Production of Radioactive Isotopes through Cosmic Muon Spallation in KamLAND

TL;DR

This paper investigates radioactive isotopes produced by cosmic muon spallation in KamLAND, providing measurements of neutron and isotope production yields to improve background understanding for rare-event physics experiments.

Contribution

It offers the first detailed measurements of cosmogenic isotope yields in liquid scintillator using KamLAND data, challenging existing extrapolations from accelerator experiments.

Findings

Neutron production yield measured as (2.8 ± 0.3) × 10^{-4} μ^{-1} g^{-1} cm^{2}

Some isotope yields differ from accelerator-based extrapolations

Results improve understanding of cosmogenic backgrounds in neutrino and dark matter experiments

Abstract

Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in $\nu$ detectors, double-$\beta$-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of $^{11}$C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be $(2.8 \pm 0.3) \times 10^{-4} \mu^{-1} g^{-1} cm^{2}$. For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment.