Range of 6- to 18-Mev Protons in Be, Al, Cu, Ag, and Au

An experimental study has been made of the range and straggling of protons of 6 to 18 Mev in Be, Al, Cu, Ag, and Au. The following values of $I$ have been obtained: Be: 63.4 ev, Al: 166.4 ev, Cu: 375.6 ev, Ag: 585 ev, and Au: 1037 ev. New range-energy curves are computed using these data and the low-energy data summarized by Allison and Warshaw. The mean straggling is evaluated to approximately 5%. In magnitude it is in agreement with theory but there is a lack of symmetry above and below the 50% point which remains unexplained.