Advanced Measurement Technology ORTEC A-576 A-PAD Service manual

Model A-576 A-PAD
Preamplifier, Amplifier, Discriminator
with Bias Supply
Operating and Service Manual
Printed in U.S.A. ORTEC Part No. 761930 0202
Manual Revision D

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a/k/a/ ORTEC , a subsidiary of AMETEK , Inc.
®®
WARRANTY
ORTEC* warrantsthat the items will be delivered free from defects in material or workmanship. ORTEC makes no
other warranties, express or implied, and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR
A PARTICULAR PURPOSE.
ORTEC’s exclusive liability is limited to repairing or replacing at ORTEC’s option, items found by ORTEC to be
defective in workmanship or materials within one year from the date of delivery. 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
agreement 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 ORTEC fails to manufacture or deliver items called for in this
agreement or purchase order, 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 ORTEC be liable for special or consequential
damages.
Quality Control
Before being approved for shipment, each ORTEC instrument must pass a stringent set of quality control
tests designed to expose any flaws in materials or workmanship. Permanent records of these tests are
maintained for use in warranty repair and as a source of statistical information for design improvements.
Repair Service
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, ORTEC must be
informed, either in writing, by telephone [[phone]] or by facsimile transmission [[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 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 designated 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 should follow the same procedure and
ORTEC will provide a quotation.
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 ORTEC of the circumstances so that assistance can be
provided in making damage claims and in providing replacement equipment, if necessary.
Copyright © 2002, Advanced Measurement Technology, Inc. All rights reserved.
*ORTEC is a registered trademark of Advanced Measurement Technology, Inc. All other trademarks used
®
herein are the property of their respective owners.

iii
CONTENTS
WARRANTY ........................................................................... ii
PHOTOGRAPH........................................................................ iv
1. DESCRIPTION...................................................................... 1
2. SPECIFICATIONS .................................................................. 2
2.1. PERFORMANCE ............................................................... 2
2.2. CONTROLS ................................................................... 2
2.3. INPUT ....................................................................... 2
2.4. OUTPUTS..................................................................... 2
2.5. ELECTRICALANDMECHANICAL .................................................. 3
3. INSTALLATION ..................................................................... 3
3.1. JUMPERSETTINGS............................................................. 3
3.2. CONNECTIONTODETECTOR .................................................... 4
3.3. CONNECTIONTOPOWER ....................................................... 4
3.4. OUTPUTCONNECTIONS ........................................................ 4
3.5. ENERGYOUTPUTFULL-SCALEADJUSTMENT ...................................... 4
4. OPERATION ....................................................................... 5
4.1. GENERAL..................................................................... 5
4.2. CONNECTINGADETECTOR ..................................................... 5
5. THEORYOFOPERATION ............................................................ 6
LIST OF FIGURES
Fig. 1. Block diagram of Alpha Spectrometer.................................................. 1
Fig.2. JumperLocationsforSettingPolarityonthePWB. ....................................... 3
Fig. 3. Side-Panel Test Pulser Selection. .................................................... 4
Fig.4. TypicalA-PADOutputWaveformswith5-MeVTestPulser. ................................ 5
Fig. 5. Detailed Block Diagram of the Model A-576 A-PAD. ...................................... 7

iv

1
Fig. 1. Block diagram of Alpha Spectrometer.
ORTEC MODEL A-576 A-PAD
Preamplifier, Amplifier, Discriminator with Bias Supply
1. DESCRIPTION
The ORTEC Model A-576 A-PAD is a single- wide The energy ranges controllable from the front panel
NIM module intended for performing alpha are 3 to 8 MeV, 4 to 7 MeV, 3 to 5 MeV, 4 to 6 MeV, 5
spectroscopy and counting when used in conjunction to 7 MeV, and 6 to 8 MeV. The internal test pulser can
with a silicon surface barrier detector. The instrument provide a signal at 5 MeV, 6 MeV, or 7 MeV by
includes a variable detector bias supply, a internal jumper selection.
preamplifier, a shaping and stretching amplifier, a
biased amplifier, a test pulser, and a discriminator In addition to the calibrated Energy output, the
(Fig. 1). The detector bias supply and the amplifier COUNT front-panel BNC connector provides a NIM-
have selectable polarity so that it can be ued with any standard positive logic pulse for gross alpha counting
charged-particle silicon semiconductor detector. and/or routing. The DET BIAS MONITOR front-panel
Examples are ORTEC's conventional and test points permit monitoring detector leakage current
Ruggedized
- Si surface barrier detectors and its ion- and detector bias voltage.
implanted Si detectors.

2
2. SPECIFICATIONS
2.1. PERFORMANCE ENERGY RANGE Six positions on the front-panel
switch for selecting the desired energy range (see
DETECTOR AND ELECTRONIC NOISE <25 keV PERFORMANCE).
FWHM when used with ORTEC R Series, 300 mm2
and 450 mm charged-particle detectors, and <35 keV E BIAS 15-turn potentiometer on the front panel
2
for 600 mm and 900 mm R Series charged-particle permits screwdriver adjustment of the energy output
22
detectors when connection of the Model A-576 to the bias point to be varied by ±10% for ease of setup with
detector is made with <2 ft of RG-62A/U cable. the data acquisition system.
System noise is dependent on detector capacitance
plus cable capacitance and leakage current. Electronic


E15-turn potentiometer on the front panel permits
noise is typically 5 keV with a slope of 25 eV/pF silicon screwdriver adjustment of the maximum energy output
equivalent (based on

= 3.6 eV and t = 0.5 µs range to be varied from 7.75 to 10.25 V for ease of
(internal amplifier). setup with the data acquisition system.
PULSE SHAPING Internal 0.5-µs active filter semi- TEST PULSER PWB jumper (J2) allows selection of
Gaussian pulse shaping amplifier provides a pulse that internal pulser energies of 5 MeV, 6 MeV, or 7 MeV.
is stretched prior to being output through the Bias
Amplifier to give a 4-µs-wide positive output pulse. INPUT/BIAS POLARITY PWB jumpers allow
ENERGY RANGES 3 TO 8 MeV, 4 to 7 MeV, 3 to 5 polarity. Negative for ORTEC Surface Barrier or Ion-
MeV, 4 to 6 MeV, 5 to 7 MeV, 6 to 8 MeV. Implanted Ruggedized detectors, or positive for
conventional detectors. (Shipped in Negative position.)
CALIBRATED TEST PULSER Equivalent Energy
5 MeV, 6 MeV, or 7 MeV. (Shipped at 5 MeV). Rate is
100 Hz. 2.3. INPUT
DETECTOR BIAS VOLTAGE Continuously variable PREAMP IN Front- and rear-panel BNCs accept an
over range of 0 to 100 V. Polarity selectable with input signal from semiconductor charged-particle
printed wiring board (PWB) jumper shipped in negative detectors. Either RG-62A/U or RG-71A/U cable is
position (appropriate for ORTEC R Series detectors). recommended to minimize excess capacitance and
Shipped set to 100 V. hence noise.
2.2. CONTROLS 2.4. OUTPUTS
TEST/BIAS/OFF Front-panel, three-position toggle ENERGY Front- and rear-panel BNC connectors
switch controls both the detector bias voltage and the provides a positive stretched pulse from 7.75 to
test pulser. Front-panel LED is illuminated when the 10.25 V maximum, depending on the setting of the

E
bias voltage is on. gain control corresponding to an energy range
DET BIAS ADJ Front-panel potentiometer for 4 µs; Z = 100
6
; dc-coupled.
controlling the bias voltage applied to the detector.
Continuously variable from 0 to ±100 V.
selection of either positive or negative detector voltage
selected on the front-panel switch. Pulse width =
0

3
Fig. 2. Jumper Locations for Setting Polarity on the PWB.
COUNT Front-panel BNC connector provides a NIM- 2.5. ELECTRICAL AND MECHANICAL
standard positive pulse for gross alpha counting or
routing. Pulse width 3.5 µs for any event with energy POWER REQUIRED +12 V, 90 mA; -12 V, 45 mA;
>2.5 MeV. Z = 50
6
; dc-coupled. +24 V, 100 mA; -24 V, 45 mA.
0
DET BIAS MONITOR Voltage can be monitored
between front-panel test point (labeled HV) and
ground. Detector current can be monitored across
resistor between front-panel test points DET and HV.
The current is 1 µA per volt when using a voltmeter
with 10-M
6
input impedance.
WEIGHT
Net 0.9 kg (2.0 lb).
Shipping 2.25 kg (5.0 lb).
DIMENSIONS NIM-standard single-width module
3.43 ×22.13 cm (1.35 ×8.714 in.) per TID-20893
(Rev).
3. INSTALLATION
3.1. JUMPER SETTINGS
Six plug-in jumpers on the printed circuit board (PWB)
must be set for compatible operation. These jumpers
are accessible when the side panel is removed from
the instrument chassis. Five of the jumpers are used
to select either positive or negative detector voltage
polarity and the corresponding correct amplifier
polarity. Negative bias is required for ORTEC
Ruggedized detectors; positive for conventional
surface-barrier or ion-implanted detectors. These five
internal jumpers need to be changed only when a
Ruggedized detector is replaced with one of the other
detectors or vice versa. The sixth jumper is used to
set the pulse generator equivalent energy (see TEST
PULSE).
POLARITY When polarity selection needs to be
changed:
"


" orientation for each of the jumpers is
a. Remove the A-PAD module from the bin and
power supply.
b. Remove the side panel from the right side of the
module as viewed from the front panel.
c. Note the locations of all five jumpers on the
components side of the PWB (Fig. 2). The "+" and
etched on the PWB.
d. Place all five of these jumpers at " 

" for a
Ruggedized detector, or at "+" for a conventional
surface barrier detector or silicon dioxide-
passivated, ion-implanted detector.

4
Fig. 3. Side-Panel Test Pulser Selection.
Damage may result to the preamplifier or the
detector unless the following precautions are
taken:
The TEST/BIAS/OFF switch must be in the OFF
position before connecting a low impedance or a
cable, capacitor, or other capacitive device to the
PREAMP IN connector on the A-PAD.
Turn the BIAS switch to OFF before making ANY
connections to the PREAMP IN connector and
before disconnecting the detector.
TEST PULSE The sixth jumper is used to set the 3.4. OUTPUT CONNECTIONS
equivalent energy of the test pulser to 5, 6, or 7 MeV.
Change this jumper only if an energy other than 5 MeV When an external BNC cable longer than 10 ft is used
is desired from the test pulser. The jumper can be for the output connection, the characteristic
changed through the hole in the side panel to an impedance of the cable should match the impedance
alternate position (Fig. 3). of the output used. The ENERGY output should use
3.2. CONNECTION TO DETECTOR and trigger on the COUNT output. The output
A direct connection with 93-
6
or 100-
6
shielded cable
should be made between the detector and the 3. Adjust the front-panel E control for 8-V output.
PREAMP IN connector on the A-PAD. For best Continue with operation of the A-576.
results, keep the length of this cable as short as
possible (due to the capacitive loading of the cable) to
minimize preamplifier noise and maintain the
preamplifier stability.
Type RG-62/U cable is recommended for the detector-
to preamplifier connection. This is 93-
6
cable with a
capacity of 13.5 pF/ft.
3.3. CONNECTION TO POWER
The A-PAD is designed for operation in a NIM-
standard bin and power supply such as the ORTEC
4001/4002/402 series. The power supply furnishes
operating power requirements at ±12 V and ±24 V.
These NIM bins have test points on the power supply
control panel to monitor the dc-voltage level.
93-
6
RG-62A/U cable, and the COUNT outputs
should be connected using 50-
6
RG-58A/U cable.
3.5. ENERGY OUTPUT FULL-SCALE
ADJUSTMENT (Other than 10 V)
The full-scale output from the ENERGY output is
normally set to 10 V, which matches the input range of
many multichannel analyzers (MCAs). The second
most common input range for MCAs is 8 V. The
procedure for 8-V full scale is as follows:
1. Set the TEST/BIAS/OFF switch to TEST. Set the
ENERGY RANGE switch to 3
& 5 MeV with the TEST
Pulser jumper set to 5 MeV. Note: Any Range can be
used when the TEST Pulser is set to the top of the
Range.
2. Observe the ENERGY output on an oscilloscope
amplitude should be about 10 V.
NOTICE

5
Fig. 4. Typical A-PAD Output Waveforms with 5-MeV Test Pulser.
4. OPERATION
4.1. GENERAL between 0 and 100 V. The bias voltage can be
The information in Section 3 includes all of the voltmeter. After turning ON, or adjusting, the bias
preliminary selections that are to be made for the A- voltage, wait for the preamplifier to settle; this takes
PAD. Operation consists of connecting a detector and about one minute.
proceeding with data collection.
4.2. CONNECTING A DETECTOR 5 V (shown in Fig. 4), if the Range is set to 4
&
6 MeV
Start with the TEST/BIAS/OFF switch in the OFF The COUNT output should have a positive logic pulse
position. Connecting the detector with the bias voltage with a 6-µs width (shown in Fig. 4).
ON may damage the FET transistor at the input of the
preamplifier or destroy the detector. 4. System electronic noise can be tested by
Then proceed as follows: the MCA from the ENERGY output.
1. With the bias OFF, connect the detector to the 5. The test pulser can then be turned OFF by moving
A-PAD with a short cable (preferably RG-62A/U). the TEST/BIAS/OFF switch to the BIAS position. The
2. Set the TEST/BIAS/OFF switch at TEST and adjust alpha spectrometry.
the front-panel HV control for the desired bias voltage
monitored on the front-panel test point jacks with a
3. The ENERGY output should display positive,
stretched pulses at a 100-Hz rate with an amplitude of
and the TEST pulser jumper is in the 5 MeV position.
measuring the FWHM spread of the pulser peak on
A-PAD is now ready to count alpha samples or do

6
5. THEORY OF OPERATION
The complete schematic for the A-576 A-PAD (No. amplitude for 5, 6, and 7 MeV to the input to the
752500) is included at the back of this manual. preamplifier. A screwdriver calibration, included on the
Fig. 5 is a block diagram of the electronics. PWB for factory adjustment of the test pulser circuit,
The detector voltage (TEST/BIAS/OFF) switch on the front-panel toggle switch is set at BIAS, the test pulser
front panel turns power ON and OFF for the variable is turned off and does not appear in the output
100-V bias power supply. The power is on to the BIAS spectrum.
supply in both the TEST and BIAS positions.
The polarity is set by Jumper J1, which is actually inverted by the preamplifier and are furnished as the
three separate jumpers (see schematic). The indicated input to the amplifier that includes the first integration
polarity is negative, which is appropriate when an and differentiation shaping circuits. The amplifier can
ORTEC Ruggedized detector is used. When the be calibrated by a factory-adjusted trim potentiometer
detector voltage is negative, its output pulses are on the PWB. The output is a shaped negative pulse
positive. When they pass through the inverting charge- that can be observed at test point TP3.
sensitive preamplifier, they are negative, and this is
the polarity that is then selected by the pair of jumpers The pulse at TP3 is furnished into a fixed-level
(J3) on the PWB. If a conventional surface barrier, or discriminator (U3), and through a diode dc-restorer
ion-implanted, detector is used, all five of these and integration network. If the amplitude represents
jumpers must be changed to "+" because these ~2.5 MeV or more, the discriminator fires and
detectors, positively biased, generate negative output generates a positive-shaped pulse that is used to
pulses, which are then inverted, resulting in positive enable the stretcher. This pulse is also provided as the
pulses at the J3 location in the circuit. COUNT output signal. The pulse from the second
The 100-V power supply output on the PWB can be If the stretcher is enabled, the peak amplitude is
tested for both polarity and amplitude at test point stretched to improve the measurement accuracy of the
TP1, which is identified on the PWB. The variable 0 to multichannel analyzer, which uses the ENERGY
100 V bias voltage can be measured at the front-panel output for measurement. If the stretcher is not enabled
test point jack labeled HV. (because the pulse represents <2.5 MeV), the output
The detector leakage current can be measured across stretched. The output of the stretcher is a negative
the 1.1-M
6
resistor between front-panel test points HV pulse that can be monitored at test point TP4 on
and DET, using a 10-M
6
impedance meter. The the PWB.
voltage (in volts) converts to µA of detector current.
The output of the Bias supply is applied through a The biased amplifier accepts the stretcher output and
high impedance (totaling 11 M
6
) to the dc connection the bias level selected by the front-panel ENERGY
between the detector and the preamplifier. RANGE switch (low end of range). The bias level, or
The output from the charge-sensitive preamplifier can at 3, 4, 5, or 6 MeV by the ENERGY RANGE switch,
be checked at TP2. The nominal conversion gain is which can be adjusted by ±10% by the front-panel
45 mV/MeV. The preamplifier gain from the External screwdriver control, E BIAS.
Pulser input is nominally "
 1" at TP2.
The pulser switch (TEST/BIAS/OFF) on the front bias level from the input pulse amplitude and to
panel turns power on and off for the test pulser. The amplify the excess amplitude by a factor of 10 on the
test pulser can be set to furnish the equivalent pulse 3 & 5, 4 & 6, 5 & 7, and 6 & 8 MeV ranges, and by a factor
should not be changed by the customer. When the
Pulses from the detector and/or the test pulser are
integration shaping circuit is furnished to the stretcher.
is passed to the biased amplifier without being
lower level, accepted into the bias amplifier can be set
The function of the biased amplifier is to subtract the

7
Fig. 5. Detailed Block Diagram of the Model A-576 A-PAD.
6.7 on the 4
&
7 MeV range, or a factor of 4 on the 3
&
8 the detected input energy exceeds the selected bias
MeV range. The output of the biased amplifier is a level. The full-scale output of 10 V can be adjusted
positive pulse with an amplitude, in the range from 0.1 down to 7.75 V, using the front-panel screwdriver
to 10 V, which is proportional to the amount by which control (E).