Cosmic-Ray Anisotropy

Description

This experiment was designed primarily to measure the directional characteristics of galactic and solar cosmic ray fluxes. The particle detector was a CsI (Tl) scintillator crystal that was set into an anticoincidence plastic scintillator collimator cup. Separate photomultiplier tubes viewed the two scintillators. Pulses from the CsI crystal that were not accompanied by pulses from the plastic scintillator were sorted by a three-window pulse-height analyzer, the windows corresponding to energy depositions of 7.2 to 47.4, 47.4 to 64.5, and 64.5 to 81.2 MeV. No positive species identification was made, although most of the counts in each window were usually due to protons with the window energies. For each energy window, counts were separately accumulated in each of four angular sectors as the spacecraft spun. Each angular sector was normally 89.5 deg in width, with the sun either near a sector boundary or in the middle of a sector, depending on the operating mode. However, when large fluxes were encountered, each angular sector was reduced to 11.2 deg, with the sun either in a sector or near the midpoint between two sectors. A spin-integrated (isotropic) mode, in which all particles depositing 7.2 MeV in the CsI crystal (no anticoincidence requirement) were counted, was also used. Accumulation times for each of the 12 directional modes and for the omnidirectional mode varied between 14 and 112 s (spacecraft spin period was about 1 s) depending on the telemetry bit rate. See Bartley et al., Rev. Sci. Instrum., v. 38, p. 266, 1967, for a more detailed experiment description.