Model 584 Constant-Fraction Discriminator Operating and Service Manual Printed in U.S.A. ORTEC® Part No.
$GYDQFHG 0HDVXUHPHQW 7HFKQRORJ\ ,QF 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 STANDARD 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 584 CONSTANT-FRACTION DISCRIMINATOR 1. DESCRIPTION 1.1. PURPOSE The ORTEC 584 allows excellent time resolution from all commonly used detectors such as highpurity germanium (HPGe), surface barrier, fast plastic, Nal(TI), and photomultiplier tubes. This unit accepts input pulses in the range of 0 to -5 V and generates NIM fast negative outputs and a slow positive output that are based on the constantfraction time derivation technique.
2 2. SPECIFICATIONS 2.1. PERFORMANCE INPUT Accepts negative input signals from 0 V to -5 V without saturation; dc-coupled; Zin = 50 ; reflections +5% for tr 2 ns. THRESHOLD RANGE -5 mV to -1 V. THRESHOLD INTEGRAL NONLINEARITY ±0.25% of full scale. THRESHOLD INSTABILITY 50( C. ±100 µV/(C to PROPAGATION DELAY Nominally 25 ns, with external CF Delay x2 ns. MINIMUM PULSE-PAIR RESOLUTION 20 ns. DEADTIME Nominally 20 ns or blocking output width, whichever is greater.
3 NOTES: (1) The module is within the current allotment for a single NlM width when using the -6V position with a NIM Class V Power Supply or equivalent. (2) The module exceeds the current allotment for a single NlM width on the -12V supply when using the -12 V position. However, this position permits using the discriminator in bins with power supplies not providing -6 V. GATE INPUT JUMPER (G+, G-, or BG) PWB jumper selects one, of three Gate Input signal paths.
4 3. INSTALLATION 3.1. GENERAL The 584 power requirements must be furnished from a NIM-standard bin and power supply such as the ORTEC 4001/4002 Series. The bin and power supply into which the 584 will normally be installed for operation is designed for rack-mounting. If the equipment is rack-mounted, there must be adequate ventilation to prevent any localized heating in the 584. The temperature of equipment mounted in racks can easily exceed the maxi mum limit of 50(C (323 K) unless precautions are taken.
5 Another important use of the 584 is timing with HPGe detectors. ln this application, the constantfraction shaping delay selected is less than the minimum signal rise time. Depending on the size and shape of the HPGe detector, the rise time can range from 50 to 400 ns. A typical optimal constantfraction shaping delay can range from 10 to 30 ns with 20 ns a reasonable first choice. An ORTEC 425A Nanosecond Delay can be used to adjust the shaping delay.
6 Fig. 5.1. Simplified Block Diagram of the ORTEC 584 Constant Fraction Discriminator. The CF signal crosses the logic threshold of G1 at constant-fraction time, tcf. Constant-fraction time is determined by the selection of the external constant-fraction shaping delay, td(Ext), subject to the rise times and pulse shapes of the input signals. A fixed internal delay of about 0.8 ns must be added to t d(Ext) to determine the total constant-fraction shaping delay, td(Tot).
7 pulse. This clipped pulse is furnished through current drivers CD1 and CD2 to the timing outputs, and to an inverting ECL-to-TTL converter to produce the positive output. The width of the positive output is adjustable from 0.5 µs to 2.5 µs by a printed-wiring board mounted potentiometer. Additional output signals are blocked by the blocking one-shot composed of FF3, A4, C2, and the Blocking Width control. The blocking period is determined by the adjustable delay time to reset FF3.
8 6. APPLICATIONS 6.1. TIMING WITH FAST SCINTILATORS Figure 6.1. shows a typical system for timing with fast scintillation detectors such as Naton-136, Pilot B, KL-236, NE-102, NE-111, NE-213, etc. A 584 Constant-Fraction Discriminator is used in each of the two channels of the Time-to-Amplitude Converter (TAC). Selection of the constant-fraction shaping delay for best timing performance with a given scintillator and PMT is usually accomplished experimentally (Section 3.5).
9 6.2. TIMING WITH Nal(TI) SCINTILLATORS Timing with Nal(Tl)) scintillators is similar to timing measurements with fast scintillators. However, one additional problem must be considered. The photoelectron statistics for low-energy gamma-ray applications are so poor that individual events near the trailing edge of Nal(TI) pulses can trigger the 584. Thus a single scintillation event can produce two or more discriminator output pulses.
10 The slow rise time reject mode is particularly useful with HPGe detectors operated over a wide dynamic range of energies. Operation in the SRT mode will have minimum effect on the FWHM resolution but can dramatically improve the FWTM and FW(1/100)M values. The disadvantage of the SRT mode is that the effective relative efficiency of the HPGe detector for timing is reduced since some events of valid energy are removed from the timing spectra.
11 7. FACTORY SERVICE This instrument can be returned to the ORTEC factory for service and repair at a nominal cost. The ORTEC standard procedure for repair ensures that the same quality control and checkout procedures that are used for a new instrument will be used for the repaired unit. Always contact Customer Services at ORTEC, (865) 482-4411, before sending in an instrument for repair to obtain shipping instructions and so that the required Return Authorization Number can be assigned to the unit.
12 Bin/Module Connector Pin Assignments For Standard Nuclear Instrument Modules per DOE/ER-0457T.
