Production of 7Be, 10Be, 22Na, and 26Al by 4He-Induced Reactions up to 170 MeV

Details Production of 7Be, 10Be, 22Na, and 26Al by 4He-Induced Reactions up to 170 MeV Production of 7Be, 10Be, 22Na, and 26Al by 4He-Induced Reactions up to 170 MeV

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27..314l&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 314

Physics

Scientific paper

Solar and galactic ^4He particles up to now are not properly considered in model calculations of the production of cosmogenic nuclides in extraterrestrial matter and in the upper atmosphere. ^4He-particles are either neglected because of their low abundances (<10%) in the cosmic radiation or are taken into account in a crude approximation simply on the basis of their contribution to energy input. This situation is partially caused by the fact, that most excitation functions for the ^4He-induced production of cosmogenic nuclides from cosmochemically relevant target elements are poorly known, if at all. In order to improve this situation, a systematic investigation of the production of residual nuclides by ^4He-induced reactions involving the target elements C, N, O, Mg, Al, Si, Mn, Cu, Zr, and Nb was performed. The target element Mn was included in this study in order to allow for comparison with an earlier investigation from our group (1). Irradiation experiments with ^4He were performed at the sector cyclotron at PSI/Villigen (E = 119.7 MeV) and at the isochronous cyclotron JULIC at KFA Julich (E = 170.5 MeV). The stacked foil technique was used to measure the excitation functions over wide energy ranges. Most target elements were irradiated as pure element foils with thicknesses between 0.025 mm and 1 mm. Only for N, O, and Mn disks of Si3N4 and SiO2 and foils from a Mn/Ni alloy were used, respectively. The contributions to the residual nuclei production from Si resp. from Ni was later corrected for. The beam currents were determined using ^27Al(^4He,4p5n)^22Na as monitor reaction and were additionally checked by Faraday cup measurements. Residual nuclides were measured by gamma spectrometry and by accelerator mass spectrometry. So, excitation functions for 92 reactions were measured. Together with earlier work from our group (1-3) there now exists a consistent set of excitation functions for the production of residual nuclides from thresholds to 170 MeV for the target elements C, N, O, Mg, Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zr, and Nb, covering most cosmochemically relevant target elements, which allows, moreover, to test nuclear reaction models of ^4He-induced reactions for light and medium-weight elements. Here we report the results of the new measurements laying particular emphasis on the production of the important cosmogenic nuclides ^7Be, ^10Be, ^22Na, and ^26Al. The new data are compared with earlier measurements and analyzed within the framework of the hybrid model of preequilibrium reactions (4) using the code ALICE LIVERMORE 87 (5). Furthermore, the new excitation functions are used to estimate the contribution of cosmic ray ^4He particles to the production of cosmogenic nuclides. Acknowledgement: This work was supported by the Deutsche Forschungsgemeinschaft and by the Swiss National Science Foundation. References: (1) Michel R. et al. (1983) In Nuclear Data for Science and Technology (ed. K.H. Bockhoff), pp. 599-602. D. Reidel Publ. Company, Dordrecht, Holland. (2) Michel R. and Brinkmann G. (1980) Nucl. Phys. A 338, 167-189. (3) Michel R. et al. (1983) Radiochimica Acta 32, 173-189. (4) Blann M. (1972) Phys. Rev. Letters 27, 337-340. (5) Blann M., ALICE LIVERMORE 87, priv. comm. (1987).

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