NEW MEASUREMENTS OF CHARGE-CHANGING CROSS-SECTIONS IN CARBON AND HYDROGEN TARGETS ABOVE 2-GEV PER NUCLEON - EVIDENCE FOR AN ENERGY-DEPENDENCE THAT MAY STRONGLY AFFECT ESTIMATES OF THE ENERGY-DEPENDENCE OF COSMIC-RAY DIFFUSION IN THE GALAXY

We have recently measured the fragmentation of approximately 15 GeV pe r nucleon Si nuclei in CH2 and C targets and, by subtraction, H target s, at Brookhaven. The total-charge-changing cross section for Si is la rger than we measured earlier at approximately 1.3 GeV per nucleon. At the same time the partial cross sections for charge changes of 1 and 2 are approximately 20%-50% smaller for all targets including H. An ov erall systematic behavior is observed for the ratio of the 15 GeV per nucleon to 1.3 GeV per nucleon partial cross sections as a function of the magnitude of the charge change. These results, when coupled with earlier measurements of the fragmentation of high energy O --> N and S i --> Al by the Siegen group (Hirzebruch et al. 1991), which also show a decrease in the partial cross sections for charge changes of 1 and 2 above 1-2 GeV per nucleon in H targets, have major implications for the energy dependence of the propagation of Galactic cosmic rays. This is because the B/C ratio is used to determine this dependence and the main channel for B production, C --> B, should also show a decreasing cross section with increasing energy according to the above argument. We will present this new cross-section data and examine their implica tions for the propagation of cosmic rays.