Ultra Stable Reference Pulser for High Resolution Spectrometers

Abstract

A solid state, double pulse generator with a pulse amplitude temperature coefficient of 0 to -8 ppm/°C was developed. It is shown that when a servo-stabilized spectrometer is locked on the pulser peaks, the gain and zero-intercept of the system drift only ±20 ppm/day or less than 1/10 of the optimum resolution of Ge(Li) detectors. The pulser generates signals which rise in 15 nsec, remain flat-topped for 40 μsec and then fall exponentially to the baseline in 250 μsec. The pulse rate can be varied from 0.1 - 1000 pulse-pairs/sec in 9 steps. The amplitude of the two pulses can be set independently from 5.5-700 mV, using a 7-bit precision R-2R attenuator. When used in conjunction with a preamplifier test capacitor of 1 pF, this amplitude range corresponds to 0.1 - 12.7 MeV (Ge). A "tag" pulse, generated in coincidence with each reference pulse, can be used for gating a multichannel analyzer, a coincidence system or a stabilizer. The performance of the pulser was measured with a computer based, servo-stabilized multichannel analyzer in which the two 60Co lines from a Ge(Li) detector were used as the stabilizer reference peaks. The pulser signal was injected into the preamplifier via a 1 pF air-dielectric capacitor mounted in a temperature regulated oven. The pulser peak was set between the 60Co peaks, and its location was measured as a function of temperature, supply voltage and repetition rate.