A method for measuring the uniformity of thin targets by means of an alpha source and a Q3D-spectrograph

Abstract The energy straggling of 8.78 MeV α-particles from a 212 Po source in thin targets was investigated. The α-particles were momentum-analyzed in a Q3D-spectrograph and detected in a multiwire proportional counter in the focal plane of the spectrograph. Targets of various materials, 5–100 μm/cm 2 thick, prepared with different parting agents, were investigated. The incident angle of the α-particles was varied from 0° (normal incidence) to 50°. The observed energy loss distributions of the transmitted α-particles are compared to calculated theoretical distributions. The ratio of experimental to theoretical straggling width is used to characterize target non-uniformity. In all cases the non-uniformity defined in this way was found to increase with the angle of incidence. The size of this effect is however strongly dependent of the parting agent used in the production of the targets.