Investigations into electronic stopping regime sputtering of uranium tetrafluoride

Yields were measured for ²³⁵U sputtered from UF₄ by ¹⁶O, ¹⁹F, and ³⁵Cl over the energy range ~.12 to 1.5 MeV/ amu sing a charge equilibrated beam in the stripped beam arrangement for all the incident ions and in the transmission arrangement for ¹⁹F and ³⁵Cl. In addition, yields were measured for ¹⁹F incident in a wide range of discrete charge states. The angular dependence of all the measured yields were consistent with cosʋ. The stripped beam and transmission data were well fit by the form (Az²eqln(BƐ)/Ɛ)⁴ (where Ɛ was the ion energy in MeV/amu and z_eq(Ɛ) was taken from Zeigler(80). The fitted values of B for the various sets of data were consistent with a constant B₀, equal to 36.3 ± 2.7, independent of incident ion. The fitted values of A show no consistent variation with incident ion although a difference can be noted between the stripped beam and transmission values, the transmission values being higher.

The incident charge data were well fit by the assumptions that the sputtering yield depended locally on a power of the incident ion charge and that the sputtering from the surface is exponentially correlated to conditions in the bulk. The equilibrated sputtering yields derived from these data are in agreement with the stripped beam yields.

In addition, to aid in the understanding of these data, the data of Hakansson(80,81a,81b) were examined and contrasted with the UF₄ results. The thermal models of Seiberling(80) and Watson(81) were discussed and compared to the data.

Relativistic force between fast electrons and planar targets

The full retarded electromagnetic force experienced by swift electrons moving parallel to planar boundaries is revisited, for both metallic and dielectric targets, with special emphasis on the consequences in electron microscopy experiments. The focus is placed on the sign of the transverse force experienced by the electron beam as a function of the impact parameter. For point probes, the force is found to be always attractive. The contribution of the induced magnetic field and the causality requirements of the target dielectric response, given by the Kramers-Kronig (K-K) relations, prove to be crucial issues at small impact parameters. For spatially extended probes, repulsive forces are predicted for close trajectories, in agreement with previous works. The force experienced by the target is also explored, with the finding that in insulators, the momentum associated to Cherenkov radiation (CR) is relevant at large impact parameters.

Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented. In all crystals, the Raman active T_(2g) vibration mode of CaF2 was observed, whose frequency shift and full-width at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice. Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U^(6+):CaF2 crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.

Concepts of spawning targets

This report discusses the concepts of spawning targets. Spawning target setting is based on the fact that the number of smolts produced by any given river is constrained by habitat availability. This means smolt numbers depend on spawner numbers up to a point, but thereafter smolt production reaches a ceiling. It has been shown, in some rivers at least, that the relationship between egg deposition and smolt production may approximately be described by a mathematical equation. The equation will vary between rivers and there is uncertainty over its exact form. The concept of Maximum Gain (MG) is explained and its application in fisheries management discussed. The author also critically examines the concept of Density Independent Mortality (DIM).

Estimating species and size composition of rockfishes to verify targets in acoustic surveys of untrawlable areas

Rockfish (Sebastes spp.) biomass is difficult to assess with standard bottom trawl or acoustic surveys because of their propensity to aggregate near the seafloor in highrelief areas that are inaccessible to sampling by trawling. We compared the ability of a remotely operated vehicle (ROV), a modified bottom trawl, and a stereo drop camera system (SDC) to identify rockfish species and estimate their size composition. The ability to discriminate species was highest for the bottom trawl and lowest for the SDC. Mean lengths and size distributions varied among the gear types, although a larger number of length measurements could be collected with the bottom trawl and SDC than with the ROV. Dusky (S. variabilis), harlequin (S. variegatus), and northern rockfish (S. polyspinis), and Pacific ocean perch (S. alutus) were the species observed in greatest abundance. Only dusky and northern rockfish regularly occurred in trawlable areas, whereas these two species and many more occurred in untrawlable areas. The SDC was able to resolve the height of fish off the seafloor, and some of the rockfish species were observed only near the seafloor in the acoustic dead zone. This finding is important, in that fish found exclusively in the acoustic dead zone cannot be assessed acoustically. For these species, methods such as bottom trawls, long-lines, or optical surveys using line transect or area swept methods will be the only adequate means to estimate the abundance of these fishes. Our results suggest that the selection of appropriate methods for verifying targets will depend on the habitat types and species complexes to be examined.