Straggling effects in a proton recoil neutron spectrometer

The influence of proton straggling on the efficiency and resolution of a combined proton recoil and time-of-flight neutron spectrometer, TANSY, is studied. The spectrometer is designed for 14 MeV neutron diagnostics at JET (Joint European Torus). Energy and angular distributions for 14 MeV protons slowing down in polyethylene foils with various thicknesses are presented. The results indicate that for a foil thickness of 1.24 mg cm⁻² about 10% of the protons lose more than twice the average energy loss. Furthermore, the angular straggling leads to a coincidence loss of 4.6 ± 0.4%.