Neutron Monitor as a Calorimeter to Measure Particle Spectra

Abstract

Magnetic activity on the sun influences the flux of galactic cosmic rays at Earth in the process known as solar modulation. While most pronounced at 1 GeV and below, it also operates at much higher energy, still exhibiting solar magnetic polarity dependence. Historically, an observational gap exists between approximately 17 GeV (the highest geomagnetic cutoff) neutron monitor data and muon observations of primary cosmic rays that are mostly above 50 GeV. We have shown that a neutron monitor can be used as a calorimeter to measure the spectrum of atmospheric secondaries, and thus to infer the primary spectrum. In this paper we examine data over an extended time interval to explore the need to correct for barometric pressure. We compare the results of the calorimeter method to other local measures of the particle spectrum, such as the leader fraction.