Ga-substituted cobalt ferrite oxides show promise as high magnetostriction, high sensitivity magnetoelastic materials for sensor and actuator applications, but their atomic-level behavior is not yet well understood. In this study, the magnetic environments of the Fe atoms in Ga-substituted cobalt ferrite have been investigated using Mossbauer spectroscopy. A series of five powder samples with CoGa x Fe 2−x O 4 compositions ͑x = 0.0-0.8͒ was investigated using transmission geometry. Results show two distinct six-line hyperfine patterns, which are identified as Fe in A ͑tetrahedral͒ and B ͑octahedral͒ spinel sites. Increasing Ga concentration is seen to decrease the hyperfine field strength for both A and B sites, as well as increasing the width of those distributions, consistent with the nonmagnetic nature of Ga 3+ ions. Effects are more pronounced for the B sites than the A sites. Results for Ga substitution show more pronounced effects than for previous studies with Cr 3+ or Mn 3+ substitution: the hyperfine fields decrease and distribution widths increase at greater rates, and the differences between A and B site behavior are more pronounced. Results indicate that at least for the lower Ga concentrations, the Ga 3+ ions substitute predominantly into the A sites, in contrast to Cr 3+ and Mn 3+ which substitute into the B sites. This interpretation is supported by measurements of magnetization at low temperatures. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2834721͔ INTRODUCTIONThe development of cobalt ferrite-based materials has received recent attention for the potential applicability of such materials as magnetoelastic sensors and actuators, and as the magnetoelastic component in composite "multiferroics." 1,2 Substitution of elements such as Mn or Cr for some of the Fe has shown promise of adjusting the magnetic and magnetoelastic properties of these materials through control of chemical composition. 3,4 In order to fully enable the practical applications of these compounds, a more complete family of materials is needed, such that the desired properties can be tailored to a specific application. In the present study, we report on the magnetic characterization of the series of Ga-substituted cobalt ferrites CoGa x Fe 2−x O 4 ͑x = 0.0-0.8͒ as a function of gallium concentration using transmission Mossbauer spectroscopy. The effects of this substitution were expected to be different for Mn and Cr substitution. [5][6][7] EXPERIMENTAL DETAILSThe samples used in this study were prepared at Ames Laboratory, USDOE. The samples were of the composition CoGa x Fe 2−x O 4 ͑where x = 0.0-0.8͒. Standard powder ceramic techniques were employed using Fe 2 O 3 , Ga 2 O 3 , and Co 3 O 4 powders as precursors. The powders were calcined twice, sintered at 1350°C for 24 h, and furnace cooled ͑see Ref. 7 for details͒. The final compositions of the samples were determined by energy-dispersive x-ray spectroscopy, and all samples were confirmed by x-ray powder diffractometry to be single phase and have the cubic spinel ...

Measurements of partial 235U(n,2ny) y-ray cross sections have been carried out as a function of incident neutron energy using the GEANIE spectrometer at LANSCE/WNR+ The yields of y rays resulting from the population of discrete levels in the residual nucleus 234U have been measured at incident neutron energies in the 1-20-MeV range. These data provide, with the aid of nuclear reaction modeling, a measurement of the 235U(n,2n) reaction cross section and serve as a proof of principle of the y-ray technique for the parallel 23gPu(n,2n) measurement [l]. This paper presents the analysis of the y-ray data and the extraction of partial y-ray cross sections as a function of incident neutron energy, Uncertainties associated with the spectroscopic analysis of the data and validation of the results are discussed in detail.

Absolute partial γ-ray cross sections for the production of discrete γ-rays from the reaction 150 Sm(n,2nγi) 149 Sm were measured using the GEANIE γ-ray spectrometer coupled with the intense white neutron source at WNR/LANSCE. The measurements were made for incident neutron energies between threshold (8.04 MeV) and 20 MeV. The partial cross sections for 21 γ-rays were extracted from the data. Of these, 17 were compared to calculations performed using the enhanced Hauser-Feshbach code STAPRE. The partial γ−ray cross sections of the observed parallel decay paths to the ground state were summed, forming a lower bound for the (n,2n) reaction channel. A combination of theory and experiment was then used to deduce the (n,2n) reaction channel cross section.

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The Chi-Nu experiment aims to accurately measure the prompt fission neutron spectrum (PFNS) for the major actinides. At the Los Alamos Neutron Science Center (LANSCE), fission can be induced using the white neutron source. Using a two arm time of flight (T.O.F) technique; Chi-Nu presents a preliminary result of the low energy component of the 235 U PFNS measured using an array of 22-Lithium glass scintillators.