Cosmogenic activation of sodium iodide

Authors :: R. Saldanha
W. G. Thompson
Y. Y. Zhong
L. J. Bignell
R. H. M. Tsang
S. J. Hollick
S. R. Elliott
G. J. Lane
R. H. Maruyama
L. Yang
Source :: Physical Review
Publication Year :: 2022
Publisher :: arXiv, 2022.
Abstract: The production of radioactive isotopes by interactions of cosmic-ray particles with sodium iodide (NaI) crystals can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of NaI crystals with a neutron beam that matches the cosmic-ray neutron spectrum, followed by direct counting and fitting the resulting spectrum across a broad range of energies, we determined the integrated production rate of several long-lived radioisotopes. The measurements were then extrapolated to determine the sea-level cosmogenic neutron activation rate, including the first experimental determination of the tritium production rate: $(80 \pm 21)$ atoms/kg/day. These results will help constrain background estimates and determine the maximum time that NaI-based detectors can remain unshielded above ground before cosmogenic backgrounds impact the sensitivity of next-generation experiments.<br />Comment: 20 pages, 15 figures, 7 tables