Proton Energy Loss Through Thin Gold Films

The Student Proton Accelerator at Gettysburg College (SPAGetty) generates proton beams with energies between 50 and 200 keV. These low-energy beams can be used to measure energy loss by protons through thin films, a phenomenon important for solid-state ion detectors with thin "dead" layers that ions traverse before reaching the active region. Accurate modeling of this energy loss is essential for high-precision measurements, such as the ongoing neutron-lifetime measurement at NIST. To study this, a nanoscale gold film was fabricated by thermally evaporating a 99% gold wire in a high vacuum onto a portion of a PIPS detector. The film's thickness was inferred from UV-Vis measurements of glass slides evaporated at the same time. Proton energy measurements were taken by directly hitting the silicon layer or through a layer of gold. Amplified detector signals were sorted by an MCA, and their pulse heights were calibrated using known sources. SRIM ion-transport software was used to simulate intrinsic data, which was then convoluted with a Gaussian instrumental response and compared with experimental data.