Model 575A Amplifier Operating and Service Manual Printed in U.S.A. ORTEC® Part No.
Advanced Measurement Technology, Inc. a/k/a/ ORTEC®, a subsidiary of AMETEK®, Inc. WARRANTY ORTEC* warrants that 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.
iii CONTENTS WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii SAFETY INSTRUCTIONS AND SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv SAFETY WARNINGS AND CLEANING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 1. DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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.
v 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.
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1 ORTEC MODEL 575A AMPLIFIER 1. DESCRIPTION 1.1. GENERAL The 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 univ ersal application in high-resolution spectroscopy. It accepts input pulses of either polarity.
2 Pole-zero cancellation is accomplished by the network shown in Fig. 2. The pole [s + (1/To)] due to the preamplifier pulse decay time is cancelled by the zero of the network [s + (k/R2C1)]. In effect, the Fig. 1. Differentiation in an Amplifier Without Pole-Zero Cancellation. Fig. 2. Differentiation in a Pole-Zero Cancelled Amplifier. dc path across the differentiation capacitor adds an attenuated replica of the preamplifier pulse to just cancel the negative undershoot of the differentiating network.
3 Total preamplifier-amplifier pole-zero cancellation requires 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 cancellation network allows accurate cancellation for all preamplifiers having 30- s or greater decay times. Improper matching of the polezero network will degrade the overload performance and cause excessive pileup distortion at medium counting rates.
4 2. SPECIFICATIONS 2.1. PERFORMANCE 2.2. CONTROLS GAIN RANGE Continuously adjustable from 5 to 1250. FINE GAIN Ten-turn precision potentiometer with graduated dial for continuously variable directreading gain factor of ×2.5 to ×12.5. PULSE SHAPE Semi-Gaussian on all ranges with peaking time equal to 2.2J, 50% pulse width equal to 3.3 , and pulse width at 0.1% level equal to 4.0 times the peaking time. Bipolar crossover = 1.5 . J INTEGRAL NONLINEARITY shaping time. : J <±0.05% for 1.
5 ORTEC modular instruments and multichannel analyzers. WEIGHT Net 1.5 kg (3.3 lb). Shipping 3.1 kg (7.0 lb.) 2.6. ELECTRICAL AND MECHANICAL POWER REQUIRED +24 V, 55 mA; mA; +12 V, 70 mA; !12 V, 75 mA. !24 V, 40 DIMENSIONS Standard single-width NIM module 3.43 × 22.13 cm (1.35 × 8.714 in.) per TID-20893 (Rev). 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 ORTEC 4001A/4002A Series.
6 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 equiv alent) depends primarily on two considerations: the preamplifier 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.
7 For customer convenience, ORTEC stocks the proper terminators and BNC tees, or they can be ordered from a variety of commercial sources. not be harmed. When the amplifier is terminated with 100 , the maximum count rate consistent with linear output is S 3.7. SHORTING OR OVERLOADING THE AMPLIFIER OUTPUT The 575A output is dc-coupled with an output impedance of ~0.2 .
8 OUTPUTS UNI Front panel BNC connector with Zo<1 and rear panel connector with Zo = 93 . Short-circuit proof; full-scale linear range of 0 to +10 V; active filter shaped; dc-restored with dc level adjustable to ±25 mV. S S S BI Front panel BNC connector with Z o < 1 and rear panel connector with Zo = 93 . Short-circuit proof; positive lobe leading and full-scale linear range of 0 to +10 V; active filter shaped. S b. Observe the unipolar output with an oscilloscope.
9 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. Fig. 7. A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope Input. U S I N G S Q U A R E W AV E T H R O U G H 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.
10 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.
11 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 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 calibrated as described above. c.
12 4.7. OPERATION IN SPECTROSCOPY SYSTEMS H I G H-RESO L UT I O N AL PHA-PART I CL E SPECTROSCOPY SYSTEM The block diagram of a high-resolution spectroscopy system for measuring natural alpha particle radiation is shown in Fig. 14. Since natural alpha radiation occurs only above several MeV, an ORTEC 444 Biased Amplifier is used to suppress the unused portion of the spectrum; the same result can be obtained by using digital suppression on the MCA in many cases.
13 The block diagram in Fig. 17 shows a system of this type. Analysis can be accomplished by simultaneous acquisition 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. 4.8. OTHER EXPERIMENTS Fig. 16. Scintillation-Counter Gamma Spectroscopy System.
14 Fig. 19. Gamma-Ray Pair Spectrometry. Fig. 20. Gamma-Gamma Coincidence Experiment.
15 5. MAINTENANCE 5.1. TEST EQUIPMENT REQUIRED The following test equipment should be used to adequately test the specifications of the 575A amplifier: 1. ORTEC 419 Precision Pulse Generator or 448 Research Pulser. 2. Tektronix 547 Series Oscilloscope with a type 1A1 plug-in or equivalent. 3. Hewlett-Packard 3400A rms voltmeter. : FUNCTIONAL CHECKS Set the 575A controls as follows: 100 7.5 Neg 1.5 s OVERLOAD TESTS Start with maximum gain, J = 1.5 s, and a +10 V output amplitude.
16 LINEARITY The integral nonlinearity of the 575A can be measured by the technique shown in Fig. 21. In effect, the negative pulser output is subtracted from the positive amplifier output to cause a null point that can be measured with excellent sensitivity. The pulser output must be varied between 0 to 10 V, which usually requires an external control source for the pulser. The amplifier gain and the pulser attenuator must be adjusted to measure 0 V at the null point when the pulser output is 10 V.
17 Bin/Module Connector Pin Assignments For Standard Nuclear Instrument Modules per DOE/ER-0457T.
