Stopping powers of Al and Mo for protons from 0.3 to 3.0 MeV

Abstract

Stopping powers of Al and Mo have been measured for protons in the respective energy ranges of 0.3–3.0 and 0.4–3.0 MeV with a surface barrier silicon detector. The uncertainty of the present results is ±0.35%. Above 0.8 MeV the present results for Al agree well with the Aarhus data of Anderson et al. [Phys. Rev. A 16 (1977) 1929] and the tabulated values of ICRU Report 49 (Stopping Powers and Ranges for Protons and Alpha Particles (International Commission on Radiation Units and Measurements, 1993)) (ICRU values). Below 0.8 MeV, however, ratios of the present data for Al to ICRU values show a slight decrease with decreasing proton energy. The decrease amounts to ∼1% at 0.3 MeV. In the case of Mo the ratios also decrease with decreasing proton energy below 2.0 MeV. The decrease reaches ∼8% at around the lowest energy, 0.4 MeV. Because the Bethe–Bloch formula is known to well reproduce stopping powers for protons above ∼1 MeV, the mean excitation energies, the I values, of Al and Mo have been extracted from the results for 1–3 MeV protons. These I values are compared with published values.