Production of krypton and xenon isotopes in thick stony and iron targets isotropically irradiated with 1600 MeV protons

Abstract

Abstract-Two spherical targets made of gabbro with a radius of 25 ern and of steel with a radius of 10 cm were irradiated isotropically with 1600 MeV protons at the SATURNE synchrotron at Laboratoire National Satume (LNS)/CEN Saclay, in order to simulate the production of nuclides in meteorites induced by galactic cosmic-ray protons in space. These experiments supply depth-dependent production rate data for a wide range of radioactive and stable isotopes in up to 28 target elements. In this paper, we report results for 78Kr, 80-86Kr isotopes in Rb, Sr, Y and Zr and for 124Xe, 126Xe, 128-132Xe, 134Xe, 136Xeisotopes in Ba and La. Krypton and xenon concentrations have been measured at different depths in the spheres by using conventional mass spectrometry. Based on Monte-Carlo techniques, theoretical production rates are calculated by folding depth-dependent spectra ofprimary and secondary protons and secondary neutrons with the excitation functions of the relevant nuclear reactions. The comparison ofthe model calculation results with experimental data in the thick target experiments performed at LNS and previously at CERN have allowed adjustments of the poorly known excitation functions ofneutron-induced reactions. Thus, for the two experiments at SATURNE, excellent agreement is obtained between experimental and calculated production rates for most Kr and Xe isotopes in all investigated target elements. Only Xe production in Ba in the gabbro is underestimated by the calculations by -25%. This work validates the approach of the thin-target model calculations of cosmogenic nuclide production rates in the attempt ofmodeling the interaction of galactic cosmic-ray protons with stony and iron meteorites in space as well as with lunar samples.

Isotopic evidence for a Martian regolith component in shergottite meteorites

“…Also, in this context, Regnier et al [1979] pointed out that the spallation 83 Kr is produced predominantly by high‐energy reactions in Sr, Zr, and Y, but the low‐energy particle reactions on Rb are responsible for significant contributions to 84 Kr. This observation is consistent with the results obtained by Gilabert et al [2002] who irradiated Rb, Sr, Zr, and Y targets emplaced in large gabbro spheres with 1600 MeV protons at the Saclay synchrotron. They determined the spallation Kr ratios mass spectrometrically to be 84 Kr/ 83 Kr (Rb) ∼ 1.28; 84 Kr/ 83 Kr (Sr) ∼ 0.62; 84 Kr/ 83 Kr (Zr) ∼ 0.21; and 84 Kr/ 83 Kr (Y) ∼ 0.35.…”

“…For calculating the Kr isotopic contributions from GCR, SCR, and fast neutron (N, xp yn) reactions in these samples, the abundances of the main target elements, Rb and Sr, are required. In this connection, we noted earlier that Zr and Y targets do not contribute significantly to the 83 Kr and 84 Kr production by low‐energy (10–100 MeV) fast neutron reactions because their reaction thresholds are much higher, i.e., >40 MeV than Rb and Sr [ Gilabert et al , 2002]. Wooden et al [1982] and Nyquist et al [1986] determined that the Rb and Sr abundances in the 27 sample were 1 ppm and 15.5 ppm, respectively, using isotope dilution techniques.…”

“…83 Kr and 84 Kr are unlikely to be produced by thermal neutron‐capture (n, γ ) reactions, because either potential target nuclides are lacking or relevant capture cross sections are low. Only neutrons with E ≥ 10 MeV interacting with Rb and Sr targets in the Martian regolith materials can contribute to the production of 83 Kr N and 84 Kr N isotopic excesses, because the production cross sections for these reactions are relatively high [ Gilabert et al , 2002; Hohenberg et al , 1978]. Rb and Sr are the main target elements in this case because, for similar nuclear reactions on Zr and Y targets, the energy thresholds are high (>40 MeV) and hence their contribution to 83 Kr N and 84 Kr N production is small [ Gilabert et al , 2002].…”

Noble gases in angrites Northwest Africa 1296, 2999/4931, 4590, and 4801: Evolution history inferred from noble gas signatures

“…The isobaric fraction yield was previously 0.95 (Marti ) and 0.92 (Gilabert et al. ). T 81 is calculated for all angrites showing a clear spallogenic Kr signal (other than NWA 1296; Table ).…”

Xenon in Archean barite: Weak decay of 130Ba, mass-dependent isotopic fractionation and implication for barite formation

“…The high energy particle component of cosmic rays on the Moon's surface is essentially composed of protons, in contrast to a neutron-dominated cosmic ray flux at the surface of the Earth (Leya et al, 2003). The cross sections for proton-and neutron-induced productions of 126 Xe has been estimated at 50 mb and 30 mb, respectively (with an incident flux of 1600 MeV, Gilabert et al, 2002). With these corrections, the cosmogenic 126 Xe production rate at the Earth's surface from Ba spallation in samples is 3.6 ± 0.3 Â 10 À19 mol g À1 Ma À1 , and the corresponding residence time at sea level is 23,000 ± 12,000 a.…”