V. Analysis of IQSY cosmic-ray survey measurements

Abstract

In this, the last of a set of five papers reporting latitude surveys carried out in 1965 and 1966 at the time of and soon after the IQSY cosmic-ray maximum, the observations are reduced to a common atmospheric depth and at the same time the attenuation coefficients in the atmosphere for both the neutron monitor and the muon monitor are determined as functions of altitude and latitude. The latitude variation of the neutron monitor at sea level is compared with observations reported for the previous cosmic-ray maximum in 1954–55 and found to be similar. The altitude variation of the neutron-monitor attenuation coefficient is discussed in detail with reference to the maximum near 600 mm Hg currently attributed to neutrons produced in the monitor by stopping muons. It is shown that the stopping-muon effect is insufficient to account for the maximum. It is shown, using the Gross transformation, that a geometrical effect associated with the omnidirectional nature of the incident cosmic radiation may be the main factor producing the maximum. A specific absorption coefficient representing the differential effect in the neutron monitor of vertically-incident primaries of given magnetic rigidity is deduced. Good agreement is obtained with the observed attenuation in the atmosphere of solar protons of mean energy 2 GV and also with the reported results of a Monte Carlo calculation of the attenuation of the nucleonic cascade in air.