ORTEC 473A Service manual

Model 473A
Constant-Fraction
Discriminator
Operating and Service Manual
This manual applies to instruments marked
"Rev 20" on rear panel
Pfintea m U S.A
2928 02C 0180

Ill
CONTENTS
Page
WARRANTY v
PHOTOGRAPHS vi
1. GENERAL 1
1.1 Functional Description 1
1.2. Physical Description 2
2. SPECIFICATIONS 2
2.1. Performance 2
2.2. Controls 2
2.3. Input 2
2.4. Outputs 3
2.5. External Delay 3
2.6. Electrical and Mechanical 3
3. INSTALLATION 3
3.1. General 3
3.2. Connection to Power ^ ^ 3
3.3. Input Connection 3
3.4. Output Connections 3
3.5. External Control 4
4. OPERATION 4
5. THEORY OF OPERATION 4
5.1 General 4
5.2. Input Circuit 5
5.3. Lower-Level Discriminator 5
5.4. Upper-Level Threshold 5
5.5. Constant-Fraction Discriminator 5
5.6. Constant-Fraction Operation 7
5.7. S.R.T. Operation 7
5.8. Leading-Edge Operation 7
5.9. Output Pulse Generation 7
5.10. External Selections 8
5.11. Power Supplies g
6. APPLICATIONS g
6.1. Timing with Fast Scintiilators g
6.2. Timing with Nal(TI) Scintiilators 10
6.3. Timing with Large Ge(Li) Detectors 10
6.4. Timing with Other Detectors 12
7. CALIBRATION 13
7.1. Equipment Required 13
7.2. Preliminary Procedure 13
7.3. Leading-Edge Discriminator Test 13
7.4. Scintillation 1 Mode Walk Test 13
7.5. Scintillation 2 (Nal) Mode Walk Test 14
7.6. Ge(Li) Mode Walk Test 15
7.7. Factory Repair 16
BIBLIOGRAPHY 17
Schematic
Block Diagram
473A-02G1-S1
473A-G101-B1
■gjW

ILLUSTRATIONS
Fig. 5.1. Constant-Fraction Trigger Timing for Two Different Input Pulse Amplitudes 6
Fig. 5.2. C.F. Mon Waveforms Using Ge(Li) Mode 6
Fig. 5.3. C.F. Mon Waveforms Using Scint 2 (Nal) Mode 7
Fig. 5.4. Simplified Block Diagram of the 473A Constant-Fraction Discriminator 8
Fig. 6.1. A System for Gamma-Gamma Lifetime Measurement 9
Fig. 6.2. Timing Over a Narrow Dynamic Range with the System of Fig. 6.1 10
Fig. 6.3. Plot of Time Resolution vs Dynamic Range Using RCA 8850 Photomultiplier Tube 10
Fig. 6.4. Plot of Time Resolution vs Dynamic Range Using RCA 8575 Photomultiplier Tube 10
Fig. 6.5. Typical Timing Spectrum Over a Wide Dynamic Range (50:1) with Nal(TI) 10
Fig. 6.6. Plot of Time Resolution vs Dynamic Range Using Nal(TI)and RCA 8575 PMT 11
Fig. 6.7. Gamma-Gamma Coincidence System Using Plastic
Scintillator and a Large Ge(Li) Coaxial Detector 11
Fig. 6.8. Timing Spectrum for a Narrow Dynamic Range (1.1:1) for the System of Fig. 6.7 12
Fig. 6.9. Timing Spectrum for a Wide Dynamic Range (10:1) for the System of Fig. 6.7 12
Fig. 6.10. The Effect of 473A Threshold Setting on the
Apparent Efficiency of Different Ge(Li) Detectors 12
Fig. 7.1. Test Setup for Leading-Edge Discriminator Mode Calibration 13
Fig. 7.2. Test Setup for Scintillation 1 Mode Walk Test 14
Fig. 7.3. Test Setup for Scintillation 2 (Nal) Mode Walk Test 15
Fig. 7.4. Test Setup for Ge(Li) Mode Walk Test 16

STANDARD WARRANTY FOR EG&G ORTEC INSTRUMENTS
EG&G ORTEC warrants that the items will be delivered free from defects in material or workmanship. EG&G ORTEC
makes no other warranties, express or implied, and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
EG&G ORTEC's exclusive liability is limited to repairing or replacing at EG&G ORTEC's option, items found by EG&G
ORTEC to be defective in workmanship or materials within one year from the date of delivery. EG&G ORTEC's liability on
any claim of any kind, including negligence, loss or damages arising out of. connected with, or from the performance or
breach thereof, or from the manufacture, sale, delivery, resale, repair, or use of any item or services covered by this agree
ment or purchase order, shall in no case exceed the price allocable to the item or service furnished or any part thereof
that gives rise to the claim. In the event EG&G ORTEC fails to manufacture or deliver items called for in this agreement or
purchase order, EG&G ORTEC's exclusive liability and buyer's exclusive remedy shall be release of the buyer from the
obligation to pay the purchase price. In no event shall EG&G ORTEC be liable for special or consequential damages.
QUALITY CONTROL
Before being approved for shipment, each EG&G 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
If it becomes necessary to return this instrument for repair, it is essential that Customer Services be contacted in advance
of its return so that a Return Authorization Number can be assigned to the unit. Also, EG&G ORTEC must be informed,
either in writing or by telephone [[phone] ], of the nature of the fault of the instrument being returned and of the
model, serial, and revision ("Rev" on rear panel) numbers. Failure to do so may cause unnecessary delays in getting the
unit repaired. The EG&G ORTEC standard procedure requires that instruments returned for repair pass the same quality
control tests that are used for new-production instruments. Instruments that are returned should be packed so that they
will withstand normal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the
nearest EG&G ORTEC repair center. The address label and the package should include the Return Authorization Number
assigned. Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the
sender s expense, and it will be the sender's responsibility to make claim with the shipper. Instruments not in warranty
will be repaired at the standard charge unless they have been grossly misused or mishandled, in which case the user will
be notified prior to the repair being done. A quotation will be sent with the notification.
DAMAGE IN TRANSIT
Shipments should be examined immediately upon receipt for evidence of external or concealed 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, please notify EG&G ORTEC of the circumstances so that assistance can be provided
in making damage claims and in providing replacement equipment if necessary.

VI
>2(Nal
^EXT

2 (Nal) setting may give the best results. In general, if the
input to the 473A is taken from an ORTEC 454 Timing
Filter Amplifier, the optimum 473A switch setting is the
Ge(Li) position. When the 473A input is taken from an
AN302/N Quad Amplifier, the best operation with the
473A depends on the input signal rise time and dynamic
range and may be provided by either the Ge(Li) or Scint 2
(Nal) setting. In special cases, the Ext setting can be used
and a user-selected delay cable can provide the optimum
performance.
1.2. PHYSICAL DESCRIPTION
The 473A is a Nlfvl-standard single-width module that
must be installed in a bin and power supply for operation.
All of the normally-used connections and controls are
located on the front panel.
The required operating power will be furnished from the
bin and power supply into which the module is installed
for operation.
2. SPECIFICATIONS
2.1. PERFORMANCE
INPUT PULSE CHARACTERISTICS Negative pulses
accepted to^V without saturation; protected to 100 V for
duty cycle of 10%,
DISCRIMINATOR RANGE -50 mV to -5 V,
WALK AND DYNAMIC RANGE
Ge(U) Mode ^-:2 ns for range of 100 mV to 5 V with 40-
ns rise time.
Scint 1 Mode <±200 ps for range of 50 mV to 5 V
(including test attenuator walk) with 1-ns rise time.
Scint 2 (Nal) Mode <±500 ps for range of 50 mV to 5 V
with 5-ns rise time.
NOMINAL PULSE PAIR RESOLUTION For input sig
nals >0.5 V with rise time <2 ns.
Ge(LI), Scint 1, or Ext 65 ns.
Scint 2 (Nal) 1.1 mS.
TEMPERATURE CHARACTERISTICS
Disc Level Drift typically $0.5 mV/°C, 0 to 50°C.
Propagation Delay Stability typically within $15 ps/°G,
10 to 40° C.
2.2. CONTROLS
SHAPING MODE 4-position front panel switch:
Ge(Li), Scint 1, Scint 2 (Nal) Select the delay and
fraction for optimum time resolution for signals accord
ing to general detector-type classifications. The Scint 2
(Nal) setting also selects an internal dead time of ~l
to prevent multiple triggering on slow-decay signals.
Ext Allows selection of whatever delay is desired by
controlling the length of coaxial cable attached between
front panel connectors; also allows an internal jumper
selection of 10%. 20%, or 30% for the triggering fraction
(factory set for 30%).
TIMING MODE 3-position front panel switch selects
time derivation mode:
C.F, Constant-Fraction timing operation; triggering
fraction and shaping delay controlled by the shaping
mode selection.
S.R.T. Rejects slow rise-time detector pulses; less effi
cient than the C.F. mode but provides better time resolu
tion in many applications. Any signal that does not cross
the input Disc Level within ~20 ns after the response al
the constant-fraction pickoff level (50% of Disc Level]
will not generate an output. Ideal for improving time
resolution when using large Ge(Li) detectors.
L.E. Bypasses constant-fraction circuitry, allowing op
eration as a leading-edge discriminator whose couni
rate is limited by the dead time associated with the
shaping mode selectors, fvlaximum count rate limited tc
about 1 IvIHz for Scint 2 (Nal); operates to 15 MHz foi
other selections.
DISC LEVEL 10-turn precision locking potentiometei
adjusts the trigger level of the signal input discriminator
range, -50 mV to -5 V. Also adjusts the threshold leve
for an internal constant-fraction pickoff arming discrini
inator level.
EXT WLK 20-turn screwdriver adjustment for precis
setting of walk compensation for External mode opera
tion.
2.3. INPUT
NEG Front panel BNC accepts negative input signa
from a fast preamplifier such as the ORTEC 9301, a fa
amplifier such as the AN302/N or 574, or a shapm
amplifier such as the 454; normal range from Disc Lev
to -5 V; input impedance, 5011. Reflections typical
<10% for input signals to -5 V with rise time ^1 ns
put directly compatible with current pulses from f
anodes.

2.4. OUTPUTS
2.5. EXTERNAL DELAY
NEG Two NIM-standard fast-negative logic output sig
nals generated separately and furnished through two
BNC connectors on front panel; nominally -16 mA (800
mV on son load); width, ^10 ns; rise time, ^2.5 ns.
POS NIM-standard slow-positive logic output signal
furnished through BNC connector on front panel; nomi
nally ^5 V, width, 500 ns; rise time, ^25 ns; output
impedance, ^lOft.
C.F. MON Permits observation of the Constant-Frac
tion shaped signal through BNC connector on" front
panel; output impedance, 50(1.
DELAY Front panel input and output connectors for
selecting the required shaping delay by controlling the
length of 50(1 cable added between these BNCs; used for
Ext mode operation only
2.6. ELECTRICAL AND MECHANICAL
POWER REQUIRED +12 V, 21 mA; -12 V, 150 mA;
+24 V, 10 mA; -24 V, 75 mA; 115 V ac, 42 mA,
DIMENSIONS NIM-standard single-width module (1.35
by 8.714 in.) per TID-20893.
3. INSTALLATION
it
e
0
)r
ar
ir;
el
n-
3.1. GENERAL
The 473A is used in conjunction with an ORTEC 401/402
Series Bin and Power Supply, which is intended for rack
mounting. Therefore if vacuum tube equipment is oper
ated in the same rack, there must be sufficient cooling
with circulating air to prevent any localized heating of the
all-transistorized circuitry used throughout the 473A. The
temperature of equipment mounted in racks can easily
exceed the recommended maximum limit of 120° F (50° C)
unless these precautions are taken.
3.2. CONNECTION TO POWER
Always turn off power for the power supply before
inserting or removing modules. The ORTEC modular
instruments are designed so that it is not possible to
overload the power supply with even a full complement of
modules in the bin. Since, however, this may not be true if
the bin contains modules other than those of ORTEC
design, use the convenient test points on the front panel
of the 401/402 to check each power supply voltage level
after all modules are inserted.
3.3. INPUT CONNECTION
The input circuit of the 473A is designed for use with a 50fl
cable. The input impedance is 50(1, so no external
terminator is required for this connection.
The input can come from a detector or photomultiplier
directly,.provided it has negative polarity and the pulse
amplitudes for the energies of interest wiil exceed a Disc-
Level setting m the 473A. When the input signal has a fast
rise time (0.5 to 5 ns) and must be amplified, an ORTEC
AN302/N Quad Amplifier can be used between the pream
plifier output and the input of the 473A. When an ampli
tude requires both amplification and additional pulse
shaping (such as with germanium detectors), an ORTEC
454 Timing Filter Amplifier can be used to furnish both of
these functions between the output of the preamplifier
and the input of the 473A.
3.4. OUTPUT CONNECTIONS
There are four outputs on the 473A, and all connectors are
located on the front panel. Two of these are NIM-standard
fast-negative logic pulses that are generated separately
and are therefore completely isolated. A third is a NIM-
standard slow positive pulse. All three logic pulses are
furnished for each input pulse that exceeds the Disc Level
unless the front panel switch selects S.R.T. and the rise
time of the pulse is too slow. The fourth output is the C.F.
Mon, which permits observation of the Constant-Fraction
shaped signal.
The fast-negative output pulses are intended for timing
applications such as the Start and Stop inputs to a time to
pulse height converter. Either or both may be used and
the alternate connector does not need to be terminated
when not in use. Since the NIM-standard fast-negative
pulse is a current pulse, and since it is intended for use
with a 50(1 load, 50(1 cable should be used to connect it to
the point where it will be used, and that point must be
terminated in 50(1. Normally the instrument that receives
the pulse will have a 50(1 input impedance; if it does not,
use an external termination at the output end of the cable.
The NIM-standard slow-positive output pulses can be
used for coincidence work or can be counted directly in a
sealer or ratemeter. It is normal to use 9311 cable to
transfer this voltage pulse; it is furnished through an
output impedance of ^10(1. For cable lengths of more
than 2 meters (~7 ft) it is recommended that the cable be

terminated in its characteristic impedance. This output
can also drive a terminated 50n cable, but with a slightly
reduced amplitude.
3.5. EXTERNAL CONTROL
If the optional external control is selected in lieu of one of
the identified detector types, the Constant-Fraction cir
cuit is not complete until the two front panel Delay
connectors are cabled. If they are directly shorted, the
delay is zero. For a calculated delay, use a length of RG-
174 son cable for the connection. The adjusted delay is a
funption of cable length, based on 125 ps/inch of this type
of cable.
The factory-installed connection to select the fraction for
Ext operation uses the circuit for a 30% triggering frac
tion. By moving a jumper on the printed circuit board, the
triggering fraction can be changed to 10% or 20% if
desired for experimental work.
4. OPERATION
After the 473A has been installed and interconnected as
described in Section 3, the only operating functions that
are normally required are the setting of the shaping
selector switch, adjusting of the Disc Level control, and
selecting the desired operating mode.
Normally the shaping selector switch can be set at a
switch position that identifies the type of detector being
used. However, the only differences between the three
switch positions marked for detector types are the effec
tive delay time that will be used for Constant-Fraction
pickoff and the controlled dead-time duration in the
output circuit. For reference, the selectable delay times
are 14 ns for Ge(Li), 1.3 ns for Scint 1, and 1.9 ns for Scint 2
(Nal). Shaping that is provided by the preamplifier may^,
affect the relation between the optimum switch selection
and the actual class of detector that is being used. The
output circuit dead time is nominally 65 ns when the
shaping switch selects Ge(Li), Scint 1, or Ext. When the
switch selects Scint 2 (Nal), the internal dead time is
increased to 1 ^lS. If the switch is set at Ext, the delay time
is determined directly by the length of 50n cable that is
connected between the Delay BNC connectors on the
front panel. Two additional functions are selectable when
the switch selects Ext. One is the triggering fraction; the
basic setting of a jumper on the printed circuit selects
30%, but the jumper can be moved to select 20% or 10% if ^
desired. The other function is the front panel Ext Wlk
control, and its setting can be optimized for each applica
tion of the Ext switch selection.
The purpose of the Disc Level adjustment is to accept
signals with amplitudes of interest and to eliminate
response to signals with smaller amplitudes. The proper
setting of this control depends on the range of signal
amplitudes that are furnished to the input. The control
range is 50 mV to 5 V, using the 10-turn precision
potentiometer for precise adjustment and excellent re
peatability.
For most applications, the mode selector can be set at
C.F., for Constant-Fraction operation. If the signal rise
times tend to vary through a wide range, such as the
signals that can be furnished from a large-volume coaxial
germanium detector, the switch can be turned to S.R.T. to
operate as a Constant-Fraction discriminator but to also
reject each input pulse that has too slow a rise time. The
S.R.T. selection then provides a better resolution in the
timing spectrum.
Conventional leading-edge timing can be obtained with
the mode switch set at L.E. If the shaping selector switch
is set at Scint 2 (Nal), the internal dead time is held at 1.1 i
^s so the maximum input count rate is limited to just under i
1 MHz. But if the switch selects any of the other three
shaping circuits, the dead time is only 65 ns and the input
count rate can be up to about 15 MHz maximum. The i
other functions selected by the shaping selector switch '
have no effect during Leading-Edge operation because
the Constant-Fraction portion of the 473A circuits is
bypassed.
5. THEORY OF OPERATION
5.1. GENERAL
The circuits of the 473A are shown in schematic 473A-
0201-S1. included at the back of the manual.
The inputs are furnished simultaneously to three internal
circuits. One circuit is a lower-level leading edge (LLLE)
discriminator that defines the onset of a signal of interest
and arms internal logic circuits in the module. A second
circuit is an upper-level leading edge (ULLE) discrimi
nator; each input signal must exceed this level in order

n
n
1
ir
e
It
e
h
le
Is
H)
St
id
that an output will be generated. The third circuit is a
constant-fraction (C.F.) discriminator that provides a
precise timing recognition for each input signal.
A front panel Disc-Level control effectively adjusts the
response threshold for both the lower-level and upper-
level discriminators. The nominal range for this control Is
50 mV to 5 V, referred to the input pulse amplitude and
associated with the ULLE response level. The LLLE
threshold is adjusted automatically to about 50% of the
ULLE so that it is triggered earlier on the leading edge of
the input pulse.
When an output is generated it furnishes two independ
ent NIM-standard fast-negative signals and one NIM-
standard slow-positive signal. The leading edges of the
three output signals are coincident. A feedback in the
output trigger circuit ensures generation of only one set
of output pulses for each input pulse.
The Constant-Fraction mode of operation can be used
either with or without the slow-rise time reject feature.
When the S.R.T. setting is selected with the front panei
toggle switch, the C.F. timing signal is not generated if the
rise time of an input pulse is too slow. The leading-edge
(L.E.) mode of operation does not use any of the constant-
fraction or slow-rise time reject functions, but generates
an output when there is an input signal that crosses the
ULLE threshold.
5.2. INPUT CIRCUIT
Signals are accepted through front panel BNC CN1. The
input is protected against large amplitude signals by Q1,
D1, and 02. Resistor R42 provides 50fl termination for the
input signals and divides the input amplitude by a factor of
2. The input signals can be monitored at TP1 on the front
panel.
The signals are furnished through R45 to three circuits.
Buffer Q5 furnishes the signal to the LLLE discriminator;
buffer Q7 furnishes the signal to the ULLE discriminator;
and DL14 and DL15 connect the signal into the CF
discriminator.
5.3. LOWEH-LEVEL DISCRIMINATOR
The signal through Q5 is furnished to pin 9 of IC2(6) and
the signal amplitude is cornpared to a reference level at
pin 10. When the level at pin 9 exceeds the reference
level, 102(6) changes state and generates a response
called LLLE for lower-level leading edge. The LLLE signal
is used to reset the internal logic and to arm a zero
crossing discriminator in the constant-fraction circuit.
The response remains high at IC2(6) and low at 102(7)
until the input signal level decays through the reference
level.
The reference level at pin 10 of IC2(6) is furnished from
the ULLE front panel adjustment through R43 and R73,
and is about 50% of the upper-level threshold. A cali
brated baseline is furnished from R160and R65 through
Q4. The calibration, on the printed circuit, is furnished by
R65, LLLE Adj.
5.4. UPPER-LEVEL THRESHOLD
The signal through Q7 is furnished to pin 9 of IC4(6) and
its amplitude is compared to a reference level at pin 10.
Under quiescent conditions, the level at pin 9 is less
negative than the level at pin 10. When the amplitude at
pin 9 exceeds the level at pin 10, IC4(6) changes state and
generates a response called ULLE for upper-level leading
edge. If ULLE is generated, this permits an output signai
to be generated if it satisfies the other criteria. The ULLE
response remains high at IC4(6) and low at IC4(7) until
the input signal decays back through the reference level.
The reference level at pin 10 is furnished from the R66,
R67, R69 circuit through Q6. The range is calibrated by
R66 for the front panel level control, R67. The effective
range, referred to the input, is 50 mV through 5 V.
5.5. CONSTANT-FRACTION DISCRIMINATOR
Each input signal is applied to two parallel circuits that
lead into the constant-fraction discriminator. One circuit,
through DL15, delays the input pulse, and the other
circuit, through DL14, attenuates the signal. The resulting
signals are furnished into a limiting differential amplifier
to generate the unique constant-fraction signal that can
be examined at the C.F. Mon connector on the front panel.
Shaping selector switch 31 selects the delay for one path
and the attenuation factor for the other path. SIB and D
select one of four delay paths; for Ge(Li), the delay is DL1
and consists of 9 ft 4 in. of 50fl cable for a time of 14 ns;
Scint 1 uses DL2 for 1.3 ns; Scint 2 (Nal) uses DL3for 1.9
ns. When the switch selects Ext, the amount of delay is
determined exclusively by the amount of 50fl cable that
is connected externally between the two front panel Delay
connectors.
Switch sections S1A and C select R7 and R14 for Ge(Li);
R8 and R15 for Scint 1; R9 and R16 for Scint 2 (Nal); or RIO
through R13 for Ext. Each setting except Ext provides a
triggering fraction of 32%. The Ext setting uses jumper
selections in a step attenuator to choose triggering
fractions of 10%, 20%, or 30%; the jumper is set for 30%
when the unit is shipped from the factory and can be
changed to either of the alternate settings on the printed
circuit board. The value of the fraction, calculated by
resistance values, is always greater than the effective
fraction, f, because of inherent circuit delays.
A differential amplifier, 101(6), (3), and (14), accepts the
two shaped signals through buffers 02 and 03. This
circuit generates a bipolar signal with zero crossover
when the delayed signal amplitude exceeds the prompt
attenuated signal amplitude. Since both signals are the

result of the same input pulse, the actual peak amplitude,
within a normal range, does not affect the relative time at
which the crossover occurs. A zero-crossing discrimi
nator is then used to generate the C.F. response timing
signal.
The only portion of the input pulse that is used for
Constant-Fraction time derivation is the rise time. Figure
5.1 shows how two pulses with different peak amplitudes
will generate identical timing responses at 101(14). The
delayed signal is furnished to pin 10 of 101 and the
attenuated signal is furnished to pin 9. When the negative
polarity at pin 10 exceeds the amplitude at pin 9, the
polarity of the limiting differential amplifier switches and
drives gate 103(14) if it has been enabled by LLLE. The
result is that the O.F. trigger response time is the same for
any original pulse amplitude within the normal response
range for the 473A. The pulse that is generated in the
differential amplifier is also furnished to the front panel
O F. Mon BNO connector, where waveforms can be ob
served that are similar to those shown in Figs. 5.2 and
5.3. Figure 5.2 is the summed constant-fraction waveform
with the input from a Ge(Li) detector, and Fig. 5.3 is the
same information where the input is from a Nal(TI) detec
tor and the mode switch selects Scint 2 (Nal).
In Fig. 5.2(a), the time on the baseline is 20 ns/cm and the
zero crossover is difficult to determine. When the time
base is changed to 2 ns/cm, the critical portion of the
waveform is spread out so that the zero crossover point
can be seen easily, as in Fig. 5.2(b).
Ofi avert
Qefayea
Attenuated
Tnqger Time
Fig. 5.1. Constant-Fraction Trigger Timing for Two
Different Input Pulse Amplitudes.
(a) Dispiay with 20 ns/cm
iOOiV
i I
-.t • ■■'.v. '
T , 1 S
«-
-iH 'A"
a ■ '
"is;..®
(b) Dispiay with 2 ns/cm
Fig, 5.2. C.F. Mon Waveforms Using Ge(U) Mode.
In Fig. 5.3(a), the time base of 20 ns/cm permits observa- f
tion of some of the perturbations that may follow the
scintillation detector waveform. These do not interfere in |
any way with the point of interest, which is the zero
crossover that is shown clearly when the baseline is
changed to 2 ns/cm as in Fig. 5.3(b).
Amplifier feedback is furnished through Q10, Q11, and
through Q8, Q9. Potentiometer R35 is a walk adjust
control on the printed circuit that sets the C.F. baseline to
minimize time differences for all shaping modes: this
adjustment is supplemented by the front panel Walk Adj
control when shaping switch SI selects Ext.
A timing pulse is generated at pin 12 of 103(14) in
response to a negative-going input variation at Input
connector ON 1 whether this is a real signal of interest or is

1
3-
le
m
o
Is
id
St
to
is
dj
(a) Display with 20 ns/cm
{b) Display with 2 ns/cm
Fig. 5.3. C.F. Mon Wavetorms Using Scint 2 (Nal) Mode.
Simply a small amplitude pulse - generally noise - that is
to be ignored. Gate IC3(14) will have been armed to pass
the timing signal by LLLE if the signal is of interest.
5.6. CONSTANT-FRACTION OPERATION
Figure 5.4 is a simplified block diagram of the 473A that
shows the relation of internal circuits when the C.F. mode
of operation is being used.
Constant-Fraction timing discrimination provides a tim
ing pulse for each input signal variation, whether this is
converted into an output signal or not. The function
described m Section 5.5 uses the OF stage (Fig. 5.4) to
accomplish this signal generation. Note that the signal at
the C.F. Mon output is inverted relative to the internal
signal used for time derivation. If tne signal is of interest, it
will have triggered the LLLE discriminator prior to the
timing pulse, so gate Gl (in Fig. 5.4) is armed to pass the
timing puise.
After a delay of about 29 ns, during which other accept
ance criteria are checked, the timing pulse is furnished to
gate G2, which is IC3(7). A response in the ULLE circuit
must have triggered flip-flop IC6(3) and (14) to indicate
that the input signal amplitude is sufficient to satisfy the
amplitude requirements, and the timing signal passes
through G2 and G3 to trigger an output one-shot, IC10(7)
and (14), to generate the group of three output signals.
5.7. S.R.T. OPERATION
Operation with the Slow Rise Time Reject circuit is the
same as for the Constant-Fraction operation described in
Section 5.6 except that the timing signal is blocked at gatq
G3 (Fig. 5.4) if the signal rise time is too slow. The S.R.T.
(slow rise time) flip-flop, IC7(3) and (14), is reset by LLLE
and is enabled, through IC8(15), to be set by flip-flop
IC6(3) and (14). The S.R.T. flip-flop must have been set by
the time the timing pulse reaches G3, IC9(6), or the timing
pulse will not pass; the presumption is, then, that the rise
time of the input pulse was too slow to qualify it as a true
signal. The maximum rise time from LLLE to ULLE is
about 25 ns to permit the output pulses to be generated.
5.8. LEADING-EDGE OPERATION
Conventional leading-edge discrimination can be se
lected by turning the mode selector switch to L.E. This
enables IC8(2) and completes the signal path from ULLE
to gate G2 (in Fig. 5.4) through the delay, DL9. The signal
path starts at ULLE, where the input amplitude triggers a
response when it exceeds the adjusted Disc-level setting.
It is delayed while FF is triggered to enable G2. and then
passes through G2, G3, and G4 to generate a set of three
output signals and the dead-time feedback control.
The CF response is not effective because the Gl-to-G2
path is not enabled. S.R.T, is set to enable G3 each time an
FF response reaches Its input in the L.E. mode, and it is
reset from the trailing edge of LLLE. The FF continues to
toggle between reset and set at LLLE and ULLE times, but
it enables G2 each time there is a ULLE pulse coming
through the delay line.
5.9. OUTPUT PULSE GENERATION
When a decision has been made to generate a set of
output pulses, the signal is furnished to pin 5 of IC9(2).
The signal passes through IC9(15) to trigger both NIM-
standard fast-negative output pulse circuits and through
IC9(14) to start Schmitt trigger IC10(7) and (14). The
Schmitt trigger is the input to the NIM-standard slow-
positive output generator.
One fast-negative output generator uses 012 and 013 as
a current switch. The current, at a level of -16 mA.

I
Cr «ntf Le
Ovi
'n Owl
-®
Z)^
(g V»i««t:
G<(ltl 14 AS
SciniiKaiittn III 1 3 <h
SciAtdlatien I2> N*l 19
£it iiltrnti 4tllv
Fig. 5.4. Simplified Block Diagram of the 473A
Constant-Fraction Discriminator.
normally flows through Q12. When the signal is furnished
from IC9(15), Q12 is turned off and Q13 is turned on to
furnish the current through CN2 on the front panel,
assuming that the output current circuit is properly
terminated in 50n. The other fast-negative output genera
tor uses Q14 and Q15 as an identical current switch that is
triggered by the same input signal from IC9(15) to switch
-16 mA from Q14 to Q15 and through CN3 to the external
circuit.
The Schmitt output at IC10(14) is furnished to the positive
NIM one-shot circuit that includes Q16, Q17, and Q18.
When the signal is furnished through C63 to Q16, the
output at CN4 rises from 0 to a nominal +5 V for a period of
about 500 ns.
The Schmitt output at IC10(14) is also coupled back to pin
4 of IC9(3) to hold this input high and prevent response to
another input signal that arrives before a controlled dead
time has elapsed. C55 is a stretch circuit that blocks the
Schmitt circuit from recovering for a period that is
determined by the setting of shaping switch SI. When
switch SI selects Ge(Li). Scint 1, or Ext, the recovery time
of the Schmitt circuit is about 50 ns; but for the Scint 2
(Nal) setting of the switch, the recovery time is extended
to about 1 MS.
5.10. EXTERNAL SELECTIONS
If the shaping selector switch is turned to Ext, three
portions of the internal circuits shown in Fig. 5.3 are
affected. The delay time and attenuation for CF operation
and the trigger baseline level for the CF discriminator are
all controllable.
The selection of delay, is dependent on the external
circuit that is added between the two Delay BNC connec
tors on the front panel. If they are shorted directly, there
is zero delay. Normally they will be connected with a meas
ured length of 50n cable, with a delay of about 1.5 ns/ft.
The selection of the fraction for attenuation is a jumper
connection at one of three alternate locations on the
printed circuit board. They are located on the front corner
of the printed circuit nearest switch SI and are numbered
1, 2, and 3. A lead from the 2nd wafer of switch 31
completes the connection. Normally, the lead is con
nected to point 3 for a 30% dc fraction. The wire lead can
be moved to point 2 for a 20% dc fraction or to point 1 fora
10% dc fraction if desired. The value of the dc fraction is
always larger than the effective fraction, I. because of
inherent circuit delays.
After the fraction setting has been completed, test the
output signal timing for walk caused by input signal
amplitude variations. The Walk Adj control on the front
panel adjusts the reference level that is furnished to pin 9
of IC1(6) together with the attenuated input signal. It
needs to be adjusted for each change of the fraction
selected for Ext operation, and is not in the circuit for any
of the alternate shaping modes.
The remaining portion of the Fig. 5.3 circuits that are
affected by the selection of Ext is the duration of dead
time, which is in the feedback loop from the Pos Out
circuit to gate G4. Section E of switch 81 completes a
circuit from the switch wiper to ground for the Ge(LI),
Scint 1, and Ext settings, and the resulting controlled
dead time is approximately 65 ns. If a longer dead time is
desired for Ext operation, the grounded connection for
the 4th switch position can be clipped and the dead time
will then be about 1 ms, the same as for Scint 2 (Nal!
operation.

Om
-©
5.11. POWE.R SUPPLIES
Two power supply levels are generated In the 473A for use
In its integrated circuits. One level Is -'5.2 V and the other
is -2 V.
The ac Input power line Is connected through the bin and
power supply to each module location. It is accepted from
this circuit into the primary of transformer T1 on the473A
chassis. The output of T1 is a full-wave rectified source for
-5.2 V, required in most of the integrated circuits. The
voltage source is rectified by 05, regulated by 020
through 023, and filtered by 081. The -12 V bin power dc
source is used as a reference.
Another circuit uses the —12 V reference and reduces the
—5.2 V level down to —2 V for other operating require
ments. 025 is the series pass transistor in this dropping
circuit and 024 furnishes the reference level from a
bleeder in the -12 V source.
Each of the four standard dc levels (±12 V and ±24 V) Is
accepted from the bin and power supply through a filter
network. These four filters involve 112 through LI5 and
073 through 080.
6. APPLICATIONS
there
neas-
ns/ft.
mper
i
r
)ered
h SI
con-
d can
fora
on Is
se of
;t the
Ignal
front
pin 9
al. It
ction
r any
it are
dead
! Out
tes a
3(U),
oiled
me Is
n for
6.1. TIMING WITH FAST SCINTILLATORS
Figure 6.1 shows a typical system for timing with fast
scintillation detectors such as Naton-136, Pilot B, KL236,
NE-102, NE-111, NE-213, etc. A 473A Constant-Fraction
Discriminator is used in each of the two input channels to
the time to pulse height converter. Figure 6.2 is a typical
timing spectrum that was obtained with this system.
A plot of time resolution versus dynamic range is shown in
Fig. 6.3 for a system using RCA 8850 photomultiplier
tubes. A similar plot, using RCA 8575 photomultiplier
tubes is shown in Fig. 6.4. The output pulse from the RCA
8575 is slightly slower than that from the RCA 8850. Be
cause of this rise time difference, the best timing resolu
tion was obtained with the 473A in the Scint 1 mode when
using the RCA 8850. When using the RCA 8575, the best
timing resolution was obtained with the 473A set for the
Scint 2 (Nal) mode.
Input signals to the 473A should have a peak amplitude of
about 5 V for the Compton edge of the 511-keV gammas
ORTEC
456
HV POWER
SUPPLY
Oynodt
ORTEC
113
SCINTIL
LATION
PREAMP
ORTEC
RCA
3850
PM
265
PM BASE
*
RCA
3850
PM
ORTEC
265
V/<
\ /
PM BASE
ORTEC
CONSTANT
FRACTION
DISCRIMI-
NATOR
Oynoda
• 1- X 1-in. NATON- 136
ORTEC
457
TIME TO
PULSE HEIGHT
CONVERTER
ORTEC
ORTEC
Stoo
425A 473A
CONSTANT
NANOSECOND
fraction
DELAY
DISCRIMI
NATOR
ORTEC
ORTEC
460
551
SPECTROS-
COPY
TIMING
amplifier
SCA
ORTEC
414A
COINCIDENCE
ORTEC
456
HV POWER
SUPPLY
ORTEC
551
TIMING
SCA
ORTEC
460
SPECTROS-
copy
AMPLIFIER
ORTEC
113
SCINTILLA
TION
PREAMP
ORTEC
62406
MULTICHANNEL
ANALYZER
Fig. 6.1. A System (or Gamma-Gamma Lifetime Measurement.

10
aaaaosBt
60,
Co
RCA 8850 Phoiomuitipl ier Tube
1.1:1 Dynamic Range
FWHM 193 ps
FWTM 373 05
6.85 ps per channel
Fig. 6.2. Timing Over a Narrow Dynamic Range with
the System of Fig. 6.1.
8850 TUBES
! I r
ORTEC 9201 BASES
r'Xr'KL236 SCINTILLATORS
_ _
473A CF OlSC 'CF and SCINT MOOES)
FWTM
FWHM
-
- u
1 I I I
i : 1
5:1 111:1 20:1
DYNAMIC RANGE
Fig. 6.3. Plot of Time Resolution vs Dynamic Range Using
RCA 6850 Photomultlpller Tut)e.
from Co so that a dynamic range of 100:1 can be
achieved. The lower-level discriminator should be set at
about 50 mV. For some tubes, the 50n termination that is
internal to the tube base must be removed to accomplish
the maximum dynamic range.
6.2. TIMING WITH Nal(TI) SCINTILLATORS
This type of measurement is similar to timing measure
ments with fast scintillators. However, one additional
problem must be considered. The photoelectron statistics
for low-energy gamma-ray work are so poor that indi
vidual events near the trailing edge of Nai(TI) pulses will
trigger the 473A. Thus a single scintillation event can
produce two or more discriminator output pulses. In the
473A, this problem is overcome by using the Scint 2 (Nal)
mode, in which an internal dead time of about 1 ^s is
generated. The 473A can be used successfully on even
longer-decay scintillators, but the internal dead time may
have to be increased to prevent multiple triggering.
Figure 6.5 is a typical timing coincidence spectrum that
was obtained with a Nal(TI) detector and a KL236 fast
plastic scintillator. Figure 6.6 is a plot of time resolution
versus dynamic range for the timing system, with the
Nal(TI) detector mounted on an RCA 8575 PMT.
aniasBsi
1200 p
1000 f—
9S7S TUBES
OflTFC 265 BASES
y X V KL238 SCINTILLATORS
Mco
■173A Cf OlSC. tCF mil Nai MOOES)
1t1 2:1
5:1 10:1 20:1
QYNAMIC RANGE
SO:t 100:1
Fig. 6.4. Plot of Time Resolution vs Dynamic Range Using
RCA 8575 Photomultlpller Tube.
SOCo
Start: KL236 (1 xl), RCA 8575 PMT
Stop: Nal (1x1), RCA 8575 PMT
50:1 Dynamic Range
FWHM 892 05
FWTM 1.82 n5
9.7 ps per channel
Fig. 6.S. Typical Timing Spectrum Over a Wide Dynamic
Range (50:1) with Nal(TI).
6.3. TIMING WITH LARGE Ge(Li) DETECTORS
Figure 6.7 is a block diagram of another gamma-gamma
coincidence system. In this system the start channel uses
a fast scintillator and the stop channel employs a large
coaxial Ge(Li) detector. A typical timing spectrum for a
narrow dynamic range (1.1:1) is shown in Fig. 6.8 for both
the C.F. and S.R.T. modes of operation. A similar spec
trum for a wider dynamic range (10:1) is shown in Fig. 6.9.
Note that the S.R.T. mode is more effective for timing with
a wider dynamic range of signals. The S.R.T. mode can

11
-1-
r i
I I
RESOLUTION w DYNAMIC RANGE FOR ^Co
N«l - PLASTIC
START: KL236 {1" X 1") SCINT STOR: 1" X I" Nal (BICRON)
8S75 TUBE (-2200 V| 8575 TUBE (-2200 V)
473A (CF and SCINT 2 (Nai) 473A (OF and SCINT 2 (Nail MOOES)
^00£SJ (DIRECT FROM ANOOE)
FWTM
(Extra polatid)
(Extripoiattd)
SI 10:1 20:1
DYNAMIC RANGE (Both Sidt Channels)
-J--L
SOtt
100:1
Fig. 6.6. Plot o( Tlm« Resolution vs Dynamic Range Using
Nal(TI) and RCA 6575 PMT.
provide dramatic improvements in timing resolution be
low FW(1/10)M and makes reliable timing data possible
at even the FW(1/100)M level. Typical timing resolution
data for various ORTEC Ge(Li) coaxial detectors are
listed in Table 6.1.
The S.R.T, mode provides improved timing signals that
result from input signals with excessively slow rise times.
Table 6.1. Timing Resolution for Various Sizes of Ge(U)
Coaxial Detectors Using '^Na and the
System of Fig. 6.7.
8,6%
52.6 cc
VipiO
OyrMmic
RaiMH
C.F.
Mode
S.R.T. Mode
FWHM
(ns)
FW(1/10)M
(ns)
FWHM
(n«)
FWn/10)M
(ns)
rwli/tMIM
(rts)
1.1 :1
4.4
10.1
4.3
10.1
21.6
10:1
4,2
13.6
4.2
10.5 23.4
20:1 4.7
13 5 4,7
12.8
30.4
1.1 :1
5.0
10.0
5.0
9.5
17.6
10:1
4.5
13.2 4.4
9.4
17.8
20:1
5 1
14.3
5.0
12.0
24.8
1 .1 :1
7.9 16.4
8.1 16.0
27.3
10:1
8.4
24 0
7.9
17.0 30.0
20:1
8.4
26.0 8.4
23.0
40.0
Such input signals are generally associated with detector
events in a weak field region. These events can represent
valid energy data, and rejection of their respective timing
signals corresponds to a reduction of detector efficiency.
Since the 473A mode is front-panel-selectable, the ex
perimenter can select either S.R.T. for the best timing
resolution or C.F. for timing without loss of efficiency.
A plot of the percent loss of 511-keV peak counts from
'Na for the S.R.T. mode, compared to the C.F. mode, is
shown in Fig. 6.10 as a function of the 473A threshold and
the detector size.
ORTEC
473A
CONSTANT
fraction
DISCRIMI
NATOR
• bv 1
ORTEC
456
ORTEC
265
PM BASE
RCA
8575
PM TUBE
HV POWER
SUPPLY
Anode
y
/
*
Na Source
ORTEC
VlpiO
Ge(Li)
DETECTOR
ORTEC
INTEGRAL
PREAMP
ORTEC
459
DETECTOR
BIAS SUPPLY
ORTEC
416A
GATE
AND DELAY
GENERATOR
ORTEC
TIMING SCA
ORTEC
472A
SPECTROS-
copy
AMPLIFIER
ORTEC
457
Stop
ORTEC
425A
ORTEC
473A
CONSTANT
ORTEC
454
PULSE HEIGHT
CONVERTER
nanosecond
DELAY
FRACTION
DISCRIMI
NATOR
TIMING
FILTER
AMPLIFIER
loon '
ORTEC
52406
multi
channel
analyzer
Fig. 6.7. Gamma-Gamma Colnddence System Using Plastic
Scintlllator and a Large Ge(LI) Coaxial Detector.

13
7. CALIBRATION
7.1. EQUIPMENT REQUIRED
The following test equipment, or equal, is required to
calibrate the 473A circuits:
1. ORTEC 401A/402A Bin and Power Supply
2. Hewlett-Packard 8004A Pulse Generator
3. Tektronix 485 Oscilloscope
4. Tektronix 10X Probe
5. Tektronix 50 Ohm Step Attenuator
6. Tektronix CT-3 Time Pickoff
7. EH 971-5 Rise Time Integrator
8. Fluke 8000A Digital Multimeter
9. ORTEC 425A Delay
10. ORTEC 457 Biased Time to Pulse Height Converter
11. ORTEC 448 Research Pulser
2. ORTEC 454 Timing Filter Amplifier
13. ORTEC 276 Photomultiplier Tube Base and Pream
plifier
7.2. PRELIMINARY PROCEDURE
Install the 473A in the Bin and Power Supply and turn on
the power. Allow the instrument to warm up for at least ten
minutes before calibrating any of its circuits.
7.3. LEADING-EDGE DISCRIMINATOR TEST
1. Set up the system as shown in Fig. 7.1.
2. Monitor test point TPS at the base of OlO with a dc
voltmeter. Adjust R32 as necessary to read -1.23 V at TPS.
3. Turn front panel Disc Level control fully counter
clockwise to its minimum reading of 50 dial divisions, for
50 mV.
4. Turn ULLE Adjust, R66, fully clockwise.
5. Monitor IC4(14) with the 10X oscilloscope probe.
6. Adjust R66 counterclockwise until the amplitude at
IC4(14) IS about 650 mV.
Turn HP8004A amplitude switch to 2.5 V.
HPIOMA
R«#R«tt - 1K(CW)
PulM Width - JOnifCCW)
PulM Oei, . O(CCW)
Amplitudi - 5 y
Amp. Vtrmtr - CW
Pulse Polenty • Ne^.
DC Offset ■> Qff
Thru Stq. In ' ^
Output
Tl
CT
TIME P
K
3
CKOFF
Output
r
TE
SO
ATTEN
X2 X5
K
JATOR
X10
Ext. Trigger
TEK 485
SCOPE
SO ohm '
ISO ohm)
TEK 10X Probe
473A
Shapmq Mode - Scint 2 I NaO
Disc. Mode - L.E.
Oisc Level - 0.050 V ICCWI
Neq. Output
Pos. Output
MOTE Allcjljle!if«SOi;coj« IRG/SSI unl«i oiherm.se ipetilnd.
Fig. 7.1. Test Setup for Leading-Edge Discriminator
Mode Calibration.
8. Turn LLLE Adjust, R65, fully clockwise.
9. Monitor IC2(15) with the 10X oscilloscope probe.
10. Adjust R65 counterclockwise carefully until the
signal at 102(15) reaches about 800 mV.
11. Turn HP8004A amplitude switch to 5 V.
12. Monitor one of the negative output BNC connectors
with the oscilloscope.
13. Adjust R66 carefully until the 473A output starts to
appear.
14. Repeat steps 7 through 10.
7.4. SCINTILLATION 1 MODE WALK TEST
1. Set up the system as shown in Fig. 7.2.
2. Use X2X5 on the attenuator.

14
HP 8004A
Rep Rate
Pulte Width
Pulu Ot4.
Amplitude
Amp. Vernier
Pulse Polarity - Nei.
OC Offset - Off
IK (CW)
lOnslCCW)
0(CCWI
5 V
CW
Trigger Output
Output
Thru Si|. In ' t
TEK
CT3
TIME PtCKOFF
10%
Pick-OH
425A
OELAV
31 ns
TEK
50!>
ATTENUATOR
r
473A
Sbapiftq Mo
dt •
Scini 1
Disc. Mo4« C.F.
Oitc. Levtl
O.OSOV(CCW)
Scop
457
TIME to PULSE HEIGHT
CONVERTER
Ran^t
- .05
CG - to
Mulli
- 1
FC - (Adjust)
Bill
- (Adjust)
Gata - Anti
Strobf
- Int.
NOTE: All cables are SQllcoaa <RG/S8) unless othervMse specified.
ros. Output
n Met)
TEK.48S
SCOPE
Ext. Trifper
Fig. 7.2. Test Setup for Scintillation 1
Mode Walk Test.
3. Adjust the 457 Bias so that the 457 output pulse
amplitude is about 5 V on the oscilloscope.
4. Set the vertical gain of the oscilloscope at 1 V per
division.
adjust R32 to reduce it. Repeat steps 8 and 9. If R32 cannot
be adjusted to satisfy both conditions, replace the
MC10116 integrated circuit. IC1.
5. Adjust the 457 Fine Gain and Bias controls until a
change in delay of 1 ns corresponds to a 1-V (1-division)
change in the 457 output.
7.5. SCINTILLATION 2 (Nal) MODE
WALK TEST
1. Set up the system as shown in Fig. 7.3. Adjust the HP
8004A output pulse width to 25 ns.
scop
scop
6. Set the oscilloscope vertical gain at 0.2 V/division.
2. Use X2X5 on the attenuator.
8.
while
7. Adjust the 457 Fine Gain and Bias controls until a
change in delay of 1 ns corresponds to a 5-division
change in the 457 output: this calibrates the system for
200 ps/major division on the oscilloscope.
3. Adjust the 457 Bias so its output pulse shows about
6 V of amplitude as seen on the oscilloscope.
4. Set the vertical gain of the oscilloscope for 1 V per
division.
8. Change the attenuator in the following sequence
while observing the oscilloscope: X5X10, X10, XI.
9. Adjust R32 as necessary so that the 457 output
amplitude changes no more than 400 ps (2 divisions) for
the attenuator changes in step 8.
5. Adjust the 457 Bias and Fine Gain until a change of 1
ns corresponds to a 1 V (1-division) change on the
oscilloscope.
6. Change the oscilloscope vertical gain to 0.5 V per
division.
10. Set the attenuator at X2X5X10 and observe the peak
spread of the 457 output. If the spread exceeds 400 ps,
7. Adjust the 457 Fine Gain and Bias until a 1-ns change
corresponds to a change of 2 divisions on the oscillo-
9.
ampj
the a
1.
atter
into
3.
is ab

15
HP 8004A
R<0 Rati
Puts* Wi4tP
PuHa Oal.
Ampltcudc
Amp. Vtrnicr - cvv
Puls* Potantv - Mag.
OC Offset - Off
- 1K(CWI
' lOns(Adiust)
- O(CCW)
- sv
Thru Si|. In > f
Output
Triggtr Output
T
C7
TIME R
EK
3
CKOFF
r
EH-5
m RISE TIME
INTEGRATOR
r
TE
50
ATTENU
K
ATOR
10%
Pick-OH
OELAV
Slop
457
TIME 10 PUISE HEIGHT
CONVERTER
Rongo
- .05
CG
- 10
Muiti
- I
FG
* (Adjust)
8<as
- (Adjust)
Gait
- Anil
StroAt
- Int.
Ros. Output
RG/62
; 100
•173A
Shram] Mode - SCINT 2 INill
Disc. Uotfa - C.F.
Oisc. Laval - 0 OSO V (CCW)
TEK. 485
SCOPE
Eat. TriMtr
lot
:he
NOTE All crain irt 5012 Cora IHG/5JI imlKi oihotwiu igociM.
Fig. 7.3. Test Setup for Scintillation 2 (Nal)
Mode Walk Test.
HP
>ut
)er
f 1
he
er j
scope. This calibrates the system for 500 ps/major oscillo
scope division.
8. Change the attenuator in the following sequence
while observing the oscilloscope: X5X10, X10, XI.
9. Adjust R32 as necessary so that the 457 output
amplitude changes no more than 1000 ps (2 divisions) for
the attenuator changes in step 8.
7.6. Ge(U) MODE WALK TEST
1. Set up the system as shown in Fig. 7.4, With the
attenuator set at XI. adjust the attenuator output for 5 V
into 50n.
2. Set the attenuator at X2X5.
3. Adjust the 457 Bias so that the 457 output amplitude
is about 5 V on the oscilloscope.
4. Set the vertical gain of the oscilloscope at 0.5
V/division.
5. Adjust the 457 Bias and Fine Gam until a change of 4
ns corresponds to a change of 1 V (2 divisions) on the
oscilloscope. This calibrates the system so that one major
division on the oscilloscope is equal to 2 ns.
6. Change the attenuator in the following sequence
while observing the oscilloscope: X2X5. X5X10 X2X10
X10, X5. XI.
7. Adjust R32 as necessary so that the output amplitude
from the 457 changes no more than 4 ns (2 divisions) for
the attenuator changes in step 6.
8. If multipulsing occurs when the attenuator is set at
XI in step 6. turn the 473A front panel Disc-Level control
to about 200 dial divisions, for 200 mV; the multipulsing
should disappear.

16
QflTEC448
Pul$# Ht. - (Adjoft)
Normtlizt ' (Adjust)
Ral»Y ~ (3m
Puls#/$ - 100
Risa Tim# ~ 50
Tim# Const. Oacay - 50
Po)arity ~ Pos.
Anan. ^ (Adjun)
Triggar
RG/62
Output
ORTEC 276
Prtamp
RG/62
0RTEC454
CG-5to10
F6 - (Adjust)
Int. * to
Oiff. - 20
Pos
1 f Pos. Ext. Triggtf
-5V. t^ssMns
Thru Sig.
CT-3
'
TEK SO OHM
STEP
ATTENUATOR
Ga^Li)
050 V (CCW)
SCOPE
Pos. Out
ORTEC457
Rfif. . 0.1
CG
- 2
Multi - 1
F6
- (Adjust)
Bin - (Adjust)
G«»
- Anti.
StrotM Int.
NOTE: All cablts ar« 50 ohm coax (RG/SS) unlass othanMtsa sptdfiad.
Fig. 7.4. Test Setup for Ge(Li) Mode Walk Test.
7.7. FACTORY REPAIR
This instrument can be returned to the ORTEC factory for
service and repair at a nominal cost. Our standard
procedure for repair ensures that the same quality control
and checkout are used that would be used for a new
instrument. Always contact Customer Services at
ORTEC, [phone], before sending in an instrument
for repair to obtain shipping instructions and so that the
required Return Authorization Number can be assigned
to the unit. This number should be written on the address
label and on the package to ensure prompt attention
when the shipment reaches the factory.

17
BIBLIOGRAPHY
THEORY OF CONSTANT FRACTION
OF PULSE HEIGHT DISCRIMINATORS
1. D. A, Gedcke and W. J. McDonald, "A Constant Frac
tion of Pulse Height Trigger for Optimum Time Resolu
tion," Nucl. Instrum. Methods 55, 377 (1967).
2. D. A, Gedcke and W, J, McDonald, "Design of the
Constant Fraction of Pulse Height Trigger for Optimum
Time Resolution," Nucl. Instrum. Methods 58, 253 (1968).
3. W. J. McDonald and D. A. Gedcke, "Electronics for
Fast Neutron Work," International Symposium on Nu
clear Electronics, Versailles. September 1968. Vol. 1,
p. 56,
TIMING WITH Ge(Li) DETECTORS
4. R, L. Chase, "Pulse Timing System for Use with
Gamma Rays on Ge(Li) Detectors," Rev. Sci. Instrum.
39(9), 1318 (1968).
5. R. L, Graham, I, K. MacKenzie, and G,T. Ewan,
"Timing Characteristics of Large Coaxial Ge(Li) Detec
tors for Coincidence Experiments," IEEE Trans. Nucl.
Sci. NS-13{1), 72 (1966).
TIMING WITH SILICON DETECTORS
6. A. Alberigi Ouaranta, "On the Information Available
from the Rise-Time of the Charge Pulse Supplied by a
Semiconductor Particle Detector," Nucl. Instrum. Methods
35, 93 (1965).
7. M. Moszynski and B, Bengtson, "Plasma Delay and
Plasma Time Jitter in Subnanosecond Timing with Sur
face Barrier Detectors," Nucl. Instrum. Methods 91, 73
(1971).