Development of measuring and analyzing technology of radiation energy spectrum using EGS4 code

EGS4 code was applied to develop the simulation program in two steps. As a preliminary step, the feasibility of the simulation code was investigated by comparing the energy spectrum measured by HPGe detector with the calculated one. A novel collimator was made to measure the energy spectrum from the primary beam of the radiation source. It was designed to keep the scattered beam, produced by the scattering of the photon beam with the materials surrounding the detector, from entering into the detector so that only primary beam can be measured. The measured spectra were compared with the theoretical calculations obtained using EGS4 code. The comparison showed an excellent agreement with small differences for some sources. The discrepancy can be explained by the imperfect duplication of the real experimental condition and a mismatch between the β -decay electron energy spectrum applied in the calculation and the in the real photon spectrum. We have also unfolded the measured spectra obtained by the same detector in the open space with SDD of 10 cm, 30 cm and 50 cm, respectively, to obtain the real energy spectra of 60Co and 137Cs sources. For the unfolding of the measured spectra, pulse height distribution which was calculated with an EGS4 code for the incident photon energy ranging from 20 keV to 1,360 keV in 10 keV step, was used with interpolation method. For 60Co, the calculated spectra obtained with incident photon energies of 1,173 keV and 1,332 keV were normalized to the measured spectra at two peaks after they were smoothed using Gaussian distribution function. There have been excellent agreements between the measured energy spectra and those from the pure calculation for each radiation source. For 137Cs, the shape of the calculated spectrum with incident photon energy 662 keV for SDD = 10 cm appears to be little different from the measured one in the low energy region. The discrepancy is due to the contribution of electrons in the β -decay reaction. However, the difference becomes smaller as SDD increases and becomes negligible over SDD = 50 cm