Proton energy straggling measurement in metal foils by using a Si(Li) detector

Measurements of energy loss and transmitted energy straggling were performed using a Si(Li) detector for 28.6 MeV protons incident on thin foil targets of Al, Cu and Au in air. The straggling widths were studied as functions of the target thickness and the target species. The initial proton beam energy from the MC-50 cyclotron was 45 MeV and it was decreased to 28.6 MeV by passing it through a 2-mm-thick Al window, 34.5 cm of air, a 2-mm-thick Al degrader and 144.5 cm of air. This 28.6 MeV proton beam was incident on Al, Cu and Au foils of various thicknesses installed in front of a Si(Li) detector. As a result, the energy loss strongly depended on the target thickness and species and the transmitted energy straggling was not related to the target species. Compared with the calculated results based on a simple Bohr's expression, the measured values agreed with the calculated ones in the low energy loss region less than 60% of the incident proton beam energy. In the high-loss region, there was big mismatch of more than 25%.