Fast-Neutron Activation of Long-Lived Isotopes in Enriched Ge

TL;DR

This study measures the production of long-lived isotopes in enriched germanium due to high-energy neutrons, compares predictions with experimental data, and assesses implications for background in double-beta decay experiments.

Contribution

It provides new measurements of isotope production rates in enriched germanium at high neutron energies, highlighting discrepancies with existing cross-section models.

Findings

Measured production rates are about one-third of CEM03.02 predictions.

Uncertainty in high-energy cross sections dominates total production rate uncertainty.

Results inform background estimates for germanium-based double-beta decay experiments.

Abstract

We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge}, \nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are critical in understanding background in Ge detectors used for double-beta decay experiments. They are produced by cosmogenic-neutron interactions in the detectors while they reside on the Earth's surface. These production rates were measured at neutron energies of a few hundred MeV. We compared the measured production to that predicted by cross-section calculations based on CEM03.02. The cross section calculations over-predict our measurements by approximately a factor of three depending on isotope. We then use the measured cosmic-ray neutron flux, our measurements, and the CEM03.02 cross sections to predict the cosmogenic production rate of these isotopes. The uncertainty in extrapolating the cross section model to higher energies dominates the total uncertainty in the cosmogenic production rate.