EG&G ORTEC 575A Service manual

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Mode! 575A
Ampl ifier
Operating and Service Manual
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Printed in U.S.A.
Model 575A
Ampl ifier
Operating and Service Manual
This manual applies to instruments marked
"Rev 03" on rear panel
EG&G ORTEC Part Number 717460 3152 1 .OC 0189

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CONTENTS
Page
WARRANTY \
PHOTOGRAPHS
VI
1. DESCRIPTION 1
1.1. General 1
1.2. Pole-Zero Cancellation 1
1.3. Active Filter 3
2. SPECIFICATIONS 4
2.1. Performance 4
2.2. Controls 4
2.3. Input ! ! ! . 4
2.4. Outputs 4
2.5. Related Equipment 4
2.6. Electrical and Mechanical 4
3. INSTALLATION 5
3.1. General ' 5
3.2. Connection to Power 5
3.3. Connection to Preamplifier 5
3.4. Connection of Test Pulse Generator 5
3.5. Shaping Considerations 5
3.6. Linear Output Connections and Terminating Considerations 6
3.7. Shorting or Overloading the Amplifier Output 6
4. OPERATION 7
4.1. Initial Testing and Observation of Pulse Waveforms 7
4.2. Front Panel Controls 7
4.3. Panel Connectors 7
4.4. Standard Setup Procedure 8
4.5. Pole-Zero Adjustment 8
4.6. Operation with Semiconductor Detectors 9
4.7. Operation in Spectroscopy Systems 11
4.8. Other Experiments 13
5. CIRCUIT DESCRIPTION 15
6. MAINTENANCE 16
6.1. Test Equipment Required 16
6.2. Pulser Test 16
6.3. Suggestions for Troubleshooting 17
6.4. Factory Repair 17
6.5. Tabulated Test Point Voltages 17
Schematic 700000

Iv
ILLUSTRATIONS
Page
Fig. 1.1. Differentiation in an Amplifier Without Pole-Zero Cancellation 2
Fig. 1.2. Differentiation in a Pole-Zero Cancelled Amplifier 2
Fig. 1.3. Pulse Shapes for Good Signal-to-Noise Ratios 3
Fig. 4.1. Typical Unipolar and Bipolar Output Waveforms '
Fig. 4.2. Settings for Time-Constant Jumpers '
Fig. 4.3. Typical Waveforms Illustrating Pole-Zero Adjustment Effects °
Fig. 4.4. A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope 9
Fig. 4.5. Pole-Zero Adjustment Using a Square Wave Input to the Preamplifier 9
Fig. 4.6. System for Measuring Amplifier and Detector Noise Resolution 10
Fig. 4.7. Noise as a Function of Bias Voltage
Fig. 4.8. System for Measuring Resolution with a Pulse Height Analyzer 11
Fig. 4.9. System for Detector Current and Voltage Measurements 11
Fig. 4.10. Silicon Detector Back Current vs Bias Voltage 11
Fig. 4.11. System for High-Resolution Alpha-Particle Spectroscopy 12
Fig. 4.12. System for High-Resolution Gamma Spectroscopy 12
Fig. 4.13. Scintillation-Counter Gamma Spectroscopy System 12
Fig. 4.14. High-Resolution X-Ray Energy Analysis System Using a Proportional Counter 13
Fig. 4.15. Gamma-Ray Charged-Particle Coincidence Experiment 13
Fig. 4.16. Gamma-Ray Pair Spectrometry
Fig. 4.17. Gamma-Gamma Coincidence Experiment l^
Fig. 5.1. Amplifier Block Diagram
Fig. 6.1. Circuit Used to Measure Nonlinearity 16

standard Warranty
for
EG&G ORTEC Nuclear Electronic 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 ORTEO's exclusive liability is limited to repairing or replacing at EG&G ORTEO's option, items found by EG&G
ORTEC to be defective in workmanship or materials within two years from the date of delivery, EG&G ORTEO'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 pur
chase order, EG&G ORTEO's exclusive liability and buyer's exclusive remedy shall be release of the buyer from the obliga
tion 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 nuclear electronic 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 warrany 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, by telephone [[phone]] or by telex (55-7450) of the nature of the fault of the instrument being re
turned 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. (In the case where the instrument did not function upon pur
chase, EG&G ORTEC will pay shipment costs both ways.) 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.

i

EG&G ORTEC MODEL 575A AMPLIFIER
1. DESCRIPTION
1.1. GENERAL
The EG&G ORTEC 575A Amplifier is a single-width NIM
module that features a versatile combination of jumper-
selectable pulse-shaping characteristics. The amplifier
has extremely low noise, a wide gain range, and excellent
overload response for universal application in high-
resolution spectroscopy. It accepts input pulses of either
polarity. Input may originate from germanium or silicon
semiconductor detectors, from scintillation counters with
either fast or slow scintillators, from proportional count
ers, from pulsed ionization chambers, from electron
multipliers, etc.
The unit has an input impedance of ~1000 O and accepts
either positive or negative input pulses with rise times
<650 ns and fall times >30 /js. Three integration and
differentiation time constants are jumper-selectable on
the printed wiring board (PWB) to provide optimum shap
ing for resolution and count rate. The differentiation net
work has variable pole-zero cancellation that can be
adjusted to match preamplifiers with decay times >30 /js.
The pole-zero cancellation drastically reduces the under
shoot after the differentiator and greatly improves over
load 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.
The amplifier has unipolar and bipolar BNC outputs. The
unipolar output is used for spectroscopy in systems
where dc coupling can be maintained from the 575A to the
analyzer. A BLR (baseline restorer) circuit is included in
the unit for improved performance at all count rates.
Baseline correction is applied only during intervals be
tween input pulses and automatically selects a discrimi
nator level to identify input pulses. The unipolar output dc
level is within the range of -5 mV to +5 mV. This output
permits the use of the direct-coupled input of the analyzer
with a minimum amount of interface problems.
The 575A can be used for constant-fraction timing when
operated in conjunction with an EG&G ORTEC 551, 552,
or 553 Timing Single-Channel Analyzer. The EG&G
ORTEC Timing Single-Channel Analyzers feature a mini
mum of walk as a function of pulse amplitude and incor
porate a variable delay time on the output pulse to enable
the timing pickoff output to be placed in time coincidence
with other signals.
The 575A has complete provisions, including power dis
tribution, for operating any EG&G ORTEC solid-state
preamplifier. Normally, the preamplifier pulses should
have a rise time of 0.25 /js or less to properly match the
amplifier filter network and a decay time >30/us for proper
pole-zero cancellation. The input impedance is 1000 Q.
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 —0.2 Q, and the output can be connected to
other equipment by a single cable going to all equipment.
The cable must be shunt-terminated at the far end. (See
Section 3 for further information.)
1.2. POLE-ZERO CANCELLATION
Pole-zero cancellation is a method for eliminating pulse
undershoot after the differentiating network. In an am
plifier not using pole-zero cancellation (Fig. 1.1) the ex
ponential tail on the preamplifier output signal (usually
50 to 500/ys) causes an undershoot whose peak amplitude
is roughly determined from;
undershoot amplitude
differentiated pulse amplitude
_ differentiation time
preamplifier pulse decay time. '
For a 1-/7S differentiation time and a 50-/js pulse decay
time the maximum undershoot is 2%, and this decays with
a 50-/JS time constant. Under overload conditions this
undershoot is often sufficiently large to saturate the am
plifier 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 capabilities of the
preamplifier) or compensating for the undershoot by
providing pole-zero cancellation.
Pole-zero cancellation is accomplished by the network
shown in Fig. 1.2. The pole [s + (1/To)] due to the pream
plifier pulse decay time is cancelled by the zero of the
network [s + (k/R2Ci)]. 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 re
quires that the preamplifier output pulse decay time be
a single exponential decay and be matched to the pole-
zero cancellation network. The variable pole-zero cancel
lation network allows accurate cancellation for all pream
plifiers having 30-/js or greater decay times. Improper
matching of the pole-zero network will degrade the over
load performance and cause excessive pileup distortion
at medium counting rates. Improper matching causes
either an undercompensation (undershoot is not elimi
nated) or an overcompensation (output after the main
pulse does not return to the baseline but decays to the
baseline with the preamplifier time constant). The pole-

eo(t)
. (t)
Undershoot
. cir«t Differentiated
outpS '"'* X differentiate =
network rirshoot
1 s
X : = Ei(s) (Laplace transform).
■max 1
s + -^ s + „ -
To R|Ci
200409
To - r,
■To e-^^To _ T", g-t/To =e, where F, = RiC, .
Fig. 1.1. Differentiation in an Amplifier Without Pole-Zero Cancellation.
0 </<■<!
®oW = fmax "
No Undershoot
Pole-zero Differentiated
Charge loop y cancelled , pulse
output ^ differentiate without
network undershoot
Pole zero cancel by letting
1 K
s + — = s + ■
To RjCi
fmax ■
1 ^ ^ R C
^max T" * ' , 'p = fi (iF (Laplace transform).
1 KI + n2
S+ — 5+-
To R1 R: Ci
200410
S +
cmax cmax _ ^ , „ R, R,
"5—TH— 1 - 11 (s), where Rn = „ „
Ri +R2 J ^ Ri + R2
R1 R2 Cj RpCj
Fig. 1.2. Differentiation in a Pole-Zero Cancelled Amplifier.

zero adjust is accessible on the front panel of the 575A
and can easily be adjusted by observing the baseline on
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 differen
tiation and n equal RC integrations where n approaches
infinity. The Laplace transform of this transfer function is
G(s)
1
s-F(1/RG) [s+(1/RC)]"
(n - 0C),
where the first factor is the single differentiation, and the
second factor is the n integrations. The active filter ap
proximates 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 this is impractical to achieve
with normal electronic circuitry and would be difficult to
measure with an ADC. The true gaussian shape deteri
orates 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 EG&G ORTEG active filter network in the 575A
provides a fourth waveform in Fig. 1.3; this waveform has
characteristics superior to the n = 2 gaussian approxi
mation, yet obtains them with two complex poles and a
real pole. 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.
Relative
Noise
GAUSSIAN
< + ii/Hci ij + n/Rcir
GAUSSIAN APPROXIMATION
FOR n - 2
J + I1/RCI li + l1/RC)l'
ACTIVE FILTER
[s + (1/RC)
Is + (3/RC)) Is + (1 - kj)/RCl Is + {1 + ki)/RC|
i = . k = 0.8
Fig. 1.3. Pulse Shapes for Good Signal-to-Noise Ratios.

2. SPECIFICATIONS
2.1. PERFORMANCE
GAIN RANGE Continuously adjustable from 5 to 1250.
PULSE SHAPE Semigaussian on all ranges witti peak
ing time equal to 2.2t, 50% pulse width equal to 3.3r, and
pulse width at 0.1% level equal to 4.0 times the peaking
time. Bipolar crossover = 1.5t.
INTEGRAL NONLINEARITY <±0.05% for 1.5-fjis shap
ing time.
NOISE <5 //V rms referred to the input using 3 /js uni
polar shaping; <7 /iV using 1.5/iS shaping; both for a gain
>100.
TEMPERATURE INSTABILITY
Gain <±0.0075%/° 0, 0 to 50° C.
Do Level <±30 a(V/° G, 0 to 50° 0.
WALK <±5 ns at 0.5 /js shaping for 50:1 dynamic range,
including contribution of an EG&G ORTEC 551 or 552
Constant-Fraction Timing Single-Channel Analyzer.
OVERLOAD RECOVERY Recovers to within 2% of rated
output from X300 overload in 2.5 nonoverload pulse
widths using maximum gain for unipolar output. Same
recovery from X500 overload for bipolar.
RESTORER Gated active baseline stabilizer with auto
matic threshold circuit to provide the threshold level as a
function of signal noise to the baseline restorer discrimi
nator.
SPECTRUM BROADENING* Typically <10% FWHM for
a ®°Co 1.33-MeV gamma line at 85% of full scale for an
incoming count rate of 1 to 50k cps. Unipolar output,
1.5 fjs shaping.
SPECTRUM SHIFT*
Peak position shifts typically
<0.02% for a Co 1.33-MeV gamma line at 85% of full
scale (measured at the unipolar output, 1.5/iS shaping,
1 to 50k cps).
2.2. CONTROLS
FINE GAIN Ten-turn precision potentiometer with
graduated dial for continuously variable direct-reading
gain factor of X2.5 to XI 2.5.
COARSE GAIN Six-position switch selects feedback
resistors for gain factors of 2, 4, 10, 20, 40, and 100.
SHAPING TIME Three-position printed wiring board
(PWB) jumpers, easily accessible through side panel,
select time constants for active pulse-shaping filter net
work of 0.5, 1.5, or 3 /us.
POS/NEG Toggle switch selects either Pos or Neg input
pulse polarity.
PZ ADJ Screwdriver adjustable potentiometer to set the
pole-zero cancellation to compensate input decay times
from 30 /us to =«=.
2.3. INPUT
INPUT BNC (UG-1094A/U) front and rear panel con
nectors accept either positive or negative pulses with rise
times of 10 to 650 ns and decay times of 30/us to =; Zm =
1000 C1 dc-coupled; linear maximum 2 V; absolute maxi
mum 20 V.
2.4. OUTPUTS
UNI Front panel BNC connector with Zo < 1 G and rear
panel connector with Zo = 93 Q. Short-circuit proof; full-
scale linear range of 0 to +10 V; active filter shaped; dc-
restored with dc level adjustable to ±25 mV.
Bl Front panel BNC connector with Zo < 1 G and rear
panel connector with Zo = 93 G. Short-circuit proof;
positive lobe leading and full-scale linear range of 0 to
+10 V; active filter shaped.
PREAMP POWER Rear panel standard EG&G ORTEC
power connector (Amphenol 17-10090) mates with cap
tive and noncaptive power cords on all EG&G ORTEC
preamplifiers.
2.5. RELATED EQUIPMENT
The EG&G ORTEC 575A Amplifier accepts linear pulses
from, and furnishes power to, any standard EG&G ORTEC
preamplifier or equivalent. Its output pulses may be used
for linear signal analysis, using any of the EG&G ORTEC
modular instruments and multichannel analyzers.
2.6. ELECTRICAL AND MECHANICAL
POWER REQUIRED +24 V, 55 mA; - 24 V, 40 mA; +12 V,
70 mA; -12 V, 75 mA.
WEIGHT
Net 1.5 kg (3.3 lb).
Shipping 3.1 kg (7.0 lb).
DIMENSIONS Standard single-width NIM module
3.43 X 22.13 cm (1.35 x 8.714 in.) per TID-20893 (Rev).
'These count rate specifications were measured with a 10%
HPGe detector. Detectors with a large number of slow, rise-time
signals will most likely give poorer results.

3. INSTALLATION
3.1. GENERAL
The 575A operates on power that must be furnished from
a NIM-standard bin and power supply such as the EG&G
ORTEC 4001A/4002A 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 venti
lation to prevent any localized heating of the components
used inthe575A. 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 575A contains no internal power supply and must
obtain the necessary dc operating power from the bin and
power supply in which it is installed foroperation. Always
turn off power for the power supply before inserting or
removing any modules. After all modules have been in
stalled in the bin and any preamplifiers have also been
connected to the Preamp Power connectors on the am
plifiers, check the dc voltage levels from the power supply
to see that they are not overloaded. The EG&G ORTEC
4001A/4002A Series Bins and Power Supplies have con
venient 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 575A
through the Input BNC connectors on the front and rear
panels. The input impedance is —1000 Q and is de
coupled to ground: therefore, the preamplifier output
must be either ac-coupled or have approximately zero
dc voltage under no-signal conditions.
The 575A incorporates pole-zero cancellation to enhance
the overload and count rate characteristics of the ampli
fier. This technique requires matching the network to the
preamplifier decay-time constant to achieve perfect com
pensation. 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 adjust
ment see Section 4.5. An alternate method is accom
plished easily by using a monoenergetic source and
observing the amplifier baseline with an oscilloscope
after each pulse under ~X2 overload conditions. Adjust
ment should be made so that the pulse returns to the base
line in a minimum amount of time with no undershoot.
Preamplifier power at +24 V, —24 V, +12 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 re
quirements for the unit at the module position in the bin.
When the 575A is used with a remotely located pream
plifier (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 575A input is matched.
Because the input impedance of the 575A is —1000 Q,
sending-end termination will normally be preferred; the
transmission line should be series-terminated at the pre
amplifier output. All EG&G ORTEC preamplifiers contain
series terminations that are either 930 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 con
nection of a test pulse generator (such as the EG&G
ORTEC 419 Precision Pulse Generator or equivalent)
depends primarily on two considerations; the preampli
fier must be properly connected to the unit 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 575A Since the input of the 575A
has 1000-Q 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 because the 575A input is dc
coupled. The EG&G ORTEC test pulse generators are
designed for direct connection. When any one of these
units is used, it should be terminated with a 100-Q termi
nator 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 CAN
CELLATION When a tail pulser Is connected directly to
the amplifier input, the PZ ADJ should be adjusted if over
load tests are to be made (other tests are not affected).
See Section 4.5 for the pole-zero adjustment. If a pream
plifier is used and a tail pulser is connected to the pre
amplifier test input, similar precautions are necessary.
In this case the effect of the pulser decay must be re
moved; that is, a step input should be simulated.
3.5. SHAPING CONSIDERATIONS
The shaping time constant on the 575A is selectable by
PWB-mounted jumpers in steps of 0.5, 1.5, and 3/js. 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 reason
able choice (for Nal, a shaping time constant is
about optimum). For gas proportional counters, the col
lection time is normally in the 0.5 to 5 fjs range and a
1.5 /iS or greater time constant selection will generally
give optimum resolution. For surface barrier semicon
ductor detectors, a 0.5- to 2-fjs resolving time will gen
erally provide optimum resolution. Shaping time for
Ge(Li) detectors will vary from 1.5 to 6^s, depending on
the size, configuration, and collection time of the specific
detector and preamplifier. When a charge-sensitive pre
amplifier 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. The 575A has almost constant gain
for all shaping modes; therefore, the optimum shaping
can be determined by measuring the output noise with a
voltmeter as each shaping time constant is selected.
3.6. LINEAR OUTPUT CONNECTIONS AND
TERMINATING CONSIDERATIONS
Since the 575A unipolar output is normally used forspec-
troscopy, the unit is designed with the flexibility to inter
face the pulse with an analyzer. A gated baseline restorer
(BLR) circuit is included in this output for improved per
formance at all count rates. The threshold for the restorer
gate is determined automatically, according to the input
noise level. The unipolar output dc level is 0 ± 5 mV.
Three general methods of termination are used. The sim
plest 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 re
ceiving 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.
To use shunt termination at the receiving end of the cable,
connect the output from the 575A front or rear panels
through 93-0 cable to the input of the receiving instru
ment. Then use a BNC tee connector to attach both the
interconnecting cable and a 100-0 terminator at the input
connector of the receiving instrument. Since the input
impedance of the receiving instrument is normally 1000 O
or more, the effective instrument input impedance with
the 100-0 terminator will be of the order of 93 0, and this
will match the cable impedance correctly.
For customer convenience, EG&G ORTEG 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 OUTPUT
The 575A output is dc-coupled with an output impedance
of —0.2 O. 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 ICQ Q, the maximum count
rate consistent with linear output is
125 000 cps
Ratemax —— X
where Vo is the peak output pulse amplitude in volts (V)
and T is the shaping time in fjs.

4. OPERATION
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 sftows typical output waveforms.
4.2. FRONT PANEL CONTROLS
GAIN A Coarse Gain switch and a Gain control (a pre
cision 10-turn locking potentiometer) select and precisely
adjust the gain factor for the amplification in the 575A.
Switch settings are X2, 4, 10, 20, 40, and 100. Con
tinuous fine gain range is from X0.5 to XI 2.5 using mark
ings of 500 through 1250 dial divisions.
Using these controls collectively, the gain can be set at
any level from X5 through XI250.
POS/NEG A toggle switch selects an input circuit which
accepts either polarity of pulses from the preamplifier.
PZ ADJ A screwdriver control sets the pole-zero can
cellation to match the preamplifier pulse decay charac
teristics. The range is from 30 /js to =.
SHAPING PWB jumpers, easily accessed through the
side panel, select equal integration and differentiation
time constants to shape the input pulses. Settings are
0.5, 1.5, and 3 fjs. Illustrated drawings and instructions
for setting time-constant jumpers are shown in Fig. 4,2.
\ ^
\
\
\
\
%
Shaping Time 1.5 /ua
Fig. 4.1. Typical Unipolar and Bipolar Output Waveforms.
4.3. PANEL CONNECTORS
INPUTS Accept input pulses to be shaped and/or am
plified by the 575A. Compatible characteristics; positive
or negative with rise time from 10 to 650 ns; decay time
>30 fjs for proper pole-zero cancellation; input linear
0
POSITION
JUMPERS VI THRU
V7 AS SHOWN
TO SELECT VARIOUS TIME CONSTANTS
O.SyS
I .5uS
3.0uS
O [o]
O
10 O! lojo
[olo
o
O
Ef.
W6
W5
0
PB
Q
Fig. 4.2. Settings for Time-Constant Jumpers.

amplitude range 0 to 2 V with a maximum limit of ±20 V.
Input impedance is —1000 O.
OUTPUTS
UNI Front panel BNC connector with Zo < 1 O and rear
panel connector with Zo - 93 O. Short-circuit proof; full-
scale linear range of 0 to +10 V; active filter shaped; dc-
restored with dc level adjustable to ±25 mV.
Bi Front panel BNC connector with Zo < 1 O and rear
panel connector with Zo = 93 Cl. Short-circuit proof;
positive lobe leading and full-scale linear range of 0 to
+10 V; active filter shaped.
PREAMP POWER Rear panel standard EG&G ORTEC
power connector (Amphenol 17-10090) mates with cap
tive and noncaptive power cords on all EG&G ORTEC
preamplifiers.
4.4. STANDARD SETUP PROCEDURE
a. Connect the detector, preamplifier, high-voltage
power supply, and preamplifier into a basic system and
connect the amplifier output to an oscilloscope. Connect
the preamplifier power cable to the Preamp connector on
the 575A rear panel. Turn on power in the bin and power
supply and allow the electronics of the system to warm up
and stabilize.
b. Set the 575A controls initially as follows:
Shaping
Coarse Gain
Fine Gain
Pos/Neg
1.5 fjs
10
5.00
Match input pulse polarity
c. Use a Co calibration source; place it about 25 cm
from the active face of the detector. The unipolar output
pulse from the 575A should be about 8 to 10 V using a pre
amplifier with a conversion gain (charge sensitivity) 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 —9 V.
4.5. 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 A GERMANIUM 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 pulse trailing edges
return to the baseline without overshoot or undershoot
(Fig. 4.3).
The oscilloscope used must be dc coupled and must not
contribute distortion in the observed waveforms. Oscillo
scopes such as Tektronix 453,454, 465, and 475 will over
load for a 10-V signal when the vertical sensitivity is <100
: - C
verc 3mp(
insat
3d
i
^ . I
Vdjus ted F 'rope riy
i
j
: Ur iderc omp ensal ed
J
%
r
Fig. 4.3. Typical Waveforms Illustrating Pole-Zero Adjustment
Effects; Oscilloscope Trigger, Internal Pos., ''°Co Source
with 1.33-MeV Peak Adjusted —9 V; Count Rate 3 kHz;
Shaping Time Constant 1.5 fjs.

FROM AMPLIFIER
OUTPUT IK
TO OSCILLOSCOPE
INPUT
AAAr-
D
X
HPA 2800
SCHOTTKY DIODES
OR FAST G* DIODES
Fig. 4.4. A Clamp Circuit that can be used to Prevent
Overloading the Oscilloscope Input.
mV/cm. To prevent overloading the oscilloscope, use the
clamp circuit shown in Fig. 4.4.
USING SQUARE WAVE THROUGH PREAMPLIFIER
TEST INPUT
A more precise pole-zero adjustment in the 575A 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 ~1 kHz. The ampli
fier 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. 4.5 to achieve
excellent pole-zero cancellation. Use the following pro
cedure:
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 575A controls as for normal operation; this
includes gain, shaping, and input polarity.
c. Connect the source of 1-kHz square waves through
an attenuator to the Test input of the preamplifier. Adjust
the attenuator so that the 575A output amplitude is ~9 V.
d. Observe the Unipolar output of the 575A with an oscil
loscope. Adjust the PZ ADJ control for proper response
according to Fig. 4.5. Use the clamp circuit in Fig. 4.4 to
prevent overloading the oscilloscope input.
4.6.
OPERATION WITH SEMICONDUCTOR
DETECTORS
CALIBRATION OF TEST PULSER An EG&G ORTEC
419 Precision Pulse Generator (or equivalent) is easily
calibrated so that the maximum pulse height dial reading
(1000 divisions) is equivalent to 10-MeV loss in a silicon
radiation detector. The procedure is as follows:
a. Connect the detector to be used to the spectrometer
system; that is, preamplifier, main amplifier, and biased
amplifier.
b. Allow excitation from a source of known energy (e.g.
alpha particles) to fall on the detector.
L
1
1
5
A. PZ Properly Adjusted; Slow Trigger to Separate Pulses.
1
/' f
I
1
5
jiF.y
9.
' • "y
B. Overcompensated.
1"
mmm
\
IJ
1
6
C. Undercompensated.
Fig. 4.5. Pole-Zero Adjustment Using a Square Vv
to the Preampiifier.
J

10
c. Adjust the amplifier gain and the bias level of the
biased amplifier to give a suitable output pulse.
d. Set the pulser Pulse Height control at the energy of
the alpha particles striking the detector (e.g., 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 reads
directly in MeV if the number of dial divisions is divided
by 100.
AMPLIFIER NOISE AND RESOLUTION MEASURE
MENTS As shown in Fig. 4.6, a preamplifier, amplifier,
pulse generator, oscilloscope, and wide-band rms volt
meter 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:
a. Measure the rms noise voltage (E,ms) 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-half-maximum (FWHM) resolution spread
due to amplifier noise is then
2.35 Erms Edial
N(FWHM) =
Co
where Ediai is the pulser dial reading in MeV, and 2.35 is the
factor for rms to FWHM. For average-responding volt
meters such as the Hewlett-Packard 400D, the measured
noise must be multiplied by 1.13 to calculate the rms
noise.
The resolution spread will depend on the total input
capacitance, because the capacitance degrades the sig-
nal-to-noise ratio much faster than the noise.
DETECTOR NOISE-RESOLUTION MEASUREMENTS
The measurement just described can be made with a
biased detector instead of the external capacitor that
EG&G
ORTEC
EG&G
ORTEC
LINEAR
AMPLIFIER
OSCILLO
SCOPE
PRE AMP
. DETECTOR
. OR
CAPACITOR
EG&G
ORTEC
PULSE
GENERATOR
VOLTMETER
would be used to simulate detector capacitance. The
resolution spread will be larger because the detector
contributes both noise and capacitance to the input. The
detector noise-resolution spread can be isolated from the
amplifier noise spread if the detector capacitance is
known, since
(Ndet)^ + (Nelec)' - (N,o,al)^
where Ntoiai is the total resolution spread, and Neiec is the
electronic resolution spread when the detector is re
placed by its equivalent capacitance.
The detector noise tends to increase with bias voltage,
while the detector capacitance decreases. The net
change in resolution spread will depend upon which
effect is dominant. Figure 4.7 shows curves of typical
noise-resolution spread versus bias voltage using data
from several EG&G ORTEC silicon surface-barrier semi
conductor radiation detectors.
A - EG4G ORTEC BA-030-007-300
B - EG&G ORTEC BA-025-050-100 —
0 - EG&G ORTEC BA-025-100-100
D - EG&G ORTEC BA-030-2PO-100
E - EG&G ORTEC SA-045-450-100
100159
50 75
Bias Voltagt
125
Fig. 4.6. System for Measuring Amplifier and Detector
Noise Resolution.
Fig. 4.7. Noise as a Function of Bias Voltage.
AMPLIFIER NOISE-RESOLUTION MEASUREMENTS
USING MCA Probably the most convenient method of
making resolution measurements is with a pulse height
analyzer, as shown by the setup illustrated in Fig. 4.8.
The electronic noise-resolution spread can be measured
directly with a pulse height analyzer and the mercury
pulser as follows:
a. Select the energy of interest with an EG&G ORTEC
419 Precision Pulse Generator. Set the amplifier and
biased amplifier gain and bias level controls so that the
energy is in a convenient channel of the analyzer.
b. Calibrate the analyzer in keV per channel, using the
pulser: full scale on the pulser dial is 10 MeV when cali
brated as described above.
c. Obtain the amplifier noise-resolution spread by
measuring the FWHM of the pulser peak in the spectrum.
The detector noise-resolution spread for a given detector
bias can be determined in the same manner by connect
ing a detector to the preamplifier input. The amplifier

11
DETECTOR
CAPACITOR
-|
I EG&G I
j ORTEC j
I GATED BIAS I
I AMPLIFIER I
L- J
EG&G
ORTEC
PULSE
GENERATOR
MULTI
CHANNEL
PULSE HEIGHT
ANALYZER
EG&G
ORTEC
PULSE
STRETCHER
EG&G
ORTEC
BIASED
AMPLIFIER
EG&G
ORTEC
LINEAR
AMPLIFIER
EG&G
ORTEC
Fig. 4.8. System for Measuring Resolution with a Pulse
Height Analyzer.
noise-resolution spread must be subtracted as described
in "Detector Noise-Resoiution Measurements." The de
tector noise will vary with detector size and bias condi
tions and possibly with ambient conditions.
CURRENT VOLTAGE MEASUREMENTS FOR Si AND
Ge DETECTORS The amplifier system is not directly
involved in semiconductor detector current voltage
measurements, but the amplifier serves to permit noise
monitoring during the setup. The detector noise meas
urement is a more sensitive method than a current
measurement of determining the maximum detector volt
age that should be used because the noise increases more
rapidly than the reverse current at the onset of detector
breakdown. Make this measurement in the absence of a
source.
Figure 4.9 shows the setup required for current voltage
measurements. An EG&G ORTEC 428 Bias Supply is
used as the voltage source. Bias voltage should be ap-
I MICRO
I AMMETER j
DETECTOR
BIAS SUPPLY
Currant Monitorino Jacks
EG&G
ORTEC
EG&G
ORTEC
RMS
VOLTMETER
LINEAR
AMPLIFIER
PREAMP
DETECTOR
Normal
Circuit
MICRO
AMMETER
/•
BYPASS
^ CAPACITOR
plied slowly and reduced when noise increases rapidly as
a function of applied bias. Figure 4.10 shows several
typical current voltage curves for EG&G ORTEC silicon
surface-barrier detectors.
When it is possible to float the microammeter at the detec
tor bias voltage, the method of detector current measure
ment shown by the dashed lines in Fig. 4.9 is preferable.
The detector is grounded as in normal operation, and the
microammeter is connected to the current monitoring
jack on the 428 detector bias supply.
A - EG&G ORTEC BA-030-007-300
B - EG&G ORTEC BA-025-050-100
0 - EG&G ORTEC BA-025-100-100
D - EG&G ORTEC BA-030-200-100
E - EG&G ORTEC BA-045-450-100
Fig. 4.9. System for Detector Current and Voltage
Measurements.
40 60
Bias Voltage
Fig. 4.10. Silicon Detector Back Current vs Bias Voltage.
4.7. OPERATION IN SPECTROSCOPY SYSTEMS
HIGH-RESOLUTION ALPH-PARTICLE SPECTROS
COPY SYSTEM The block diagram of a high-resolution
spectroscopy system for measuring natural alpha particle
radiation is shown in Fig. 4.11. Since natural alpha radi
ation occurs only above several MeV, an EG&G ORTEC
444 Biased Amplifier is used to suppress the unused por
tion of the spectrum; the same result can be obtained by
using digital suppression on the MCA in many cases.
Alpha-particle resolution is obtained in the following
manner:
a. Use appropriate amplifier gain and minimum biased
amplifier gain and bias level. Accumulate the alpha peak
in the MCA.
b. Slowly increase the bias level and biased amplifier
gain until the alpha peak is spread over 5 to 10 channels
and the minimum- to maximum-energy range desired
corresponds to the first and last channels of the MCA.
c. Calibrate the analyzer in keV per channel using the
pulserand the known energy of the alpha peak (see "Cali
bration of Test Pulser") or two known-energy alpha
peaks.
d. Calculate the resolution by measuring the number
of channels at the FWHM level in the peak and converting
this to keV.
HIGH-RESOLUTION GAMMA SPECTROSCOPY
SYSTEM A high-resolution gamma spectroscopy sys
tem block diagram is shown in Fig. 4.12. Although a
biased amplifier is not shown (an analyzer with more
channels being preferred), it can be used if the only ana
lyzer available has fewer channels and only higher ener
gies are of interest.

12
(—
DETECTOR
To Vacuum
Pump
—a
VACUUM CHAMBER
EG&G
ORTEC
ORTEC
ORTEC
GATED
PREAMP
BIASED
EG&G
ORTEC
DETECTOR
BIAS SUPPLY
EG&G
ORTEC
PULSE
GENERATOR
EG&G
ORTEC
MULTI
CHANNEL
PULSE HEIGHT
ANALYZER
OSCILLO
SCOPE
NOISE
METER
Fig. 4.11. System for High-Resolution Alpha-Particle Spectroscopy.
GERMANIUM DETECTOR
and CRYOSTAT
EG&G
ORTEC
EG&G
ORTEC
LINEAR
AMPLIFIER
EG&G
ORTEC
PULSE HEIGHT
ANALYZER
EG&G
ORTEC
PULSE
GENERATOR
EG&G
ORTEC
HIGH-
VOLTAGE
BIAS SUPPLY
OSCILLO
SCOPE
NOISE
METER
Fig. 4.12. System for High-Resolution Gamma Spectroscopy.
in Fig. 4.13. The amplifier shaping time constants should
be selected In the region of 0.5 to 1.5/iS for Nal or plastic
sclntillators. For scintillators having longer decay times,
longer time constants should be selected.
X-RAY SPECTROSCOPY USING PROPORTIONAL
COUNTERS Space charge effects In proportional
counters, operated at high gas amplification, tend to
degrade the resolution capabilities drastically at x-ray
energies, even at relatively low counting rates. By using a
high-gain, low-noise amplifying system and lower gas
amplification, these effects can be reduced and a con
siderable improvement in resolution can be obtained.
The block diagram in Fig. 4.14 shows a system of this type.
Analysis can be accomplished by simultaneous acquisi
tion of all data on a multichannel analyzer or counting a
region of interest In a single-channel analyzer window
with a counter and timer or counting ratemeter.
When a germanium detector that Is cooled by a liquid
nitrogen cryostat is used, it Is possible to obtain reso
lutions from about 1 keV FWHM up (depending on the
energy of the incident radiation and the size and quality
of the detector). Reasonable care Is required to obtain
such results. Some guidelines for obtaining optimum
resolution are:
a. Keep Interconnection capacitance between the de
tector and preamplifier to an absolute minimum (no long
cables).
b. Keep humidity low near the detector-preamplifier
junction.
c. Operate the amplifier with the shaping time that pro
vides the best signal-to-noise ratio.,
d. Operate at the highest allowable detector bias to
keep the Input capacitance low.
SCINTILLATION-COUNTER GAMMA SPECTROS
COPY SYSTEMS The EG&G ORTEC 575A can be used
in scintillation-counter spectroscopy systems as shown
EG&G
ORTEC
HIGH
VOLTAGE
POWER SUPPLY
SCINTILLATION
COUNTER
EG&G
ORTEC
PULSE
GENERATOR
EG&G ORTEC
EG&G
SCINTIL
ORTEC
MULTICHANNEL
LINEAR
PULSE HEIGHT
LATION
COUNTER
AMPLIFIER
ANALYZER
PREAMPLIFIER
Fig. 4.13. Scintitlation-Counter Gamma
Spectroscopy System.

13
To Counting Ratemeter
or Counter and Timer
PROPORTIONAL
COUNTER
EG&G
ORTEC
LINEAR
AMPLIFIER
PULSE
GENERATOR
EG&G
ORTEC
EG&G ORTEC
PRO
PORTIONAL
COUNTER
PREAMPLIFIER
EG&G
ORTEC
HIGH
VOLTAGE
POWER SUPPLY
EG&G
ORTEC
SINGLE
CHANNEL
ANALYZER
MULTICHANNEL
PULSE HEIGHT
ANALYZER
4.8. OTHER EXPERIMENTS
Block diagrams Illustrating how the 575A and other
EG&G ORTEC modules can be used for experimental
setups for various other applications are shown In Figs.
4.15, 4.16, and 4.17.
Fig. 4.14. High-Resolution X-Ray Energy Analysis System
Using a Proportional Counter.
Linear Output
to Multichannel
Analyzer
SILICON SURFACE
^ ^ BARRIER DETECTOR
Source
□ GERMANIUM
DETECTOR
EG&G
ORTEC
DELAY
AMPLIFIER
EG&G
ORTEC
TIMING
FILTER
AMPLIFIER
EG&G
ORTEC
LINEAR
AMPLIFIER
EG&G
ORTEC
FAST
COINCIDENCE
UNIT
EG&G
ORTEC
CFT
DISCRIMI
NATOR
PR 6 AMP
EG&G
ORTEC
EG&G
ORTEC
GATED
BIASED
AMPLIFIER
EG&G
ORTEC
GATE & DELAY
GENERATOR
EG&G
ORTEC
TIMING
SCA
EG&G
ORTEC
LINEAR
AMPLIFIER
PREAMP
Fig. 4.15. Gamma-Ray Charged-Partlcle Coincidence Experiment.

14
EG&G
ORTEC
SCINTIL
LATION
PREAMP
EG&G
ORTEC
LINEAR
amplifier
ORTEC
P.M.
TUBE
&
BASE
EG&G
ORTEC
CFT
DISCRIMI
NATOR
EG&G
ORTEC
GATE& DELAY
GENERATOR
GERMANIUM
DETECTOR
EG&G
ORTEC
Nai
EG&G
ORTEC
PREAMP
TIMING
FILTER
AMPLIFIER
EG&G
ORTEC
LINEAR
P.M.
1
AMPLIFIER
TUBE
BASE
EG&G
ORTEC
EG&G
ORTEC
EG&G
ORTEC
SCINTIL
LATION
TIMING
SCA
LINEAR
AMPLIFIER
200330a
PREAMP
EG&G
ORTEC
FAST
COINCIDENCE
UNIT
EG&G
ORTEC
DELAY
AMPLIFIER
I
EG&G
ORTEC
GATED
BIASED
AMPLIFIER
Linear Output
to Multichannel
Analyzer
Fig. 4.16. Gamma-Ray Pair Speclrometry.
ORTEC
ORTEC
SCINTIL
LATION
PREAMP
L NEAR
AMPLIFIER
TUBE
EG&G
ORTEC
TIMING
SCA
I I GERMANIUM
' ' ' DETECTOR
EG&G
ORTEC
200329 a
EG&G
ORTEC
CFT
DISCRIMI
EG&G
NATOR
ORTEC
GATE & DELAY
GENERATOR
EG&G
ORTEC
TIMING
FILTER
AMPLIFIER
EG&G
EG&G
ORTEC
GATED
BIASED
AMPLIFIER
COINCIDENCE
Linear Output to
Multichannel Analyzer
LINEAR
amplifier
EG&G
ORTEC
DELAY
AMPLIFIER
Fig. 4.17. Gamma-Gamma Coincidence Experiment.