Suren Kandasamy Dissertation.pdf - University of Surrey

Counts per channelM.Sc Dissertation2.4.5 Time resolutionFigure 2.4 shows a simple system for recording a time spectrum. Twoindependent detectors are irradiated by a common radioisotope source that is assumedto emit at least two detectable quanta in true coincidence; that is both radiations arisefrom the same nuclear event within the source. The output signal from the each detectoris simultaneously sent down two signal branches such as Constant FractionDiscriminator (CFD). A CFD unit in each branch provides timing logic pulses that aresupplied to start and stop inputs of a Time-to-amplitude converter (TAC). A fixed timedelay is also present in the stop branch. The multichannel analyzer (MCA) records thenumber of time intervals [1].Detector 1 SourceDetector 2sourceCFDCFDFixed delayStartTACStopMultichannelanalyzerFigure 2.4 A simplified system for recording multichannel time spectra from asplit common source.FixeddelayFWHM=“time resolution ”Full width attenth maximumChannel numberor timeFigure 2.5 The multichannel time spectrum for the system of Fig. 2.4 [1].The full width at half maximum of the time distribution is often used as a measureof the overall timing uncertainty in the measurement system and is called the timeresolution [1].K. Suren 12