Pitch angle distributions and mirror point densities in the outer radiation zone

A method is presented for the calculation of the equatorial pitch angle distribution (unidirectional intensity distribution) of trapped radiation from the count rate of an omnidirectional detector along a line of force. An expression is derived for the calculation of the mirror point density from the equatorial pitch angle distribution. The method is applied to data obtained from the Space Technology Laboratories scintillation counter and the University of Chicago proportional counter on the Explorer VI satellite. The results from the scintillation counter show a relative absence of electrons with pitch angles of 90° during quiet periods, a sharp increase in such particles shortly after a sudden commencement magnetic storm, and restoration of the prestorm distribution at a higher intensity level after the storm. The results from the proportional counter are qualitatively similar with the exception of the apparent deficiency of 90° pitch angles during quiet periods, which does not appear.