0 as near zero as practical the draw pmts step 105 is used to provide a graphical display showing the progress of the calibration to provide status information the calibration process is performed in steps 106 112 the radiation process is not shown in this flow chart and could be continuous or intermittent over these steps for example the radiation could be limited to occur during step 107 operation the gain of the selected pmt i e pmt n is set to an initial value as discussed above and the radiation spectrum is collected in step 107 the peak location loc is determined and compared with the target value at step 108 and if the peak loc is greater than the target beyond the acceptable deviation as discussed above then step 109 is performed if the peak loc is below the target beyond the acceptable deviation then step 110 is performed if the peak loc is at the target value again within the acceptable deviation then step 111 is performed at step 109 the gain of the selected pmt n is decreased whereas at step 110 the gain is increased then after either step the spectrum is again collected in step 107 and step 108 is again performed however when the peak loc is at the target value the gain of the pmt n is saved as the calibrated gain at step 111 and then if there are additional pmts to be calibrated determined by step 112 the new pmt i e pmt n with n incremented is selected and the just set pmt i e pmt n u2212 1 is reset to about a zero gain as discussed above at step 113 and.