A gamma-ray imager for arms control
Ascertaining the number of warheads on a missile-delivery systems by a remote, nonvisual inspection may be desirable in some arms-control verification scenarios. A gamma-ray imaging system (GRIS) has been developed to inspect for nuclear warheads by imaging the highly penetrating gamma-radiation emitted by radioactive materials integral to warheads. Such an image may be used to obtain the missile loadout. The authors describe the GRIS's operating principles and capabilities, present data, and discuss the advantages and disadvantages of such a system for arms control. They also present field results where GRIS was used on an emplaced Peacekeeper missile. Improvements to GRIS in light of the field trial results are presented.<<ETX>>
3D millimeter event localization in bulk scintillator crystals
One of the primary goals of scintillator-based gamma-ray detector development is to obtain spatial resolutions in bulk crystals at the millimeter level in all three spatial dimensions. An even more challenging goal is to disentangle multiple simultaneous energy depositions with comparable spatial resolutions. We are exploring a new technique to achieve this level of performance through the use of close-coupled, coded-aperture shadow masks placed between the crystal and a position-sensitive phototransducer. We report on simulations of such a device using Monte Carlo light transport simulations performed with GEANT 4. Initial indications are promising; however, the technique will require a very high level of performance from the phototransducer.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.