Multichannel Spectrometer for the Measurement of Trapped Particles

A spectrometer has been designed to measure in detail the energy spectrum and omnidirectional flux of energetic charged particles encountered in low-altitude satellite orbits. Two versions of the instrument are described. Each detects particles in a solid angle which approaches 2π steradians and utilizes a plastic scintillator and photomultiplier combination. In each case the energy spectrum is obtained from a pulse-height analyzer having 16 channels. The first version of the instrument employs a single plastic scintillator which is shielded, except for a 2.54 cm diameter opening, and which provides sufficient path length to stop electrons and unambiguously determine their energy to 5 MeV. The analyzer is programmed in two ranges corresponding to electron energies of 0.28-2.61 MeV and 0.28-10.02 MeV. Electron spectra obtained from this instrument on a low-altitude satellite are included. The second version of the instrument has an additional anticoincidence scintillator surrounding the entire detection crystal except for the entrance aperture, thus eliminating the contribution from all particles which do not enter via the aperture and stop in the center scintillator. In addition, shielding surrounds the outer scintillator to limit the anticoincidence dead time. The energy ranges are expanded in order to obtain fluxes and spectra of electrons from 0.3-7.0 MeV and protons from 12-80 MeV. This latter instrument is scheduled for use on the manned Gemini vehicles. This work has been supported by the Lockheed Independent Research Program and by the NASA-Manned Spacecraft Center.