Variation of muon counts versus solar time

Project GRAND observes small variations in the number of incident muons when plotted versus local solar time. The total accumulated number of muons by GRAND over four years' time is 140 billion. The data obtained by Project GRAND are compared with data from neutron monitor stations at Climax and at Newark which detect secondary neutrons. Project GRAND is an array of 64 proportional wire chamber stations which are sensitive to secondary muons at energies greater than 0.1 GeV. The mean energy of cosmic ray primaries which produce these muons depends on the spectral index. For a differential spectral index of 2.4, the most probable gamma ray primary energy is about 10 GeV, the response falling steeply below this energy and slowly above this energy (Fass`o and Poirier , 2001); this most probably energy varies only slowly with spectral index.