Changes in the Low-Energy Particle Cutoff and Primary Spectrum of Cosmic Radiation

Abstract

The low-rigidity cutoff for particles in the primary cosmic-ray spectrum has decreased within the period 1948 through 1951. This decrease corresponds to a 3° change (northward) in the "knee" position of the geomagnetic latitude curve for the nucleonic component. The phenomenon is accompanied by both a change in the primary spectrum for particle rigidities less than approximately 4 Bv and by an increase in total primary intensity. The spectral change is such that if the differential primary intensity, $j$, at low rigidities in 1948 was $j=C{\left(\frac{p}{z}\right)}^{-2\mathrm{}}$; then the new spectrum for 1951 through 1954 is approximately $j\approx C^{\prime }{\left(\frac{p}{z}\right)}^{-2.7\mathrm{}}$. The total change of intensity arising from the changes in spectrum and low-rigidity cutoff is more than 13%.