Coincidence Efficiency Research Articles

Techniques and Teory of Fast Coincidence Experiments

A review of fast coincidence circuits, working in the millimicrosecond region, is presented. The main points covered are: 1) operating characteristics of the various types of coincidence circuits, 2) description of the various circuits, 3) differential coincidence method, 4) analysis of coincidence curves and the determination of time delays, 5) the resolving time, 6) effect of random time lags on coincidence curves, 7) experimental investigation of random time lags, 8) coincidence efficiency, and 9) statistical accuracy of time measurements.

New Timing Method for Scintillation Events in Fast Coincidence Experiments

The output pulses from scintillation detectors are amplified in conventional feedback amplifiers and transformed into a bipolar wave form, which passes the discrimination level of the following EFP 60 trigger circuit at a given time after inception of the scintillation pulse, independent of its amplitude within a wide range. If these standard pulses are shaped and fed into a fast coincidence circuit, even for NaI(Tl) resolving times of the order of 10−8 sec can be obtained. The main limitation of the method is due to time jitter of the standard pulses caused by statistical fluctuations of the rising edge of the photomultiplier pulses which results in a reduction of coincidence efficiency.

Statistical Theory of Delayed-Coincidence Experiments

The consistent use of a general statistical theory makes possible the elimination of ambiguities and of idealizing assumptions from the interpretation of delayed-coincidence experiments. Introduction of the concept of the "total coincidence counting rate" (which can be determined experimentally) makes possible the definition of resolving time, thereby eliminating discrepancies between earlier definitions; it also provides means for relating the coincidence efficiencies directly to the number of source events.The effect of random time lags on coincidence curves is calculated and experimental methods for the determination of time lags are derived. The statistical errors in the determination of moments of a coincidence curve are calculated and outlined in detail for first moment investigations. It is shown that: (1) the best choice of the resolving time is a (experimentally measurable) weighted rms of all time delays present in the measurement; (2) using the best choice of the resolving time the standard error of the centroid, obtained by successive measurements of the points of a coincidence curve, is approximately twice the least theoretical standard error (that could be obtained for the total time of observation); (3) the moment method can be applied generally for the determination of mean time delays; other methods, while applicable with some restrictions, can lead to similar or greater statistical errors.