SPALLATION REACTIONS IN AL-27 AND FE-56 INDUCED BY 800 MEV PROTONS

Spallation of Al-27 and Fe-56 by 800 MeV protons was investigated at t he WNR facility of the Los Alamos National Laboratory. Production cros s sections for a considerable number of residual nuclei were determine d for both targets by use of three different methods. Because of the s pecific time structure of the WNR beams it was possible to observe bot h the prompt gamma radiation resulting from the final stage of the spa llation reaction and the gamma radiation due to the decay of short-liv ed residual nuclei by delayed gamma-ray spectroscopy. The activity of long-lived residual nuclei was measured several weeks after the irradi ation with a calibrated high-purity Ge gamma-ray detector. In the prom pt gamma-ray spectrum it was possible to observe the transitions from the first excited 2(+) state to the ground state for all even-even nuc lei strongly populated in the spallation reactions and, from these dat a. to deduce the production cross sections of these mostly stable nucl ei in addition to the short- and long-lived residual nuclei mentioned before. In this way production cross sections for 36 nuclides from the proton interactions with Fe-56 and for 12 nuclides in the case of Al- 27 could be measured; in addition, meaningful upper limits were obtain ed for a number of further nuclides in both cases. The results are in reasonable agreement with previous measurements obtained by different methods; for a number of nuclides, production cross sections were dete rmined for the first time. The present data as well as the results of all previous measurements an compared with the predictions of the semi empirical systematics and with quantum molecular dynamics calculations .