671 Spectroscopy Amplifier

 Specifications

PERFORMANCE

Note: Unless otherwise stated, performance specifications are measured on the unipolar output with 2-µs Gaussian shaping and the AUTO BLR mode.

Gain Range  Continuously adjustable from 2.5 to 1500. Gain is the product of the COARSE and FINE GAIN controls.

Unipolar Pulse Shapes  Switch selection of a nearly triangular pulse shape or a nearly Gaussian pulse shape at the UNI output (Fig. 1, Table 1).

Bipolar Output Pulse Shape Rise of the bipolar output pulse from 0.1% to maximum amplitude is 1.65 times selected SHAPING TIME. Zero cross-over of the bipolar output pulse is delayed from the maximum amplitude of Gaussian unipolar output by 0.33 times the selected SHAPING TIME.

Integral Nonlinearity (UNI Output) <±0.025% from 0 to +10 V.

Noise  Equivalent input noise <5.0 µV rms for gains >100, and <4.5 µV rms for gains >1000.

Temperature Coefficient (0 to 50°C)
Unipolar Output <±0.005%/°C for gain, and <±7.5 µV/°C for dc level.
Bipolar Output <±0.007%/°C for gain, and <±30 µV/°C for dc level.

Walk Bipolar zero cross-over walk is <±3 ns over a 50:1 dynamic range.

Overload Recovery Unipolar and bipolar outputs recover to within 2% of the rated output from a X1000 overload in 2.5 nonoverloaded pulse widths using maximum gain.

Spectrum Broadening* (Fig. 2) Typically <8% broadening of the FWHM for counting rates up to 100,000 counts/s, and <15% broadening for counting rates up to 200,000 counts/s. Measured on the 1.33-MeV gamma-ray line from a ⁶⁰Co radioactive source under the following conditions: 10% efficiency ORTEC GAMMA-X PLUS detector, 8.5-V amplitude for the 1.33-MeV gamma ray on the unipolar output.

Spectrum Shift* (Fig. 2) Peak position typically shifts <±0.018% for counting rates up to 100,000 counts/s, and <±0.05% for counting rates up to 200,000 counts/s. Measured on the 1.33-MeV line under conditions specified for Spectrum Broadening.

* Results may not be reproducible if measured with a detector producing a large number or slow rise-time pulses or having quality inferior to the specified detector.

Differential Input Differential nonlinearity <±0.012% from –9 V to +9 V. Maximum input ±10 V (dc plus signal). Common mode rejection ratio >1000.

Pulse Pile-Up Rejector
Threshold  Automatically set just above noise level on fast amplifier signal. Independent of slow amplifier BLR threshold.

Minimum Detectable Signal  Limited by detector and preamplifier noise characteristics.
Pulse Pair Resolution  Typically 500 ns. Measured using the ⁶⁰Co 1.33-MeV gamma ray under the following conditions: 10% efficiency germanium detector, 4-V amplitude for the 1.33-MeV gamma ray at the unipolar output, 50,000 counts/s (Fig. 3).

ELECTRICAL AND MECHANICAL

Power Required  The Model 671 derives its power from a NIM Bin supplying ±24 V and ±12 V, such as the ORTEC Model 4001A/4002A Bin/Power Supply. The power required is +24 V at 100 mA, –24 V at 200 mA, +12 V at 325 mA, and –12 V at 180 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.) front panel per DOE/ER-0457T.

CONTROLS

FINE GAIN  Front-panel, 10-turn precision potentiometer with locking, graduated dial provides continuously variable, direct reading, gain factor from 0.5 to 1.5.

COARSE GAIN  Front-panel, eight-position switch selects gain factors of 5, 10, 20, 100, 200, 500, and 1000.

SHAPING TIME  Six-position switch on the front panel selects shaping times of 0.5, 1, 2, 3, 6, and 10 µs for the pulse-shaping filter network.

MODE  Two-position locking toggle switch on the front panel selects either GAUSS (Gaussian) or TRI (Triangular) pulse shaping for the UNI (unipolar) output.

INPUT POS/NEG  Front-panel, two-position locking toggle switch accommodates either positive or negative input polarities.

NORM/DIFF  Two-position slide switch mounted on the printed circuit board selects the normal (NORM) or differential (DIFF) input modes. In the NORM position, both front- and rear-panel INPUT connectors function as the same normal input for the preamplifier signal cable. In the DIFF mode the rear-panel INPUT connector becomes a differential ground reference input, and the front-panel INPUT remains the normal input for the preamplifier signal cable. In the DIFF mode the preamplifier signal cable is connected to the front-panel INPUT and a cable having its center conductor connected to the preamplifier ground through an impedance matching resistor is connected to the rear-panel INPUT. The impedance matching resistor must match the output impedance of the preamplifier.

BAL (Differential Input Gain Balance) A 20-turn potentiometer mounted on the PC board inside the module allows the gains of normal and differential reference inputs to be matched for maximum common mode noise rejection in DIFF mode.

PZ ADJUSTMENT  20-turn potentiometer on the front panel permits screwdriver adjustment of the PZ cancellation. The adjustment covers preamplifier exponential decay time constants from 40 µs to infinity. For transistor-reset preamplifiers or pulsed optical feedback preamplifiers, set the PZ adjustment fully counterclockwise.

LIM PUSH BUTTON  Inserts a diode limiter in series with the front-panel UNI output connector. Prevents overload distortions in the oscilloscope when observing the accuracy of the PZ adjustment on the more sensitive oscilloscope ranges.

BLR  A front-panel, three-position, locking, toggle switch selects the baseline restorer rate. PZ position offers lowest fixed rate for adjusting PZ cancellation. AUTO position matches the rate of the PZ position at low counting rates, but increases the restoration rate as the counting rate rises. HIGH rate position is provided for suppressing low-frequency interference.

PUR ACCEPT/REJECT LED  Multicolor LED indicates percentage of pulses rejected because of pulse pile-up. LED appears green for 0–40%, yellow for 40–70%, and red for >70% rejection.

INPUTS

INPUT (Front Panel)  BNC connector accepts preamplifier signals of either polarity with rise times less than the selected SHAPING TIME, and exponential decay time constants from 40 µs to infinity. For the NEG INPUT switch setting, the input impedance is 1000 W on a coarse gain of 5, and 465 W at coarse gain settings ³10. For the POS INPUT switch setting, the input impedance is 2000 W for a coarse gain of 5, and 1460 W for coarse gains ³10. Input is dc-coupled, and protected to ±25 V.

INPUT (Rear Panel)  BNC connector. Identical to front-panel INPUT when PWB- mounted NORM/DIFF slide switch is in the NORM position. When operating in the differential input mode with the slide switch set to DIFF, the rear-panel INPUT is used for the preamplifier ground reference connection. For the DIFF and POS INPUT switch settings, the input impedance is 1000 W on a coarse gain of 5, and 465 W at coarse gain settings ³10. For the DIFF and NEG INPUT switch settings, the input impedance is 2000 W for a coarse gain of 5, and 1460 W for coarse gains ³10. Input dc-coupled; protected to ±25 V.

INH IN  Rear-panel BNC inhibit input connector accepts reset signals from transistor-reset preamplifiers or pulsed optical feedback preamplifiers. Positive NIM standard logic pulses or TTL levels can be used. Logic is selectable as active high or active low via a printed circuit board jumper. Inhibit input initiates the protection against distortions caused by the preamplifier reset. This includes turning off the baseline restorers, monitoring the negative overload recovery at the unipolar output, and generating PUR (reject) and BUSY signals for the duration of the overload. The PUR and BUSY logic pulses are used to prevent analysis and correct for the reset dead time in the associated ADC or multichannel analyzer.

OUTPUTS

UNI  Front- and rear-panel BNC connectors provide positive, unipolar, shaped pulses with a linear output range of 0 to +10 V. Front- panel output impedance <1 W. Rear-panel output impedance selectable for either <1 W or 93 W using a printed circuit board jumper. Outputs are dc-restored to 0 ±5 mV and short-circuit protected

BI  Front- and rear-panel BNC connectors provide bipolar shaped pulses with the positive lobe leading. The linear output range is 0 to ±10 V. Front-panel output impedance <1 W. Rear-panel output impedance selectable for either <1 W or 93 W using a printed circuit board jumper. Baseline between pulses has a dc level of 0 ±10 mV. Short-circuit protected.

CRM  The Count Rate Meter output has a rear-panel BNC connector and provides a 250-ns-wide, +5-V logic signal for every linear input pulse that exceeds the pile-up inspector threshold. Output impedance is 50 W.

BUSY  Rear-panel BNC connector provides a +5-V logic pulse for the duration that the linear signals exceed the positive or negative baseline restorer thresholds, or the pile-up inspector threshold, or for the duration of the INH IN input signal. Useful for dead-time corrections with an associated ADC or multichannel analyzer. Positive NIM standard logic pulse is selectable as active high or active low via a printed circuit board jumper. Output impedance is 50 W.

PUR  Pile-Up Reject output is a rear-panel, BNC connector. Provides a +5-V NIM standard logic pulse when pulse pile-up is detected. Output also present for a pulsed reset preamplifier during reset, and reset overload recovery. Output pulse is selectable as active high or active low by means of a printed circuit board jumper. Output impedance is 50 W. Used with an associated ADC or multichannel analyzer to prevent analysis of distorted pulses.

PREAMP  Rear-panel standard ORTEC connector (Amphenol 17-10090) provides power for the associated pre-amplifier. Mates with power cords on all standard ORTEC preamplifiers.

Table 1. Unipolar Pulse Shape Parameters for the Triangular and Gaussian Pulse Shapes.

*Time interval equals the selected front-panel SHAPING TIME multiplied by the Shaping Time Multiplier.

Fig. 1  Gaussian, triangular, and bipolar output pulse shapes for a 2-µs shaping time. Vertical scale, 5 V per division; horizontal scale, 2 µs per division.

Fig. 2  (a) Resolution and (b) peak position stability as a function of counting rate. See specifications for spectrum broadening and spectrum shift.

Fig. 3  Demonstration of the effectiveness of the pile-up rejector in suppressing the pile-up spectrum. See Pulse Pile-Up Rejector specification.

ORDERING INFORMATION