected
by exchange of the photomultiplier; therefore, it wil l normally not re
quire readjustment. The 264 will normally be shipped with the clipping
line (DL-1) of the correct length for fast plastic phosphors such as Naton
136, Pilot-B, and NE-102; however, if a slower phosphor such as NE-213,
Stilbene or Anthracene is used, the delay line (DL-1) should be changed
to the longer line included as an accessory with the 264 and so marked.
This is accomplished merely by disconnecting DL-1, which is in the unit,
and connecting in the longer length delay line. To perform the necessary
discriminator zero adjustment, the following steps should be followed:
1. Perform steps 1-4 of Section 3.3.2.
2. Connect one of the 403A outputs to on oscilloscope.
3. Set the DISC LEVEL on the 403A to 0.00.
4. Adjust DISC ZERO control on 403A~clockwise until output signals
appear (unit is self-triggering) and back off until signals are no
longer present.
5. Connect a fast oscil loscope, preferably a sampling type oscilloscope,
to the coaxial connector on the discriminator board labeled TP-1
with 50-ohm coaxial cable making sure that the receiving end is
terminated either by the input impedance of the oscilloscope or by
an external tee and terminator.
6. Attach one of the output signals from the 403A to the trigger input
of the oscilloscope.
7. Apply high voltage (-2200 volts) to the 264.
8. Place a radiation source near the scinti 1 lator, e.g., Cobalt-60
or Sodium-22.
9. Set the DISCRIMINATOR LEVEL on the 403A to 50 dial divisions.

3-4
10. See that the oscilloscope Is triggering on the output signal from the
403A.
11 . Obtain the correct time delay by means of delay line lengths be
tween the 264 and oscilloscope input to allow viewing of the signal
from TP-1 . This should normally require only five feet or so of coble.
12. Observe the signal at TP-1 and adjust R26 on the bleeder network
(see Fig. 10) for maximum signal amplitude without pulse shape
distortion. Examples of correct and incorrect adjustment of this
potentiometer are shown in Figures 2 and 3.
13. Observe the point of zero volts, and adjust the CROSSOVER ZERO
trim control, R6, located on the time derivation board to obtain
a minimum shift in time of the zero voltage point. This assures
that there is a minimum of time shift vs. pulse height associated
with the time derivation unit. (Figures 4 and 5 show examples of
correct and incorrect adjustment of this control.)
14. Disconnect the cables, replace the high voltage cover and the unit
is ready for operation.

4- 1
4. OPERATING INSTRUCTIONS
Once the steps outlined in Section 3 of this manual are performed, the unit is
ready for use. High voltage may be applied, and adjusted for appropriate gain
associated with the specific experiment. The photomultiplier gain will vary approxi
mately a factor of two with the high voltage change of 100 volts. The time
derivation unit should now be controlled by the 403A and the output of the 403A
should be attached to the appropriate time measuring device, e.g., time to pulse
height converter. The threshold adjustment of the timing device may be set by the
fol lowing steps:
1. Connect the output of a single trace scope such as a 545 or 585 to the output of
a shaping amplifier that is connected to the linear output from the 264.
2. Connect one of the outputs of the 403A to the trigger input to the oscilloscope
and obtain scope trigger with high voltage supplied and associated radiation
source near the scintillator.
3. Observe the linear pulse height distribution on the oscil loscope. This distribution,
which is a Compton distribution, is essential ly white over the pulse height range
associated with the input energy from the source, i.e., there is a constant dens
ity of pulses from zero volts to the maximum volts of the pulse height, except for
the region below the threshold level set by the DISCRIMINATOR LEVEL control
on the 403A. For pulse heights below this level, no output signals wil l be ob
served. One may, in this manner, precisely locate the edge of the discriminator
threshold and set this edge to any desired point within the spectrum of energies
involved in the timing experiment.
Once the discriminator level is adjusted to the correct point, the equipment is ready
to perform time measurements.
4.1 Timing with Photomultipliers
Timing or time measurement implies some type of coincidence measurement.
This measurement may be performed with standard coincidence circuits such
as pulse overlap types which are essentially single channel time analyzers,
or with time to pulse height converters which are differential, or multichannel
time analyzers. The response of a photomultiplier coincidence system to a
prompt gamma cascade always has a finite width which comes from a variety of
sources. The most important of these are as follows:
1 . The variation of time of interaction of radiation with the scintillator and

4-2
Figure 2
Incorrect- Adjustment of R-26
RCA-8575 with 1" x 1" Naton 136
Source — ®°Co
H.V. = -2200V
Time Scale (Horiz.) = 2 nsec/cm
A l-f A (\/ 4- t noo mV/cm @ TP-1
Amphfude (Vert.) =(
Figure 3
Correct Adjustment of R-26
RCA-8575 with 1" x 1" Noton 136
Source — ®°Co
H.V. = -2200V
Time Scale (Horiz.) = 2 nsec/cm
(100 mV/cm @ TP-1
I 40 mA/cm (Anode Current)
Amplitude (Vert.)

4-3
Figure 4
Incorrect Adjustment of Crossover Zero R6
X 1" Noton 136 RCA-8575 with 1
Source — ®°Co
H.V. = -2200V
Time Scale (Horiz.)
Amplitude (Vert.)
2 nsec/cm
20 mV/cm @ TP-1
8 m4y/cm (Anode Current)
Figure 5
Correct Adjustment of Crossover Zero R6
RCA-8575 with 1" x 1" Noton 136
r 60/—
bource — Co
H.V. - -2200V
Time Scale (Horiz.) = 2 nsec/cm @ TP-1
A 1-4. ^ i\/ 4. \ _ (20 mV/cm @ TP-1
Amplitude (Vert.) -j 3

4-4
the amount of energy deposited therein;
2. Finite decay time of light emitting states in the phosphor and variation of
times of photon arrival at the photomultiplier cathode;
3. Variation of transient times of photoelectrons in the photomultiplier due to
a) different path lengths, and b) variation of initial energy and angle of
secondary electrons;
4. Jitter and uncertainty of times of triggering of the associated electronics.
The variation in the time of interaction can be minimized by appropriate geom
etry and small scintiIlators at a corresponding loss in efficiency and average
energy deposition. For a complete discussion of timing with photomultipliers,
the reader is referred to some of the excellent literature available on the general
subject ^ and on the specific method employed here.^
4.2 Applications
The different specific applications for the 264 are essentially limitless, but since
the unit is designed primarily for timing applications with a wide dynamic range
of input energy, a number of system diagrams utilizing this unit are given. Some
typical resolution curves for one of these systems wil l be shown, from which
operational characteristics of other systems may be applied.
4.2.1 Typical Fast Coincidence System
Figure 6 is a block diagram of a system one might use to perform life
time measurements or to study time dispersion associated with prescribed
^A. Schwarzschild, Nuclear Instr. & Methods, 21 pp 1-16 (1963)
^G. Present, etal.. Nuclear I nstr. cS; Methods, 31, No. 1 pp 71-76 (1964)
^E. Gatti and V. Svelto, Nuclear Instr. & Methods, 30 pp 213-223 (1964)
^D. L. Weiber and H. W. Lefevre, IEEE Trans, on Nucl . Sci., NS-13, No. 1
pp 406-412

4-5
coincidence events. One notes immediately the simplicity of the sys
tem. It obtains its discrete advantages from the fact that there is no
time shift associated with pulse height variation; therefore, wide dy
namic ranges of pulse amplitude may be, and normally are, used in the
timing experiment. The resolution of the system in this case will nor
mally be limited by the statistical spreading due to the scintillation
process for the lower energy events. It is important to remember that
the resolution obtainable varies as 1//N, where N represents the num
ber of photoelectrons created by each event, and is therefore represent
ative of the amount of energy deposited in the scintillating phosphor,
and is strongly influenced by photomultiplier optics. The total time
spectrum is composed of the summation from zero to of the time
dispersion associated with each unit energy interval between the discrim
inator threshold level and maximum energy.
Normal ly, this system will require no energy selection side channel
electronics; however, if it is desirable to restrict the energy range to
a small value this side channel electronics may be imposed in the nor
mal manner associated with a typical fast-slow coincidence system.
Figure 7 shows a typical time spectrum taken with this type of system
utilizing all signals detected which deposited greater than 30 keV of
gamma ray energy into the scintillator. A comparison of this spectrum
with Fig. 8, which has the energy range restricted by side channel
windows, indicates the effect of resolution broadening as a function of
the energy range utilized.
4.2.2 Matching the Time Derivation System to the Experiment
It is important to understand when the fast crossover system may be
used to ah advantage over that system utilizing a leading edge discrimi
nator. In general, the leading edge type discriminator may be used on
signals of any shape and therefore it may be used with photomuItipliers
in conjunction with al l scintillators. The advantage of a leading edge
time derivation scheme is that of time resolution for a narrow dynamic
range. One may achieve, for a very narrow dynamic range, time reso
lution in the order of a factor of two better by leading edge discriminator
than may be achieved by a fast crossover method. The disadvantages of
leading edge discrimination are primarily those associated with walk,
i.e., time shift vs. pulse height. Figure 9 presents comparative curves
on fast crossover and leading edge discrimination vs. dynamic range.
It is readily evident from Fig. 9 that if fast phosphors are used in the