High conduction neutron absorber to simulate fast reactor environment in an existing test reactor

A new metal matrix composite material has been developed to serve as a thermal neutron absorber for testing fast reactor fuels and materials in an existing pressurized water reactor. The performance of this material was evaluated by placing neutron fluence monitors within shrouded and unshrouded holders and irradiating for up to four cycles. The monitor wires were analyzed by gamma and X-ray spectrometry to determine the activities of the activation products. Adjusted neutron fluences were calculated and grouped into three bins—thermal, epithermal, and fast—to evaluate the spectral shift created by the new material. A comparison of shrouded and unshrouded fluence monitors shows a thermal fluence decrease of ~11 % for the shielded monitors. Radioisotope activity and mass for each of the major activation products is given to provide insight into the evolution of thermal absorption cross-section during irradiation. The thermal neutron absorption capability of the composite material appears to diminish at total neutron fluence levels of ~8 × 10²⁵ n/m². Calculated values for dpa in excess of 2.0 were obtained for two common structural materials (iron and nickel) of interest for future fast flux experiments.     

Optical Gas Sensing Properties of Silica Film Doped with Cobalt Oxide Nanocrystals

SiO₂ sol-gel films doped with cobalt oxide nanocrystals have been fabricated. The nanocrystals precipitate in the glass film at 500_°C, while the film is still porous. The nanocomposite films showed a reversible change in the optical transmittance when exposed to CO in the 250 < < 850 nm range. The effects of the residual porosity and testing temperature have been studied. The gas sensing properties of the cobalt oxide nanocrystals doped films are compared with those of nickel oxide nanocrystals doped silica film, previously reported.     

Moiré interferometry with ±45-deg gratings

Specimen gratings with rulings oriented +45 deg and ?45 deg to they axis can be used to determine theu andv displacement fields, i.e., the displacements in thex andy directions. The fringe patterns are identical to those obtained with (X) and (Y) specimen gratings. The analysis leading to this conclusion is presented. A vector quantity related to the fringe gradient in the interference pattern is defined and found effective for visualizing and describing the image-forming rays. Advantages relate to construction of apparatus for moiré interferometry.     

Shear-strain contours from moiré interferometry

Whole-field contour maps of shear strains _xy are derived from displacement fields obtained by moiré interferometry with 2400 /mm (60,960 /in.). Cross-derivatives of displacements are obtained by mechanical differentiation. They are summed by graphical additive moiré. The high sensitivity of moiré interferometry permits quantitative analysis in the small-strain domain.Paper was presented at V International Congress on Experimental Mechanics held in Montreal, Quebec, Canada on June 10–15, 1984.     

Cluster studies of CO adsorption: I. CO on small Li clusters

The various contributions to the adsorption energy of CO such as steric repulsion, σ bonding and π backbonding, are studied as a function of CO-cluster distance, C-O distance, adsorption site and cluster geometry. At the hollow site a double minimum is found in the adsorption energy as a function of CO-cluster distance. The effect of adsorption on the electronic structure of CO is large, in particular at the equilibrium distance close to the surface. Consequences for the C-O stretch frequency, and for the possibility of CO dissociation at the surface, are investigated.     

A crystallographic study of polymers exhibiting side-chain crystallization

Fibers were drawn from polymers of octadecyl acrylate, octadecyl methacrylate, N-octadecylacrylamide, and a series of N-substituted acrylamides with a second amide group in the side chain as well as from copolymers of octadecyl and methyl esters of acrylic and methacrylic acid. Wide-angle and small-angle x-ray diffraction patterns were recorded for these materials. The interpretation of the characteristic difference between the behavior of the polycrylates and polymethacrylates, as proposed by Platé and his collaborators, is found to be inconsistent with a number of features of the experimental evidence. In the case of poly(octadecyl methacrylate) the data allow the estimation of two parameters of the electron density distribution in the side-chain crystallites. With polyacrylamide derivatives, a second amide group in the side chain is found to destabilize the side chain crystallites. The bahavior of the copolymers is very complex and exhibits, in one case, evidence for a long periodicity parallel to the fiber axis.     

Magnetic symmetry,improper symmetry,and Neumann's principle

Mathematical tradition has it that transformations characterized by a negative Jacobian determinant are referred to as improper transformations. The symmetry of a physical object corresponding to such an improper transformation becomes an improper symmetry. Improper symmetries have been successfully used for the purpose of crystal symmetry. The extension of these purely spatial symmetries to the domain of spacetime has led to a prejudicial use of light-cone properties, thus affecting adversely an unbiased symmetry classification. We pinpoint these prejudicial procedures and trace their historical origin, while presenting an alternative that restores an unbiased treatment of improper spacetime symmetries. The applications discussed relate to recent developments in the symmetry classification of magnetic crystals and to the extension of Neumann's principle to the time domain.     

Hydrogenation of ferrocene

Ferrocene and derivatives can be hydrogenated in acidic medium at ambien temperature and atmospheric hydrogen pressure using supported palladium as the catalyst.     

Synthesis of adenosine triphosphate by way of potassium-sensitive phosphoenzyme of sodium, potassium adenosine triphosphatase.

The sodium and potassium ion pump is an intrinsic enzyme of plasma membranes. In these experiments it was driven backward in a transient two-step operation involving, first, phosphorylation of the enzyme from inorganic phosphate, and second, transfer of the phosphate group from the enzyme to ADP upon addition of a high concentration of Na+. There was no evidence of a significant concentration gradient across the membranes. Na+ presumably reached the solutions on both faces of the membrane simultaneously and provided the energy for synthesis simply as a consequence of ligand binding. An interaction free energy between the free energy of the binding of Na+ and the free energy of hydrolysis of the phosphate group on the enzyme was estimated. The experiments also suggested a feature of the transport mechanism. This is control by phosphorylation of access pathways from the solutions in contact with the faces of the membrane to an active center for cation binding. In the dephosphoenzyme access would be to the intracellular solution and in the phosphoenzyme access would be to the extracellular solution.