[en] The EGRET high energy gamma-ray telescope is one of four instruments to be included on the Gamma Ray Observatory mission, a Shuttle-launched free-flying satellite scheduled for launch in the late 1980's. This instrument, a spark chamber telescope with a Na(Tl) crystal energy spectrometer, will cover the energy range from 12 MeV to 24,000 MeV, with much better sensitivity and spectral and spatial resolution than any previous experiment in this energy range. The design and performance of the EGRET instrument with particular reference to those components that are the responsibility of Stanford University are described

[en] X-ray computed tomography (CT) is a widely used method of obtaining cross-sectional views of objects. The high intensity, natural collimation, monochromaticity and energy tunability of synchrotron x-ray sources could potentially be used to provide CT images of improved quality. The advantages of these systems would be that images could be produced more rapidly with better spatial resolution and reduced beam artifacts. In addition, images, in some cases, could be acquired with elemental sensitivity. As a demonstration of the capability of such a system, CT images were obtained of four slices of an excised pig heart in which the arteries and the cardiac chambers were filled with an iodinated medium. Images were taken with incident x-rays tuned successively to energies just above and below the iodine K edge. Iodine specific images were obtained by logarithmically subtracting the low energy image data from the high energy data and then reconstructing the image. CT imaging using synchrotron radiation may become a convenient and non-destructive method of imaging samples difficult to study by other methods

[en] A large NaI(T1) spectrometer is expected to play a crucial role in the measurement of the energy spectra from an all-sky survey of high-energy celestial gamma rays on the Gamma Ray Observatory. The crystal size and requirements of space flight have resulted in a novel crystal-packaging and optics combination. The structure of this spectrometer and the operating characteristics determined in a test program using high energy positrons are described