A High-Sensitivity Particle Spectrometer for the Measurement of Polar-Cap-Absorption Events

A hybrid particle spectrometer possessing high-sensitivity and high-time resolution for the measurement of precipitating protons, electrons, and alpha particles during Polar-Cap-Absorption (PCA) events has been successfully operating in space aboard the OV1-18 satellite since 23 March 1969. Detection of protons in the energy range 1.2 to 46 MeV and integral above 70 MeV, electrons in the range 0.4 to 1.9 MeV and alpha particles in the range 7 to 20 MeV is performed with sensitivities as high as 0.1 particle/cm2-sec and with a dynamic intensity range of six decades through the use of a transmission solid-state detector in conjunction with a total-energy, plastic-scintillation detector. Acceptable pulses from each detector, as determined by various combinations of coincidence logic, are analyzed with separate 15-channel pulse-height analyzers of the analog-to-digital type. A detailed description of the spectrometer, including a unique biasing technique which maintains a constant potential across the solid-state detector, independent of leakage variations due to temperature and radiation damage, will be given. Some typical characteristics of the particles measured during several PCA events will also be presented.