A Mediator Spectrometric Unit

Abstract

The mediator unit (mediator) generates a strobe pulse when a scintillation signal is at its maximum (peak moment). The strobe pulse starts the analog-to-digital converter, which performs digitization on a special command. The parameters of the mediator circuit presented are optimized to handle the signals from the detection unit, which comprises a CsI(Tl) scintillator, a silicon p–i–n photodiode, and a squaring amplifier. The maximum input-signal amplitude is 5 V, and the time of rise to the maximum is ∼7 μs (quasi-Gaussian signal). When such signals are used, the strobe pulse is shifted in time with respect to the signal peak by ∼5 ns if the amplitude of the analyzed signals varies from 5 to 0.2 V. The unit is tested in operation (with minimal circuit alterations) over a rise-time range from 1 μs (NaI(Tl)) to 20 μs. The mediator includes a baseline-potential restorer and an adjustable-threshold comparator. Owing to these features, the mediator can also be used as an amplitude integral discriminator and can operate from signal sources with unstable base levels, including systems that require a signal time lock. When the recorded signals are superimposed on the leading and trailing edges, a considerable part of the superimposed signals is rejected.