Study on Proton Energy Measurement by Using a Si(Li) Detector Stack

Abstract

Proton energy measurements using a Si(Li) detector stack composed of two 2-mm-thick and one 5-mm-thick Si(Li) detectors were performed at the MC-50 cyclotron of KIRAMS (Korea Institute of Radiological and Medical Sciences). The maximum energy that could be measured with semiconductor detector was limited by the thickness of the detector. In the case of the energy measurement using a 5-mm-thick Si(Li) detector, it was not possible to measure a proton energy above 30 MeV [1]. This measurable range can be extended to 40 MeV by using a Si(Li) detector stack with a 9-mm total thickness. The proton energy from the cyclotron was 45 MeV, and the active areas of the 2-mmand 5-mm-thick detectors were 150 mm2 and 75 mm2, respectively. The electronic signals from the three detectors were processed by using preampli ers (ORTEC 142AH), shaping ampli ers (ORTEC 572A), attenuators and fast analog-to-digital converter (VME FADC, 64 k). And a summing and analysis process was performed using a ROOT-based data acquisition (DAQ) program developed by the European Council for Nuclear Research (CERN). The proton energy was changed from 6.9 MeV to 37.5 MeV by using 0.55.7-mm-thick Al degraders. The proton energy was calculated by using SRIM 2003. The response function of the Si(Li) detector stack had good linearity and agreed well with the calculated results. Also, the experiments to measure the same proton energy using multiple stacked Si(Li) detectors instead of a single Si(Li) detector with a similar thickness showed no big di erence or any problems. The maximum di erence between these two cases was less than 3 %.