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Detailed introduction
The unipolar output of the half-Gaussian amplifier is the same as the ORTEC type 572, except that the shaping time constant is in the range 0.25 to 6 μs. The long shaping time constant at this output provides energy resolution at low count rates.
At high count rates, short shaping time constants are necessary to achieve high throughput. Charge collection time variations in Ge radiation detectors often severely degrade energy resolution at such short time constants. The gated integrator solves this problem by integrating the area under the unipolar pulse and setting an integration period that ensures integration of longer pulses resulting from slower charge collection in the Ge radiation detector. The resulting energy resolution is significantly improved, with a throughput of approximately four times the count rate of conventional half-Gaussian shaping. The Type 673 gated integrator output maintains excellent resolution and peak position stability at much higher count rates than half-Gaussian shaping.
A stacking rejector is used to minimize spectral distortion caused by two or more rays reaching the radiation detector within one amplifier pulse width. The stack rejector connects to the anti-coincidence gate of the multichannel analyzer and provides protection for the unipolar or gated integrator output. Front panel switches allow manual or automatic adjustment of the noise threshold for the stacker and baseline restorer. Manual mode is for transistor reset preamplifiers.
Type 673 is suitable for resistive feedback preamplifiers and transistor reset preamplifiers (TRP). Using a transistor to reset the preamplifier allows logic pulses derived from the preamplifier reset signal to be supplied to the gate input of the Model 673 for the duration of the overload caused by the preamplifier reset. The stacked rejector signal at the gate input is ORed with the GI INH output and is used by multi-channel analyzers to prevent analysis of pulses that are distorted by reset.
The unipolar output also functions as a high-performance half-Gaussian shaping amplifier for use with various types of radiation detectors, including germanium radiation detectors, silicon charged particle radiation detectors, Si (Li) radiation detectors, proportional counters, and scintillation radiation detectors.
