Thin-target cross sections of proton-induced reactions on barium and solar cosmic ray production rates of xenon-isotopes in lunar surface materials

Thin-target excitation functions for the proton-induced production of radionuclides and stable Xe-isotopes from barium were measured at the JULIC isochronous cyclotron of the IKP/KFA Jülich up to E_p=45MeV using the stacked-foil technique. Additionally, thin-target cross sections for the production of radionuclides from Ba were determined at 147.5 MeV using the synchrocyclotron of the IPN Orsay. For stable Xe-isotopes the thin-target data are in severe disagreement with earlier measurements. The reasons for these discrepancies are discussed. For the experimental excitation functions a detailed hybrid model analysis was performed using the code ALICE LIVERMORE 87, which in contrast to earlier formulations of the model takes into account experimental mass data, multiple preequilibrium nucleon emission and non-integer initial exciton numbers. In general, the a priori calculations satisfactorily reproduce the experimental excitation functions. Some discrepancies have to be attributed to the neglect of preequilibrium emission of alpha-particles and to the use of average nuclear parameters in the calculations for ¹³⁸Ba, which has a magic neutron configuration. Using the new experimental excitation functions up to 45 MeV and calculated ones between 45 to 200 MeV, depth-dependent production rates for the production of stable Xe isotopes from Ba by solar cosmic ray protons in the lunar surface are calculated and compared with the results of earlier investigations. The improvements still necessary to come to a complete and adequate description of cosmogenic Xe isotopes in extraterrestrial matter are outlined.