Cutoff rigidity calculations for cosmic ray neutron sensors

The local baseline neutron intensity for a cosmic ray neutron sensor (CRNS) is partly determined by its cutoff rigidity, which is closely related to geomagnetic latitude. The best available methods of calculating cutoff rigidity involve using numerical ray tracing algorithms to find allowed and forbidden trajectories of primary cosmic ray particles. This allows one to precisely determine the lower, upper and effective cutoff values. In this paper we give an overview of the cutoff rigidity calculation methods employed in our online calculators (available at https://crnslab.org) and compare our calculated cutoff values to published values for the same sites and geomagnetic epochs. In CRNS work, cutoff rigidity calculations are used in scaling the calibration parameter N0 to new locations, or in scaling various N0 values to a common location for the sake of comparison. Such comparisons of N0 are valuable in work with both stationary and mobile CRNS