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23 results on '"Stoyer, M A"'

1. Fission Product Yield Measurements from Neutron-Induced Fission of 235,238 U and 239Pu.

Author

Mitchell, A.J., Pavetich, S., Koll, D., Stoyer, M. A., Tonchev, A. P., Silano, J. A., Gooden, M. E., Wilhelmy, J. B., Tornow, W., Howell, C. R., Krishichayan, F., and Finch, S.

Subjects
FISSION products, NEUTRON beams, NEUTRON temperature, NUCLEAR physics, SELF-consistent field theory
Abstract

Fission product yields (FPY) are one of the most fundamental quantities that can be measured for a fissioning nucleus and are important for basic and applied nuclear physics. Recent measurements using mono-energetic and pulsed neutron beams generated using Triangle Universities Nuclear Laboratory's tandem accelerator and employing a dual fission chamber setup have produced self-consistent, high-precision data critical for testing fission models for the neutron-induced fission of 235,238U and 239Pu between neutron energies of 0.5 to 15.0 MeV. These data have elucidated a low-energy dependence of FPY for several fission products using irradiations of varying lengths and neutron energies. This paper will discuss new measurements just beginning utilizing a RApid Belt-driven Irradiated Target Transfer System (RABITTS) to measure shorterlived fission products and the time dependence of fission yields, expanding the measurements from cumulative towards independent fission yields. The uniqueness of these FPY data and the impact on the development of fission theory will be discussed. [ABSTRACT FROM AUTHOR]

Published
2020
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2. New features of superdeformed bands in 194Hg

Author

Cederwall, Bo, Lee, I Y, Deleplanque, M A, Diamond, R M, Fallon, P, Macchiavelli, A O, Stephens, F S, Janssens, R V F, Ahmad, I, Carpenter, M P, Crowell, B, Henry, R G, Khoo, T L, Lauritsen, T, Brinkman, M J, Becker, J A, Farris, L P, Henry, E A, Hughes, J R, Stoyer, M A, Draper, J E, Duyar, C, Rubel, E, Satula, W, Wiedenhöver, I, and Wyss, R

Subjects
Nuclear Physics
Published
1994

3. EXOTIC NUCLEI RESEARCH AT LLNL.

Author

STOYER, M. A., AHLE, L. E., BECKER, J. A., BERNSTEIN, L. A., BLEUEL, D. L., BURKE, J. T., CASPERSON, R. J., CHODASH, P. A., CHYZH, A., CZESZUMSKA, A., KWAN, E., MORAN, M. J., NORMAN, E. B., PADGETT, S. W., PEDRETTI, M., RESSLER, J. J., SAYRE, D. B., SCIELZO, N. D., SHEETS, S. A., and STOEFFL, W.

Subjects
EXOTIC nuclei, NUCLEAR physics, EXCITATION energy (In situ microanalysis), NUCLEAR reactions, NUCLEAR structure
Published
2013

4. MEASUREMENT OF FISSION PRODUCT YIELDS FROM FAST-NEUTRON-INDUCED FISSION.

Author

ARNOLD, C. W., BOND, E. M., BREDEWEG, T. A., FOWLER, M. M., MOODY, W. A., RUSEV, G., VIEIRA, D. J., WILHELMY, J. B., BECKER, J. A., HENDERSON, R., KENNEALLY, J., MACRI, R., MCNABB, D., RYAN, C., SHEETS, S., STOYER, M. A., TONCHEV, A. P., BHATIA, C., BHIKE, M., and FALLIN, B.

Subjects
FISSION products, NUCLEAR fission, FISSION neutrons, NUCLEAR physics, NEUTRON flux
Published
2013

5. NEW INSIGHTS INTO THE NUCLEAR STRUCTURE IN NEUTRON-RICH 112,114,115,116,117,118Pd.

Author

LUO, Y. X., RASMUSSEN, J. O., HAMILTON, J. H., RAMAYYA, A. V., FRAUENDORF, S., HWANG, J. K., STONE, N. J., ZHU, S. J., BREWER, N. T., WANG, E., LEE, I. Y., TER-AKOPIAN, G. M., LIU, S. H., DANIEL, A. V., OGANESSIAN, YU. TS., STOYER, M. A., DONANGELO, R., MA, W. C., COLE, J. D., and SHI, YUE

Subjects
NUCLEAR structure, NEUTRONS, NUCLEAR physics, COULOMB functions, CHIRALITY of nuclear particles
Published
2013

6. Fragment yields obtained at gammasphere for the ternary fission of 252Cf.

Author

Ter-Akopian, G. M., Popeko, G. S., Daniel, A. V., Hamilton, J. H., Ramayya, A. V., Kormicki, J., Fomichev, A. S., Rodin, A. M., Oganessian, Yu. Ts., Rasmussen, J. O., Hwang, J. K., Fong, D., Luo, Y. X., Gore, P., Lee, I. Y., Cole, J. D., Stoyer, M. A., Jandel, M., Kliman, J., and Krupa, L.

Subjects
GAMMASPHERE, PARTICLES (Nuclear physics), NUCLEAR fission, NUCLEAR reactions, NUCLEAR physics
Abstract

In an experiment carried out at the 4π Ge detector facility Gammasphere the yields of ternary fission events of 252Cf accompanied by the emission of He, Be and C LCPs were measured. For the first time independent yields were measured for 59 pairs of secondary fragments of the He ternary fission and for many fission fragments detected together with the He, Be and C LCPs. With a reasonable assumption that the detected LCPs predominantly are 4He, 10Be and 14C their yields and the charge distributions of fission fragments were conjointly analyzed in terms of the “energy cost” concept first suggested by Halpern. [ABSTRACT FROM AUTHOR]

Published
2009
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7. Search For Enhanced Alpha Preformation in the N=Z+1 Nuclei 113Ba, 109Xe, 105Te.

Author

Hecht, A. A., Lister, C. J., Davids, C. N., Heinz, A., Hoteling, N., Mazzocchi, C., Palombo, J., Seweryniak, D., Shergur, J., Stoyer, M., Walters, W. B., Woods, P. J., and Zhu, S.

Subjects
ALPHA decay, ISOBARIC spin, NUCLEAR physics, PHYSICAL sciences, NEUTRONS
Abstract

α-decay is known in a few cases just above 100Sn. The lowest isospin nuclei in which it has been observed are the Tz=1 nuclei 114Ba, 110Xe, and 106Te. For the next lower isospin with Tz=1/2, N=Z+1, we used the reactions 58Ni + 58Ni and 58Ni + 54Fe to search for the 113Ba→109Xe→105Te→101Sn α-decay chain. We found no candidates in our study. We set upper limits on the production of 113Ba via the 58Ni + 58Ni reaction and upper limits on the production of 109Xe via the 58Ni + 54Fe reaction. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2006
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8. SHAPE EVOLUTION AND TRIAXIALITY IN NEUTRON RICH Y, Nb, Tc, Rh AND Ag.

Author

LUO, Y. X., RASMUSSEN, J. O., HAMILTON, J. H., RAMAYYA, A. V., HWANG, J. K., ZHU, S. J., GORE, P. M., WU, S. C., GILAT, J., LEE, I. Y., FALLON, P., GINTER, T. N., TER-AKOPIAN, G., DANIEL, A. V., STOYER, M. A., DONANGELO, R., GELBERG, A., and JONES, E. F.

Subjects
NUCLEAR physics, GAMMASPHERE, EXOTIC nuclei, NUCLEAR structure, PHASE transitions
Published
2005

9. UNEXPECTED DECREASE IN MOMENT OF INERTIA BETWEEN N = 98 -100 IN 162,164GD.

Author

JONES, E. F., HAMILTON, J. H., GORE, P. M., RAMAYYA, A. V., HWANG, J. K., DELIMA, A. P., ZHU, S. J., LU0, Y. X., BEYER, C. J., KORMICKI, J., ZHANG, X. Q., MA, W. C., LEE, I. Y., RASMUSSEN, J. O., WU, S. C., GINTER, T. N., FALLON, P., STOYER, M., COLE, J. D., and DANIEL, A. V.

Subjects
NUCLEAR physics, YRAST states, NEUTRONS, PROTONS, NUCLEAR structure
Published
2005

10. YIELDS OF FRAGMENT PAIRS IN TERNARY FISSION OF 252Cf.

Author

JANDEL, M., KLIMAN, J., KRUPA, L., MORHÁČ, M., HAMILTON, J. H., KORMICKI, J., RAMAYYA, A. V., HWANG, J. K., LUO, Y. X., FONG, D., GORE, P., TERAKOPIAN, G. M., OGANESSIAN, YU. TS., RODIN, A. M., FOMICHEV, A. S., POPEKO, G. S., DANIEL, A. V., RASMUSSEN, J. O., MACCHIAVELL, A. O., and STOYER, M. A.

Subjects
NUCLEAR fission, NUCLEAR fragmentation, PAIR production, PARTICLES (Nuclear physics), NUCLEAR physics
Published
2003

11. LEVEL STRUCTURE OF 141BA AND I39XE AND LEVEL SYSTEMATICS OF N=85 EVEN-ODD ISOTONES.

Author

LUO, Y. X., Rasmussen, J. O., Hamilton, J. H., Ramayya, A. V., Hwang, J. K., Beyer, C. J., Zhu, S. J., Kormicki, J., Zhang, X. Q., Jones, E. F., Gore, P. M., Ginter, T. N., Lee, I. Y., Gregorich, K. E., Macchiavelli, A. O., Ter-Akopian, G. M., Oganessian, Yu.Ts., Daniel, A. V., Stoyer, M. A., and Asztalos, S. J.

Subjects
NUCLEAR shell theory, NEUTRONS, QUASIPARTICLES, HEAVY ion collisions, NUCLEAR physics
Published
2003

12. GAMMA SPECTROSCOPY OF 335U AND 234mPa.

Author

PATIN, J. B., STOYER, M. A., MOODY, K. J., SHAUGHNESSY, D. A., STOYER, N. J., WILD, J. F., WOODDY, P. T., and GUTMAN, E.

Subjects
GAMMA ray spectroscopy, NUCLEAR structure, RADIOACTIVE decay, GERMANIUM, NUCLEAR physics
Published
2003

13. NUCLEAR STRUCTURE OF NEUTRON-RICH N=83 ISOTONES BY 252CF FISSION AT GAMMASPHERE.

Author

Luo, Y. X., Rasmussen, J. O., Hamilton, J. H., Ramayya, A.V., Hwang, J. K., Beyer, C. J., Zhu, S. J., Kormicki, J., Zhang, X. Q., Jones, E. F., Gore, P. M., Ginter, T. N., Lee, I. Y., Gregorich, K. E., Macchiavelli, A. O., Ter-Akopian, G. M., Oganessian, Yu.Ts., Daniel, A.V., Stoyer, M. A., and Asztalos, S. J.

Subjects
NUCLEAR structure, NEUTRONS, NUCLEAR fission, GAMMASPHERE, NUCLEAR physics
Published
2003

14. Gammasphere fission-gamma-ray studies: Even-odd nuclei near N=82.

Author

Luo, Y. X., Rasmussen, J. O., Hamilton, J. H., Ramayya, A. V., Hwang, J. K., Beyer, C. J., Kormicki, J., Zhang, X. Q., Jones, E. F., Gore, P. M., Ginter, T. N., Gregorich, K. E., Lee, I. Y., Macchiavelli, A., Zhu, S. J., Ter-Akopian, G. M., Oganessian, Yu. Ts., Daniel, A. V., Stoyer, M. A., and Asztalos, S.J.

Subjects
SPONTANEOUS fission, GAMMASPHERE, NUCLEAR physics
Abstract

New analyses of spontaneous-fission gamma data from our [sup 252]Cf Gammasphere runs of 1995 and 2000 have identified new transitions and given improved transition energy and intensity values for known transitions in even-odd fission-product nuclei just beyond the 82-neutron closed shell. New level schemes of N=83 isotones [sup 139]Ba[sub 83] and [sup 135]Te[sub 83] and of N=85 isotones [sup 141]Ba[sub 85], and [sup 139]Xe[sub 85] are established. Single-particle (hole) excitations and couplings, core excitations, and octupole excitations are assigned to these isotones. A regular sequence found in [sup 135]Te is interpreted as a shears band within the tilted-axis cranking model of Frauendorf. The level systematics of N=85 isotones indicate that the octupole excitation moves to higher excitation energy as the Z=50 shell is approached. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2002

15. Neutron-induced partial gamma-ray cross-section measurements with GEANIE at LANSCE/WNR.

Author

McNabb, D. P., Becker, J. A., Archer, D., Bernstein, L. A., Drake, D. M., Garrett, P. E., Johns, G. D., McGrath, C. A., Nelson, R. O., Stoyer, M. A., Wilburn, W. S., and Younes, W.

Subjects
NUCLEAR physics, GAMMA ray measurement, NEUTRON cross sections
Abstract

GEANIE is the first large-scale Ge detector array used in conjunction with a high-energy neutron spallation source. GEANIE consists of eleven Compton-suppressed planar detectors, nine suppressed and six unsuppressed co-axial detectors. Spallation neutrons are provided by the LANSCE/WNR facility, and reaction neutron energies are determined via time-of-flight. Neutron flux is monitored in-beam with a fission chamber. GEANIE at LANSCE/WNR currently emphasizes the measurement of partial gamma-ray cross sections as a function of neutron energy. Absolute cross section measurements require a complete understanding of array performance. Important effects include intrinsic detector efficiency, beam and detector geometry corrections, target attenuation, and deadtime. Measurements and calculations of these effects will be presented for the specific cases of iron and actinide targets. The use of radioactive targets incurs a large deadtime penalty. In order to increase data throughput we are making plans to move to a triggerless data acquisition system. These modifications and other improvements to the electronics for better timing will be discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

16. ODD-PARITY BANDS OF 108,110,112Ru.

Author

LUO, Y. X., ZHU, S. J., HAMILTON, J. H., RAMAYYA, A. V., GOODIN, C., LI, K., CHE, X. L., HWANG, J. K., LEE, I. Y., JIANG, Z., TER-AKOPIAN, G. M., DANIEL, A. V., STOYER, M. A., DONANGELO, R., FRAUENDORF, S., DIMITROV, V., JING-YE ZHANG, COLE, J. D., STONE, N. J., and RASMUSSEN, J. O.

Subjects
GAMMA rays, GAMMASPHERE, PARTICLES (Nuclear physics), ELECTROMAGNETIC waves, NUCLEAR physics
Abstract

Two similar sets of odd-parity bands are observed in each of three even–even neighbors, 108,110,112Ru, from a study of prompt spontaneous-fission gamma rays at Gammasphere. A careful study of the odd-parity levels of these nuclei shows evidence for the features of chiral doubling. Comparisons are made with reported other candidates for chiral doubling. [ABSTRACT FROM AUTHOR]

Published
2009
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17. EVEN-PARITY BANDS OF 108, 110, 112Ru.

Author

ZHU, S. J., LUO, Y. X., HAMILTON, J. H., RAMAYYA, A. V., CHE, X. L., JIANG, Z., HWANG, J. K., WOOD, J. L., STOYER, M. A., DONANGELO, R., COLE, J. D., GOODIN, C., and RASMUSSEN, J. O.

Subjects
PARTICLES (Nuclear physics), NUCLEAR fission, GAMMASPHERE, NUCLEAR reactions, NUCLEAR physics
Abstract

High-spin, even-parity bands in neutron-rich 108, 110, 112Ru nuclei were reinvestigated and considerably expanded by measuring many-fold prompt γ-ray coincidence events following the spontaneous fission of 252Cf with Gammasphere. Our high statistics data allow us to detect weaker transitions and bands not previously published. Also, gamma branching ratios, which are important for theory, are carefully measured from all levels. In 110Ru, we find a doubling of levels for both ground and quasi-gamma bands above the 8+ levels. There are likely two-phonon quasi-gamma bands in 110, 112Ru, as well as a bandhead level in 108Ru. The odd–even spin energy band staggering observed in the quasi-gamma bands in 108, 110, 112Ru and the doubling of levels in 110Ru present a challenge to theory. [ABSTRACT FROM AUTHOR]

Published
2009
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18. Angular momenta of fission fragments in the α-accompanied fission of252Cf.

Author

Jandel, M., Kliman, J., Krupa, L., Morháč, M., Hamilton, J. H., Kormicki, J., Ramayya, A. V., Hwang, J. K., Luo, Y. X., Fong, D., Gore, P., Ter-Akopian, G. M., Oganessian, Yu. Ts., Rodin, A. M., Fomichev, A. S., Popeko, G. S., Daniel, A. V., Rasmussen, J. O., Macchiavelli, A. O., and Stoyer, M. A.

Subjects
ANGULAR momentum (Nuclear physics), NUCLEAR moments, NUCLEAR fission in art, PARTICLES (Nuclear physics), NUCLEAR physics
Abstract

For the first time, average angular momenta of the ternary fission fragments100, 102Zr,106Mo,144, 146Ba and138, 140, 142Xe from the α-accompanied fission of252Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of252Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of106Mo and140Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed. [ABSTRACT FROM AUTHOR]

Published
2005
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19. Random probability analysis of recent 48Ca experiments.

Author

Stoyer, M. A., Patin, J. B., Kenneally, J. M., Moody, K. J., Shaughnessy, D. A., Stoyer, N. J., Wild, J. F., Wilk, P. A., Utyonkov, V. K., and Oganessian, Yu. Ts.

Subjects
*MONTE Carlo method, *NUCLIDES, *PROBABILITY theory, *NUCLEAR physics, *PHYSICS
Abstract

A Monte Carlo random probability analysis developed at LLNL for heavy element research was performed for recent experiments aimed at the synthesis of nuclides with Z≥112 and N≥170, to estimate the probability that observed decay chains were a result of a random event. Low probabilities ( < 10-4% for most decay chains) were found. [ABSTRACT FROM AUTHOR]

Published
2005
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20. Half-life measurement of excited states in neutron-rich nuclei.

Author

Hwang, J. K., Ramayya, A. V., Hamilton, J. H., Fong, D., Beyer, C. J., Li, K., Gore, P. M., Jones, E. F., Luo, Y. X., Rasmussen, J. O., Zhu, S. J., Wu, S. C., Lee, I. Y., Stoyer, M. A., Cole, J. D., Ter-Akopian, G. M., Daniel, A., and Donangelo, R.

Subjects
NEUTRONS, EXOTIC nuclei, EXCITED state chemistry, NUCLEAR physics, PHYSICS
Abstract

Half-lives ( T1/2) of several states which decay by delayed γ transitions were determined from time-gated triple γ coincidence method. We determined, for the first time, the half-life of 330.6 + x state in 108Tc and the half-life of 19/2- state in 133Te based on the new level schemes. Five half-lives of 95, 97Sr, 99Zr, 134Te and 137Xe are consistent with the previously reported ones. These results indicate that this new method is useful for measuring the half-lives. [ABSTRACT FROM AUTHOR]

Published
2005
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21. Shape transitions and triaxiality in neutron-rich odd-mass Y and Nb isotopes.

Author

Luo, Y. X., Rasmussen, J. O., Hamilton, J. H., Ramayya, A. V., Gelberg, A., Stefanescu, I., Hwang, J. K., Zhu, S. J., Gore, P. M., Fong, D., Jones, E. F., Wu, S. C., Lee, I. Y., Ginter, T. N., Ma, W. C., Ter-Akopian, G. M., Daniel, A. V., Stoyer, M. A., and Donangelo, R.

Subjects
NUCLEAR fission, NUCLEAR reactions, DELAYED neutrons, NEUTRONS, NUCLEAR physics, PHYSICS
Abstract

New level schemes of 99, 101Y and 101, 105Nd are established based on the measurement of prompt γ-rays from the fission of 252Cf at Gammasphere. Triaxial-rotor-plus-particle model calculations and fitting suggest that in the A ≈ 100 neutron-rich nuclei triaxial shape is prevalent in the region with Z > 41. [ABSTRACT FROM AUTHOR]

Published
2005
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22. Investigations of short half-life states from SF of 252Cf.

Author

Fong, D., Hwang, J. K., Ramayya, A. V., Hamilton, J. H., Beyer, C. J., Li, K., Gore, P. M., Jones, E. F., Luo, Y. X., Rasmussen, J. O., Zhu, S. J., Wu, S. C., Lee, I. Y., Fallon, P., Stoyer, M. A., Asztalos, S. J., Ginter, T. N., Cole, J. D., Ter-Akopian, G. M., and Daniel, A.

Subjects
NEUTRONS, EXOTIC nuclei, NUCLEAR physics, BETA decay, PHYSICS
Abstract

By using different time-gated triple γ coincidence data, the half-lives ( T1/2) of several short lived states in neutron-rich nuclei have been studied. The first excited states in the ground state bands often decay by delayed γ emission. By creating triple γ coincidence spectra with time windows of 8, 16, 20, 28, and 48 ns, we have studied states with half-lives below 10 ns. The estimated half-lives of 102Zr, 137Xe, and 143Ba are in reasonable agreement with previously reported values. We extract the first estimates of the half lives of the 2+ states in 104Zr and 152Ce. [ABSTRACT FROM AUTHOR]

Published
2005
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23. Unexpected rapid variations in odd-even level staggering in gamma-vibrational bands.

Author

Gore, P. M., Jones, E. F., Hamilton, J. H., Ramayya, A. V., Zhang, X. Q., Hwang, J. K., Luo, Y. X., Li, K., Zhu, S. J., Ma, W. C., Rasmussen, J. O., Lee, I. Y., Stoyer, M., Cole, J. D., Daniel, A. V., Ter-Akopian, G. M., Oganessian, Yu. Ts., Donangelo, R., and Gupta, J. B.

Subjects
NUCLIDES, PARTICLES (Nuclear physics), ENERGY levels (Quantum mechanics), NUCLEAR excitation, NEUTRONS, NUCLEAR physics
Abstract

Triple-γ coincidence data were used to study the γ-vibrational bands to 14+ in 104-106Mo, to 13+ in 108,110Ru and 17+ in 112Ru, and to 13+, 15+ in 112-116Pd. The even-odd spin energy level splittings show rapid variations with spin and neutron number in these nuclides. With one exception, the Sm-Pt nuclei show no such reversal and much smaller staggering. [ABSTRACT FROM AUTHOR]

Published
2005
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