Latitude survey of cosmic-ray intensity by Explorer 7, October 1959 to February 1961

Abstract

Using a shielded Geiger tube in the Explorer 7 satellite a comprehensive geographic survey of the intensity of charged particles in the latitude range ±50.5°, in the altitude range 550 to 1100 km, and over the 16-month period October 13, 1959, to February 17, 1961, has been conducted. It has been found possible to identify and eliminate contributions by geomagnetically trapped particles and thus to obtain the sum of the absolute intensities of primary galactic cosmic rays and of their charged-particle secondaries (albedo) produced in the atmosphere. Specific results are as follows: (1) The counting-rate data from both northern and southern hemispheres and over a considerable range of longitudes are represented in a simple and coherent manner as a function of a single parameter, the Mcllwain magnetic shell parameter L. (2) The counting rate increases monotonically with increasing L and has an accurately constant value for L>2.9. (3) The high-latitude knee of the counting rate versus L curve occurs at L = 2.6 (corresponding to the invariant latitude 52°) and is indiscernibly different in the northern and southern hemispheres. (4) The absolute omnidirectional intensity is 0.56 (cm2 sec)−1 at the equator and 2.0 (cm2 sec)−1 at high latitudes, the ratio being 3.6. (5) At high latitudes the intensity increases by the factor 1.046±0.045 during the 16-rnonth period. (6) In terms of the Quenby-Wenk vertical cutoff rigidity R, in billion volts, the total omnidirectional intensity J0(>R) = 4.3R−0.83±0.02 (cm2 sec)−1 for 3<R<12 bv and J0 = 2.0 (cm2 sec)−1 for R<1.7 bv.