Suren Kandasamy Dissertation.pdf - University of Surrey

Total number of net countsM.Sc DissertationFigure 4.1 shows the graph of total number of net counts versus supply voltage.This graph was plotted using the values shown in Table 4.1 for LaCl 3 :Ce(10%)detector.29000024000019000014000090000850 900 950 1000 1050 1100 1150 1200 1250Supply voltage(V)Figure 4.1 The counting curve of LaCl 3 :Ce(10%) detector as a function ofsupply voltage.The operating voltage was chosen by the high voltage corresponding to the centrepoints on the plateaus [6]. According to the Fig. 4.1 for the LaCl 3 :Ce(10%) detector theoperating voltage has been found as 950 Volts. When using PMTs for scintillatordetectors, there is a trade between dynamic range, linearity (proportionality of response)and resolution. This can discussed as follows. The very high photon yields of thescintillator could with its fast emission time means that standard PMTs can easilysaturate when operated at nominal anode to cathode biases of ~ 1000 V purely due totheir very high gains [10]. This can result in gross non linearities being into spectra.Reducing the PMT bias may reduce these non linearities and extend the dynamic range,but at the expense of a deteriorated energy resolution. Therefore, a trade is requiredbetween range, linearity and resolution [10].From the Fig. 4.1 shows below 860 Volts less number of counts was recorded.From that point the recorded count was suddenly increased. That means the PMTworking active voltage bias region. The maximum recommended high voltage powerK. Suren 18