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46 results on '"Keksis, A. L."'

1. Neutron Capture on Actinides Studied with DANCE

Author

Ullmann, J. L., Baramsai, B., Bredeweg, T. A., Couture, A. J., Haight, R. C., Jandel, M., Kawano, T., Keksis, A. L., Mosby, S., O’Donnell, J. M., Prokop, C., Rundberg, R. S., Rusev, G., Vieira, D. J., Walker, C., Wilhelmy, J. B., Wu, C. -Y., Becker, J. A., Chyzch, A., Henderson, R. A., Mitchell, G. E., Krticka, M., Escher, Jutta, editor, Alhassid, Yoram, editor, Bernstein, Lee A., editor, Brown, David, editor, Fröhlich, Carla, editor, Talou, Patrick, editor, and Younes, Walid, editor

Published
2021
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2. Experimental evidence of quantum quenching of fluctuations in heavy ion collisions

Author

Stein, B. C., Zheng, H., Bonasera, A., Soisson, S. N., McIntosh, A., Tripathi, R., Souliotis, G. A., Marini, P., Keksis, A. L., Wuenschel, S., Kohley, Z., May, L. W., and Yennello, S. J.

Subjects
Nuclear Experiment
Abstract

The first experimental results of a new quantum method for calculating nuclear temperature and density of fragmenting heavy ions is presented. This method is based on fluctuations in the event quadrupole momentum and fragment multiplicity distributions of light Fermions. The cal- culated temperatures are lower than those obtained with a similar classical method. Quenching of the normalized multiplicity distributions of light fermions due to Pauli blocking is also observed. These results indicate a need for a quantum treatment when dealing with statistical properties of fragmenting heavy-ions., Comment: 4 pages, 4 figures

Published
2011

3. Statistical and dynamical aspects in the decay of hot neutron-rich nuclei

Author

Veselsky, M., Keksis, A. L., Souliotis, G. A., Wang, K., Bell, E., Shetty, D. V., Jandel, M., Yennello, S. J., and Ma, Y. G.

Subjects
Nuclear Experiment
Abstract

The signal of isospin-asymmetric phase transition in the evolution of the chemical potential was observed for hot quasi-projectiles produced in the reactions 40,48Ca + 27Al confirming an analogous observation in the lighter system 28Si + 112,124Sn. With increasing mass, the properties of hot quasi-projectiles become increasingly influenced by the secondary emission. Thermodynamical observables exhibit no sensitivity to the different number of missing neutrons in the two reactions 40,48Ca + 27Al, thus providing a signal of dynamical emission of neutrons, which can be related to formation of a very neutron-rich low-density region (neck) between the projectile and target., Comment: LaTeX, article expanded, 2 figures added, 17 pages, 7 figures

Published
2008
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4. Neutron Capture on Actinides Studied with DANCE

Author

Ullmann, J. L., primary, Baramsai, B., additional, Bredeweg, T. A., additional, Couture, A. J., additional, Haight, R. C., additional, Jandel, M., additional, Kawano, T., additional, Keksis, A. L., additional, Mosby, S., additional, O’Donnell, J. M., additional, Prokop, C., additional, Rundberg, R. S., additional, Rusev, G., additional, Vieira, D. J., additional, Walker, C., additional, Wilhelmy, J. B., additional, Wu, C. -Y., additional, Becker, J. A., additional, Chyzch, A., additional, Henderson, R. A., additional, Mitchell, G. E., additional, and Krticka, M., additional

Published
2020
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5. Symmetry Energy, Temperature, Density and Isoscaling Parameter as a Function of Excitation energy in A $\sim$ 100 mass region

Author

Shetty, D. V., Yennello, S. J., Souliotis, G. A., Keksis, A. L., Soisson, S. N., Stein, B. C., and Wuenschel, S.

Subjects
Nuclear Experiment, Nuclear Theory
Abstract

The symmetry energy, temperature, density and isoscaling parameter, in $^{58}$Ni + $^{58}$Ni, $^{58}$Fe + $^{58}$Ni and $^{58}$Fe + $^{58}$Fe reactions at beam energies of 30, 40 and 47 MeV/nucleon, are studied as a function of excitation energy of the multifragmenting source. It is shown that the decrease in the isoscaling parameter is related to the near flattening of the temperature in the caloric curve, and the decrease in the density and the symmetry energy with increasing excitation energy. The decrease in the symmetry energy is mainly a consequence of decreasing density with increasing excitation rather than the increasing temperature. The symmetry energy as a function of density obtained from the correlation is in close agreement with the form, E$_{sym}(\rho)$ $=$ 31.6 ($\rho/\rho_{\circ})^{0.69}$., Comment: 5 pages, 5 figures

Published
2006

6. Neutron to proton ratios of quasiprojectile and midrapidity emission in the $^{64}$Zn + $^{64}$Zn reaction at 45 MeV/nucleon

Author

Theriault, D., Gauthier, J., Grenier, F., Moisan, F., St-Pierre, C., Roy, R., Davin, B., Hudan, S., Paduszynski, T., de Souza, R. T., Bell, E., Garey, J., Iglio, J., Keksis, A. L., Parketon, S., Richers, C., Shetty, D. V., Soisson, S. N., Souliotis, G. A., Stein, B. C., and Yennello, S. J.

Subjects
Nuclear Experiment
Abstract

Simultaneous measurement of both neutrons and charged particles emitted in the reaction $^{64}$Zn + $^{64}$Zn at 45 MeV/nucleon allows comparison of the neutron to proton ratio at midrapidity with that at projectile rapidity. The evolution of N/Z in both rapidity regimes with increasing centrality is examined. For the completely re-constructed midrapidity material one finds that the neutron-to-proton ratio is above that of the overall $^{64}$Zn + $^{64}$Zn system. In contrast, the re-constructed ratio for the quasiprojectile is below that of the overall system. This difference provides the most complete evidence to date of neutron enrichment of midrapidity nuclear matter at the expense of the quasiprojectile.

Published
2006
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7. Tracing the evolution of the symmetry energy of hot nuclear fragments from the compound nucleus towards multifragmentation

Author

Souliotis, G. A., Botvina, A. S., Shetty, D. V., Keksis, A. L., Jandel, M., Veselsky, M., and Yennello, S. J.

Subjects
Nuclear Experiment
Abstract

The evolution of the symmetry energy coefficient of the binding energy of hot fragments with increasing excitation is explored in multifragmentation processes following heavy-ion collisions below the Fermi energy. In this work, high-resolution mass spectrometric data on isotopic distributions of projectile-like fragments from collisions of 25 MeV/nucleon 86Kr and 64Ni beams on heavy neutron-rich targets are systematically compared to calculations involving the Statistical Multifragmentation Model. The study reveals a gradual decrease of the symmetry energy coefficient from 25 MeV at the compound nucleus regime (E*/A < 2 MeV) towards 15 MeV in the bulk multifragmentation regime (E*/A > 4 MeV). The ensuing isotopic distributions of the hot fragments are found to be very wide and extend towards the neutron drip-line. These findings may have important implications to the composition and evolution of hot astrophysical environments, such as core-collapse supernova., Comment: 5 pages, 4 figures, submitted to Phys. Rev. C

Published
2006
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8. New capability for indirect neutron capture measurements: The DICER instrument at LANSCE

Author

Stamatopoulos A., Koehler P., Matyskin A., Bond E. M., Bredeweg T.A., Couture A., Di Giovine B., Fassbender M.E., Hayes-Sterbenz A. C., Keksis A. L., Parsons K., Rusev G., Ullmann J., and Vermeulen C.

Subjects
Physics, QC1-999
Abstract

The Device for Indirect Capture on Radionuclides (DICER) implements a new indirect technique for (n,γ) studies in which the neutron capture rate is determined from analysis of resonance neutron transmission data. The DICER instrument and associated radionuclide production at the Isotope Production Facility (IPF), both at the Los Alamos Neutron Science Center (LANSCE), as well radioactive sample fabrication, have been under development in the last few years. First measurements on a radioactive sample (88Zr, t½=83.4 days), which was recently reported to have an extremely large thermal neutron capture cross section and resonance integral [1, 2], are planned for the winter of 2021. A performance overview, brief details on the 88Zr fabrication and proof of good operation results will be presented.

Published
2022
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9. The new Device for Indirect Capture Experiments on Radionuclides at LANSCE: Efforts on measuring the resonance(s) responsible for the extremely large 88Zr (n,γ) cross section

Author

Stamatopoulos, A., primary, Bond, E. M., additional, Bredeweg, T.A., additional, Couture, A., additional, Di Giovine, B., additional, Fassbender, M.E., additional, Hayes-Sterbenz, A. C., additional, Keksis, A. L., additional, Matyskin, A., additional, Mocko, V., additional, Parsons, K., additional, Rusev, G., additional, Ullmann, J., additional, and Vermeulen, C., additional

Published
2023
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10. The new Device for Indirect Capture Experiments on Radionuclides at LANSCE: Efforts on measuring the resonance(s) responsible for the extremely large 88Zr (n,γ) cross section.

Author

Stamatopoulos, A., Bond, E. M., Bredeweg, T.A., Couture, A., Di Giovine, B., Fassbender, M.E., Hayes-Sterbenz, A. C., Keksis, A. L., Matyskin, A., Mocko, V., Parsons, K., Rusev, G., Ullmann, J., and Vermeulen, C.

Subjects
RADIOISOTOPES, THERMAL neutron capture, NUCLEAR cross sections, RESONANCE, RADIOACTIVE substances
Abstract

The thermal neutron capture cross section of 88Zr was recently reported to be the second largest in nature with the largest resonance integral measured. Presumably, these very large values are caused by a resonance or resonances very near thermal energy. Determining their energies and widths, and hence the shape of the cross section away from thermal energies,is useful for applications. The short half-life (83.4 days) and associated large background, renders direct measurements of the neutron capture cross section impossible using current techniques. However, it is possible to measure the total neutron cross section, and hence the resonance properties, using the newly commissioned Device for Indirect Capture Experiments on Radionuclides (DICER) at the Los Alamos Neutron Science Center (LANSCE). Transmission measurements are utilized as a surrogate method to perform capture measurements. The 88Zr needed for a DICER measurement was produced at the Isotope Production Facility (IPF) and cleanly separated from the production target material. A description of the new instrument, efforts and preliminary results on 88Zr will be presented. [ABSTRACT FROM AUTHOR]

Published
2023
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11. Los Alamos National Laboratory Fission Basis

Author

Keksis, A. L., primary, Chadwick, M. B., additional, Selby, H. D., additional, Mac Innes, M. R., additional, Barr, D. W., additional, Meade, R. A., additional, Burns, C. J., additional, and Wallstrom, T. C., additional

Published
2012
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13. Photon strength functions in Gd isotopes studied from radiative capture of resonance neutrons

Author

Kroll J., Baramsai B., Mitchell G. E., Agvaanluvsan U., Bečvář F., Bredeweg T. A., Chyzh A., Couture A., Dashdorj D., Haight R. C., Jandel M., Keksis A. L., Krtička M., O’Donnell J. M., Parker W., Rundberg R. S., Ullmann J. L., Valenta S., Vieira D. J., Walker C., and Wu C. Y.

Subjects
Physics, QC1-999
Abstract

The experimental spectra of γ rays following radiative neutron capture on isolated resonances of stable 152,154–158Gd targets were measured by the DANCE calorimeter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd isotopes. The scissors mode strength observed in 157,159Gd products is significantly higher than in neighboring even-even nuclei 156,158Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the experimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ′) data for the ground-state transitions and with the results from 3He-induced reactions.

Published
2014
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15. Isomeric ratio measurements for the radiative neutron capture Lu176(n,γ) at the LANL DANCE facility

Author

Denis-Petit, D., primary, Roig, O., additional, Méot, V., additional, Morillon, B., additional, Romain, P., additional, Jandel, M., additional, Kawano, T., additional, Vieira, D. J., additional, Bond, E. M., additional, Bredeweg, T. A., additional, Couture, A. J., additional, Haight, R. C., additional, Keksis, A. L., additional, Rundberg, R. S., additional, and Ullmann, J. L., additional

Published
2016
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16. Radiative neutron capture cross sections onLu176at DANCE

Author

Roig, O., primary, Jandel, M., additional, Méot, V., additional, Bond, E. M., additional, Bredeweg, T. A., additional, Couture, A. J., additional, Haight, R. C., additional, Keksis, A. L., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, and Vieira, D. J., additional

Published
2016
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17. Isomeric ratio measurements for the radiative neutron capture 176Lu(n,γ) at DANCE.

Author

Denis-Petit, D., Roig, O., Méot, V., Morillon, B., Romain, P., Jandel, M., Kawano, T., Vieira, D. J., Bond, E. M., Bredeweg, T. A., Couture, A. J., Haight, R. C., Keksis, A. L., Rundberg, R. S., and Ullmann, J. L.

Subjects
NEUTRON capture, LUTETIUM isotopes, METASTABLE states, NUCLEAR reactions
Abstract

The isomeric ratios for the neutron capture reaction 176Lu(n,γ) to the Jπ = 5/2-, 761.7 keV, T1/2 = 32.8 ns and the Jπ = 15/2+, 1356.9 keV, T1/2 = 11.1 ns levels of 177Lu, have been measured for the first time with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory. These measured isomeric ratios are compared with TALYS calculations. [ABSTRACT FROM AUTHOR]

Published
2017
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18. Isomeric ratio measurements for the radiative neutron capture 176Lu(n,γ) at DANCE.

Author

Denis-Petit, D., Roig, O., Méot, V., Jandel, M., Vieira, D. J., Bond, E. M., Bredeweg, T. A., Couture, A. J., Haight, R. C., Keksis, A. L., Rundberg, R. S., and Ullmann, J. L.

Subjects
NEUTRON capture, NUCLEAR research, NEUTRON temperature, EXCITATION energy (In situ microanalysis)
Abstract

The isomeric ratio for the neutron capture reaction 176Lu(n,γ) on the Jπ = 5/2-, 761.7 keV, T1/2 = 32.8 ns level of 177mLu, has been determined in the neutron energy range 8.5 eV-100 keV for the first time using the DANCE array at the Los Alamos National Laboratory. [ABSTRACT FROM AUTHOR]

Published
2016
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19. Quantum suppression of fluctuations and temperatures of reconstructedA∼ 30 quasi-projectiles

Author

Stein, B C, primary, Bonasera, A, additional, Souliotis, G A, additional, Zheng, H, additional, Cammarata, P J, additional, Echeverria, A J, additional, Heilborn, L, additional, Keksis, A L, additional, Kohley, Z, additional, Mabiala, J, additional, Marini, P, additional, May, L W, additional, McIntosh, A B, additional, Richers, C, additional, Shetty, D V, additional, Soisson, S N, additional, Tripathi, R, additional, Wuenschel, S, additional, and Yennello, S J, additional

Published
2014
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20. Strength of the scissors mode in odd-mass Gd isotopes from the radiative capture of resonance neutrons

Author

Kroll, J., primary, Baramsai, B., additional, Mitchell, G. E., additional, Agvaanluvsan, U., additional, Bečvář, F., additional, Bredeweg, T. A., additional, Chyzh, A., additional, Couture, A., additional, Dashdorj, D., additional, Haight, R. C., additional, Jandel, M., additional, Keksis, A. L., additional, Krtička, M., additional, O’Donnell, J. M., additional, Parker, W., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, Valenta, S., additional, Vieira, D. J., additional, Walker, C., additional, and Wu, C. Y., additional

Published
2013
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21. NEUTRON CAPTURE REACTIONS ON Lu ISOTOPES AT DANCE

Author

ROIG, O., primary, MEOT, V., additional, DAUGAS, J. -M., additional, MOREL, P., additional, JANDEL, M., additional, VIEIRA, D. J., additional, BOND, E. M., additional, BREDEWEG, T. A., additional, COUTURE, A. J., additional, HAIGHT, R. C., additional, KEKSIS, A. L., additional, RUNDBERG, R. S., additional, ULLMANN, J. L., additional, and WOUTERS, J. M., additional

Published
2013
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22. GAMMA EMISSION SPECTRA FROM NEUTRON RESONANCES IN 234,236,238U MEASURED USING THE DANCE DETECTOR AT LANSCE

Author

ULLMANN, J. L., primary, BREDEWEG, T. A., additional, COUTURE, A. J., additional, HAIGHT, R. C., additional, JANDEL, M., additional, KAWANO, T., additional, KEKSIS, A. L., additional, O'DONNELL, J. M., additional, RUNDBERG, R. S., additional, VIEIRA, D. J., additional, WOUTERS, J. M., additional, WILHELMY, J. B., additional, WU, C. Y., additional, BECKER, J. A., additional, CHYZH, A., additional, BARAMSAI, B., additional, MITCHELL, G. E., additional, and KRTICKA, M., additional

Published
2013
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23. Photon strength functions of156Gd from radiative capture of resonance neutrons

Author

Baramsai, B., primary, Kroll, J., additional, Mitchell, G. E., additional, Agvaanluvsan, U., additional, Bečvář, F., additional, Bredeweg, T. A., additional, Chyzh, A., additional, Couture, A., additional, Dashdorj, D., additional, Haight, R. C., additional, Jandel, M., additional, Keksis, A. L., additional, Krtička, M., additional, O’Donnell, J. M., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, Vieira, D. J., additional, and Walker, C. L., additional

Published
2013
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25. Neutron resonance parameters in155Gd measured with the DANCEγ-ray calorimeter array

Author

Baramsai, B., primary, Mitchell, G. E., additional, Agvaanluvsan, U., additional, Bečvář, F., additional, Bredeweg, T. A., additional, Chyzh, A., additional, Couture, A., additional, Dashdorj, D., additional, Haight, R. C., additional, Jandel, M., additional, Keksis, A. L., additional, Krtička, M., additional, O'Donnell, J. M., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, Vieira, D. J., additional, and Walker, C. L., additional

Published
2012
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26. Measurement of the 238U Neutron-capture Cross Section and Gamma-emission Spectra from 10 eV to 100 keV Using the DANCE Detector at LANSCE

Author

Ullmann, J. L., primary, Couture, A. J., additional, Keksis, A. L., additional, Vieira, D. J., additional, O'Donnell, J. M., additional, Wouters, J. M., additional, Jandel, M., additional, Haight, R. C., additional, Rundberg, R. S., additional, Bredeweg, T. A., additional, Kawano, T., additional, Wu, C. Y., additional, Becker, J. A., additional, Chyzh, A., additional, Baramsai, B., additional, Mitchell, G. E., additional, and Krticka, M., additional

Published
2011
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27. Neutron Resonance Spin Determination Using Multi-Segmented Detector DANCE

Author

Baramsai, B., primary, Mitchell, G. E., additional, Agvaanluvsan, U., additional, Becvar, F., additional, Bredeweg, T. A., additional, Couture, A., additional, Chyzh, A., additional, Dashdorj, D., additional, Haight, R. C., additional, Jandel, M., additional, Keksis, A. L., additional, Krticka, M., additional, O’Donnell, J. M., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, Vieira, D. J., additional, Walker, C., additional, Wouters, J. M., additional, McDaniel, Floyd D., additional, and Doyle, Barney L., additional

Published
2011
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30. Recent Updates to the FAUST Array

Author

Stein, B. C., primary, Soisson, S. N., additional, May, L. W., additional, Dienhoffer, R. Q., additional, Souliotis, G. A., additional, Shetty, D. V., additional, Keksis, A. L., additional, Wuenschel, S., additional, Kohley, Z., additional, Yennello, S. J., additional, McDaniel, Floyd D., additional, and Doyle, Barney L., additional

Published
2009
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31. DANCEing with the Stars: Measuring Neutron Capture on Unstable Isotopes with DANCE

Author

Couture, A., primary, Agvaanluvsan, U., additional, Baker, J. D., additional, Bayarbadrahk, B., additional, Becker, J. A., additional, Bond, E., additional, Bredeweg, T. A., additional, Chyzh, A., additional, Dashdorj, D., additional, Fowler, M., additional, Haight, R. C., additional, Jandel, M., additional, Keksis, A. L., additional, O’Donnell, J. M., additional, Reifarth, R., additional, Rundberg, R., additional, Ullmann, J. L., additional, Vieira, D. J., additional, Wouters, J. M., additional, McDaniel, Floyd D., additional, and Doyle, Barney L., additional

Published
2009
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32. Systematic Investigation of Isoscaling of Reconstructed Quasiprojectiles from Collisions in the Fermi Energy Regime

Author

Galanopoulos, S., primary, Souliotis, G. A., additional, Keksis, A. L., additional, Veselsky, M., additional, Jandel, M., additional, Shetty, D. V., additional, Kohley, Z., additional, Soisson, S., additional, Stein, B., additional, Wuenschel, S., additional, Yennello, S. J., additional, McDaniel, Floyd D., additional, and Doyle, Barney L., additional

Published
2009
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33. Neutron capture and neutron-induced fission experiments on americium isotopes with DANCE

Author

Jandel, M., primary, Bredeweg, T. A., additional, Stoyer, M. A., additional, Wu, C. Y., additional, Fowler, M. M., additional, Becker, J. A., additional, Bond, E. M., additional, Couture, A., additional, Haight, R. C., additional, Haslett, R. J., additional, Henderson, R. A., additional, Keksis, A. L., additional, O’Donnell, J. M., additional, Rundberg, R. S., additional, Ullmann, J. L., additional, Vieira, D. J., additional, Wilhelmy, J. B., additional, Wouters, J. M., additional, Jolie, Jan, additional, Zilges, Andreas, additional, Warr, Nigel, additional, and Blazhev, Andrey, additional

Published
2009
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34. Prompt radiochemistry at the National Ignition Facility (invited)

Author

Grim, G. P., primary, Bradley, P. A., additional, Bredeweg, T. A., additional, Keksis, A. L., additional, Fowler, M. M., additional, Hayes, A. C., additional, Jungman, G., additional, Obst, A. W., additional, Rundberg, R. S., additional, Vieira, D. J., additional, Wilhelmy, J. B., additional, Bernstein, L. A., additional, Cerjan, C. J., additional, Fortner, R. J., additional, Moody, K. J., additional, Schneider, D. H., additional, Shaughnessy, D. A., additional, Stoeffl, W., additional, and Stoyer, M. A., additional

Published
2008
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35. FISSION MEASUREMENTS WITH DANCE

Author

JANDEL, M., primary, BREDEWEG, T. A., additional, FOWLER, M. M., additional, BOND, E. M., additional, CHADWICK, M. B., additional, CLEMENT, R. R., additional, COUTURE, A., additional, O' DONNELL, J. M., additional, HAIGHT, R. C., additional, KEKSIS, A. L., additional, REIFARTH, R., additional, RUNDBERG, R. S., additional, ULLMANN, J. L., additional, VIEIRA, D. J., additional, WILHELMY, J. B., additional, WOUTERS, J. M., additional, AGVAANLUVSAN, U., additional, DASHDORJ, D., additional, MACRI, R. A., additional, PARKER, W. E., additional, WILK, P. A., additional, WU, C. Y., additional, BECKER, J. A., additional, ANGELL, C. T., additional, TONCHEV, A. P., additional, and BAKER, J.D., additional

Published
2008
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37. Neutron-to-proton ratios of quasiprojectile and midrapidity emission in theZn64+Zn64reaction at 45 MeV/nucleon

Author

Thériault, D., primary, Gauthier, J., additional, Grenier, F., additional, Moisan, F., additional, St-Pierre, C., additional, Roy, R., additional, Davin, B., additional, Hudan, S., additional, Paduszynski, T., additional, Souza, R. T. de, additional, Bell, E., additional, Garey, J., additional, Iglio, J., additional, Keksis, A. L., additional, Parketon, S., additional, Richers, C., additional, Shetty, D. V., additional, Soisson, S. N., additional, Souliotis, G. A., additional, Stein, B. C., additional, and Yennello, S. J., additional

Published
2006
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40. GAMMA EMISSION SPECTRA FROM NEUTRON RESONANCES IN 234;236;238U MEASURED USING THE DANCE DETECTOR AT LANSCE.

Author

ULLMANN, J. L., BREDEWEG, T. A., COUTURE, A. J., HAIGHT, R. C., JANDEL, M., KAWANO, T., KEKSIS, A. L., O'DONNELL, J. M., RUNDBERG, R. S., VIEIRA, D. J., WOUTERS, J. M., WILHELMY, J. B., WU, C. Y., BECKER, J. A., CHYZH, A., BARAMSAI, B., MITCHELL, G. E., and KRTICKA, M.

Subjects
NEUTRON resonance, GAMMA rays, NEUTRON capture, NUCLEAR cross sections, NUCLEOSYNTHESIS, NUCLEAR reactions, NEUTRON scattering measurement
Published
2013

41. Neutron Resonance Spin Determination Using Multi-Segmented Detector DANCE.

Author

Baramsai, B., Mitchell, G. E., Agvaanluvsan, U., Becvar, F., Bredeweg, T. A., Couture, A., Chyzh, A., Dashdorj, D., Haight, R. C., Jandel, M., Keksis, A. L., Krticka, M., O'Donnell, J. M., Rundberg, R. S., Ullmann, J. L., Vieira, D. J., Walker, C., and Wouters, J. M.

Subjects
NEUTRON resonance, NEUTRON spin echoes, NEUTRON counters, PATTERN recognition systems, NEUTRON capture, CALORIMETRY, NEUTRON multiplicity
Abstract

A sensitive method to determine the spin of neutron resonances is introduced based on the statistical pattern recognition technique. The new method was used to assign the spins of s-wave resonances in 155Gd. The experimental neutron capture data for these nuclei were measured with the DANCE (Detector for Advanced Neutron Capture Experiment) calorimeter at the Los Alamos Neutron Science Center. The highly segmented calorimeter provided detailed multiplicity distributions of the capture γ-rays. Using this information, the spins of the neutron capture resonances were determined. With these new spin assignments, level spacings are determined separately for s-wave resonances with Jπ = 1- and 2-. [ABSTRACT FROM AUTHOR]

Published
2011
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42. Quantum suppression of fluctuations and temperatures of reconstructed A ∼ 30 quasi-projectiles.

Author

Stein, B C, Bonasera, A, Souliotis, G A, Zheng, H, Cammarata, P J, Echeverria, A J, Heilborn, L, Keksis, A L, Kohley, Z, Mabiala, J, Marini, P, May, L W, McIntosh, A B, Richers, C, Shetty, D V, Soisson, S N, Tripathi, R, Wuenschel, S, and Yennello, S J

Subjects
ELECTRON gas research, INTERACTING boson-fermion models, FERMIONS, COLLISIONS (Physics), NUCLEAR reactions, NUCLEAR particle research, HEAVY ions
Abstract

Suppression of multiplicity fluctuations has been observed for three light fermions (protons, tritons and 3He) in the multifragmentation of reconstructed hot quasi-projectiles produced in collisions of 32S (45 MeV/nucleon) with 112Sn. This suppression, predicted by recent calculations, is attributed to Pauli blocking and has also been observed in experiments with trapped Fermi gases. Experimental results on nuclear temperature and density employing a quantal approach based on momentum and multiplicity fluctuations are also presented. The extracted temperatures show a noticeable reduction when compared to a similarly derived classical method. This reduction in temperature is in agreement with previous predictions indicating that classically derived methods overpredict nuclear temperature as they do not take into account the Fermi motion of the nucleons. The present results underline the role of quantum statistics in nuclear disassembly and suggest the need for proper quantum treatment when dealing with the thermodynamic properties of fragmenting heavy ions. [ABSTRACT FROM AUTHOR]

Published
2014
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43. Photon strength functions of 156Gd from radiative capture of resonance neutrons.

Author

Baramsai, B., Kroll, J., Mitchell, G. E., Agvaanluvsan, U., Bečvár, F., Bredeweg, T. A., Chyzh, A., Couture, A., Dashdoij, D., Haight, R. C., Jandel, M., Keksis, A. L., Krtička, M., O'Donnell, J. M., Rundberg, R. S., Ullmann, J. L., Vieira, D. J., and Walker, C. L.

Subjects
*PHOTONS, *GADOLINIUM, *RESONANCE, *RADIATIVE capture, *CALORIMETRY, *SIMULATION methods & models
Abstract

The 155Gd(n,γ) reaction was measured with the DANCE γ-ray calorimeter (consisting of 160 BaF2 scintillation detectors) at the Los Alamos Neutron Science Center. The γ-ray energy spectra for different multiplicities were obtained for the s-wave resonances. The shapes of these spectra were compared with simulations based on the use of the DICEBOX statistical model code. Simulations showed that the photon strength functions (PSFs) successfully describing the decay of 156Gd are very similar to the PSFs describing the decay of previously published 158Gd results. It was demonstrated that the scissors mode is required not only for the ground-state transitions, but also for transitions between excited states. [ABSTRACT FROM AUTHOR]

Published
2013
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44. Neutron resonance parameters in 155Gd measured with the DANCE &ggr;-ray calorimeter array.

Author

Baramsai, B., Mitchell, G. E., Agvaanluvsan, U., Becvâf, F., Bredeweg, T. A., Chyzh, A., Couture, A., Dashdorj, D., Haight, R. C., Jandel, M., Keksis, A. L., Krticka, M., O'Donnell, J. M., Rundberg, R. S., Ullmann, J. L., Vieira, D. J., and Walker, C. L.

Subjects
*NEUTRON resonance, *PARAMETER estimation, *CALORIMETERS, *DISTRIBUTION (Probability theory), *PATTERN recognition systems, *SHEAR waves, GADOLINIUM isotopes
Abstract

The l55Gd(n,&ggr;) reaction was measured with the DANCE &ggr;-ray calorimeter at the Los Alamos Neutron Science Center. Spins were determined for the s-wave resonances by analysis of the &ggr;-ray multiplicity distributions. The analysis was performed with a pattern recognition method. The resulting level densities for the J = 1 and 2 resonances are in qualitative agreement with the expected 2J + 1 dependence. The average s-wave resonance spacing was determined to be D0 = 1.62 ± 0.15 eV. Analysis of the neutron resonances with the code SAMMY yielded the s-wave strength function S0 = 1.99 ± 0.28 x 10∼4 and the average total radiative width &Ggr;y = 120 ± 3meV. [ABSTRACT FROM AUTHOR]

Published
2012
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45. Isomeric ratio measurements for the radiative neutron capture 176Lu(n,γ) at the LANL DANCE facility.

Author

Denis-Petit, D., Roig, O., Méot, V., Morillon, B., Romain, P., Jandel, M., Kawano, T., Vieira, D. J., Bond, E. M., Bredeweg, T. A., Couture, A. J., Haight, R. C., Keksis, A. L., Rundberg, R. S., and Ullmann, J. L.

Subjects
*ISOMERS, *LUTETIUM isotopes, *NEUTRON capture
Abstract

The isomeric ratios for the neutron capture reaction 176Lu(n,γ) to the Jp=5/2-, 761.7 keV, T1/2=32.8 ns and the Jp=15/2+, 1356.9 keV, T1/2=11.1 ns levels of Lu177 have been measured for the first time. The experiment was carried out with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory. Measured isomeric ratios are compared with talys calculations using different models for photon strength functions, level densities, and optical potentials. In order to reproduce the experimental γ-ray spectra, a low-energy resonance must be added in the photon strength function used in our Hauser-Feshbach calculations. [ABSTRACT FROM AUTHOR]

Published
2016
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46. Radiative neutron capture cross sections on 176Lu at DANCE.

Author

Roig, O., Jandel, M., Méot, V., Bond, E. M., Bredeweg, T. A., Couture, A. J., Haight, R. C., Keksis, A. L., Rundberg, R. S., Ullmann, J. L., and Vieira, D. J.

Subjects
*PHYSICS periodicals, *LUTETIUM isotopes, *NEUTRON capture, *NEUTRON temperature
Abstract

The cross section of the neutron capture reaction 176Lu(n,γ) has been measured for a wide incident neutron energy range with the Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The thermal neutron capture cross section was determined to be (1912±132) b for one of the Lu natural isotopes, 176Lu. The resonance part was measured and compared to the Mughabghab's atlas using the R-matrix code, sammy. At higher neutron energies the measured cross sections are compared to ENDF/B-VII.1, JEFF-3.2, and BRC evaluated nuclear data. The Maxwellian averaged cross sections in a stellar plasma for thermal energies between 5 keV and 100 keV were extracted using these data. [ABSTRACT FROM AUTHOR]

Published
2016
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