February 15, 2024
Journal Article

Cosmogenic activation of sodium iodide


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 activation rate ((80 ± 21) atoms/kg/day). These results will help constrain background estimates and determine the maximum time that NaIbased detectors can remain unshielded above ground before cosmogenic backgrounds impact the sensitivity of next-generation detectors.

Published: February 15, 2024


Saldanha R.N., W.G. Thompson, Y. Zhong, L.J. Bignell, R. Tsang, S.J. Hollick, and S.R. Elliott, et al. 2023. Cosmogenic activation of sodium iodide. Physical Review D 107, no. 2:Art. No. 022006. PNNL-33431. doi:10.1103/PhysRevD.107.022006

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