The dependence of N _KR versus K _R: the initial, thermal, volumetric recombination and screening effect on the efficiency of collected charges on the calibration of si HDR1000 plus well chambers with ¹⁹²Ir HDR sources ^*

Abstract

By using the statistical techniques of ANOVA: mean test and regression, it was found that the NKR calibration factor of Standard Imaging (SI) model HDR 1000 plus chambers presents a quadratic dependence with the reference air kerma rate KR (from 6.9 mGy h-1 to 43.9 mGy h-1). In order to understand and correct this dependency one model is presented for total recombination: ks=I300/I150=1+kini+ kd +kvol I300+kscreenI300 2 , where kini is the initial recombination, kd the thermal diffusion recombination, kvol the volumetric recombination and kscreen the screening for the currents/charges collected at the potential differences of 300 and 150 V. In conclusion, the total recombination ks is composed by one kini with a constant contribution of 0.019%, one kd contribution of 0.017%, one kvol I300 contribution from 0.022% to 0.138%, and the kscreenI300 2 effects from 0.002% to 0.09% in the range of KR rate above. However, when this model for ks is applied to try to correct the quadratic dependence of the NKR vs KR , explicitly there is no improvement in the variation range of 0.5% of the NKR vs KR .Nonetheless, it allows to obtain NKR values consistent with a uc ≤ 0.7 %, which is less than 1.25% reported in the literature by ADCL or SSDL.