A High-Resolution, Multiple Particle Spectrometer for the Measurement of Solar Particle Events

A particle spectrometer possessing high spectral and spatial/temporal resolution for the measurement of energetic protons, electrons and alpha particles over a broad energy and intensity range during solar particle events (SPE) was successfully launched aboard a polar-orbiting satellite on 17 October 1971. The spectrometer consists of a multi-element, silicon detector stack mounted within a plastic scintillator guard counter to form a particle telescope. The spectra of protons in the energy range 1.2-100 MeV, electrons from 0.88-1.6 MeV and alpha particles from 1.6-500 MeV are measured in four time-shared modes of operation with dual 256-channel pulse-height analyzers (PHA) of the successive-approximation type. Integral counting rates from each of the main elements of the telescope and the guard counter are measured every 32 milliseconds with low-power CMOS digital counters to provide high spatial/temporal resolution on the solar particle fluxes. Complete spectra on all three particle types over the above energy ranges are obtained every few seconds. A detailed description of the spectrometer, including a discussion of the mode logic which enhances the counting statistics in selected energy ranges, the dual pulse-height analyzers and the methods of obtaining the high temporal resolution is presented. Preliminary worldwide flight data obtained from two identical spectrometers oriented at different directions to the particle flux are also presented.