“…In general, such measurements require detailed and experiment-specific Monte Carlo simulations to correct for the neutron contribution from rock as well as the metallic components of the detectors, but this is difficult, especially for the older experiments like those in Refs. [4,6,10]. Recent measurements [7][8][9] are all byproducts of advanced neutrino experiments, which are carried out at great depths (>2500 m.w.e.).…”