Fast-Neutron Activation of Long-Lived Nuclides in Natural Pb

TL;DR

This study quantifies the production rates of long-lived nuclides in natural lead caused by high-energy neutrons, providing data relevant for low-background experiments using lead shielding.

Contribution

It presents the first measurements of cosmogenic production rates of specific long-lived nuclides in natural lead using a neutron beam and scaling to cosmic ray flux.

Findings

Measured production rates of Hg-194, Pb-202, and Bi-207 in natural lead.

Provided scaling of neutron-induced activation to cosmic ray conditions.

Data aids in understanding background in low-background physics experiments.

Abstract

We measured the production of the long-lived nuclides Bi-207, Pb-202, and Hg-194 in a sample of natural Pb due to high-energy neutron interactions using a neutron beam at the Los Alamos Neutron Science Center. The activated sample was counted by a HPGe detector to measure the amount of radioactive nuclides present. These nuclides are critical in understanding potential backgrounds in low background experiments utilizing large amounts of Pb shielding due to cosmogenic neutron interactions in the Pb while residing on the Earth's surface. By scaling the LANSCE neutron flux to a cosmic neutron flux, we measure the sea level cosmic ray production rates of 8.0 +/- 1.3 atoms/kg/day of Hg-194, 120 +/- 25 atoms/kg/day Pb-202, and 0.17 +/- 0.04 atoms/kg/day Bi-207.