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

Abstract

Abstract-A purely physical model based on a Monte Carlo simulation of galactic cosmic ray (GCR) particle interaction with meteoroids is used to investigate neutron interactions down to thermal energies. Experimental and/or evaluated excitation functions are used to calculate neutron capture production rates as a function of the size of the meteoroid and the depth below its surface. Presented are the depth profiles of cosmogenic radionuclides 36 Cl, 41 Ca, 60 Co, 59 Ni, and 129 I for meteoroid radii from 10 cm up to 500 cm and a 2π irradiation. Effects of bulk chemical composition on n-capture processes are studied and discussed for various chondritic and lunar compositions. The mean GCR particle flux over the last 300 ka was determined from the comparison of simulations with measured 41 Ca activities in the Apollo 15 drill core. The determined value significantly differs from that obtained using equivalent models of spallation residue production.

Pd–Ag chronometry of iron meteorites: Correction of neutron capture-effects and application to the cooling history of differentiated protoplanets

“…In brief, the model is based on the same particle spectra as used by Ammon et al (2008), and the cross sections for thermal and epithermal neutron capture reactions were taken from the JEFF-3.0A database. For the primary GCR particle flux we assume 2.99 cm À2 s À1 (Kollár et al, 2006). In addition to the thermal and epithermal neutron capture reactions on Pd and Ag, we also consider reactions induced by fast particles (i.e., protons and neutrons with energies of a few MeV) on Ag, Pd, and Cd to fully cover all possible reaction pathways.…”

Correlated cosmogenic W and Os isotopic variations in Carbo and implications for Hf–W chronology

“…Briefly, the model is based on the particle spectra for primary protons, secondary protons, and secondary neutrons, calculated via Monte-Carlo techniques and the cross sections for the relevant nuclear reactions. For calculating neutron capture rates we rely on cross sections compiled in the JEFF-3.0A database and we assume a primary GCR particle flux of 2.99 cm À2 s À1 (Kollár et al, 2006). In addition to the thermal and epithermal neutron capture reactions, we also consider reactions by fast particles, i.e., protons and neutrons with energies above a few MeV.…”

THE ELUSIVE60Fe IN THE SOLAR NEBULA

“…Using Equation (4), we calculated the 60 Ni production for the four iron meteorites Bogou, Sikhote Alin, Ningbo, and Yardymly to be less than 0.01 ppm (see Table 2). In addition, we computed an extreme case with low Ni and high Co concentrations and a maximum exposure age of 1.5 Ga. For the production rates, we used the maximum production rate of 60 Ni due to the decay of 60 Co reported by Kollar et al (2006) for H chondrites of 100,000 atom 60 Co minute −1 [kg Co] −1 and we get an effect of 1.5 ppm.…”