Comparison of the total cosmic radiation in deep space and at the Earth during the March-April 1960 events

A study is made of the intensity of the total radiation in the interplanetary medium before and after the March 28 to April 9, 1960, solar proton events and the March 31, 1960, Forbush decrease as Pioneer 5 moved to a distance of 0.07 AU from the earth. By means of regression plots the space probe ion chamber is compared with a group of neutron monitors and with balloon ion chambers flown at Minneapolis. The comparison covers an energy range from several bev down to 25 Mev. It is found that the ion chamber rates in the period April 10 to April 26,1960, return within approximately 1 per cent to the same regression line observed during the period March 11–28 established before the large solar injection of particles. Thus an upper limit for a possible permanent change in the flux of interplanetary radiation greater than 25 Mev caused by these solar events may be derived using the ion chamber absolute calibration for alternative choice of energies as follows: 5 protons/m2 sec ster having energies 25–100 Mev, 10 protons/m2 sec ster having energies 100–250 Mev, or 20 protons/m2 sec ster having energies 250–1000 Mev. Simpson et al. [1962] have reported a permanent 10 per cent reduction in the interplanetary radiation between 75 Mev and several bev also measured aboard Pioneer 5 during the same events. Very special assumptions about spectral changes are necessary to reconcile these two measurements.