Isis 2 satellite carried, among other ionospheric instruments, an ion mass spectrometer designed to measure the composition of the ionosphere in the mass range 1–64 amu. The satellite, in a nearly constant 1400‐km orbit, was launched on April 1, 1971. Examples of data show a wide variation in ion composition from 99% H+ at night near the equator to greater than 95% O+ (and N+) in the daytime poleward of the plasmapause. Both H+ and He+ are observed to be streaming outward from the high‐latitude regions with velocities of several kilometers per second (the polar wind), determined from phase shifts in roll modulation maximums between light and heavy ion species. During the August 1972 magnetic storm a unique ionosphere developed consisting of N+ as the dominant species between 55° and 80° invariant latitude (above the plasmapause) and N2+, NO+, and O2+ at the 10³‐cm−3 concentration level, whereas these molecular species are usually below the detection limit of 1 ion cm−3 in quiet times at this altitude.

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Scintillating optical fibers have been used to build small detectors for whole-body imaging of small rodents by nuclear medicine techniques. Cylindrical detectors with entrance apertures of 6.8 cm and active lengths of 1 1 .3 cm were constructed using both 3 mm and 1 mm BCF-10 fibers. Fiber readout was performed using position sensitive photomultipliers and a specialized flash ADC system. The efficiencies of these detectors were determined as a function of energy, their resolution was studied, and their potential use for SPECT (single photon emission computed tomography) was explored.

The energy resolution is measured for a plastic scintillating fiber detector coupled to position sensitive photomultiplier tubes. A point source (Mn-54) is placed at a distance in front of an xy plastic scintillating fiber stack which is coupled to two Hamamatsu R2486 position sensitive photomultiplier tubes. At some distance behind this detector another plastic scintillating detector coupled to another position sensitive photomultiplier is placed. Gamma rays interacting in the 1st detector are scattered, and interact with the 2nd detector. By the knowledge of the source location, the Compton interaction location in the 1st detector, and the interaction location of the scattered gamma in detector 2, the scattering angle of the Compton interaction in detector 1 can be determined. From this scattering angle and the known primary gamma energy the Compton electron energy can be calculated. The energy resolution of the scintillating fiber stack-photomultiplier unit of detector 1 for different Compton electron energies is determined by plotting the experimentally measured electron energies obtained from the light output of the photomultiplier tubes of detector 1, comparing them with the electron energy calculated above, and expressed in terms of the FWHM.