Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.579s&link_type=abstract
Meteoritics, vol. 30, no. 5, page 579-580
Other
Beryllium-10, Carbon-14, Cobalt-56, Cosmic Rays, Galactic, Solar, Cosmogenic Nuclides, Lunar Rocks, Manganese-54, Meteorites, Salem, Sodium-22
Scientific paper
Radionuclides produced by cosmic rays in extraterrestrial materials archive information that can be used to determine cosmic-ray fluxes and to study the history of the irradiated object. Long-lived radionuclides give information about the last ~5 Myr; short-lived radionuclides give information about recent events. To calculate the solar cosmic ray (SCR) flux from measured depth profiles for cosmogenic radionuclides produced in lunar rocks, accurate and precise cross section values for the production of these radionuclides from all relevant elements are needed. About 98% of SCR and ~87% of galactic cosmic rays (GCR) falling on extraterrestrial materials are protons. Cross section measurements were made using three proton accelerators to cover the energy range ~20 - 500 MeV. Thin target techniques used in the irradiations minimized the number of protons scattered out of the stack and the neutron production within the stack. After irradiation, the short-lived radionuclides e.g. 22Na, 7Be, 24Na, 54Mn, and 56Co were determined using gamma-ray spectroscopy. 14C, 10Be, and 26Al were determined using Accelerator Mass Spectrometry. Our main objective is to measure the production cross sections of long-lived radionuclides. We have reported new cross section values for making 10Be from O and 14C from O, Mg, Al, Si, Fe, and Ni [1,2]. Using these new results, better estimates for the solar proton flux over several time periods in the past were determined [3]. However, no single value for the SCR flux could explain the measured data from different time periods. Further cross section measurements are being made to verify that the values used in these estimates were accurate. Irradiations designed to give good cross section measurements for long-lived radionuclides also give good cross section measurements for short-lived radionuclides. Results will be presented for proton production cross sections of 22Na from Mg, Al and Si, and 54Mn and 56Co from Fe and Ni; some values at low energies were reported previously [4]. These cross sections and other reported measurements [5, 6] will be used to improve the estimates of the recent SCR fluxes from the depth profiles for 22Na measured in lunar rocks [7, 8], and to better understand the SCR cosmogenic radionuclide production observed in Salem [9] and other other extraterrestrial materials. References: [1] Sisterson J. M. et al. (1992) LPS XXIII, 1305. [2] Sisterson J. M. et al. (1995) LPS XXVI, 1309. [3] Rao M. N. et al. (1994) GCA, 58, 4231. [4] Beverding A. M. et al. (1994) USGS Circular 1107, 29. [5] Michel R. and Stueck R. (1984) Proc. LPSC 14th, in JGR, 89, B673. [6] Bodemann R. et al. (1993) Nucl. Instr. Meth. Phys. Res., B82, 9. [7] Reedy R. C. (1977) Proc. LSC 8th, 825. [8] Fruchter J. S. et al. (1982) LPS XIII, 243. [9] Evans J. C. et al. (1987) LPS XVIII, 271.
Beverding A.
Caffee Marc W.
Castaneda C.
Cloudt S.
Donahue Douglas J.
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