9406016 Marti In the last few years, several cosmic ray produced radionuclides (10Be, 14C, 26Al, 36Cl), as well as stable nuclides 3He, 21Ne and 22Ne have been discovered in terrestrial surface materials. Some of these nuclides are now employed as tracers in studies of geophysical and geological phenomena and open up a new field of study that is expected to provide essential data on rates of change in global change research. Such studies require accurate production rates, present and past, which are not currently available . We are using a direct method for the determination of some present production rates by exposing relevant targets at mountain altitudes. Furthermore, we are evaluating the production rate ratio P21/P26 of the cosmic ray produced nuclides 21Ne and 26Al by isotopic measurements of Ne in samples whic1h were exposed for 104-1047a. Our experimental data are consistent with inferred neutron reactions in a 600 MeV proton irradiation experiment (Aylmer et al., 1987), but do not agree with theoretical predictions. Measurements of the 3He21Ne ratio show that 3He is incompletely retained in quartz. Therefore, 21Ne production rates and accurate 21Ne10Be and 21Ne/26Al production rate ratios are expected to provide essential information for the evaluation of erosion rates and to define geological processes (uplift, variations in ice cover, etc.) Further calibrations, such as activation energies for long-term retention of Nec, are still required, but we are now ready for research on global change issues. We propose to study the long-term exposure history of the Antarctic ice field (the major controlling unit of the sea level). We plan to evaluate the 21Ne records in quartz separates of documented rocks from the Allan Hills region and to study a section adjacent to the ice field in which the radionuclides 26Al and 10Be were measured (Nishiizumi et al., 1991). These authors estimate that rocks in this region may have been exposed for millio ns of years without ice cover, but caution that the record of an integrating stable nuclide is required to define the early history. We plan to also include samples from the same area which indicate very erosion rates. The purpose is to increase the recorded time interval of cosmic ray exposure which is limited by the "erosion equilibrium".
