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Crystals of Yb{sup 3+}:Sr{sub 1-x}Ba{sub x}(PO{sub 4}){sub 3}F (0 < x < 5) have been investigated as a means to obtain broader absorption bands than are currently available with Yb{sup 3+}:S-FAP [Yb{sup 3+}: Sr{sub 5}(PO{sub 4}){sub 3}F], thereby improving diode-pumping efficiency for high peak power applications. Large diode-arrays have a FWHM pump band of >5 nm while the FWHM of the 900 nm absorption band for Yb:S-FAP is 5.5 nm; therefore, a significant amount of pump power can be wasted due to the nonideal overlap. Spectroscopic analysis of Yb:Sr{sub 5-x}Ba{sub x}-FAP crystals indicates that adding barium to the lattice increases the pump band to 13-16 run which more than compensates for the diode-array pump source without a detrimental reduction in absorption cross section. However, the emission cross section decreases by approximately half with relatively no effect on the emission lifetime. The small signal gain has also been measured and compared to the parent material Yb:S-FAP and emission cross sections have been determined by the method of reciprocity, the Filchtbauer-Ladenburg method, and small signal gain. Overall, Yb{sup 3+}:Sr{sub 5-x}Ba{sub x}(PO{sub 4}){sub 3}F crystals appear to achieve the goal of nearly matching the favorable thermal and laser performance properties of Yb:S-FAP while …

The purpose of this analysis is to systematically identify and evaluate hazards related to the tunnel boring machine (TBM) used in the Exploratory Studies Facility (ESF) at the Yucca Mountain Site Characterization Project. This process is an integral part of the systems engineering process; whereby safety is considered during planning, design, testing, and construction. Since the TBM is an ''as built'' system, the M&amp;O is conducting the System Safety Analysis during the construction or assembly phase of the TBM. A largely qualitative approach was used since a radiological System Safety Analysis is not required. The risk assessment in this analysis characterizes the accident scenarios associated with the TBM in terms of relative risk and includes recommendations for mitigating all identified risks. The priority for recommending and implementing mitigation control features is: (1) Incorporate measures to reduce risks and hazards into the system/subsystem/component design, (2) add safety features and capabilities to existing designs, and (3) develop procedures and conduct training to increase worker awareness of potential hazards, on methods to reduce exposure to hazards, and on the actions required to avoid accidents or correct hazardous conditions. The scope of this analysis is limited to the TBM during normal operations, excluding hazards …

Using an end-pumped technology developed at LLNL we have demonstrated a Yb:YAG laser capable of delivering up to 434 W of CW power and 226 W of Q-switched power. In addition, we have frequency doubled the output to 515 nm using a dual crystal scheme to produce 76 W at 10 kHz in a 30 ns pulse length.

High power laser diodes at various wavelengths are described. First, performance and reliability of an optimized large transverse mode diode structure at 808 and 941 nm are presented. Next, data are presented on a 9.5 kW peak power array at 900 nm having a narrow emission bandwidth suitable for pumping Yb:S-FAP laser materials. Finally, results on a fiber-coupled laser diode array at {approx}730 nm are presented.

Absorption lines in the Ly{alpha} forest can be thought of as peaks in neutral hydrogen density along lines of sight. The column density distribution (the number density of absorption lines as a function of column density) is then a statistic of density peaks, which contains information about the underlying power spectrum. In particular, we show that the slope of the distribution provides a measure of power on scales smaller than those probed by studies of present day large scale structure. 2 refs., 1 fig.

Plant photosynthesis has created a unique planetary-wide geochemistry - an oxidizing atmosphere with oxidizing surface waters on a planetary body with chemically reducing conditions near or at some distance below the surface. Uranium is four orders of magnitude more soluble under chemically oxidizing conditions than it is under chemically reducing conditions. Thus, uranium tends to leach from surface rock and disposal sites, move with groundwater, and concentrate where chemically reducing conditions appear. Earth`s geochemistry concentrates uranium and can separate uranium from all other elements except oxygen, hydrogen (in water), and silicon (silicates, etc). Fissile isotopes include {sup 235}U, {sup 233}U, and many higher actinides that eventually decay to one of these two uranium isotopes. The potential for nuclear criticality exists if the precipitated uranium from disposal sites has a significant fissile enrichment, mass, and volume. The earth`s geochemistry suggests that isotopic dilution of fissile materials in waste with {sup 238}U is a preferred strategy to prevent long-term nuclear criticality in and beyond the boundaries of waste disposal facilities because the {sup 238}U does not separate from the fissile uranium isotopes. Geological, laboratory, and theoretical data indicate that the potential for nuclear criticality can be minimized by diluting fissile materials with-{sup …