This report discusses the following topics: Circular magnetic x-ray dichroism at the ER L{sub 3} Edge; angular dependence of circular magnetic x-ray dichroism in rare earth compounds: and circular magnetic x-ray dichroism in crystalline and amorphous GDFE{sub 2}.

The development of probability of detection (POD) models for a variety of nondestructive evaluation (NDE) methods is motivated by a desire to quantify the variability introduced during the process of testing. Sources of variability involved in eddy current methods of NDE include those caused by variations in liftoff, material properties, probe canting angle, scan format, surface roughness and measurement noise. This thesis presents a comprehensive POD model for eddy current NDE. Eddy current methods of nondestructive testing are used widely in industry to inspect a variety of nonferromagnetic and ferromagnetic materials. The development of a comprehensive POD model is therefore of significant importance. The model incorporates several sources of variability characterized by a multivariate Gaussian distribution and employs finite element analysis to predict the signal distribution. The method of mixtures is then used for estimating optimal threshold values. The research demonstrates the use of a finite element model within a probabilistic framework to the spread in the measured signal for eddy current nondestructive methods. Using the signal distributions for various flaw sizes the POD curves for varying defect parameters have been computed. In contrast to experimental POD models, the cost of generating such curves is very low and complex defect …

We present {tau}{sup {minus}} lepton branching fraction measurements based on data from the TPC/Two-Gamma detector at PEP. Using a sample of{tau}{sup {minus}} {yields} {nu}{sub {tau}}K{sup {minus}}{pi}{sup +}{pi}{sup {minus}} events, we examine the resonance structure of the K{sup {minus}}{pi}{sup +}{pi}{sup {minus}} system and obtain the first measurements of branching fractions for {tau}{sup {minus}} {yields} {nu}{sub {tau}}K{sub 1}{sup {minus}}(1270) and {tau}{sup {minus}} {yields} {nu}{sub {tau}}K{sub 1}{sup {minus}}(1400). We also describe a complete set of branching fraction measurements in which all the decays of the {tau}{sup {minus}} lepton are separated into classes defined by the identities of the charged particles and an estimate of the number of neutrals. This is the first such global measurement with decay classes defined by the four possible charged particle species, e, {mu}, {pi}, and K.

Theoretical electronic structure techniques are used to analyze widely different systems from Si clusters to transition metal solids and surfaces. For the Si clusters, first principles density functional methods are used to investigate Si{sub N} for N=2-8. Goal is to understand the different types of bonding that can occur in such small clusters where the atomic coordination differs substantially from tetrahedral bonding; such uncoordinated structures can test approximate models of Si surfaces. For the transition metal systems, non-self-consistent electronic structure methods are used to understand the driving force for surface relaxations. In-depth analysis of results is presented and physical basis of surface relaxation within the theory is discussed. Limitations inherent in calculations of metal surface relaxation are addressed. Finally, in an effort to understand approximate methods, a novel non-self- consistent density functional electronic structure method is developed that is about 1000 times faster than more sophisticated methods; this method is tested for various systems including diatomics, mixed clusters, surfaces, and bulk lattices.

Radioactive metal waste makes up a significant portion of the waste currently being sent for disposal. Recovery of this metal as a valuable resource is possible through the use of decontamination technologies. Through the development and use of expert systems a comparison can be made of laser decontamination, a technology currently under development at Ames Laboratory, with currently available decontamination technologies for applicability to the types of metal waste being generated and the effectiveness of these versus simply disposing of the waste. These technologies can be technically and economically evaluated by the use of expert systems techniques to provide a waste management decision making tool that generates, given an identified metal waste, waste management recommendations. The user enters waste characteristic information as input and the system then recommends decontamination technologies, determines residual contamination levels and possible waste management strategies, carries out a cost analysis and then ranks, according to cost, the possibilities for management of the waste. The expert system was developed using information from literature and personnel experienced in the use of decontamination technologies and requires validation by human experts and assignment of confidence factors to the knowledge represented within.