Model calculations for neutron-induced reactions in meteorites and planetary surfaces

Abstract This study investigates the capabilities of the GEANT4 Monte Carlo toolkit to quantitatively predict neutron production, neutron transport, and nuclide production by neutron capture reactions in cosmochemical relevant objects. The model reproduces neutron densities measured in the lunar surface within the experimental uncertainties, which is a major improvement compared to earlier studies. Since, for many applications in meteorites and planetary surfaces, nuclide production by neutron capture is of importance, the production of $$^{41}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>41</mml:mn> </mml:mmultiscripts> </mml:math> Ca and $$^{60}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>60</mml:mn> </mml:mmultiscripts> </mml:math> Co is studied as an example. In addition, shifts in the stable isotope ratios $$^{157}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>157</mml:mn> </mml:mmultiscripts> </mml:math> Gd/ $$^{160}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>160</mml:mn> </mml:mmultiscripts> </mml:math> Gd, $$^{158}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>158</mml:mn> </mml:mmultiscripts> </mml:math> Gd/ $$^{160}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>160</mml:mn> </mml:mmultiscripts> </mml:math> Gd, $$^{149}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>149</mml:mn> </mml:mmultiscripts> </mml:math> Sm/ $$^{152}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>152</mml:mn> </mml:mmultiscripts> </mml:math> Sm, and $$^{150}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>150</mml:mn> </mml:mmultiscripts> </mml:math> Sm/ $$^{152}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>152</mml:mn> </mml:mmultiscripts> </mml:math> Sm (and combinations thereof) are modeled and compared to experimental data. The model describes experimental $$^{41}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>41</mml:mn> </mml:mmultiscripts> </mml:math> Ca activity concentrations in different types of meteorites and the lunar surface within the uncertainties. In contrast, it fails to describe $$^{60}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>60</mml:mn> </mml:mmultiscripts> </mml:math> Co activity concentrations. In addition, it is difficult to consistently model the isotope shifts $$^{157}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>157</mml:mn> </mml:mmultiscripts> </mml:math> Gd/ $$^{160}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>160</mml:mn> </mml:mmultiscripts> </mml:math> Gd and $$^{150}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>150</mml:mn> </mml:mmultiscripts> </mml:math> </jats:inline-form