Energy straggling ofHe4ions below 2.0 MeV in Al, Ni, and Au

Energy straggling of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ ions has been measured in thin films of Ni, Al, and Au. The observed straggling is roughly proportional to the square root of thickness and appears to have a slight energy dependence for all these materials. The results are compared with predictions of the theories of Bohr, Lindhard and Scharff, and of Chu and Mayer. Both the Ni and Au results are below the predictions of Bohr and are above the predictions of Chu and Mayer, and of Lindhard and Scharff. The Al measurements are above predictions of all these theories.