Production rates and proton‐induced production cross sections of ¹²⁹I from Te and Ba: An attempt to model the ¹²⁹I production in stony meteoroids and ¹²⁹I in a Knyahinya sample

Abstract

Abstract-Proton-induced production cross sections of 129 I from Te and Ba are presented. Earlier assumptions that Te is the most important target element in meteoroids are confirmed. Based on this data set and the experimental production rates of 129 I from thick-target experiments, the production of 129 I in stony meteoroids is modeled using a GCR flux density of 4.06 cm −2 s −1 . The results of this modeling must be considered preliminary because the contribution from neutron capture on 128 Te needs further investigation. We obtained modeled production rates that agree with experimental results for samples from two medium-sized meteorites (Abee and Knyahinya). However, we find that this model does not describe 41 Ca in lunar rocks well and seems to overestimate 129

Cosmogenic nuclides in stony meteorites revisited

“…about a factor of two lower than the experimental value. The new model prediction for Allende is substantially different from our earlier estimate (Schnabel et al 2004), which is due to the fact that in the current study we use particle spectra for C chondrites, whereas in our earlier approach we approximated the spectra for C chondrites with spectra for H chondrites, which was obviously not correct. With L-chondrite spectra we calculate a production rate of 1.3 × 10 −3 dpm/kg.…”

“…Assuming 6260 µg/kg Ba and 526 µg/kg Te (cf. Schnabel et al 2004), the modeled production rate is ~3.31 × 10 −4 dpm/kg, which is in perfect agreement. In a 13 cm deep sample of the EH4 chondrite Abee, which had a preatmospheric radius of ~30 cm (Goswami 1983), Nishiizumi et al (1983) measured a 129 I production rate of 1.4 × 10 −3 dpm/kg.…”

“…In contrast, the 27% effect for high shielding depths and in large objects directly compromises our interpretation of 129 I production rates in such objects, because its production in them is dominated by thermal neutron capture. Schnabel et al (2004) measured a 129 I production rate of (3.30 ± 0.25) × 10 −4 dpm/kg in a Knyahinya sample with a shielding depth of about 10 cm. Assuming 6260 µg/kg Ba and 526 µg/kg Te (cf.…”

“…For 129 I the new model calculations update our earlier estimates (cf. Schnabel et al 1998Schnabel et al , 2004. In large meteoroids a significant part of 129 I is produced via neutron capture on 128 Te with subsequent α-decay.…”

Monte Carlo simulation of GCR neutron capture production of cosmogenic nuclides in stony meteorites and lunar surface

“…The advantage of today's microscopic Monte Carlo codes such as MCNP is that the ENDF/B-VI library is directly coupled to the code and allows for direct nuclide production rate values as an output of the transport calculation. Recently, the JEF-2.2 data were also used for the n-capture CN production calculations on some isotopes (Schnabel et al 2004).…”