Proton Energy Loss Through Thin Films

The neutron lifetime is vital to particle physics and cosmology, impacting predictions from Big Bang Nucleosynthesis. In-beam measurements, which detect proton decay products, are sensitive to proton energy loss in detector dead layers. This study quantifies that loss using a Van de Graaff accelerator to direct 40–200 keV protons onto PIPS detectors with and without thin evaporated metal films. Technical problems prevented deposits of gold layers similar to those present on surface-barrier detectors, so we deposited silver as a test case. Film thicknesses were measured using a 3D optical profiler. Proton energy spectra were analyzed to determine energy loss through shifts in spectral peaks between bare and coated detectors. The experimental results were benchmarked against SRIM (Stopping and Range of Ions in Matter) simulations, demonstrating strong agreement across multiple proton beam energies and varying silver film thicknesses.