Efficiency Calibration Of Silicon Drift Detector In Low Energy Region And Energy Spectrum Simulation

The silicon drift detector(SDD)is a nuclear radiation detector based on the principle of lateral depletion.Because this kind of detector have advantages of smaller output capacitance and lower noise than conventional Si(Li)detector,and with simple semiconductor refrigeration can achieve the energy resolution of Si(Li)detector with liquid nitrogen refrigeration,which making it have important applications in the quantitative analysis of energy spectrum,medical imaging,space exploration and so on.The detection efficiency is one of the most important technical target of SDD.The dimension parameters of detector and the difference of geometry between experimental sample and detector would all cause different detection efficiency.Therefore,the study of detector efficiency calibration has important practical significance.This paper is based on the VITUS H80 type SDD detector with large probe produced by the German KETEK company to complete the following work.Firstly,the relative efficiency calibration method,the theoretical model calculation and passive calibration method are used to calibrate SDD detector in lower energy region.The relative efficiency calibration method is based on the ratio of the bremsstrahlung spectrum of 19 keV electron impact pure thick carbon target collected by the SDD detector to the theoretical bremsstrahlung spectrum obtained by PENELOPE simulation,and the relative efficiency calibration curve of the SDD detector is acquired.Then it is normalized to the absolute detection efficiency curve through the absolute efficiency of a 241Am standard radioactive sources.The theoretical model calculation method is according to a theoretical model calculation formula.The passive calibration method uses the PENELOPE program to model the geometric structure of SDD detector.And the initial conditions of the simulation are consistent with the experiment,then detection efficiency is simulated.Secondly,the simulation of 241 Am standard radioactive source spectrum.The same geometric model of SDD detector is modeled by using PENELOPE program.In order to compare with the experimental spectrum,the corresponding code of the program is modified,so that the full peak of spectrum simulated by PENELOPE program accord with the Gauss distribution.Thirdly,the simulation of X-ray energy spectrum of positrons bombarding the Al thick target.Similarly,the PENELOPE program is also used to build a geometric model of the A1 thick target the same as experiment and SDD detector,and then simulate the corresponding physical process.Finally,we develope the element characteristic X-ray recognition program.By using Fortran language,the K,L and M shell characteristic X-ray information of elements are extracted from the database of ENDF/B-?.1,and then achieved the search function of the corresponding characteristic X-ray information.By comparison,the detection efficiency curves obtained by the three calibration methods mentioned above are in a good agreement in the calibration energy range.And the simulated spectrum of 241 Am is consistent with the corresponding experimental spectrum in the higher energy range,the discrepancy in the lower energy range has been discussed.Meanwhile,differences between the simulated X-ray spectrum of positrons bombarding thick carbon target and experimental spectrum have also been discussed in this paper.