Measurement of radiation in the lower Van Allen belt

In the first of a series of experiments, an instrument package of eight Geiger counters, shielded and collimated in various ways, was carried aloft and released by an Atlas ICBM; its trajectory passed into the lower Van Allen radiation belt. Since there are variations in altitude at the isocount contours of the belt at several latitudes, the trajectory achieved its deepest penetration into the radiation belt somewhat after reaching its maximum height of 990 km (Fig. 1). Of the eight counters, two with relatively large area and low shielding were saturated by the high flux at deepest penetration and were used only as aids in determining the orientation of the instrument package. The remaining six counters, which provided the data discussed below, were shielded with five different absorber thicknesses (in milligrams per square centimeter of the material indicated) as follows: A, 1.7 mica; B and C, 30 aluminum (2 counters) ; D, 150 aluminum; E, 400 aluminum; and F, 2000 brass.