Stopping powers of N-2 and O-2 for protons from 4.0 to 13.0 MeV

Stopping powers of N-2 and O-2 for protons from 4.0 to 13.0 MeV were measur ed with an accuracy of +/-0.8% using a surface barrier silicon detector set inside a sealed gas cell. Energy loss in the gases was obtained from the p eak shift of the proton pulse heights measured separately with and without gas filling. One-half of the experimental data obtained for molecules N-2 a nd O-2 was compared with that of experimental data for 4.4 MeV protons repo rted by Brolley and Ribe [Phys. Rev. 98 (1955)1112], the calculated values given in ICRU Report 49 [Stopping Powers and Ranges for Protons and Alpha P articles (International Commission on Radiation Units and Measurements, 199 3)], and the values calculated by Andersen and Ziegler's formula [Hydrogen Stopping Powers and Ranges in All Elements (Pergamon, New York, 1977)] for atoms N and O. By analyzing the experimental results with the modified Beth e-Bloch formula that includes the Parkas correction term, we extracted the mean excitation energies, the I values, for N and O. The I values were comp ared with other reported values. (C) 1999 Elsevier Science B.V. All rights reserved.