776 Matching Results

Search Results

Advanced search parameters have been applied.

1/2/sup +/. -->. 1/2/sup -/ beta decay of /sup 19/Ne and the parity nonconserving NN force

Description: A branching ratio of (1.20 +- 0.20) x 10/sup -4/ is obtained for the ..beta../sup +/ decay of /sup 19/Ne to the 110 keV 1/2/sup -/ level of /sup 19/F. This transition (presumably dominated by the ..delta..J/sup ..pi../ = 0/sup -/ axial charge operator) provides a crucial test of wavefunctions used in interpreting the parity mixing of the ground and 110 keV levels of /sup 19/F. These wavefunctions, which yield a parity mixing larger than that observed experimentally, also predict too large a ..beta../sup +/ decay rate.
Date: January 1, 1978
Creator: Adelberger, E.G.; Hindi, M.M.; Hoyle, C.D.; Swanson, H.E. & Von Lintig, R.D.
Partner: UNT Libraries Government Documents Department

4. pi. data of relativistic nuclear collisions. [Plastic ball]

Description: During the past two years, complete events of relativistic nuclear collisions are being studied with the Plastic Ball, the first electronic nonmagnetic particle-identifying 4..pi.. spectrometer. It is well suited to handle the large multiplicities in these reactions and allows collection of data at a rate sufficient to make further software selections to look at rare events. The analysis of the data follows various lines covering topics like thermalization, stopping or transparency, cluster-production mechanism (--can it tell entropy), search for collective flow through various global analyzing methods that allow determination of the scattering plane, projectile fragmentation (--is there a bounce-off), pion distribution, two-particle correlations: Hanbury-Brown Twiss, and excited nuclear states (--nucleosynthesis at the freezeout point or from chemical equilibrium). We will cover in this contribution only two subjects: stopping and thermalization and cluster production.
Date: May 1, 1983
Creator: Gutbrod, H.H.; Gustafsson, H.A. & Kolb, B.
Partner: UNT Libraries Government Documents Department

The 239 Pu(n,2n)238Pu cross section: preliminary calculations

Description: The primary motivation for the present work is to provide theoretical values for the ratio of the partial <sup>239</sup>Pu(n,2nx{gamma})<sup>238</sup>Pu to total <sup>239</sup> Pu(n,2n)<sup>238</sup>Pu cross section for several discrete gamma transitions. Results and conclusions of preliminary calculations from threshold to 20 MeV are presented. Calculations are based on theoretical models with parameters obtained from the literature or from our ad hoc systematics. Optical model cross sections and transmission coefficients were determined using the coupled-channels method. The calculations included a preequilibrium component followed by multiple particle and gamma-ray emissions. Fission competition was included at all stages of de-excitation. Suggestions for further verifications and possible improvements are provided.
Date: March 12, 1999
Creator: Chen, H.; Reffo, G.; Ross, M. A. & White, R. M.
Partner: UNT Libraries Government Documents Department

1989 report on the IAEA research agreement No. 4412/CF

Description: My contribution to this CRP is the provision of double-differential neutron-scattering cross section data on the mono-isotopic elements Nb, Rh, In, Ho, Ta, Au, and Bi. These data cover the ranges incident neutron energies, E{sub in} = 5--8 Mev, angular range, 30--158 {degrees}, excitation energies, {approx} 2 to E{sub in}--1 MeV. In this report I will briefly review the original purpose of these measurements, indicate the assumptions and procedures required to obtain the requested cross sections, present the results of this effort, give a few examples of how these results compare to calculations made with relevant nuclear model codes, describe the data files that I have prepared for the participants of this CRP, briefly describe sources of error. An appendix contains a short discussion of some experimental concerns. 8 refs., 9 figs.
Date: January 1, 1989
Creator: Guenther, P.T.
Partner: UNT Libraries Government Documents Department

The 1992 FRDM mass model and unstable nuclei

Description: We discuss the reliability of a recent global nuclear-structure calculation in regions far from {beta} stability. We focus on the results for nuclear masses, but also mention other results obtained in the nuclear-structure calculation, for example ground-state spins. We discuss what should be some minimal requirements of a nuclear mass model and study how the macroscopic-microscopic method and other nuclear mass models fullfil such basic requirements. We study in particular the reliability of nuclear mass models in regions of nuclei that were not considered in the determination of the model parameters.
Date: February 1, 1994
Creator: Moeller, P. & Nix, R. J.
Partner: UNT Libraries Government Documents Department

An accurate nucleon-nucleon potential with charge-independence breaking

Description: The authors present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which they designate Argonne {upsilon}{sub 18}. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne {upsilon}{sub 14} potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen pp and np scattering data base, low-energy nn scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a {chi}{sup 2} per datum of 1.09 for 4,301 pp and np data in the range 0--350 MeV.
Date: August 1, 1994
Creator: Wiringa, R. B.; Stoks, V. G. J. & Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Actinide production in /sup 136/Xe bombardments of /sup 249/Cf

Description: The production cross sections for the actinide products from /sup 136/Xe bombardments of /sup 249/Cf at energies 1.02, 1.09, and 1.16 times the Coulomb barrier were determined. Fractions of the individual actinide elements were chemically separated from recoil catcher foils. The production cross sections of the actinide products were determined by measuring the radiations emitted from the nuclides within the chemical fractions. The chemical separation techniques used in this work are described in detail, and a description of the data analysis procedure is included. The actinide production cross section distributions from these /sup 136/Xe + /sup 249/Cf bombardments are compared with the production cross section distributions from other heavy ion bombardments of actinide targets, with emphasis on the comparison with the /sup 136/Xe + /sup 248/Cm reaction. A technique for modeling the final actinide cross section distributions has been developed and is presented. In this model, the initial (before deexcitation) cross section distribution with respect to the separation energy of a dinuclear complex and with respect to the Z of the target-like fragment is given by an empirical procedure. It is then assumed that the N/Z equilibration in the dinuclear complex occurs by the transfer of neutrons between the two participants in the dinuclear complex. The neutrons and the excitation energy are statistically distributed between the two fragments using a simple Fermi gas level density formalism. The resulting target-like fragment initial cross section distribution with respect to Z, N, and excitation energy is then allowed to deexcite by emission of neutrons in competition with fission. The result is a final cross section distribution with respect to Z and N for the actinide products. 68 refs., 33 figs., 6 tabs.
Date: August 1, 1985
Creator: Gregorich, K.E.
Partner: UNT Libraries Government Documents Department

Additional degrees of freedom in skyrmion motion

Description: The authors consider the quantization of chiral solitons with baryon number B &gt; 1. Classical solitons are obtained within the framework of a variational approach. From the form of the soliton solution it can be seen that besides the group of symmetry describing transformations of the configuration as a whole there are additional symmetries corresponding to internal transformations. Taking into account the additional degrees of freedom leads to some sort of spin alignment for light nuclei and gives constraints on their spectra.
Date: September 1, 1994
Creator: Musatov, I.; Nikolaev, V. & Tkachev, O.
Partner: UNT Libraries Government Documents Department

Advanced modeling of reaction cross sections for light nuclei

Description: The shell model/R-matrix technique of calculating nuclear reaction cross sections for light projectiles incident on light nuclei is discussed, particularly in the application of the technique to thermonuclear reactions. Details are presented on the computational methods for the shell model which display how easily the calculations can be performed. Results of the shell model/R-matrix technique are discussed as are some of the problems encountered in picking an appropriate nucleon-nucleon interaction for the large model spaces which must be used for current problems. The status of our work on developing an effective nucleon-nucleon interaction for use in large-basis shell model calculations is presented. This new interaction is based on a combination of global constraints and microscopic nuclear data. 23 refs., 6 figs., 2 tabs.
Date: January 1, 1991
Creator: Resler, D.A.
Partner: UNT Libraries Government Documents Department

Algebraic description of intrinsic modes in nuclei

Description: We present a procedure for extracting normal modes in algebraic number-conserving systems of interacting bosons relevant for collective states in even-even nuclei. The Hamiltonian is resolved into intrinsic (bandhead related) and collective (in-band related) parts. Shape parameters are introduced through non-spherical boson bases. Intrinsic modes decoupled from the spurious modes are obtained from the intinsic part of the Hamiltonian in the limit of large number of bosons. Intrinsic states are constructed and serve to evaluate electromagnetic transition rates. The method is illustrated for systems with one type of boson as well as with proton-neutron bosons. 28 refs., 1 fig.
Date: January 1, 1989
Creator: Leviatan, A.
Partner: UNT Libraries Government Documents Department

Alpha-particle emission as a probe of nuclear shapes and structure effects in proton evaporation spectra

Description: Emission barriers and subbarrier anisotropies from {alpha} decay of Sn* and Yb* compound nuclei are examined in the light of calculations incorporating deformation effects in the decay process. For the Yb* systems deformation which increases with spin is necessary to explain the data. For the Sn* systems the spectral shapes and anisotropies can be explained without deformation. For systems lighter than Sn this probe is not sensitive to the deformation. Energy spectra and angular correlations of evaporated protons from the {sup 52}Cr({sup 34}S, 2n2p){sup 82}Sr reaction were measured in coincidence with discrete transitions. Large shifts in proton spectra were observed when high spin states in different rotational bands are populated. They are interpreted as due to near-yrast stretched proton emission preferentially populating the yrast band by subbarrier protons. Simulations show that channel selected proton spectra cannot be used as probes of deformation.
Date: January 1, 1990
Creator: Nicolis, N.G.; Sarantites, D.G.; Abenante, V.; Adler, L.A.; Dilmanian, F.A.; Majka, Z. et al.
Partner: UNT Libraries Government Documents Department

Alpha-particles as probes of nuclear shape and structure effects in proton evaporation spectra

Description: The emission barriers and subbarrier anisotropies in the alpha-particle decay with respect to the spin direction on Sn and rare earth compound nuclei are examined in the light of recent calculations incorporating deformation effects in the decay process. For the Sn systems the spectral shapes and anisotropies can be examined without involving deformation. For the rare earth systems deformation which increases with spin is necessary to explain the data. Energy spectra and angular correlations of evaporated protons from the {sup 52}Cr ({sup 34}S, 2p2n){sup 82}Sr reaction were measured in coincidence with discrete transitions. Large shifts in proton spectra were observed when high spin states in different rotational bands are populated. These effects cannot be explained by statistical model calculations that do not include explicitly nuclear structure effects in the deexcitation process. They are interpreted as due to near-yrast stretched proton emission, which preferentially populates the yrast band by subbarrier protons.
Date: January 1, 1990
Creator: Sarantites, D.G.; Nicolis, N.G.; Abenante, V.; Majka, Z.; Semkow, T.M. (Washington Univ., St. Louis, MO (USA)); Baktash, C. et al.
Partner: UNT Libraries Government Documents Department

Alpha-transfer reactions

Description: Some of the essential features of the experimental results and theoretical interpretations of ..cap alpha..-transfer reactions are summarized. (WHK)
Date: October 1, 1981
Creator: Betts, R.R.
Partner: UNT Libraries Government Documents Department

Alternate Approach to the 239Pu(n,2n) Cross Section

Description: Using existing experimental data for neutron-induced total, elastic, inelastic, reaction and fission cross sections, as well as results from nuclear model calculations and evaluations from nuclear reaction data libraries, we derived an estimate for the cross sections for the {sup 235}U(n,2n) and {sup 239}Pu(n,2n) reactions for the neutron energy range from threshold to approximately 12 MeV. In effect, our approach is based on subtracting the fission and inelastic cross sections from the total reaction cross section where the difference is expected to yield the (n,2n) cross section. In addition to this subtraction approach, a ratio method and a differential method have also been explored. For {sup 235}U(n,2n), as a test case, we arrive at a cross section consistent with previous measurements, and for {sup 239}Pu(n,2n) we obtain a peak value of 400 {+-} 60 mb for the incident neutron energy range of 10 {le} E{sub n} {le} 12 MeV.
Date: September 1, 2000
Creator: Anderson, J D; Bauer, R W; Becker, J A; Dietrich, F S & McNabb, D P
Partner: UNT Libraries Government Documents Department

Analysis of forward and inverse problems in chemical dynamics and spectroscopy

Description: This research is concerned with the development and application of advanced analysis tools for studying dynamics, kinetics, and spectroscopic phenomena from a forward and inverse perspective. In particular, the forward problem is concerned with understanding how detailed interatomic potential information maps onto a hierarchy of chemical dynamic and kinetic observables. The inverse aspects of the research are concerned with exactly the reverse of this process, whereby we desire to understand how particular measurements project back to yield information regarding the potential surface. Thus, in the latter domain, our research is concerned with the development of theoretically based tools ultimately aimed at applications to the inversion of quality laboratory data for the extraction of microscopic potential information.
Date: January 1, 1991
Creator: Rabitz, H.
Partner: UNT Libraries Government Documents Department

Analysis of neutron yield produced by high energy proton. [400 and 660 MeV]

Description: Vasil'kov et al.'s experiments for neutron yield and neutron capture distribution produced by 400 and 660 MeV protons were analyzed by using ENDF/B-IV data and the BNL codes NMTC and TWOTRAN. The calculated total neutron radiative capture by /sup 238/U is 77 and 60% of the measured values for protons of 660 and 400 MeV, respectively. The calculated distribution has the higher peak in the central part of the target system, and steeper gradient both in the r and z directions, compared to experimental. The leakage rate of neutrons from the target assembly is calculated as more than 20%, which is much higher than the 10% estimated from the experiment. The total neutron captures determined using ENDF/B-IV are 3.8 and 3.0% higher than those determined using ENDF/B-III for protons of 660 and 400 MeV, respectively. 12 references.
Date: January 1, 1979
Creator: Takahashi, H. & Nakanara, Y.
Partner: UNT Libraries Government Documents Department

Analysis of nucleon-induced fission cross sections of lead and bismuth at energies from 45 to 500 MeV

Description: In order to investigate the applicability of the Cascade-Exciton model (CEM) of nuclear reactions to fission cross sections and hoping to learn more about intermediate-energy fission, the authors use an extended version of the CEM, as realized in the code CEM95 to perform a detailed analysis of proton- and neutron-induced fission cross sections of {sup 209}Bi and {sup 208}Pb nuclei and of the linear momentum transfer to the fissioning nuclei in the 45--500 meV energy range.
Date: August 1, 1998
Creator: Prokofyev, A.V.; Mashnik, S.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

The Angular Distribution of Fission Fragments From the Fast Neutron-Induced Fission of U-234

Description: Submitted to Univ. of Tennessee, Knoxville. The fast neutron-induced fission cross section of U/sup 234/ was measured from threshold to 4-Mev neutron energy. A maximum of 1.26 barns was found at 850 kev followed by a minimum of 1.10 barns at 8050 kev. The angular ani-sotropy of the fragment distribution was measured for neutron energies from 400 kev to 4 Mev. Extrema in the ratio sigma /sub f//( sigma /sub f(90 deg ) were found at 500, 850, and 1050 kev; the distribution at 500 kev showing a maximum in the direction normal to the beam (side-wise peaking) while that at 850 kev showed a maximum along the beam direction. The distribution at 8050 kev showed forward peaking but to a lesser extent than for energies immediately higher or lower. The behavior was analyzed according to the theories of Bohr and Wheeler. The dip in cross section between 850 and 1050 kev is consistent with the suggestion of Wheeler that neutron competition in the decay of the compound nucleus enters with increased strength in this area. Vibration-rotational levels in U/sup 234/ beginning at 790 kev are known to exist and inelastic neutron scattering to these levels serves to depress the fission cross section. The changes in fragment angular distribution are shown to be explainable in terms of the theory of Bohr which states that fission occurs through distinct channels composed of a K-band structure analogous to that observed at low excitations in heavy deformed nuclei. More detailed angular distribution measurements were carried out at 850 and 1050 kev. The overall picture is consistent with a K-band structure in U/sup 235/* near the saddle point deformation of K equals 1/2+, 3/2--, 1/2-- in that order, the bands being separated from each other by a few hundred kilovolts. (auth)
Date: August 27, 1962
Creator: Lamphere, R. W.
Partner: UNT Libraries Government Documents Department

Angular momentum and the collective modes excited in deep-inelastic processes and in fission. [288 MeV]

Description: The angular momentum effects in deep inelastic processes and fission were studied in the limit of statistical equilibrium. The model consists of two touching liquid drop spheres. Angular momentum fractionation was found to occur along the mass asymmetry coordinate. Thermal excitation of fragment spin is predicted to occur in the degrees of freedom which can bear angular momentum, like wriggling, tilting, bending, and twisting. 17 references.
Date: May 1, 1979
Creator: Moretto, L.G.
Partner: UNT Libraries Government Documents Department