Proton Energy Measurement Using Si(Li) and Scintillation Crystal Detector in the MC-50 Cyclotron

Absolute proton beam energy measurement with Si(Li) detector has been performed in the MC-50 cyclotron. It is known that the measurement of the absolute energy of the medium energy proton with high accuracy is very important for some experiments concerned with nuclear physics, space device test, etc. For the absolute particle energy measurement, the semiconductor detector has been recognized as a very useful tool because of their total particle energy absorbing characteristics. In the case of a scintillation detector, a part of particle energy can be lost through quenching process during penetrating the detector material and it could be a reason to increase the energy measurement error. The thicknesses of Si(Li) detector and BGO scintillation detector were 5mm and 30mm, and the sizes of active area are 75mm(2) and 49mm(2). Even though, the Si(Li) detector was originally designed and fabricated proper to the operation at the atmosphere, Si(Li) detector was installed in the vacuum chamber with the 50um thickness Al beam entrance window for more accurate measurement. The energy calibration of Si(Li) detector was done with Am-241 alpha sources. The proton beam energies from the cyclotron are 35MeV and 45MeV, and the beam current is below 0.5nA. The proton beam energy extracted through the 2mm thickness Al exit window was changed and controlled by Al degrader and air thickness between exit window and detector. The change of proton beam energy property such as mean energy and energy spread has been measured using Si(Li). The results are compared to the calculated results by Monte-Carlo code simulation and measured results by the BGO scintillation detector.