Canberra 2015A User manual

Model 2015A
Spectroscopy
Amplifier/Timing SCA
User’s Manual
9231694B 01/05

Copyright 2005, Canberra Industries, Inc. All rights reserved.
The material in this document, including all information, pictures,
graphics and text, is the property of Canberra Industries, Inc. and
is protected by U.S. copyright laws and international copyright
conventions.
Canberra expressly grants the purchaser of this product the right
to copy any material in this document for the purchaser’s own use,
including as part of a submission to regulatory or legal authorities
pursuant to the purchaser’s legitimate business needs.
No material in this document may be copied by any third party, or
used for any commercial purpose, or for any use other than that
granted to the purchaser, without the written permission of
Canberra Industries, Inc.
Canberra Industries, 800 Research Parkway, Meriden, CT 06450
Tel: [phone] FAX: [phone] http://www.canberra.com
The information in this document describes the product as
accurately as possible, but is subject to change without notice.
Printed in the United States of America.

Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Low Level α/β Counting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Controls and Connectors . . . . . . . . . . . . . . . . . . . . . . 4
Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . 7
Spectroscopy System Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Performance Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Resolution Versus Count Rate and Shaping . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Resolution Destroying Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
SCA Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Reference Data on Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Preventative Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4. Performance Check . . . . . . . . . . . . . . . . . . . . . . . . 20
Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
NIM Voltage Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Current Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Amplifier Operational Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Pole/Zero Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Coarse and Fine Gain Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Shaping Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Noise Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Linearity Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
SCA Operational Checks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Timing Walk Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
External Lower Level Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Normal Internal Control Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5. Circuit Description . . . . . . . . . . . . . . . . . . . . . . . . . 30
Block Diagram Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
The Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
The SCA Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Description of Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Gain Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Input Amplifier K1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Gain Amplifier K2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Integrator Amplifier A5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Amp OUTPUT Integrator and Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Restorer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
SCA Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
SCA OUTPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Disc Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Lower Level (E) Threshold Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Window (∆E) Threshold Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Fast Discriminator Reference Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5 Volt Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Troubleshooting Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Troubleshooting Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Component Replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
A. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
ii

Input/Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Internal Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Physical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
B. Installation Considerations . . . . . . . . . . . . . . . . . . . . 44
iii

Notes
iv

1. Introduction
The Canberra Model 2015A combines, in one singlewidth module, the functions of a
spectroscopy amplifier and a timing single channel pulse height analyzer.
The Model 2015A Amplifier/TSCA uses integrated circuit construction for maximum
reliability and simplicity. The entire unit is designed to optimize energy resolution in
spectroscopy applications with Ge and Si detectors even at high count rates. The am-
plifier’s restorer includes circuitry for use with optical feedback preamplifiers. The
Model 2015’s broad gain range (X12 to X1280) makes it equally compatible with high
purity Ge, scintillation, photomultipliers, gas proportional and surface-barrier detec-
tors.
The usefulness and application of the Canberra Model 2015A is enhanced by the fol-
lowing unique design features not found in comparable amplifiers: internally
selectable shaping time constants of 0.5 µs or 2 µs, count rate optimization with Can-
berra’s unique gated restorer, front panel pole/zero adjustment, a ten turn fine gain
control, and low noise design (less than 7 microvolts referred to the input at 2 ms
shaping).
The Model 2015A is further enhanced by the addition of a timing SCA contained in
the same package, offering two modes of single channel pulse height (energy) analy-
sis. In the SCA mode of operation an SCA OUTPUT is generated whenever the peak
value of the unipolar falls between the energy levels defined by the front panel
LOWER LEVEL (E) and WINDOW (∆E) settings. In the Timing (TSCA) mode the
SCA OUTPUT is generated for the same E and ∆E conditions except that it is time
referenced to the preamp’s leading edge. This develops a true leading edge timing
technique, while minimizing timing jitter.
In addition to the SCA output the Model 2015A offers a multifunction DISC connec-
tor which can be used as a LOWER LEVEL (E) discriminator output, an Upper Level
(E + ∆E) discriminator output, or an LLD SWEEP input. One of the three modes is in-
ternally selected with jumper plugs.
The Model 2015A has one additional unique feature: a LED indicator electronically
linked to the LOWER LEVEL (E) control. The LED indicator is a visual means of ad-
justing the LOWER LEVEL (E) control above the system noise level.
Both the LOWER LEVEL (E) and WINDOW (∆E) controls are ten turn potentiom-
eters for maximum accuracy, resolution and resetability. A rear panel switch controls
the WINDOW (E) range: 0 to 10 volts, or 0 to 1 volt.

Applications
This section is not intended as a complete survey of applications. It is intended to
highlight the most important features of the module and to indicate representative ar-
eas where they might be applied.
The Model 2015A overcomes the past necessity of using two individual modules, an
amplifier and single channel analyzer, by performing both tasks in one convenient sin-
gle-width module.
The amplifier’s two selectable time constants, 0.5 µs for high count rates and 2 µs for
optimum resolution, makes it useful for NaI, Ge(Li), surface barrier and proportional
counter applications. Using the amplifier and single channel analyzer outputs, the
Model 2015A, in conjunction with a delay module, represents an ideal method for per-
forming energy discrimination. The SCA OUTPUT can gate the multichannel analyzer
to control the acceptance or rejection of the amplifier’s delayed linear output signal. In
addition, the amplifier’s output allows the signal to be analyzed by other energy
discriminators so that more than one energy band may be selectively studied from the
same amplifier.
The Single Channel Analyzer section is used in either the Timing SCA (TSCA) or
SCA mode. In the timing mode, the SCA OUTPUT logic pulse is placed consistently
in time (200 nanoseconds) past the AMPLifier OUTPUT pulse peak. Thus, the Model
2015A may serve to replace an amplifier and individual timing SCA, sometimes re-
quired for coincidence experiments. With its SCA and ULD or LLD DISC outputs, the
2015A Amp/TSCA may be used to identify two different energies or particles depend-
ing on the particular setting of the discriminator levels.
Low Level Counting System
The Canberra LOW BACKGROUND ALPHA/BETA DETECTOR SYSTEM (2200
& 2201) depicts a particular application of the Model 2015A. In this system, two de-
tectors are used in anti-coincidence to distinguish true sample events from cosmic or
interference radiation associated with the local environment. The system is ideally
suited for measuring isotopes such as 14C, 89Sr, 210Po, and so forth.
There are two Model 2015A Amp/TSCA modules involved in this system configura-
tion. One is used in the guard channel path and the other in the sample channel path. In
the guard channel the Model 2015A is used as an amplifier/discriminator combination,
where the extremely low threshold setting of the LOWER LEVEL (E) discriminator is
used to detect the cosmic events. The Model 2209A, monitoring the guard 2015A
DISC (ULD = LLD) output, gates off or inhibits the Scaler/Timer when a cosmic
INPUT signal exceeds the LOWER LEVEL (E) threshold.
2
Introduction

In the sample channel, the Model 2015A accepts the signal from the preamplifier,
shapes, delays and directs it through the SCA section for two simultaneous discrimina-
tions. In this application the proportional counter detector is biased to the beta plateau;
the output information from the detector is then indicative of both alpha and beta ener-
gies. Typically, the Single Channel Analyzer is set such that the SCA OUTPUT repre-
sents beta particles and the DISC (ULD) OUTPUT represents alpha particles. the
DISC (LLD) OUTPUT represents the sum of the alpha and beta particles.
The desired outputs from the single channel analyzer section are connected to the
Model 2209A AUTO FLOW METER and subsequent scalers. Figure 1 shows the
SCA and DISC information being routed by the 2209A to the respective scalers indi-
cating alpha and beta events. Both 2015A’s use the DISC output to provide ULD in-
formation. However, the WINDOW (∆E) control on the 2015A associated with the
cosmic channel is set to 0.00, thus its threshold is equal to that provided by the
LOWER LEVEL (E) control. The equipment setup is simplified since the 2015A in-
ternal controls are set the same. By utilizing the WINDOW (∆E) function, the cosmic
channel 2015A provides LLD information. The model 2015A’s included in this instru-
mentation makes the Alpha/Beta System a versatile, accurate, and cost effective sys-
tem.
3
Low Level α/β Counting System
Figure 1 Block Diagram of 2015A Application
in Low Level α/β Counting System

2. Controls and Connectors
Front Panel
This is a brief description of the 2015A’s front panel controls and connectors. For
more detailed information, refer to Appendix A.
4
Controls and Connectors
Figure 2 Front Panel Controls and Connectors

Rear Panel
This is a brief description of the 2015A’s rear panel connectors. For more detailed in-
formation, refer to Appendix A.
5
Rear Panel
Figure 3 Rear Panel Connectors

Internal Controls
6
Controls and Connectors
Figure 4 Internal Controls

3. Operating Instructions
The purpose of this section is to familiarize you with the operation and controls of the
Model 2015A Amplifier/TSCA so that best performance can be obtained. Since it is
difficult to determine the exact system configuration in which the module will be used,
explicit operating instructions cannot be given. However, if the following procedures
are carried out, you will gain sufficient familiarity with this instrument to permit its
proper use in the system at hand.
Spectroscopy System Operation
Setup
A block diagram of a typical Canberra gamma spectroscopy system is shown in Figure
5.
1. Prior to installation and setup, the internal jumper plugs should be set to their
desired positions. See Figure 4 (Internal Controls) on page 6.
The ZOUT jumper plug controls the output impedance of the front panel
(only) AMP OUTPUT. The output impedance can be changed from 0 ohms
7
Spectroscopy System Operation
Figure 5 Typical Gamma Spectroscopy System

to 93 ohms. The 2015A is shipped with the front panel output impedance set
for ≤1 ohm. The rear output has a fixed output impedance of approximately
93 ohms, series connected.
When using the front panel low impedance output, short lengths of
interconnecting coaxial cable need not be terminated. To prevent possible
oscillations, longer cable lengths should be terminated at the receiving end in
a resistive load equal to the cable impedance (93 ohms for type RG-62
cable).
The rear panel 93 ohm output may be safely used with RG-62 cable up to a
few hundred feet. However, the 93 ohm output impedance is in series with
the load impedance, and a decrease in the total signal range may occur. For
example, a 50% loss will result if the load impedance is 93 ohms.
2. Insert the 2015A into a standard NIM BIN. Preamp power is provided by a 9
pin connector located on the 2015A rear panel. Allow the total system to
warm up and stabilize.
3. Set the 2015A controls as indicated below:
SHAPING: 2 ms (internal)
COARSE GAIN: 16
FINE GAIN: 2.2
This will give approximately 9 volts output when using a preamp gain of 100
mV/MeV and 60Co radioactive source.
4. Install a “tee” connector on the 2015A AMP OUTPUT. Connect one end of
the “tee” connector to the analyzer ADC input. To fully exploit the count rate
capabilities of the Model 2015A Amplifier the ADC should be direct
coupled. All Canberra ADC’s are dc coupled. Connect the second end of the
“tee” connector to an oscilloscope and monitor the AMP OUTPUT.
Performance Adjustments
1. The pole/zero is extremely critical for good high count rate resolution. See
note 1 on page 11. Adjust the radiation source count rate between 2 kcps and
25 kcps. While observing the AMP OUTPUT on the scope, adjust the
pole/zero so that the trailing edge of the unipolar pulse returns to the baseline
with no over or undershoots.
8
Operating Instructions

Figure 6 shows the correct setting of the pole/zero control, with Figures 7 and 8 show-
ing under and over compensation, respectively for the preamplifier decay time con-
stant. Notice some small amplitude signals with long decay times in Figure 6. These
are due to charge trapping in the detector and cannot be corrected by the pole/zero
control.
9
Spectroscopy System Operation
Figure 6 Correct Pole/Zero Compensation Figure 7 Undercompensated Pole/Zero
Scope
Vertical: 50 mV/cm
Horizontal: 10µs/cm
Source 60Co
1.33 MeV peak: 9 V amplitude
Count rate: ≈3kcps
Shaping: 2 µs
Figure 8 Overcompensated Pole/Zero

2. Pole/zero adjustment using a square wave and preamp test input. See note 2
on page 12.
Driving the preamp test input with a square wave, will allow a more precise
adjustment of the amplifier pole/zero.
a. The Amplifier’s controls should be basically set for its intended
application: COARSE GAIN, shaping, INPUT POLARITY.
b. Adjust the square wave generator for a frequency of approximately 1
kHz.
c. Connect the square wave generator’s output to the preamp’s TEST
INPUT.
d. Remove all radioactive sources from the vicinity of the detector.
e. Set the scope’s channel 1 vertical sensitivity to 5 volts/cm, and adjust the
main time base to 0.2 ms/cm. Monitor the 2015A’s AMP OUTPUT and
adjust the square wave generator’s amplitude control (attenuator) for
output signals of ±10 volts.
Note Both positive and negative near-Gaussian linear pulses will be observed at
the output.
f. Reduce the scope vertical sensitivity to 50 mV/cm. See Note 1 on page
11.
Figure 9 shows the correct setting of the pole/zero control. Figures 10
and 11 show under and over compensation, respectively for the
preamplifier decay time constant. As illustrated in Figure 9, the AMP
OUTPUT signal should have a clean return to the baseline with no
bumps, overshoots or undershoots.
10
Operating Instructions

3. HPGe detectors and Si Systems with Optical Feedback Preamps.
For normal Si Systems, the pole/zero is usually set at ∞fully
counterclockwise. However, on some systems, the pole/zero may need to be
slightly tweaked for optimum overload recovery when responding to the
preamps reset pulse.
Note 1: At high Count rates the pole. zero adjustment is extremely critical for main-
taining good resolution and low peak shift. For precise and optimum
pole/zero setting, a scope vertical sensitivity of 50 mV cm should be used.
11
Spectroscopy System Operation
Figure 9 Correct Pole/Zero Compensation Figure 10 Undercompensation Pole/Zero
Figure 11 Overcompensation Pole/Zero
Scope
Vertical: 50 mV/cm
Horizontal: 0.2 µs/cm
Source
Square wave pulse and preamp
test input.

Higher scope sensitivities can also be used, but result in a less precise pole
zero adjustment. However, most scopes will overload for a 10 volt input sig-
nal when the vertical sensitivity is set for 50 mV/cm. Scope overload will
distort the signals recovery to the baseline. Thus the pole/zero will be incor-
rectly adjusted resulting in a loss of resolution at high count rates. To prevent
scope overloading a clamping circuit, such as the one illustrated in Figure 12
can be used at the scope input.
Note 2: When adjusting the pole/zero using the square wave technique, the calibra-
tion square wave generated by the oscilloscope can be used Most scopes gen-
erate a 1 kHz square wave used to calibrate the vertical gain and probe
compensation. Connect the scope CALIBRATION output through an attenu-
ator to the preamp test input and repeat Performance Adjustments step 2
(pole/zero adjustment).
4. The AMP OUTPUT DC level is factory calibrated to 0 ±5 millivolt.
5. To get optimum resolution. the Lower Level Discriminator on the MCA
ADO should be set just above the noise so that the effects of pileup are
minimized.
Resolution Versus Count Rate and Shaping
A 2 µs shaping is optimum for Ge(Li) detector systems over a wide range of incoming
count rates. For high resolution larger shaping time constants offer a better signal to
noise ratio, resulting in better resolution. However, as the count rate increases, the ef-
fects of pileup degrade the resolution much sooner. The optimum shaping time con-
stant depends on the detector (such as its size, configuration and collection
characteristics), preamplifier and incoming count rate. Below is a list of optimum
shaping time constants for some other common detectors.
12
Operating Instructions
Figure 12 Scope Input Clamp

Detector Optimum Shaping (µsec)
Scintillation Pholomultiplier 0.5
Gas Proportional Counters 0.5 through 2
Silicon Surface-Barrier 0.5 through 2
Lithium Dialed Germanium [Ge(Li)] 2 through 4
Cooled Silicon 8 through 12
The Model 2015A is factory set for 0.5 or 2 µs shaping time constants. However, the
shaping time constants can be changed to 8 and 12 µs to be compatible with cooled
Silicon detectors. Change the components as follows:
1. Change C1 from 560 pF to 9100 pF
2. Change C2 from 1600 pF to 560 pF
3. Change R1 from 19.1 k ohms to 226 k ohms
4. Change R2 from 52.3 k ohms to 11 k ohms
5. Change C3 from 130 pF to 2000 pF
6. Change C4 from 360 pF to 1300 pF
7. Change C5 from 200 pF to 2400 pF
8. Change C6 from 510 pF to 1600 pF
9. Change C25 from 47 pF to 1000 pF
10. Change C26 from 200 pF to 510 pF
11. Change C76 from 390 pF to 1800 pF
12. Change R143 from 604 k to 499 k ohms
13. Change RV12 from 20 k to 50 k ohms
All resistors are RN60Cs and capacitors are 1% silver mica or 1% ceramic NPO. (See
Figure 13)
13
Spectroscopy System Operation

Resolution Destroying Interfaces
1. Vibration transmitted to the detector and cryostat. This can be through the
floor or mounting, as well as direct audio coupling through the air. Vibration
isolators in the mounting and sound absorbing covers around the detector can
reduce this problem.
2. The close proximity of a radio station can be picked up by the “dipstick” of
the cryostat. Good contact between the dipstick and the cryostat can often
help solve this problem. Beware of grounding the cryostat and dipstick as
this may increase power line frequency (50 or 60 cycle) ground loops.
3. Ground Loops: power line frequency interference can be caused by long
cable connections between the detector, preamplifier, and shaping amplifier.
There is no general solution for this problem. As a first step, the preamp
should use the power supplied by the main shaping amplifier. Second, the
system should have a single point house ground. For example, on a general
system connect the NIM Bin to house ground via the ac line cord. Isolate all
other equipment requiring ac voltage from the house ground. Connect all
chassis’ in the system to the grounded NIM Bin using heavy braided wire.
14
Operating Instructions
Figure 13 Internal Shaping Components