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Simulation of HPGe detector efficiency . Eunkyung Lee Ewha Womans University. 1. Introduction. It is important to obtain efficiency by simulation in order to calculate accurate amount of radioactive isotopes.
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Simulation of HPGe detector efficiency Eunkyung Lee Ewha Womans University
1. Introduction • It is important to obtain efficiency by simulation in order to calculate accurate amount of radioactive isotopes. • Compare experimental efficiency with simulation one with a mixed source in Marinelli Beaker. - Efficiency discrepancy was 40~50%. • We assumed several reason of this efficiency discrepancy then check it various ways. • Test with point sources placed top and side of HPGe detector • Compare gamma peaks and Compton edge part • Check relative efficiency : compare HPGe to NaI using a Co-60 source with simulation results • Consider inactive Ge layer – active Ge volume • Using this geometry we will calculate amount of radioactive isotopes in CsI crystal, CsI powder and PMT background.
Geometry of 100% HPGe detector at CPL (provided by manufacturer) R 41mm H 86.3mm
Efficiency Calculation ⅰ) Calculation of measured efficiency ⅱ) Calculation of simulated efficiency
Compare experimental data to simulation of HPGe detector at CPL Experiment data * 1.4 Experiment data • Efficiency discrepancy was shown in CPL HPGe detector. • We assumed three possibilities. • 1. due to incorrect detector geometry • 2. due to problems in GEANT4 program • 3. due to incorrect source information Simulation result 40% more larger than experiment result
Experiment data * 1.4 Experiment data • 2.2 Efficiency difference • Compare experimental data to simulation of HPGe at NETEC Simulation result 40% more larger than experiment result
Compare two simulation results CPL NETEC Almost same
Simulation tests • EGS4 and GEANT3 test with mixed source-within 7% agreeable • Relative efficiency check CPL and NETEC simulation result 18% more larger than NaI crystal
137Cs source at top and side position • Compare efficiency and Compton edge shape Simulation efficiency larger than experiment result but Compton Edge shape is almost same
Top 204mm HPGe Side 128mm • Testing with 152Eu and 137Cs sources • Two Eu-152 (KRISS, NIST) at top position
3 Ge dead layer • Dead layer correction check-up mentioned on other papers • NIMA vol.496 p390 dead layer correction HPGe 28% dead layer 0.65mm Active volume 121.574 /124.879 (2.65% reduced) • NIMA vol.498 p340 charge collection time correction • NIMA vol.487 p477 dead layer correction HPGe 40% dead layer 0.6mm Al-Ge distance increased by 8mm
The CPL HPGe detector geometry correction • Outer Ge dead layer : 1.12mm • Active volume : 374.15cm3 (7.2% reduced)
137Cs source • Relative efficiency
6. Conclusion • With manufacturer geometry, efficiency differences was occurred between experimental data and simulation data. • We assumed three possibilities-a. detector geometry, b. simulation program, c. source information, then tested each possibility. • Our tests indicate that there are unknown parameters like inactive layers in HPGe detector. • Adding inactive Ge layer in simulation code, efficiency difference reduced. • Using this HPGe geometry included inactive Ge layer, calculation of amount radioactive isotopes in CsI crystal and PMT can be obtained.