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The 150Sm(n,n′γ) reaction was measured from En = 1 to 15 MeV at the Los Alamos Neutron Science Cemter (LANSCE). The γ rays were detected with the Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Measured γ-ray excitation functions were converted to partial γ-ray cross sections, Twenty four individual γ-rays up to Ex = 1.8 MeV in 150Sm were measured. Results are compared with enhanced Hauser Feshbach model calculations: the spin distribution in the pre-equilibrium reaction is calculated with the quantum mechanical model of Feshbach, Kerman and Koonin. The particle transmission coefficients were calculated with two different global optical model potential parameter sets. We employed the coupled-channel optical model based on the soft rotor model and with spherical potential. [ABSTRACT FROM AUTHOR]

We have implemented a Monte-Carlo simulation of the statistical decay of fission fragments by sequential neutron emission. In this presentation, we report on some numerical results obtained for the spontaneous fission of 252Cf and neutron-induced fission of 235U at 0.53 MeV neutron energy, and compare them to the results of the Los Alamos model for the calculation of the average number of prompt fission neutrons v and the prompt fission neutrons spectrum N(E). Within this approach, we also calculate neutron multiplicity distributions P(v) as well as neutron-neutron correlations such as the full matrix v(A, T K E). Two assumptions for partitioning the total available excitation energy among the light and heavy fragments are considered. The influence of the fission fragments excitation energy for low total kinetic energies on prompt neutron energy spectrum, multiplicity distributions and v(A, T K E) is discussed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Covariance data are required to correctly assess uncertainties in design parameters in nuclear applications. The error estimation of calculated quantities relies on the nuclear data uncertainty information available in the basic nuclear data libraries, such as the U.S. Evaluated Nuclear Data File, ENDF/B. The uncertainty files in the ENDF/B library are obtained from the analysis of experimental data and are stored as variance and covariance data. The computer code SAMMY is used in the analysis of the experimental data in the resolved and unresolved resonance energy regions. The data fitting of cross sections is based on generalized least-squares formalism (Bayes’ theory) together with the resonance formalism described by R-matrix theory. Two approaches are used in SAMMY for the generation of resonance-parameter covariance data. In the evaluation process SAMMY generates a set of resonance parameters that fit the data, and, in addition, it also provides the resonance-parameter covariances. For existing resonance-parameter evaluations where no resonance-parameter covariance data are available, the alternative is to use an approach called the “retroactive” resonance-parameter covariance generation. In the high-energy region the methodology for generating covariance data consists of least-squares fitting and model parameter adjustment. The least-squares fitting method calculates covariances directly from experimental data. The parameter adjustment method employs a nuclear model calculation such as the optical model and the Hauser-Feshbach model, and estimates a covariance for the nuclear model parameters. In this paper we describe the application of the retroactive method and the parameter adjustment method to generate covariance data for the gadolinium isotopes. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

McGNASH is a modern statitistical/preequilibrium nuclear reaction code, being developed at Los Alamos, which can simulate neutron-, proton- and photon-induced reactions in the energy range from a few-keV to about 150 MeV. It is written in modern Fortran 95 scientific language, offering new capabilities both for the developer and the user. McGNASH is still in a development stage, and a first public release is planned for later in 2005. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have implemented a Monte Carlo simulation of the fission-fragment statistical decay by sequential neutron emission. Within this approach, we calculate both the center-of-mass and laboratory prompt-neutron energy spectra, the prompt neutron multiplicity distribution P(v), and the average total number of emitted neutrons as a function of the mass of the fission fragment v(A). Two assumptions for partitioning the total available excitation energy among the light and heavy fragments are considered. Preliminary results are reported for the neutron-induced fission of 235U (at 0.53 MeV neutron energy) and for the spontaneous fission of 252Cf. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]