ORTEC 572A Service manual

ORTEC
Model 572A
Spectroscopy Amplifier
Operating and Service Manual

Model 572A
Spectroscopy Amplifier
Operating and Service Manual
Printed in U.S.A. ORTEC® Part No. 785100 0901
Manual Revision B

STANDARD WARRANTY
for
PerkinElmer Instruments
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items found by PerkinElmer Instruments to be defective in workmanship or materials within one year from the date
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Ml
CONTENTS
STANDARD WARRANTY jj
SAFETY INSTRUCTIONS AND SYMBOLS iv
SAFETY WARNINGS AND CLEANING INSTRUCTIONS V
1. DESCRIPTION 1
1.1. GENERAL 1
1.2. POLE-ZERO CANCELLATION 1
1.3. ACTIVE FILTER 2
2. SPECIFICATIONS 4
2.1. PERFORMANCE 4
2.2. CONTROLS 5
2.3. INPUT 5
2.4. OUTPUTS 5
2.5. ELECTRICAL AND MECHANICAL 5
3. INSTALLATION 6
3.1. GENERAL ^ ^ 6
3.2. CONNECTION TO POWER ! . .'! !!."! !! 6
3.3. CONNECTION TO PREAMPLIFIER ! . ! . !! 6
3.4. CONNECTION OF TEST PULSE GENERATOR 6
3.5. SHAPING CONSIDERATIONS 7
3.6. LINEAR OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS 7
3.7. SHORTING OR OVERLOADING THE AMPLIFIER OUTPUTS 8
3.8. INHIBIT OUTPUT CONNECTION 8
3.9. BUSY OUTPUT CONNECTION 8
3.10. CRM OUTPUT CONNECTION 8
4. OPERATING INSTRUCTIONS 8
4.1. INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS 8
4.2. FRONT PANEL CONTROLS 8
4.3. FRONT PANEL CONNECTORS 9
4.4. REAR PANEL CONNECTORS 10
4.5. STANDARD SETUP PROCEDURE 10
4.6. POLE-ZERO ADJUSTMENT 10
4.7. BLR THRESHOLD ADJUSTMENT 11
4.8. OPERATION WITH SEMICONDUCTOR DETECTORS 12
4.9. OPERATION IN SPECTROSCOPY SYSTEMS 15
4.10. OTHER EXPERIMENTS 17
5. CIRCUIT DESCRIPTION 17
6. MAINTENANCE 20
6.1. TEST EQUIPMENT REQUIRED ! . ! ! !! !!! ! ! 20
6.2. PULSER TEST 20
6.3. SUGGESTIONS FOR TROUBLESHOOTING 22
6.4. FACTORY REPAIR 22
6.5. TABULATED TEST POINT VOLTAGES 22

IV
SAFETY INSTRUCTIONS AND SYMBOLS
This manual contains up to three levels of safety instructions that must be observed in order to avoid
personal injury and/or damage to equipment or other property. These are:
DANGER Indicates a hazard that could result in death or serious bodily harm if the safety instruction is
not observed.
WARNING indicates a hazard that could result in bodily harm if the safety instruction is not observed.
CAUTION Indicates a hazard that could result in property damage if the safety instruction is not
observed.
Please read all safety instructions carefully and make sure you understand them fully before attempting to
use this product.
In addition, the following symbol may appear on the product:
l\ ATTENTION - Refer to Manual
A
DANGER - High Voltage
Please read all safety instructions carefully and make sure you understand them fully before attempting to
use this product.

SAFETY WARNINGS AND CLEANING INSTRUCTIONS
DANGER Opening the cover of this instrument is likely to expose dangerous voltages. Disconnect the
instrument from all voltage sources while it is being opened.
WARNING Using this instrument in a manner not specified by the manufacturer may impair the
protection provided by the instrument.
Cleaning Instructions
To clean the instrument exterior:
• Unplug the instrument from the ac power supply.
• Remove loose dust on the outside of the instrument with a lint-free cloth.
• Remove remaining dirt with a lint-free cloth dampened in a general-purpose detergent and water
solution. Do not use abrasive cleaners.
CAUTION To prevent moisture inside of the instrument during external cleaning, use only enough liquid
to dampen the cloth or applicator.
Allow the instrument to dry completely before reconnecting it to the power source.

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ORTEC MODEL 572A
SPECTROSCOPY PILE-UP AMPLIFIER
1. DESCRIPTION
1.1. GENERAL
The ORTEC 572A Spectroscopy Amplifier and
Pile-Lip Rejector is a single-width NIM module with
a versatile combination of switch-selectable pulse-
shaping and output characteristics. It features
extremely low noise, wide gain range, and excellent
overload response for universal application in high-
resolution spectroscopy. It accepts input pulses of
either polarity that originate in germanium or silicon
semiconductor detectors, in scintillation counters
with either fast or slow scintillators, in proportional
counters, in pulsed ionization chambers, in electron
multipliers, etc.
The 572A has an input impedance of approximately
500Q and accepts either positive or negative input
pulses with rise times <650 ns and fall times >40
ps. Six integrate and differentiate time constants
are switch-selectable to provide optimum shaping
for resolution and count rate. The first differentiation
network has variable pole-zero cancellation that can
be adjusted to match preamplifiers with decay times
>40 ps. The pole-zero cancellation drastically
reduces the undershoot after the first differentiator
and greatly improves overload and count rate
characteristics. In addition, the amplifier contains an
active filter shaping network that optimizes the
signal-to-noise ratio and minimizes the overall
resolving time. Both unipolar and bipolar outputs
are provided simultaneously on the front and rear
panels.
The unipolar output should be used for
spectroscopy when dc coupling can be maintained,
from the 572A to the analyzer. A BLR (baseline
restorer) circuit is included in the 572A for improved
performance at all count rates. Baseline correction
is applied during intervals between input pulses only
and a front panel switch selects a discriminator
level to identify input pulses. The unipolar output dc
level can be adjusted in the range from -100 mV to
-rlOO mV. This output permits the use of the direct-
coupled input of the analyzer with a minimum
amount of interface problems. The 572A bipolar
output may be preferable for spectroscopy when
operating into an ac-coupled system at high
counting rates.
Internal pulse pileup (a second pulse arriving before
the first pulse has been completed) is sensed
internally. The 572A includes an Inhibit output BNC
connector on the rear panel that can be used to
inhibit measurement of the result of a pulse pileup
when it occurs.
The 572A can be used for constant-fraction timing
when operated in conjunction with an ORTEC 551
or 552 Timing Single-Channel Analyzer. The
ORTEC timing single-channel analyzers feature a
minimum of walk as a function of pulse amplitude
and incorporate a variable delay time on the output
pulse to enable the timing pickoff output to be
placed in time coincidence with other signals.
The 572A has complete provisions, including
power, for operating any ORTEC solid-state
preamplifier. Normally, the preamplifier pulses
should have a rise time of 0.25 ps or less to
properly match the amplifier filter network and a
decay time greater than 40 ps for proper pole-zero
cancellation. The 572A input impedance is 500Q.
When long preamplifier cables are used, the cables
can be terminated in series at the preamplifier end
or in shunt at the amplifier end with the proper
resistors. The output impedance is about 0.1 D at
the front panel connectors and 93Q at the rear
panel connectors. The front panel outputs can be
connected to other equipment by a single cable
going to all equipment and shunt terminated at the
far end of the cabling. If series termination is
desired, the rear panel connectors can be used to
connect the 572A to other modules. See Section 3
for further information.
1.2. POLE-ZERO CANCELLATION
Pole-zero cancellation is a method for eliminating
pulse undershoot after the first differentiating
network. In an amplifier not using pole-zero
cancellation (Fig. 1.1), the exponential tail on the
preamplifier output signal (usually 50 to 500 ps)
causes an undershoot whose peak amplitude is
roughly determined from:

undershoot amplitude ^
differentiated pulse amplitude
differentiation time
preamplifier pulse decay time
For a 1 -ps differentiation time constant and a 50-ps
preamplifier pulse decay time, the maximum
undershoot is 2% and this decays with a 50-ps time
constant. Under overload conditions, this
undershoot is often sufficiently large to saturate the
amplifier during a considerable portion of the
undershoot, causing excessive dead time. This
effect can be reduced by increasing the preamplifier
pulse decay time (which generally reduces the
counting rate capat)ilities of the preamplifier) or
compensating for the undershoot by using pole-zero
cancellation.
Pole-zero cancellation is accomplished by the
network shown in Fig. 1.2. The pole [s + (1/rJ] due
to the preamplifier pulse decay time is canceled by
the zero of the network [s + (K/RjC,)]. In effect, the
dc path across the differentiation capacitor adds an
attenuated replica of the preamplifier pulse to just
cancel the negative undershoot of the
differentiating network.
Total preamplifier-amplifier pole-zero cancellation
requires that the preamplifier output pulse decay
time be a single exponential decay and matched to
the pole-zero-cancellation network. The variable
pole-zero-cancellation network allows accurate
cancellation for all preamplifiers having 40-ps or
greater decay times. Improper matching of the
pole-zero-cancellation network will degrade the
overload performance and cause excessive pileup
distortion at medium counting rates. Improper
matching causes either an under-compensation
(undershoot is not eliminated) or an over-
compensation (output after the main pulse does not
return to the baseline and decays to the baseline
with the preamplifier time constant). The pole-zero
adjust is accessible from the front panel of the 572A
and can easily be adjusted by observing the
baseline with an oscilloscope with a monoenergetic
source or pulser having the same decay time as the
preamplifier under overload conditions. The
adjustment should be made so that the pulse
returns to the baseline in the minimum time with no
undershoot.
1.3. ACTIVE FILTER
When only FET gate current and drain thermal
noise are considered, the best signal-to-noise ratio
occurs when the two noise contributions are equal
for a given input pulse shape. The Gaussian pulse
shape (Fig. 1.3) for this condition requires an
amplifier with a single RC differentiate and n equal
RG integrates where n approaches infinity.
The Laplace transform of this transfer function is:
G{s) =
1
S + (1/RC) [s+(1//?C)f
(n - <»)
where the first factor is the single differentiate and
the second factor is the n integrates. The 572A
active filter approximates this transfer function.
Figure 1.3 illustrates the results of pulse shaping in
an amplifier. Of the four pulse shapes shown the
cusp would produce minimum noise but is
impractical to achieve with normal electronic
circuitry and would be difficult to measure with an
ADC. The true Gaussian shape deteriorates the
signal-to-noise ratio by only about 12% from that of
the cusp and produces a signal that is easy to
measure, but requires many sections of integration
(n - °°). With two sections of integration the
waveform identified as a Gaussian approximation
can be obtained, and this deteriorates the signal-to-
noise ratio by about 22%. The ORTEC active filter
network in the 572A Amplifier provides the fourth
waveform in Fig. 1.3; this waveform has
characteristics superior to the Gaussian
approximation, yet obtains them with four complex
poles. By this method the output pulse shape has a
good signal-to-noise ratio, is easy to measure, and
yet requires only a practical amount of electronic
circuitry to achieve the desired results.

9| (X)
Undershoot
rita^M* t^w*. Difforontiotod
Srt^ X dHlerontiatlon « poitm
^ network »Mth
undorehoot
fmax * GW=e,fr;.
1 s
X
^ 1 1
s 4 — f 4 —
^0 n,c,
£ifs) (Laplace tranjtomi).
To-T,
Fig. 1.1. Differentiation in an Amplifier Without Pole-Zero Cancellation.
To a'" " —T, b"^ '"=61 ((), where F, = R,Cv
0 KKK^
max
Bi/t)
No Undorohoot
Polo-zefO Differentiated
Charge loop „ cancellod _ pulse
output dlttercntlatlon iwithout
network undershoot
Pole zero cancel bv letting
1 K
S* s +
RtC, •
^max e'^TTa ^ Q^j .
K
1
-ma* * n—+ R ° £ I/s/. (Laplace transform).
i +'— I + —^ ^
Tq R I Rj C
£ma* £ma* ^ . . . „ RiRs
tteue: ' ttt: '
R,R:C, RpC.
fmax "Xllt).
Fig. 1.2. Differentiation in a Pole-Zero Canceled Amplifier.

Relative
Noise
j + n/Rci
1.12
li + II/RCtI"
GAUSSIAN APPROXIMATION
FOR/i • 2
1.22
1 * (l/RCI
U + 11/RC)I'
ACTIVE FILTER
^1.17
Is + (1/HC)J
1
|i + (3/RC)] (s + (1 - l(j)/RC) |s + (1 + kj)/RCl
I ' y/~^. k =0.8
Fig. 1.3. Pulse Shapes for Good Signal-to-Noise Ratios.
2. SPECIFICATIONS
2.1. PERFORMANCE
GAIN RANGE Continuously adjustable from X1
through XI500.
PULSE SHAPING Gaussian on all ranges with
peaking time equal to 2.2i and pulse width at 0.1%
level equal to 2.9 times the peaking time.
INTEGRAL NONLINEARITY <0.05% (0.025%
typical) using 2 ps shaping.
NOISE <8 pV referred to the input (5 pV typical)
using 2 ps shaping and gain 2100.
TEMPERATURE INSTABILITY
Gain <0.0075%/°C, 0 to 50°G.
DC Level <±50 pV/°C, 0 to 50°C.
CROSSOVER WALK <±3 ns for 50:1 dynamic
range, including contribution of ORTEC 551 or 552
Constant-Fraction Timing Single-Channel Analyzer
using 50% fraction and 0.5 ps shaping.
COUNT RATE STABILITY The 1.33 MeV gamma
ray peak from a ®°Co source, positioned at 85% of
analyzer range, typically shifts <0.024%, and its
FWHM broadens <16% when its incoming count
rate changes from 0 to 100000 counts/s using 2 ps
shaping. The amplifier will hold the baseline
reference up to count rates in excess of 150000
counts/s.
OVERLOADRECOVERY Recovers to within 2%
of rated output from X300 overload in 2.5
nonoverloaded unipolar pulse widths, using
maximum gain; same recovery from XI000
overload for bipolar pulses.

2.2. CONTROLS
GAIN Ten-turn precision potentiometer for
continuously variable direct-reading gain factor of
X0.5toX1.5.
COARSE GAIN Six-position selector switch selects
feedback resistors for gain factors of 20, 50, 100,
200, 500, and 1 K.
INPUT ATTENUATOR Jumper on printed circuit
board selects an input attenuation factor of 1 orl 0
(gain factor of XI or X0.1).
POS/NEG Toggle switch selects input circuit for
either polarity of input pulses from the preamplifier.
SHAPING TIME Six-position switch selects time
constant for active filter network pulse shaping;
selections are 0.5, 1, 2, 3, 6, and 10 ps.
PZ ADJ Potentiometer to adjust pole-zero
cancellation for decay times from 40 ps to «>.
Factory preset at 50 ps to match normal
characteristics of ORTEC preamplifiers.
BLR Toggle switch selects a source for the gated
baseline restorer discriminator threshold level from
one of three positions.
• Auto The BLR threshold is automatically set to
an optimum level as a function of the signal
noise level by an intemal circuit. This allows
easy setup and very good performance under
most conditions.
• PZ Adj The BLR threshold is determined by the
threshold potentiometer. The BLR time constant
is greatly increased to facilitate PZ adjustment.
This position may give the lowest noise for
conditions of low count rate and/or longer
shaping times.
• Threshold The BLR threshold is set manually by
the threshold potentiometer. Range is 0 to 300
mV referred to the positive output signal. The
BLR time constant is the same as for the Auto
switch setting.
DC Screwdriver potentiometer adjusts the unipolar
output baseline dc level; range, +100 mV to
-100 mV.
2.3. INPUT
INPUT Type BNC front and rear panel connectors
accept either positive or negative pulses with rise
times in the range from 10 to 650 ns and decay
times from 40 to 2000 ps; Zi„ ~500Q, dc coupled;
linear maximum, 1 V (10V with attenuator jumper
set at X0.1); absolute maximum, 20 V.
2.4. OUTPUTS
UNI Unipolar front panel BNC with Z^, <1Q and
rear panel BNC with = 93Q. Short-circuit proof;
prompt; full-scale linear range 0 to +10 V; active
filter shaped and dc restored; dc level adjustable to
±100 mV.
Bi Bipolar front panel BNC with Z^ <10Q and rear
panel BNC with Z^ = 93Q. Short-circuit proof;
prompt output with positive lobe leading and linear
range of ±10V; active filter shaped.
BUSY Rear panel BNC vi/ith Zj^ <10Q provides a
+5 V logic pulse for the duration that the input pulse
exceeds the baseline restorer discriminator level.
Connect to the ORTEC MCA Busy input for dead
time correction.
INH Inhibit rear panel BNC with Z|„ <10Q provides
a nominal +5 V logic signal when an internal pulse
pileup occurs: width ~6t in coincidence with the
pileup; to be used for an MCA anticoincidence input
to prevent storage of pileup data in the spectrum.
CRM Count Ratemeter rear panel BNC furnishes
a nominal +5 V logic signal for every linear input
pulse; width, 300 ns; to be used as an input to a
ratemeter or counter.
PREAMP POWER Rear panel standard ORTEC
power connector; Amphenol 17-10090; mates with
captive and non-captive power cords on all
standard ORTEC preamplifiers.
2.5. ELECTRICAL AND MECHANICAL
POWER REQUIRED (not including any load on
the Preamp Power connector)
+24 V, 100 mA; -24 V, 105 mA;
+12 V, 85 mA;-12 V, 50 mA.
FRONT PANEL DIMENSIONS NIM-standard
single-width module (1.35 by 8.714 in.) per TID-
20893.

3. INSTALLATION
3.1. GENERAL
The 572A operates on powerthat must be furnished
from a NIM-standard bin and power supply such as
the ORTEC 4001/4002 Series. The bin and power
supply is designed for relay rack mounting. If the
equipment is to be rack mounted, be sure that there
is adequate ventilation to prevent any localized
heating of the components that are used in the
572A. The temperature of equipment mounted in
racks can easily exceed the maximum limit of 50°C
unless precautions are taken.
3.2. CONNECTION TO POWER
The 572A contains no internal power supply and
must obtain the necessary dc operating power from
the bin and power supply in which it is installed for
operation. Always turn off power for the power
supply before inserting or removing any modules.
After all modules have been installed in the bin and
any preamplifiers have also been connected to the
Preamp Power connectors on the amplifiers, check
the dc voltage levels from the power supply to see
that they are not overloaded. The ORTEC
4001/4002 Series Bins and Power Supplies have
convenient test points on the power supply control
panel to permit monitoring these dc levels. If any
one or more of the dc levels indicates an overload,
some of the modules will need to be moved to
another bin to achieve operation.
3.3. CONNECTION TO PREAMPLIFIER
The preamplifier output signal is connected to the
572A through the appropriate Input BNC connector
on the front or rear panel. The input impedance is
about 500Q and is dc-coupled to ground; therefore
the preamplifier output must be either ac-coupled or
have approximately zero dc voltage under no-signal
conditions.
The 572A incorporates pole-zero cancellation in
order to enhance the overload and count rate
characteristics of the amplifier. This technique
requires matching the network to the preamplifier
decay time constant in order to achieve perfect
compensation. The pole-zero adjustment should be
set each time the preamplifier or the shaping time
constant of the amplifier is changed. For details of
the pole-zero adjustment see Section 4.6. An
alternate method is accomplished easily by using a
monoenergetic source and observing the amplifier
baseline with an oscilloscope after each pulse under
approximately X2 overload conditions. Adjustment
should be made so that the pulse returns to the
baseline in a minimum amount of time with no
undershoot.
Preamplifier power at -t-24 V, -24 V, -ft 2 V, and
-12 V is available through the Preamp Power
connector on the rear panel. When the preamplifier
is connected, its power requirements are obtained
from the same bin and power supply as is used for
the amplifier, and this increases the dc loading on
each voltage level over and above the
requirements for the 572A at the module position in
the bin.
When the 572A is used with a remotely located
preamplifier (i.e., preamplifier-to-amplifier
connection through 25 ft or more of coaxial cable),
be careful to ensure that the characteristic
impedance of the transmission line from the
preamplifier output to the 572A input is matched.
Since the input impedance of the 572A is about
500Q, sending-end termination will normally be
preferred; the transmission line should be series-
terminated at the preamplifier output. All ORTEC
preamplifiers contain series terminations that are
either 93Q or variable; coaxial cable type RG-62/U
or RG-71/U is recommended.
3.4. CONNECTION OF TEST PULSE
GENERATOR
THROUGH A PREAMPLIFIER The satisfactory
connection of a test pulse generator such as the
ORTEC 419 Precision Pulse Generator or
equivalent depends primarily on two considerations;
the preamplifier must be properly connected to the
572A as discussed in Section 3.3, and the proper
input signal simulation must be applied to the
preamplifier. To ensure proper input signal
simulation, refer to the instruction manual for the
particular preamplifier being used.
DIRECTLY INTO THE 572A Since the input of
the 572A has 500Q of input impedance, the test
pulse generator will normally have to be terminated
at the amplifier input with an additional shunt
resistor. In addition, if the test pulse generator has
a dc offset, a large series isolating capacitor is also
required since the 572A input is dc coupled. The
ORTEC test pulse generators are designed for
direct connection. When any one of these units is

used, it should be terminated with a 100Q
terminator at the amplifier input or be used with at
least one of the output attenuators set at In. (The
small error due to the finite input impedance of the
amplifier can normally be neglected.)
SPECIAL CONSIDERATIONS FOR POLE-ZERO
CANCELLATION When a tail pulser is connected
directly to the amplifier input, the PZ Adj should be
adjusted if overload tests are to be made (other
tests are not affected). See Section 4.6 for the pole-
zero adjustment. If a preamplifier is used and a tail
pulser is connected to the preamplifier test input,
similar precautions are necessary. In this case the
effect of the pulser decay must be removed; i.e., a
step input should be simulated.
3.5. SHAPING CONSIDERATIONS
The shaping time constant on the 572A is switch-
selectable in steps of 0.5, 1, 2, 3, 6, and 10 ps. The
choice of the proper shaping time constant is
generally a compromise between operating at a
shorter time constant for accommodation of high
counting rates and operating with a longer time
constant for a better signal-to-noise ratio. For
scintillation counters the energy resolution depends
largely on the scintillator and photomultiplier, and
therefore a shaping time constant of about four
times the decay-time constant of the scintillator is a
reasonable choice (for Nal, a 1-ps shaping time
constant is about optimum). For gas proportionaL
counters the collection time is normally in the 0.5 to
5 ps range and a 2 ps or greater time constant
selection will generally give optimum resolution. For
surface barrier semiconductor detectors, a 0.5 to 2
ps resolving time will generally provide optimum
resolution. Shaping time for Ge(Li) detectors will
vary from 1 to 6 ps, depending on the size,
configuration, and collection time of the specific
detectorand preamplifier. When a charge-sensitive
preamplifier is used, the optimum shaping time
constant to minimize the noise of a system can be
determined by measuring the output noise of the
system and dividing it by the system gain. Since the
572A has almost constant gain for all shaping
modes, the optimum shaping can be determined by
measuring the output noise of the 572A with a
voltmeter as each shaping time constant is
selected.
The 572A provides both unipolar, and bipolar
outputs. The unipolar output pulses should be used
in applications where the best signal-to-noise ratio
(resolution) is most important, such as high-
resolution spectroscopy using semiconductor
detectors. Use of the unipolar output with baseline
restoration will also give excellent resolution at high
counting rates. The bipolar output should be used in
high count rate systems when the analyzer system
is ac-coupled and noise, or resolution, is a
secondary consideration.
3.6. LINEAR OUTPUT CONNECTIONS
AND TERMINATING CONSIDERATIONS
Since the 572A unipolar output is normally used for
spectroscopy the 572A is designed with a great
amount of flexibility in order for the pulse to be
interfaced with an analyzer. A gated baseline
restorer (BLR) circuit is included in this output for
improved performance at all count rates. A switch
on the front panel permits the threshold for the
restorer gate to be determined automatically,
according to the input noise level, or manually, with
a screwdriver adjustment. The switch also has a
center PZ Adj setting that can be used to eliminate
the BLR effect when making pole-zero adjustments.
The unipolar output dc level can be adjusted from
-0.1 to +0.1 V to set the zero intercept on the
analyzer when direct coupling is used. The bipolar
output, with a 0 to 10 V range, can be used for
crossover timing or may be preferred for
spectroscopy when operating into ac-coupled
systems at high counting rates. Typical system
block diagrams for a variety of experiments are
described in Section 4.
Three general methods of termination are used.
The simplest of these is shunt termination at the
receiving end of the cable. A second method is
series termination at the sending end. The third is a
combination of series and shunt termination, where
the cable impedance is matched both in series at
the sending end and in shunt at the receiving end.
The combination is most effective, but this reduces
the amount of signal strength at the receiving end
to 50% of that which is available in the sending
instrument.
T0 use shunt termination at the receiving end of the
cable, connect the <1Q output of the 572A (on the
front panel) through 93Q cable to the. input of the
receiving instrument. Then use a BNC tee
connector to attach both the interconnecting cable
and a 1 GOD terminator at the input connector of the
receiving instrument. Since the input impedance of
the receiving instrument is normally 1GOOQ or more,
the effective instrument input impedance with the

10OQ terminator will be of tfie order of 93Q and this
matches the cable impedance correctly.
For series termination use the 93Q output of the
572A for the cable connection. Use 93Q cable to
interconnect this into the input of the receiving
instrument. The 1000Q (or more) normal input
impedance at the input connector represents an
essentially open circuit, and the series impedance
in the 572A now provides the proper termination for
the cable.
For the combination of series and shunt
termination, use the 93Q output on the rear panel of
the 572A and use 93Q cable. At the input for the
receiving instrument use a BNC tee to attach both
the signal cable and a 100Q resistive terminator.
Note that the signal span at the receiving end of
this type of circuit will always be reduced to 50% of
the signal span fumished by the sending
instrument.
For customer convenience, ORTEC stocks the
proper terminators and BNC tees, or they can be
ordered from a variety of commercial sources.
3.7. SHORTING OR OVERLOADING THE
AMPLIFIER OUTPUTS
All outputs of the 572A are dc-coupled with an
output impedance of about 0.1Q for the front panel
connectors and 93Q for the rear panel connectors.
If the output is shorted with a direct short circuit the
output stage will limit the peak current of the output
so that the amplifier will not be harmed. When the
amplifier is terminated with 100Q, the maximum
rate allowed to maintain the linear output is
[200000 cps/T(ps)] X [1077„,(V)].
3.8. INHIBIT OUTPUT CONNECTION
The Inhibit output on the rear panel is intended for
application at the anticoincidence input of the
Analyzer. An output pulse is generated through this
connector when a pulse pileup is sensed in the
572A, and the pulse can then be used to prevent
the Analyzer from measuring and storing a false
amplitude. The signal is dc-coupled and rises from
0 to about +5 V for a time equal to 6t, starting when
a pileup occurs.
3.9. BUSY OUTPUT CONNECTION
The signal through the rear panel Busy output
connector rises from 0 to about +5 V at the onset of
each linear input Pulse. Its width is equal to the
time the input pulse amplitude exceeds the BLR
discriminator level, and is extended automatically
by the generation of an Inhibit output signal. It can
be used to provide MCA live-time correction, to
control the generation of input pulses, to observe
normal operation with an oscilloscope, or for any of
a variety of other applications. Its use is optional
and no termination is required if the output is not
being used.
3.10. CRM OUTPUT CONNECTION
One NIM-standard positive logic pulse is generated
to correspond to each linear input pulse into the
572A. The pulses are available through the CRM
(Count Rate Meter) output BNC on the rear panel
and are intended for use in a count rate meter or
counter to monitor the true input count rate into the
amplifier. Its use is optional and no termination is
required if the output is not being used.
4. OPERATING INSTRUCTIONS
4.1. INITIAL TESTING AND OBSERVATION
OF PULSE WAVEFORMS
Refer to Section 6 for information on testing
performance and observing waveforms at front
panel test points. Figure 4.1 shows some typical
unipolar and bipolar output waveforms.
4.2. FRONT PANEL CONTROLS
GAIN A coarse Gain switch and a Gain 10-turn
locking precision potentiometer select and precisely
adjust the gain factor for the amplification in the
572A. Switch settings are X20, 50, 100, 200, 500,
and 1000. Continuous fine gain range is from X0.5
to XI.5, using markings of 500 through 1500 dial
divisions. An internal jumper setting provides one
additional gain factor selection of either XI.0 or

Sr aping
Shaping
Time 2 as
rmm&msa
Fig. 4.1. Typical Effects of Shaping-Time Selection on
Output Waveforms.
X0.1. Collectively the range of gain can be set at
any level from XI.0 through X1500, using all three
of these controls.
POS/NEG A toggle switch selects an input circuit
that accepts either polarity of pulses from the
preamplifier.
PZ ADJ A screwdriver control to set the pole-zero
cancellation to match the preamplifier pulse decay
characteristics. The range is from 40 ps to infinity.
DC A screwdriver control adjusts the dc baseline
level of the unipolar output in the range of -0.1 V to
H-0.1 V.
SHAPING A 6-position switch selects equal
integrate and differentiate time constants to shape
the input pulses. Settings are 0.5, 1, 2, 3, 6, and
10 ps.
BLR A 3-position toggle switch controls the
operation of the internal baseline restorer (BLR)
circuit. The center setting of the switch is effectively
Off, and this permits adjustment of the PZ Adj
control without interference from the BLR circuit.
The Auto setting of the switch selects a circuit that
regulates the threshold of the BLR gate according
to the output noise level. The Threshold setting
permits manual control of the BLR gate threshold
using the screwdriver control immediately below the
toggle switch.
4.3. FRONT PANEL CONNECTORS
INPUT Accepts input pulses to be shaped and/or
amplified by the 572A. Compatible characteristics;
positive or negative with rise time from 10 to 650
ns; decay time greater than 40 ps for proper pole-
zero cancellation; input linear amplitude range 0 to
10 V, with a maximum limit of ±20 V. Input
impedance is approximately 500Q.
UNI Provides a unipolar positive output with
characteristics that are related to input peak
amplitude, gain, shaping time constants, pole-zero
cancellation, and baseline stabilization. The dc
baseline level is adjustable for offset to ±0.1 V.
Output impedance through this connector is about
0. 1 Q, dc coupled. Linear range 0 to +10 V.
81 Provides a bipolar pulse with positive lobe
leading and with characteristics that are related to
input peak amplitude, gain, and shaping time
constants. Timing is prompt with respect to the
input. Crossover walk of this output is less than 3 ns
(see Specifications). Output impedance through this
connector is about 0.1Q. Linear range of 0 to ±10 V.

10
4.4. REAR PANEL CONNECTORS
IN Bridged with front panel input connector for
optional use as an alternate input connection
location.
INH Provides an output signal to identify a pulse
pileup in the 572A. Connect it to the
anticoincidence input of the multichannel analyzer
to inhibit measurement and storage of false
amplitudes.
UNI Provides a unipolar positive output with the
same characteristics as described for the front
panel Uni connector; the output impedance through
this connector is 93Q.
81 Provides a bipolar output with the same
characteristics as described for the front panel 81
connector; the output impedance through this
connector is 93Q.
CRM Provides a NIM-standard (a+5 V) slow
positive logic output for each linear input pulse. The
output can be connected into a ratemeter or counter
to monitor the true input count rate for the amplifier.
BUSY Provides a signal that rises to approximately
+5V for the time that the input pulse amplitude
exceeds the BLR discriminator level, which can be
controlled manually or automatically. The output
can be used to correct for live time in the ORTEC
MCA by connecting it to the MCA Busy input.
PREAMP Provides power connections from the bin
and power supply to the ORTEC preamplifier. The
dc levels include +24 V, -24 V, +12 V, and -12 V.
4.5. STANDARD SETUP PROCEDURE
a. Connect the detector, preamplifier, high voltage
power supply, and amplifier into a basic system and
connect the amplifier unipolar output to an
oscilloscope. Connect the preamplifier power cable
to the Preamp power connector on the rear panel of
the 572A. Turn on power in the Bin and Power
Supply and allow the electronics of the system to
warm up and stabilize.
b. Set the 572A controls initially as follows;
Shaping 2 ps
Coarse Gain 50
Gain 1.000
Internal Jumper XI.0
BLR
Thresh
Pos/Neg
PZ Adj
Fully clockwise
Match preamplifier
output polarity
c. Use a ®°Co calibration source, set about 25 cm
from the active face of the detector. The unipolar
output pulse from the 572A should be about 8 to
10 V, using a preamplifier with a conversion gain of
170 mV/MeV.
d. Readjust the Gain control so that the higher peak
from the ®°Co source (1.33 MeV) provides an
amplifier output at about 9 V.
4.6. POLE-ZERO ADJUSTMENT
The pole-zero adjustment is extremely critical for
good performance at high count rates. This
adjustment should be checked carefully for the best
possible results.
USING Ge(Li) SYSTEM AND «°Co
a. Adjust the radiation source count rate between
2 kHz and 10 kHz.
b. Observe the unipolar output with an oscilloscope.
Adjust the PZ Adj control so that the trailing edge of
the pulses returns to the baseline without overshoot
or undershoot (see Fig. 4.2).
The oscilloscope used must be dc-coupled and
must not contribute distortion in the observed
waveforms. Oscilloscopes such as Tektronix 453,
454, 465, and 475 will overload for a 10-V signal
when the vertical sensitivity is less than 100
mV/cm. To prevent overloading the oscilloscope,
use the clamp circuit shown in Fig. 4.3.
USING SQUARE WAVE THROUGH
PREAMPLIFIER TEST INPUT
A more precise pole-zero adjustment in the 572A
can be obtained by using a square wave signal as
the input to the preamplifier. Many oscilloscopes
include a calibration output on the front panel and
this is a good source of square wave signals at a
frequency of about 1 kHz. The amplifier
differentiates the signal from the preamplifier so
that it generates output signals of alternate
polarities on the leading and trailing edges of the
square wave input signal, and these can be
compared as shown in Fig. 4.4 to achieve excellent
pole-zero cancellation.

11
Ovefcompen50ted
Adjusted
Properly
FI^OM AMPLIFIER
OimvT IK
TO OSCILLOSCOPE
INPUT
^VW
U if derco m pen sated
Fig. 4.2. Typical Waveforms Illustrating Pole-Zero
Adjustment Effects; Oscilloscope Trigger, 572A Busy
Output: ^°Co Source with 1.33-MeV Peak Adjusted -9 V;
Count Rate, 3 kHz; Shaping Time Constant, 2 ps.
D
X
HPA2800
SCHOTTItY DtODES
OH FAST G» CHOOES
Fig. 4.3. A Clamp Circuit that Can Be Used to Prevent
Overloading the Oscilloscope Input.
Use the following procedure:
a. Remove ail radioactive sources from the vicinity
of the detector. Set up the system as for normal
operation, including detector bias.
b. Set the 572A controls as tor normal operation;
this includes gain, shaping, and input polarity.
0. Connect the source of 1-kHz square waves
through an attenuator to the Test input of the
preamplifier. Adjust the attenuator so that the 572A
output amplitude is about 9 V.
d. Observe the unipolar output of the 572A with an
oscilloscope, triggered from the 572A Busy output.
Adjust the PZ Adj control tor proper response
according to Fig. 4.4. Use the clamp circuit of
Fig. 4.3 to prevent overloading the oscilloscope
input.
Figure 4.4A shows the amplifier output as a series
of alternate positive and negative Gaussian pulses.
In the other three pictures of this figure the
oscilloscope was triggered to show both positive
and negative pulses simultaneously. These pictures
show more detail to aid in proper adjustment.
4.7. BLR THRESHOLD ADJUSTMENT
After the amplifier gain and shaping have been
selected and the PZ Adj control has been set to
operate properly for the particular shaping time, the
BLR Thresh control can be used to establish the
correct discriminator threshold for the baseline
restorer circuit. Normally, the toggle switch can be
set at Auto and the threshold level will be set
automatically just above the noise level. It desired,
the switch can be set at Threshold and the manual
control just below the switch can then be used to
select the level manually as follows:

12
' l l ' i *« ■ \" *1
??3fV>4S5bf^^S ■ ^
A. PZ Property AdjusleeJ; Slow Trigger to Separate Pulsee,
B. Overcompenaated; Fast Trigger to Superimpose Poises.
- .! •.;■?«« ■'- ■■: TJ
C. Property Adjusied; Pulses Superimposed.
O. Undcrcompensaled; Pulses Superimposed.
Fig. 4.4. Pole-Zero Adjustment Using a Square Wave Input to ttie Preamplifier.
a. Remove all radioactive sources from the vicinity
of the detector. Set up the system as for normal
operation, including detector bias.
b. Set the BLR switch at Threshold and turn the
control fully clockwise, for 300 mV.
c. Observe the unipolar output on the lOOmV/cm
scale of the oscilloscope, using 5 ps/cm horizontal
deflection. Trigger the oscilloscope with the Busy
output from the 572A.
d. Reduce the control setting until the baseline
discriminator begins to trigger on noise; this
corresponds to about 200 counts/s from the Busy
output. Adjust the trigger level according to the
information in Fig. 4.5.
If a ratemeter or counter-timer is available, it can be
connected to the Busy output and the threshold
level can then be adjusted for about 200 counts/s.
4.8. OPERATION WITH SEMICONDUCTOR
DETECTORS
CALIBRATION OF TEST PULSER An ORTEC
419 Precision Pulse Generator, or equivalent, is
easily calibrated so that the maximum pulse height
dial reading (1000 divisions) is equivalent to a
10-MeV loss in a silicon radiation detector. The
procedure is as follows:
a. Connect the detector to be used to the
spectrometer system, i.e., preamplifier, main
amplifier, and biased amplifier.
b. Allow excitation from a source of known energy
(for example, alpha particles) to fall on the detector.

13
A. S«1 to o High
aiL;:!r..h^.u^A„M:.Atf.V<-,.. .WA •iJiif^T.
mmi
B. Adlusteo Properly
C, Set too Low
d. Set the pulser Pulse Height control at the energy
of the alpha particles striking the detector (for
example, set the dial at 547 divisions for a
5.47-MeV alpha particle energy).
e. Turn on the pulser and use its Normalize control
and attenuators to set the output due to the pulser
for the same pulse height as the pulse obtained in
step c. Lock the Normalize control and do not move
it again until recalibration is required.
The pulser is now calibrated; the Pulse Height dial
read directly in MeV if the number of dial divisions
is divided by 100.
AMPLIFIER NOISE AND RESOLUTION
MEASUREMENTS As shown in Fig. 4.6, a
preamplifier, amplifier, pulse generator,
oscilloscope, and wide-band rms voltmeter such as
the Hewlett-Packard 3400A are required for this
measurement. Connect a suitable capacitor to the
input to simulate the detector capacitance desired.
To obtain the resolution spread due to amplifier
noise:
ORTEC
ORTEC
LINEAR
AMPLIFIER
OSCILLO
SCOPE
PREAMP
CAPACITOR
PULSE
GENERATOR
VOLTMETER
Fig. 4.6. System for Measuring Amplifier and Detector
Noise Resolution.
a. Measure the rms noise voltage (E„„s) at the
amplifier output.
b. Turn on the 419 Precision Pulse Generator and
adjust the pulser output to any convenient readable
voltage, Eo, as determined by the oscilloscope.
The full width at half maximum (FWHM) resolution
spread due to amplifier noise is then:
Fig. 4.5. BLR Threshold Variable Control Settings.
N{FWHM) =
2-35E^£,,„
c. Adjust the amplifier gain and the bias level of the
biased amplifier to give a suitable output pulse.
where E^iai is the pulser dial reading in MeV and
2.35 is the factor for rms to FWHM. For average-