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Sample records for neutron rich si

  1. Intruder negative-parity states of neutron-rich {sup 33}Si

    SciTech Connect

    Wang, Z. M.; Chapman, R.; Liang, X.; Burns, M.; Hodsdon, A.; Keyes, K.; Kumar, V.; Papenberg, A.; Smith, J. F.; Spohr, K. M.; Haas, F.; Bouhelal, M.; Caurier, E.; Curien, D.; Nowacki, F.; Azaiez, F.; Ibrahim, F.; Verney, D.; Behera, B. R.; Corradi, L.

    2010-06-15

    Yrast states in the neutron-rich {sub 14}{sup 33}Si{sub 19} nucleus have been studied using binary grazing reactions produced by the interaction of a 215-MeV beam of {sup 36}S ions with a thin {sup 208}Pb target. An experimental setup that combines the large-acceptance magnetic spectrometer PRISMA and the high-efficiency gamma-ray detection array CLARA was used in the experiment. Four new gamma-ray photopeaks at energies of 971, 1724, 1772, and 2655 keV were observed and assigned to the {sup 33}Si level scheme. The experimental level scheme is compared with the results of 1(Planck constant/2pi)omega p-sd-pf large-scale shell-model calculations using the recently developed PSDPFB effective interaction; good agreement is obtained. The structure of the populated states of {sup 33}Si is discussed within the context of an odd neutron coupled to states of the {sup 32}Si core.

  2. New isotope {sup 44}Si and systematics of the production cross sections of the most neutron-rich nuclei

    SciTech Connect

    Tarasov, O. B.; Baumann, T.; Bazin, D.; III, C. M. Folden; Ginter, T. N.; Hausmann, M.; Matos, M.; Portillo, M.; Schiller, A.; Stolz, A.; Amthor, A. M.; Gade, A.; Nettleton, A.; Sherrill, B. M.; Thoennessen, M.; Morrissey, D. J.

    2007-06-15

    The results of measurements of the production of neutron-rich nuclei by the fragmentation of a {sup 48}Ca beam at 142 MeV/nucleon are presented. Evidence was found for the production of a new isotope that is the most neutron-rich silicon nuclide, {sup 44}Si, in a net neutron pickup process. A simple systematic framework was found to describe the production cross sections based on thermal evaporation from excited prefragments that allows extrapolation to other weak reaction products.

  3. Probing neutron rich matter with parity violation

    NASA Astrophysics Data System (ADS)

    Horowitz, Charles

    2016-03-01

    Many compact and energetic astrophysical systems are made of neutron rich matter. In contrast, most terrestrial nuclei involve approximately symmetric nuclear matter with more equal numbers of neutrons and protons. However, heavy nuclei have a surface region that contains many extra neutrons. Precision measurements of this neutron rich skin can determine properties of neutron rich matter. Parity violating electron scattering provides a uniquely clean probe of neutrons, because the weak charge of a neutron is much larger than that of a proton. We describe first results and future plans for the Jefferson Laboratory experiment PREX that measures the thickness of the neutron skin in 208Pb. Another JLAB experiment CREX will measure the neutron radius of 48Ca and test recent microscopic calculations of this neutron rich 48 nucleon system. Finally, we show how measuring parity violation at multiple momentum transfers can determine not just the neutron radius but the full radial structure of the neutron density in 48Ca. A neutron star is eighteen orders of magnitude larger than a nucleus (km vs fm) but both the star and the neutron rich nuclear skin are made of the same neutrons, with the same strong interactions, and the same equation of state. A large pressure pushes neutrons out against surface tension and gives a thick neutron skin. Therefore, PREX will constrain the equation of state of neutron rich matter and improve predictions for the structure of neutron stars. Supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

  4. Effective Interactions in Neutron-Rich Matter

    SciTech Connect

    Sammarruca, F.; Krastev, P.; Barredo, W.

    2005-10-14

    We are generally concerned with probing the behavior of the isospin-asymmetric equation of state. In particular, we will discuss the one-body potentials for protons and neutrons obtained from our Dirac-Brueckner-Hartree-Fock calculations of neutron-rich matter properties. We will also present predictions of proton-proton and neutron-neutron cross sections in the isospin-asymmetric nuclear medium.

  5. Thermodynamics of neutron-rich nuclear matter

    SciTech Connect

    López, Jorge A.; Porras, Sergio Terrazas Gutiérrez, Araceli Rodríguez

    2016-07-07

    This manuscript presents methods to obtain properties of neutron-rich nuclear matter from classical molecular dynamics. Some of these are bulk properties of infinite nuclear matter, phase information, the Maxwell construction, spinodal lines and symmetry energy.

  6. The new neutron rich nuclei

    SciTech Connect

    Gridnev, K. A.; Gridnev, D. K.; Tarasov, V. N.; Tarasov, D. V.; Viñas, X.; Greiner, W.

    2014-07-23

    Using HF+BCS method with Skyrme forces we analyze the neutron drip line. It is shown that around magic and new magic numbers the drip line may form stability peninsulas. It is shown that the location of these peninsulas does not depend on the choice of Skyrme forces. It is found that the size of the peninsulas is sensitive to the choice of Skyrme forces and the most extended peninsulas appear with the SkI2 set.

  7. Nuclear Forces and Their Impact on Neutron-Rich Nuclei and Neutron-Rich Matter

    NASA Astrophysics Data System (ADS)

    Hebeler, K.; Holt, J. D.; Menéndez, J.; Schwenk, A.

    2015-10-01

    We review the impact of nuclear forces on matter at neutron-rich extremes. Recent results have shown that neutron-rich nuclei become increasingly sensitive to three-nucleon forces, which are at the forefront of theoretical developments based on effective field theories of quantum chromodynamics. These developments include the formation of shell structure, the spectroscopy of exotic nuclei, and the location of the neutron drip line. Nuclear forces also constrain the properties of neutron-rich matter, including the neutron skin, the symmetry energy, and the structure of neutron stars. First, we review our understanding of three-nucleon forces and show how chiral effective field theory makes unique predictions for many-body forces. Then, we survey results with three-nucleon forces in neutron-rich oxygen and calcium isotopes and neutron-rich matter, which have been explored with a range of many-body methods. Three-nucleon forces therefore provide an exciting link between theoretical, experimental, and observational nuclear physics frontiers.

  8. Experiments with neutron-rich isomeric beams

    SciTech Connect

    Rykaczewski, K. |; Grzywacz, R. |; Lewitowicz, M.; Pfuetzner, M.; Grawe, H.

    1998-01-01

    A review of experimental results obtained on microsecond-isomeric states in neutron-rich nuclei produced in fragmentation reactions and studied with SISSI-Alpha-LISE3 spectrometer system at GANIL Caen is given. The perspectives of experiments based on secondary reactions with isomeric beams are presented.

  9. Higher spin states in neutron rich nuclei

    NASA Astrophysics Data System (ADS)

    Zhu, S.; Zhao, X.; Hamilton, J. H.; Ramayya, A. V.; Ma, W. C.; Peker, L. K.; Kormicki, J.; Hong, X.; Gao, W. B.; Deng, J. K.

    Nuclei on the neutron rich side of beta stability have long been of interest for nuclear structure studies because they probe different regions of the single particle spectrum and different shell gap combinations for both spherical and deformed shapes. However, such nuclei have been a difficult challenge experimentally. Much information has been gained about the properties of neutron rich nuclei at low spin from the study of radioactive isotopes produced in neutron induced, and more recently, proton induced fission of uranium. Such studies have been made possible by the use of isotope separators on line to reactors and more recently to low energy proton accelerators. However, to test many of the theoretical predictions of nuclear models one needs information about the higher spin states in nuclei in addition to their low spin states populated in radioactive decays. Higher spin states in neutron rich nuclei have been an even more difficult challenge than the lower spin states accessible through decay studies. One cannot reach the higher spin states in these nuclei by heavy ion fusion evaporation in reactions as carried out extensively for proton rich nuclei. Many years ago prompt spontaneous fission studies were used to suggest for the first time that Sr-98 and Zr-100 had unusually large ground state of deformations. The availability of higher efficiency multi-detector arrays of Compton suppressed Ge detectors has brought on a renewed interest in studies of the prompt gamma rays of the fragments from spontaneous and induced fission. Groups at Argonne, Daresbury, and a Vanderbilt-Oak Ridge-Idaho-Dubna collaboration have carried out several such studies from spontaneous and heavy-ion induced fission which have revealed new insights into our knowledge of neutron rich nuclei. This paper is primarily a review of these studies, including recent, unpublished results.

  10. Beta-Delayed Neutron Emission in Neutron-Rich Nuclei

    NASA Astrophysics Data System (ADS)

    Marketin, Tomislav; Sieverding, André; Wu, Meng-Ru; Paar, Nils; Martínez-Pinedo, Gabriel

    β-delayed neutron emission is the process of emission of one or more neutrons, after β-decay, from the excited daughter nucleus. The probabilities of emission are an important physical quantity in a variety of nuclear physics applications, from the simulations of heavy element nucleosynthesis to control of reactor power levels and nuclear waste management. However, it is relatively difficult to measure and much less data is available than for β-decay, particularly for nuclei that are expected to take part in the r-process. In this work we will present a calculation of β-decay half-lives and β-delayed neutron emission probabilities in neutron-rich nuclei using the transition strength obtained with a microscopic model combined with a statistical calculation of level densities. We explore the effect of altered emission probabilities, with respect to the simple calculation, on the r-process.

  11. Excited states of neutron rich Pd from fragmentation

    NASA Astrophysics Data System (ADS)

    Hecht, A. A.; Walters, W. B.; Hoteling, N.; Mantica, P. F.; Becerril, A.; Fleckenstein, T.; Lorusso, G.; Pereira, J.; Pinter, J.; Stoker, J.; Quinn, M.

    2007-04-01

    The neutron rich region approaching N=82 and Z=50 is interesting for nuclear structure and nuclear astrophysics, both as a test of the shell closures far from stability and as the path for r-process nucleosynthesis. This region is difficult to access with fusion-evaporation reactions and novel techniques must be used. At the National Superconducting Cyclotron Laboratory (NSCL) an experiment was recently performed by fragmentation of a Xe beam using a Be target to examine isomers and beta decay from these neutron rich nuclei. The radioisotope fragments passed through several Si planar detectors and were implanted in a double-sided Si strip detector (DSSD) in the Beta Counting System (BCS). Fragments were identified via δE and TOF. Particle emitting decays were tracked in several layers of single sided strip detectors following the DSSD, while the SEGA array surrounding the DSSD was used to collect gamma emission following beta and isomer decay. Several neutron rich nuclei were observed in this experiment, including Ru, Rh, Pd, Ag, Cd, and In. Results on Pd will be discussed.

  12. Structure of neutron-rich nuclei

    SciTech Connect

    Nazarewicz, W. ||

    1997-11-01

    One of the frontiers of today`s nuclear science is the ``journey to the limits``: of atomic charge and nuclear mass, of neutron-to-proton ratio, and of angular momentum. The new data on exotic nuclei are expected to bring qualitatively new information about the fundamental properties of the nucleonic many-body system, the nature of the nuclear interaction, and nucleonic correlations at various energy-distance scales. In this talk, current developments in nuclear structure of neutron-rich nuclei are discussed from a theoretical perspective.

  13. EOS of neutron-rich matter and pure neutron matter

    NASA Astrophysics Data System (ADS)

    Manisa, Kaan

    2012-03-01

    We report the equation of state (EOS) of pure neutron matter (PNM) and neutron-rich matter (NRM) for the realistic Urbana V14 two nucleon interaction, obtained by using a Variational Monte Carlo (VMC) method. Also, many body interactions are included as a phenomenological density dependent term in the potential. The binding energy per nucleon is calculated for different densities and various isospin asymmetry parameters. Our results on NRM and PNM are compared with relativistic Brueckner-Hartree-Fock theory and relativistic Hartree-Fock model with the unitary correlation operator method. The results obtained in this study show reasonable agreement with both of these relativistic Hartree-Fock approaches. We also compare the binding energies obtained in this study with those obtained by various authors employing different methods and techniques.

  14. Production cross sections of neutron-rich No-263261 isotopes

    NASA Astrophysics Data System (ADS)

    Li, Jingjing; Li, Cheng; Zhang, Gen; Zhu, Long; Liu, Zhong; Zhang, Feng-Shou

    2017-05-01

    The fusion excitation functions of No-263249 are studied by using various reaction systems based on the dinuclear system model. The neutron-rich radioactive beam 22O is used to produce neutron-rich nobelium isotopes, and the new neutron-rich isotopes No-263261 are synthesized by 242Pu(22O,3 n )261No , 244Pu(22O,4 n )262No , and 244Pu(22O,3 n )263No reactions, respectively. The corresponding maximum evaporation residue cross sections are 0.628, 4.649, and 1.638 μ b , respectively. The effects of the three processes (capture, fusion, and survival) in the complete fusion reaction are also analyzed. From investigation, a neutron-rich radioactive beam as the projectile and neutron-rich actinide as the target could be a new selection of the projectile-target combination to produce a neutron-rich heavy nuclide.

  15. Clusters in neutron-rich light nuclei

    NASA Astrophysics Data System (ADS)

    Jelavić Malenica, D.; Milin, M.; Di Pietro, A.; Figuera, P.; Lattuada, M.; Miljanić, D.; Musumarra, A.; Pellegriti, M. G.; Prepolec, L.; Scuderi, V.; Skukan, N.; Soić, N.; Torresi, D.; Uroić, M.

    2016-05-01

    Due to their high selectivity, transfer and sequential decay reactions are powerful tools for studies of both single particle (nucleon) and cluster states in light nuclei. Their use is particularly simple for investigations of α-particle clustering (because α-particle has Jπ=0+, which simplifies spin and parity assignments to observed cluster states), but they are also easily applicable to other types of clustering. Recent results on clustering in neutron-rich isotopes of beryllium, boron and carbon obtained measuring the 10B+10B reactions (at 50 and 72 MeV) are presented. The highly efficient and segmented detector systems used, built from 4 Double Sided Silicon Strip Detectors (DSSSD) allowed detection of double and multiple coincidences and, in that way, studies of states populated in transfer reactions, as well as their sequential decay.

  16. The Spectroscopy of Neutron-Rich sdf-Shell Nuclei Using the CLARA-PRISMA Setup

    SciTech Connect

    Liang, X.; Hodsdon, A.; Chapman, R.; Burns, M.; Keyes, K.; Ollier, J.; Papenberg, A.; Spohr, K.; Azaiez, F.; Ibrahim, F.; Stanoiu, M.; Haas, F.; Caurier, E.; Curien, D.; Nowacki, F.; Salsac, M.-D.; Bazzacco, D.; Beghini, S.; Farnea, E.; Menegazzo, R.

    2006-08-14

    Since the discovery of the breakdown of shell effects in very neutron-rich N=20 and 28 nuclei, studies of the properties of nuclei far from stability have been of intense interest since they provide a unique opportunity to increase our understanding of nuclear interactions in extreme conditions and often challenge our theoretical models.Deep-inelastic processes can be used to populated high spin states of neutron-rich nuclei. In the deep-inelastic processes, an equilibration in N/Z between the target and projectile nuclei is achieved. For most heavy neutron-rich target nuclei, the N/Z ratio is 1.5 - 1.6, while for the possible neutron-rich sdf-shell projectile it is about 1.2. Thus by using deep-inelastic processes one can populate neutron-rich nuclei around N=20 and N=28.New results for the spectroscopy of neutron-rich N=22 36Si and 37P are presented here.

  17. Relativistic mean field calculations in neutron-rich nuclei

    SciTech Connect

    Gangopadhyay, G.; Bhattacharya, Madhubrata; Roy, Subinit

    2014-08-14

    Relativistic mean field calculations have been employed to study neutron rich nuclei. The Lagrange's equations have been solved in the co-ordinate space. The effect of the continuum has been effectively taken into account through the method of resonant continuum. It is found that BCS approximation performs as well as a more involved Relativistic Continuum Hartree Bogoliubov approach. Calculations reveal the possibility of modification of magic numbers in neutron rich nuclei. Calculation for low energy proton scattering cross sections shows that the present approach reproduces the density in very light neutron rich nuclei.

  18. Proton radii of neutron-rich B isotopes and neutron surface thickness in 17B

    NASA Astrophysics Data System (ADS)

    Kanungo, Rituparna; Estrade, Alfredo; Horiuchi, Wataru

    2014-09-01

    As the neutron to proton asymmetry increases nuclei develop exotic structures such as neutron skin and halo. It is important to investigate how this asymmetry affects the proton distribution. The matter and proton radii have started unfolding a complete picture of the halo. For two-neutron halos the correlation between the halo neutrons and their distance from the core can be derived to define the average halo geometry. The proton radii are crucial information to extract the neutron skin thickness to constrain the equation of state of asymmetric nuclear matter. Very limited information is available on the proton radii of very neutron-rich nuclei. In this presentation, we will describe the new technique of extracting proton radii from charge changing cross sections using relativistic beams at GSI, Germany. The presentation will show first measurements of proton radii of the neutron-rich boron isotopes. The implications of the results in understanding the neutron surface thickness in the Borromean 17B and its possible halo structure will be discussed. As the neutron to proton asymmetry increases nuclei develop exotic structures such as neutron skin and halo. It is important to investigate how this asymmetry affects the proton distribution. The matter and proton radii have started unfolding a complete picture of the halo. For two-neutron halos the correlation between the halo neutrons and their distance from the core can be derived to define the average halo geometry. The proton radii are crucial information to extract the neutron skin thickness to constrain the equation of state of asymmetric nuclear matter. Very limited information is available on the proton radii of very neutron-rich nuclei. In this presentation, we will describe the new technique of extracting proton radii from charge changing cross sections using relativistic beams at GSI, Germany. The presentation will show first measurements of proton radii of the neutron-rich boron isotopes. The implications

  19. Informing Neutron-Capture Rates through (d,p) Reactions on Neutron-Rich Tin Isotopes

    NASA Astrophysics Data System (ADS)

    Manning, B.; Cizewski, J. A.; Kozub, R. L.; Ahn, S.; Allmond, J. M.; Bardayan, D. W.; Chae, K. Y.; Chipps, K. A.; Howard, M. E.; Jones, K. L.; Liang, J. F.; Matos, M.; Nunes, F. M.; Nesaraja, C. D.; O'Malley, P. D.; Pain, S. D.; Peters, W. A.; Pittman, S. T.; Ratkiewicz, A.; Schmitt, K. T.; Shapira, D.; Smith, M. S.; Titus, L.

    2014-03-01

    Level energies and spectroscopic information for neutron-rich nuclei provide important input for r-process nucleosynthesis calculations; specifically, the location and strength of single-neutron l = 1 states when calculating neutron-capture rates. Surman and collaborators have performed sensitivity studies to show that varying neutron-capture rates can significantly alter final r-process abundances. However, there are many nuclei important to the r-process that cannot be studied. Extending studies to more neutron-rich nuclei will help constrain the nuclear shell-model in extrapolating to nuclei even further from stability. The (d,p) reaction has been measured with radioactive ion beams of 126Sn and 128Sn to complete the set of (d,p) studies on even mass tin isotopes from doubly-magic 132 to stable 124Sn. Work supported in part by the U.S. Department of Energy and National Science Foundation.

  20. Octupole strength in the neutron-rich calcium isotopes

    NASA Astrophysics Data System (ADS)

    Riley, L. A.; McPherson, D. M.; Agiorgousis, M. L.; Baugher, T. R.; Bazin, D.; Bowry, M.; Cottle, P. D.; DeVone, F. G.; Gade, A.; Glowacki, M. T.; Gregory, S. D.; Haldeman, E. B.; Kemper, K. W.; Lunderberg, E.; Noji, S.; Recchia, F.; Sadler, B. V.; Scott, M.; Weisshaar, D.; Zegers, R. G. T.

    2016-04-01

    Low-lying excited states of the neutron-rich calcium isotopes Ca-5248 have been studied via γ -ray spectroscopy following inverse-kinematics proton scattering on a liquid hydrogen target using the GRETINA γ -ray tracking array. The energies and strengths of the octupole states in these isotopes are remarkably constant, indicating that these states are dominated by proton excitations.

  1. Fusion of neutron-rich oxygen isotopes in the crust of accreting neutron stars

    SciTech Connect

    Horowitz, C. J.; Dussan, H.; Berry, D. K.

    2008-04-15

    Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge Z. Nuclei with Z{<=}6 can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the S factor for fusion reactions of neutron rich nuclei including {sup 24}O+{sup 24}O and {sup 28}Ne+{sup 28}Ne. We use a simple barrier penetration model. The S factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in S should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear {sup 24}O+{sup 24}O fusion and find that {sup 24}O should burn at densities near 10{sup 11} g/cm{sup 3}. The energy released from this and similar reactions may be important for the temperature profile of the star.

  2. Physics with Heavy Neutron Rich Ribs at the Hribf

    NASA Astrophysics Data System (ADS)

    Radford, David

    2002-10-01

    The Holifield Radioactive Ion Beam Facility at the Oak Ridge National Laboratory has recently produced the world's first post-accelerated beams of heavy neutron-rich nuclei. B(E2;0^+ arrow 2^+) values for neutron-rich ^126,128Sn and ^132,134,136Te isotopes have been measured by Coulomb excitation of radioactive ion beams in inverse kinematics. The results for ^132Te and ^134Te (N=80,82) show excellent agreement with systematics of lighter Te isotopes, but the B(E2) value for ^136Te (N=84) is unexpectedly small. Single-neutron transfer reactions leading to ^135Te were identified using a ^134Te beam on ^natBe and ^13C targets at energies just above the Coulomb barrier. The use of the Be target provided an unambiguous signature for neutron transfer through the detection of two correlated α particles, arising from the breakup of unstable ^8Be. The results of these experiments will be discussed, togther with plans for future experiments with these heavy n-rich RIBs.

  3. Photoneutron cross sections for unstable neutron-rich oxygen isotopes.

    PubMed

    Leistenschneider, A; Aumann, T; Boretzky, K; Cortina, D; Cub, J; Datta Pramanik, U; Dostal, W; Elze, T W; Emling, H; Geissel, H; Grünschloss, A; Hellstr, M; Holzmann, R; Ilievski, S; Iwasa, N; Kaspar, M; Kleinböhl, A; Kratz, J V; Kulessa, R; Leifels, Y; Lubkiewicz, E; Münzenberg, G; Reiter, P; Rejmund, M; Scheidenberger, C; Schlegel, C; Simon, H; Stroth, J; Sümmerer, K; Wajda, E; Walús, W; Wan, S

    2001-06-11

    The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A = 17 to A = 22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections d sigma/dE were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.

  4. Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

    NASA Technical Reports Server (NTRS)

    Starrfield, S. G.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1981-01-01

    A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to evolve thermonuclear runaways in the accreted hydrogen rich envelopes of 1.0 Msub solar neutron stars with radii of 10 km and 20 km. Simulations produce outbursts which last from about 750 seconds to about one week. Peak effective temeratures and luninosities were 26 million K and 80 thousand Lsub solar for the 10 km study and 5.3 millison and 600 Lsub solar for the 20 km study. Hydrodynamic expansion on the 10 km neutron star produced a precursor lasting about one ten thousandth seconds.

  5. Exotic modes of excitation in deformed neutron-rich nuclei

    SciTech Connect

    Yoshida, Kenichi

    2011-05-06

    Low-lying dipole excitation mode in neutron-rich Mg isotopes close to the drip line is investigated in the framework of the Hartree-Fock-Bogoliubov and the quasiparticle random-phase approximation employing the Skyrme and the pairing energy-density functionals. It is found that the low-lying dipole-strength distribution splits into the K{sup {pi}} = 0{sup -} and 1{sup -} components due to the nuclear deformation. The low-lying dipole strength increases as the neutron drip-line is approached.

  6. New mass measurements of neutron rich nuclides at the NSCL.

    NASA Astrophysics Data System (ADS)

    Estrade, Alfredo; Matos, Milan; Amthor, Matthew; Bazin, Daniel; Becerril, Ana; Elliot, Thom; Gade, Alexandra; Galaviz, Daniel; Lorusso, Giuseppe; Pereira, Jorge; Portillo, Mauricio; Rogers, Andrew; Schatz, Hendrik; Shapira, Dan; Smith, Ed; Stolz, Andreas; Wallace, Mark

    2007-10-01

    A mass measurement of exotic isotopes in the region of 68Fe has been performed at the NSCL using the time-of-flight technique recently established. Experimental knowledge of the mass of very neutron rich nuclides is an important input for astrophysical applications, such as nucleosynthesis during the r-process and the evolution of matter in the crust of an accreting neutron star, where present calculations are mostly limited to using theoretical mass extrapolations. We present the details of the experimental set up, as well as preliminary results.

  7. Experimental determination of one- and two-neutron separation energies for neutron-rich copper isotopes

    NASA Astrophysics Data System (ADS)

    Yu, Mian; Wei, Hui-Ling; Song, Yi-Dan; Ma, Chun-Wang

    2017-09-01

    A method is proposed to determine the one-neutron Sn or two-neutron S2n separation energy of neutron-rich isotopes. Relationships between Sn (S2n) and isotopic cross sections have been deduced from an empirical formula, i.e., the cross section of an isotope exponentially depends on the average binding energy per nucleon B/A. The proposed relationships have been verified using the neutron-rich copper isotopes measured in the 64A MeV 86Kr + 9Be reaction. Sn, S2n, and B/A for the very neutron-rich 77,78,79Cu isotopes are determined from the proposed correlations. It is also proposed that the correlations between Sn, S2n and isotopic cross sections can be used to find the location of neutron drip line isotopes. Supported by Program for Science and Technology Innovation Talents at Universities of Henan Province (13HASTIT046), Natural and Science Foundation in Henan Province (162300410179), Program for the Excellent Youth at Henan Normal University (154100510007) and Y-D Song thanks the support from the Creative Experimental Project of National Undergraduate Students (CEPNU 201510476017)

  8. New Neutron Rich Nuclei Near {sup 208}Pb

    SciTech Connect

    Aeystoe, J.; Andreyev, A.; Evensen, A.-H.; Hoff, P.; Huhta, M.; Huyse, M.; ISOLDE Collaboration; Jokinen, A.; Karny, M.; Kugler, E.; Kurpeta, J.; Lettry, J.; Nieminen, A.; Plochocki, A.; Ramdhane, M.; Ravn, H.; Rykaczewski, K.; Szerypo, J.; VanDuppen, P.; Walter, G.; Woehr, A.

    1998-11-13

    The level properties near the stable doubly-magic nuclei formed the experimental grounds for the theoretical description of nuclear structure. However with a departure from the beta-stability line, the classical well-established shell structure might be modified. In particular, it may even vanish for extremely exotic neutron-rich nuclei near the neutron-drip line. Presently, it is impossible to verify such predictions by a direct experimental studies of these exotic objects. However, one may try to observe and understand the evolution of the nuclear structure while departing in the experiment as far as possible from the stable nuclei. An extension of experimental nuclear structure studies towards the nuclei characterized by high neutron excess is crucial for such verifications as well as for the {tau}-process nucleosynthesis scenario. Heavy neutron-rich nuclei, south-east of doubly-magic {sup 208}Pb, were always very difficult to produce and investigate. The nuclei like {sup 218}Po and {sup 214}Pb or {sup 210}Tl marked the border line of known nuclei from the beginning of the radioactivity era for over ninety years. To illustrate the difficulties, one can refer to the experiments employing the on-line mass separator technique. A spallation of heavy targets like {sup 232}Th and {sup 238}U by high-energy protons was proven as a source of heavy neutron-rich nuclei. The isotopes near and beyond doubly-magic {sup 208}Pb were produced too. However, such studies often suffered from an isobaric contamination of much more strongly produced and efficiently released elements like francium or radon and their decay products. A new experimental technique, based on the pulsed release element selective method recently developed at the PS Booster-ISOLDE at CERN [7,8,9] greatly reduces the contamination of these very short-lived {alpha}-emitters (Z {ge} 84) for the isobaric mass chains A=215 to A=218.

  9. Dipole response of neutron-rich Sn isotopes

    NASA Astrophysics Data System (ADS)

    Klimkiewicz, A.; Adrich, P.; Boretzky, K.; Fallot, M.; Aumann, T.; Cortina-Gil, D.; Datta Pramanik, U.; Elze, Th. W.; Emling, H.; Geissel, H.; Hellstroem, M.; Jones, K. L.; Kratz, J. V.; Kulessa, R.; Leifels, Y.; Nociforo, C.; Palit, R.; Simon, H.; Surowka, G.; Sümmerer, K.; Typel, S.; Walus, W.

    2007-05-01

    The neutron-rich isotopes 129-133Sn were studied in a Coulomb excitation experiment at about 500 AMeV using the FRS-LAND setup at GSI. From the exclusive measurement of all projectile-like particles following the excitation and decay of the projectile in a high-Z target, the energy differential cross section can be extracted. At these beam energies dipole transitions are dominating, and within the semi-classical approach the Coulomb excitation cross sections can be transformed into photoabsorption cross sections. In contrast to stable Sn nuclei, a substantial fraction of dipole strength is observed at energies below the giant dipole resonance (GDR). For 130Sn and 132Sn this strength is located in a peak-like structure around 10 MeV excitation energy and exhibits a few percent of the Thomas-Reiche Kuhn (TRK) sum-rule strength. Several calculations predict the appearance of dipole strength at low excitation energies in neutron-rich nuclei. This low-lying strength is often referred to as pygmy dipole resonance (PDR) and, in a macroscopic picture, is discussed in terms of a collective oscillation of excess neutrons versus the core nucleons. Moreover, a sharp rise is observed at the neutron separation threshold around 5 MeV for the odd isotopes. A possible contribution of 'threshold strength', which can be described within the direct-breakup model is discussed. The results for the neutron-rich Sn isotopes are confronted with results on stable nuclei investigated in experiments using real photons.

  10. A microscopic description of neutron-rich lithium isotopes

    SciTech Connect

    Burov, V.V.; Rzjanin, M.V.; Miller, H.G.; Shitikova, K.V.; Yen, G.D.

    1994-12-01

    A unified calculation of neutron-rich isotopes in lithium is performed using the hyperspherical basis in which the underlying symmetry of each isotope exhibits a simple structure. The variation of the binding energy as a function of mass number is qualitatively reproduced, and the asymptotic of radial distribution of each isotope decreases exponentially. The form factors of the lithium isotopes are calculated and display diffraction minima. 27 refs., 3 figs., 3 tabs.

  11. First principle-based AKMC modelling of the formation and medium-term evolution of point defect and solute-rich clusters in a neutron irradiated complex Fe-CuMnNiSiP alloy representative of reactor pressure vessel steels

    NASA Astrophysics Data System (ADS)

    Ngayam-Happy, R.; Becquart, C. S.; Domain, C.

    2013-09-01

    The formation and medium-term evolution of point defect and solute-rich clusters under neutron irradiation have been modelled in a complex Fe-CuMnNiSiP alloy representative of RPV steels, by means of first principle-based atomistic kinetic Monte Carlo simulations. The results obtained reproduce most features observed in available experimental studies, highlighting the very good agreement between both series. According to simulation, solute-rich clusters form and develop via an induced segregation mechanism on either the vacancy or interstitial clusters, and these point defect clusters are efficiently generated only in cascade debris and not Frenkel pair flux. The results have revealed the existence of two distinct populations of clusters with different characteristic features. Solute-rich clusters in the first group are bound essentially to interstitial clusters and they are enriched in Mn mostly, but also Ni to a lesser extent. Over the low dose regime, their density increases in the alloy as a result of the accumulation of highly stable interstitial clusters. In the second group, the solute-rich clusters are merged with vacancy clusters, and they contain mostly Cu and Si, but also substantial amount of Mn and Ni. The formation of a sub-population of pure solute clusters has been observed, which results from annihilation of the low stable vacancy clusters on sinks. The results indicate finally that the Mn content in clusters is up to 50%, Cu, Si, and Ni sharing the other half in more or less equivalent amounts. This composition has not demonstrated any noticeable modification with increasing dose over irradiation.

  12. Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1982-01-01

    A Lagrangian, fully implicit, one-dimensional hydrodynamic computer code is used to evolve thermonuclear runaways in the accreted hydrogen-rich envelopes of 1.0-solar-mass neutron stars with radii of 10 km and 20 km. The simulations produce outbursts lasting from approximately 750 seconds to approximately one week. The peak effective temperatures and luminosities are 2.6 x 10 to the 7th K and 8 x 10 to the 4th solar luminosities for the 10 km study and 5.3 x 10 to the 6th K and 600 solar luminosities for the 20 km study. It is found that hydrodynamic expansion on the 10 km neutron star produced a precursor lasting approximately 0.0001 second. The study assumes that the bursters and transient X-ray sources occur as a result of mass transfer from a secondary onto a neutron star in a fashion analogous to the nova phenomena. The peak temperatures and luminosities are found to be inversely proportional to the radius of the neutron stars and the calculations here, together with those in the literature, indicate that the actual radii of most neutron stars must be closer to 10 km than 20 km.

  13. Beta-Decay and Delayed Neutron Emission of Very Neutron-Rich Nuclei

    NASA Astrophysics Data System (ADS)

    Borzov, I. N.

    2014-09-01

    Extended self-consistent beta-decay model has been applied for beta-decay rates and delayed multi-neutron emission probabilities of quasi-spherical neutron-rich isotopes. The Gamow-Teller and first-forbidden decays are treated within the coordinate-space formalism of the continuum QRPA based on the density functional theory description of the ground state. A new set of the Fayans density functional parameters (DF3a) have been employed giving a better spin-orbit splitting due to a stronger tensor term. A provision has been included to fix the odd particle in the proper orbit (before variation). This accounts for ground-state spin inversion effect which has been shown to exist in the region of the most neutron-rich doubly-magic nucleus 78Ni.

  14. One-neutron removal from ^34,35Si and ^37S

    NASA Astrophysics Data System (ADS)

    Enders, J.; Bauer, A.; Anthony, D. W.; Aumann, T.; Bazin, D.; Blumenfeld, Y.; Brown, B. A.; Glasmacher, T.; Hansen, P. G.; Ibbotson, R. W.; Lofy, P. A.; Maddalena, V.; Miller, K. L.; Nakamura, T.; Navin, A.; Pritychenko, B. V.; Sherrill, B. M.; Spears, E. J.; Steiner, M.; Yurkon, J.; Wagner, A.; Tostevin, J. A.

    2000-10-01

    One-neutron removal reactions in inverse kinematics have been used recently to study the structure of low-lying states in neutron-rich nuclei. In these reactions, momentum distributions corresponding to ground states with l =0,1,2 have already been observed (T. Aumann et al./), Phys. Rev. Lett. 84, 35 (2000).. We report on preliminary results of an ongoing analysis of one-neutron removal reactions in ^37S and ^35Si with an expected dominant contribution of the ν f_7/2 amplitude to the ground state wave function (l=3) as compared with ^34Si at the N=20 shell closure. Data have been taken at the S800 spectrograph of the National Superconducting Cyclotron Laboratory using the A1200 fragment separator with secondary beam energies of ~ 70 A MeV.

  15. Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

    2014-09-01

    Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiNx/SiNy multilayers with high on/off ratio of 109. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

  16. Neutron transfer and flow in reactions between heavy neutron-rich nuclei.

    NASA Astrophysics Data System (ADS)

    Shapira, Dan; Liang, Felix J.; Gross, Carl J.; Varner, Robert L.; Beene, James R.

    2006-10-01

    Two Step WKB calcualtions of nucleus nucleus capture were carried out. In our calcualtions we nvestigate the possibility of enhanced capture cross sectins for neutron rich heavy nuclei. The model calculation uses a systematic potential [1] that incorporates the effect of barrier distributions due to excitation and deformation in the entrance channel. Neutron transfer is treated in a semiclassical approximation [2][3]. The transfer form factor used in neutron transfer saturates at an internuclear distance where where neutron can flow freely between the two nuclear centers [4]. [1] K. Siwek-Wilczynska and J. Wilczynski Phys. Rev. C69, 024611 (2004). [2] V. Yu. Denisov Eur. Phys. A7, 87 (2000). [3] V. I. Zagrebaev Phys. Rev. C7, 061601R (2003). [4] P.H. Stelson Phys. Lett. B205, 190 (1988).

  17. Neutron-rich hypernuclei: H6Λ and beyond

    NASA Astrophysics Data System (ADS)

    Gal, A.; Millener, D. J.

    2013-10-01

    Recent experimental evidence presented by the FINUDA Collaboration for a particle-stable H6Λ has stirred renewed interest in charting domains of particle-stable neutron-rich Λ hypernuclei, particularly for unbound nuclear cores. We have studied within a shell-model approach several neutron-rich Λ hypernuclei in the nuclear p shell that could be formed in (π-, K+) or in (K-, π+) reactions on stable nuclear targets. Hypernuclear shell-model input is taken from a theoretically inspired successful fit of γ-ray transitions in p-shell Λ hypernuclei which includes also ΛN ↔ ΣN coupling (ΛΣ coupling). The particle stability of H6Λ is discussed and predictions are made for binding energies of He9Λ, Li10Λ, Be12Λ, B14Λ. None of the large effects conjectured by some authors to arise from ΛΣ coupling is borne out, neither by these realistic p-shell calculations, nor by quantitative estimates outlined for heavier hypernuclei with substantial neutron excess.

  18. Unexpectedly large charge radii of neutron-rich calcium isotopes

    NASA Astrophysics Data System (ADS)

    Garcia Ruiz, R. F.; Bissell, M. L.; Blaum, K.; Ekström, A.; Frömmgen, N.; Hagen, G.; Hammen, M.; Hebeler, K.; Holt, J. D.; Jansen, G. R.; Kowalska, M.; Kreim, K.; Nazarewicz, W.; Neugart, R.; Neyens, G.; Nörtershäuser, W.; Papenbrock, T.; Papuga, J.; Schwenk, A.; Simonis, J.; Wendt, K. A.; Yordanov, D. T.

    2016-06-01

    Despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain `magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.

  19. Unexpectedly large charge radii of neutron-rich calcium isotopes

    DOE PAGES

    Garcia Ruiz, R. F.; Bissell, M. L.; Blaum, K.; ...

    2016-02-08

    Here, despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results aremore » complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.« less

  20. Unexpectedly large charge radii of neutron-rich calcium isotopes

    SciTech Connect

    Garcia Ruiz, R. F.; Bissell, M. L.; Blaum, K.; Ekstrom, A.; Frommgen, N.; Hagen, G.; Hammen, M.; Hebeler, K.; Holt, J. D.; Jansen, G. R.; Kowalska, M.; Kreim, K.; Nazarewicz, W.; Neugart, R.; Neyens, G.; Nortershauser, W.; Papenbrock, T.; Papuga, J.; Schwenk, A.; Simonis, J.; Wendt, K. A.; Yordanov, D. T.

    2016-02-08

    Here, despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.

  1. Fission and Properties of Neutron-Rich Nuclei

    NASA Astrophysics Data System (ADS)

    Hamilton, Joseph H.; Ramayya, A. V.; Carter, H. K.

    2008-08-01

    Opening session. Nuclear processes in stellar explosions / M. Wiescher. In-beam [symbol]-ray spectroscopy of neutron-rich nuclei at NSCL / A. Gade -- Nuclear structure I. Shell-model structure of neutron-rich nuclei beyond [symbol]Sn / A. Covello ... [et al.]. Shell structure and evolution of collectivity in nuclei above the [symbol]Sn core / S. Sarkar and M. S. Sarkar. Heavy-ion fusion using density-constrained TDHF / A. S. Umar and V. E. Oberacker. Towards an extended microscopic theory for upper-fp shell nuclei / K. P. Drumev. Properties of the Zr and Pb isotopes near the drip-line / V. N. Tarasov ... [et al.]. Identification of high spin states in [symbol] Cs nuclei and shell model calculations / K. Li ... [et al.]. Recent measurements of spherical and deformed isomers using the Lohengrin fission-fragment spectrometer / G. S. Simpson ... [et al.] -- Nuclear structure II. Nuclear structure investigation with rare isotope spectroscopic investigations at GSI / P. Boutachkov. Exploring the evolution of the shell structures by means of deep inelastic reactions / G. de Anaelis. Probing shell closures in neutron-rich nuclei / R. Krücken for the S277 and REX-ISOLDEMINIBALL collaborations. Structure of Fe isotopes at the limits of the pf-shell / N. Hoteling ... [et al.]. Spectroscopy of K isomers in shell-stabilized trans-fermium nuclei / S. K. Tandel ... [et al.] -- Radioactive ion beam facilities. SPIRAL2 at GANIL: a world leading ISOL facility for the next decade / S. Gales. New physics at the International Facility for Antiproton and Ion Research (FAIR) next to GSI / I. Augustin ... [et al.]. Radioactive beams from a high powered ISOL system / A. C. Shotter. RlKEN RT beam factory / T. Motobayashi. NSCL - ongoing activities and future perspectives / C. K. Gelbke. Rare isotope beams at Argonne / W. F. Henning. HRIBF: scientific highlights and future prospects / J. R. Beene. Radioactive ion beam research done in Dubna / G. M. Ter-Akopian ... [et al.] -- Fission I

  2. Conservation of Isospin in Neutron-rich Fission Fragments

    SciTech Connect

    Jain, A.K.; Choudhury, D.; Maheshwari, B.

    2014-06-15

    On the occasion of the 75{sup th} anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions {sup 238}U({sup 18}O,f) and {sup 208}Pb({sup 18}O,f) as well as a thermal neutron fission reaction {sup 245}Cm(n{sup th},f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

  3. Quadrupole collectivity in neutron-rich Fe and Cr isotopes.

    PubMed

    Crawford, H L; Clark, R M; Fallon, P; Macchiavelli, A O; Baugher, T; Bazin, D; Beausang, C W; Berryman, J S; Bleuel, D L; Campbell, C M; Cromaz, M; de Angelis, G; Gade, A; Hughes, R O; Lee, I Y; Lenzi, S M; Nowacki, F; Paschalis, S; Petri, M; Poves, A; Ratkiewicz, A; Ross, T J; Sahin, E; Weisshaar, D; Wimmer, K; Winkler, R

    2013-06-14

    Intermediate-energy Coulomb excitation measurements are performed on the N ≥ 40 neutron-rich nuclei (66,68)Fe and (64)Cr. The reduced transition matrix elements providing a direct measure of the quadrupole collectivity B(E2;2(1)(+) → 0(1)(+)) are determined for the first time in (68)Fe(42) and (64)Cr(40) and confirm a previous recoil distance method lifetime measurement in (66)Fe(40). The results are compared to state-of-the-art large-scale shell-model calculations within the full fpgd neutron orbital model space using the Lenzi-Nowacki-Poves-Sieja effective interaction and confirm the results of the calculations that show these nuclei are well deformed.

  4. Measuring the collectivity of neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Görgen, Andreas

    2012-10-01

    Measuring the lifetimes of excited nuclear states provides direct information on electromagnetic transition rates and on the collectivity of nuclear excitations. The recoil distance Doppler-shift (RDDS) method is a well-established technique for measuring picosecond lifetimes of excited states, which has been extensively used in combination with fusion-evaporation reactions to measure lifetimes in neutron-deficient nuclei. Here we discuss novel ways of combining the RDDS technique with multi-nucleon transfer and fusion-fission reactions, which allow measurement of picosecond lifetimes in neutron-rich nuclei. Experiments were performed at both GANIL and Legnaro National Laboratories (LNL) with the goal to investigate the onset of collectivity around 68Ni and the evolution of shapes and shape coexistence in medium-heavy fission fragments.

  5. Quadrupole Collectivity in Neutron-Rich Fe and Cr Isotopes

    NASA Astrophysics Data System (ADS)

    Crawford, H. L.; Clark, R. M.; Fallon, P.; Macchiavelli, A. O.; Baugher, T.; Bazin, D.; Beausang, C. W.; Berryman, J. S.; Bleuel, D. L.; Campbell, C. M.; Cromaz, M.; de Angelis, G.; Gade, A.; Hughes, R. O.; Lee, I. Y.; Lenzi, S. M.; Nowacki, F.; Paschalis, S.; Petri, M.; Poves, A.; Ratkiewicz, A.; Ross, T. J.; Sahin, E.; Weisshaar, D.; Wimmer, K.; Winkler, R.

    2013-06-01

    Intermediate-energy Coulomb excitation measurements are performed on the N≥40 neutron-rich nuclei Fe66,68 and Cr64. The reduced transition matrix elements providing a direct measure of the quadrupole collectivity B(E2;21+→01+) are determined for the first time in Fe4268 and Cr4064 and confirm a previous recoil distance method lifetime measurement in Fe4066. The results are compared to state-of-the-art large-scale shell-model calculations within the full fpgd neutron orbital model space using the Lenzi-Nowacki-Poves-Sieja effective interaction and confirm the results of the calculations that show these nuclei are well deformed.

  6. NEUTRON-RICH CHROMIUM ISOTOPE ANOMALIES IN SUPERNOVA NANOPARTICLES

    SciTech Connect

    Dauphas, N.; Remusat, L.; Papanastassiou, D. A.; Guan, Y.; Ma, C.; Eiler, J. M.; Chen, J. H.; Roskosz, M.; Stodolna, J.

    2010-09-10

    Neutron-rich isotopes with masses near that of iron are produced in Type Ia and II supernovae (SNeIa and SNeII). Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of {sup 54}Cr, the most neutron-rich stable isotope of chromium. The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of SNe, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of {sup 54}Cr anomalies is still unknown, presumably because it is fine grained and is chemically labile. Here, we identify in the primitive meteorite Orgueil the carrier of {sup 54}Cr anomalies as nanoparticles (<100 nm), most likely spinels that show large enrichments in {sup 54}Cr relative to solar composition ({sup 54}Cr/{sup 52}Cr ratio >3.6 x solar). Such large enrichments in {sup 54}Cr can only be produced in SNe. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of an SNII, although a Type Ia origin cannot be excluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby SN that also delivered {sup 26}Al and {sup 60}Fe to the solar system. This idea explains why the relative abundance of {sup 54}Cr and other neutron-rich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions in SNe.

  7. Neutron-Rich Nuclei and Neutron Stars: A New Accurately Calibrated Interaction for the Study of Neutron-Rich Matter

    SciTech Connect

    Todd-Rutel, B.G.; Piekarewicz, J.

    2005-09-16

    An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in {sup 208}Pb of R{sub n}-R{sub p}=0.21 fm. The impact of such a softening on various neutron-star properties is also examined.

  8. Neutron-rich nuclei and neutron stars: a new accurately calibrated interaction for the study of neutron-rich matter.

    PubMed

    Todd-Rutel, B G; Piekarewicz, J

    2005-09-16

    An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in 208 Pb of Rn-Rp=0.21 fm. The impact of such a softening on various neutron-star properties is also examined.

  9. Measurement of picosecond lifetimes in neutron-rich Xe isotopes

    NASA Astrophysics Data System (ADS)

    Ilieva, S.; Kröll, Th.; Régis, J.-M.; Saed-Samii, N.; Blanc, A.; Bruce, A. M.; Fraile, L. M.; de France, G.; Hartig, A.-L.; Henrich, C.; Ignatov, A.; Jentschel, M.; Jolie, J.; Korten, W.; Köster, U.; Lalkovski, S.; Lozeva, R.; Mach, H.; Mǎrginean, N.; Mutti, P.; Paziy, V.; Regan, P. H.; Simpson, G. S.; Soldner, T.; Thürauf, M.; Ur, C. A.; Urban, W.; Warr, N.

    2016-09-01

    Background: Lifetimes of nuclear excited states in fission fragments have been studied in the past following isotope separation, thus giving access mainly to the fragments' daughters and only to long-lived isomeric states in the primary fragments. For the first time now, short-lived excited states in the primary fragments, produced in neutron-induced prompt fission of 235U and 241Pu, were studied within the EXILL&FATIMA campaign at the intense neutron-beam facility of the Institute Laue-Langevin in Grenoble. Purpose: We aim to investigate the quadrupole collective properties of neutron-rich even-even 138,140,142Xe isotopes lying between the double shell closure N =82 and Z =50 and a deformed region with octupole collectivity. Method: The γ rays emitted from the excited fragments were detected with a mixed array consisting of 8 HPGe EXOGAM Clover detectors (EXILL) and 16 LaBr3(Ce) fast scintillators (FATIMA). The detector system has the unique ability to select the interesting fragment making use of the high resolution of the HPGe detectors and determine subnanosecond lifetimes using the fast scintillators. For the analysis the generalized centroid difference method was used. Results: We show that quadrupole collectivity increases smoothly with increasing neutron number above the closed N =82 neutron shell. Our measurements are complemented by state-of-the-art theory calculations based on shell-model descriptions. Conclusions: The observed smooth increase in quadrupole collectivity is similar to the evolution seen in the measured masses of the xenon isotopic chain and is well reproduced by theory. This behavior is in contrast to higher Z even-even nuclei where abrupt change in deformation occurs around N =90 .

  10. Level structures of neutron-rich Xe isotopes

    SciTech Connect

    Ahmad, I.; Lister, C.J.; Morss, L.R.

    1995-08-01

    The level structures of neutron-rich Xe isotopes were determined by observing prompt gamma-ray coincidences in {sup 248}Cm fission fragments. A 5-mg {sup 248}Cm, in the form of {sup 248}Cm-KCl pellet, was placed inside Eurogam array which consisted of 45 Compton-suppressed Ge detectors and 5 Low-Energy Photon Spectrometers. Transitions in Xe isotopes were identified by the appearance of new peaks in the {gamma}-ray spectra obtained by gating on the gamma peaks of the complementary Mo fragments.

  11. Electromagnetic transitions in neutron-rich /sup 40/Cl

    SciTech Connect

    Kozub, R.L.; Shriner J.F. Jr.; Hindi, M.M.; Holzmann, R.; Janssens, R.V.F.; Khoo, T.; Ma, W.C.; Drigert, M.; Garg, U.; Kolata, J.J.; and others

    1988-04-01

    In-beam ..gamma..-rays from excited states of the neutron-rich (T/sub z/ = 3) nucleus /sup 40/Cl have been identified in a threefold coincidence experiment in which ..gamma.. rays and light charged particles were observed. The resulting decay scheme is presented, and implications for the structure of low-lying levels in /sup 40/Cl are discussed in light of recent data from charge-exchange and ..beta..-decay work. The ordering of levels would seem to be quite different from the predictions of recent shell-model calculations.

  12. Search for octupole deformation in neutron rich Xe isotopes

    SciTech Connect

    Bentaleb, M.; Schulz, N.; Lubkiewicz, E.

    1994-07-01

    A search for octupole deformation in neutron rich Xe isotopes has been conducted through gamma-ray spectroscopy of primary fragments produced in the spontaneous fission of {sup 248}Cm. The spectrometer consisted of the Eurogam array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with masses ranging from 138 to 144. Except for {sup 139}Xe, none of them exhibit an alternating parity quasimolecular band, {alpha} feature usually encountered in octupole deformed nuclei. Substantial evidence for reflection asymmetric shape in the intrinsic system of the nucleus exists for the light actinide nuclei.

  13. Time-of-Flight Mass Measurements of Neutron Rich Nuclides

    NASA Astrophysics Data System (ADS)

    Estrade, A.; Matos, M.; Amthor, A. M.; Becerril, A.; Elliot, T.; Lorusso, G.; Rogers, A.; Schatz, H.; Bazin, D.; Gade, A.; Portillo, M.; Stolz, A.; Galaviz, D.; Pereira, J.; Shapira, D.; Smith, E.; Wallace, M.

    2008-10-01

    Nuclear masses of neutron rich isotopes in the region of Z ˜ 20-30 have been measured using the time-of-flight technique at the National Superconducting Cyclotron Laboratory (NSCL). The masses of 5 isotopes have been measured for the first time, and the precision of several other masses has been improved. The time-of-flight technique has shown the potential to access nuclear masses very far from stability when applied at radioactive beam facilities like the NSCL. Such measurements are important for understanding nuclear structure far from the valley of β-stability, and provide valuable information for astrophysical model calculations of processes involving very unstable nuclides.

  14. Microstructural evolution of neutron irradiated 3C-SiC

    DOE PAGES

    Sprouster, David J.; Koyanagi, Takaaki; Dooryhee, Eric; ...

    2017-03-18

    The microstructural response of neutron irradiated 3C-SiC have been investigated over a wide irradiation temperature and fluence range via qualitative and quantitative synchrotron-based X-ray diffraction characterization. Here, we identify several neutron fluence- and irradiation temperature-dependent changes in the microstructure, and directly highlight the specific defects introduced through the course of irradiation. By quantifying the microstructure, we aim to develop a more detailed understanding of the radiation response of SiC. Such studies are important to build mechanistic models of material performance and to understand the susceptibility of various microstructures to radiation damage for advanced energy applications.

  15. Amorphization of SiC under ion and neutron irradiation

    NASA Astrophysics Data System (ADS)

    Snead, L. L.; Zinkle, S. J.; Hay, J. C.; Osborne, M. C.

    1998-05-01

    This paper presents results on the microstructure and physical properties of SiC amorphized by both ion and neutron irradiation. Specifically, 0.56 MeV Si ions have been implanted in single crystal 6H-SiC from ambient through >200°C and the critical threshold for amorphization was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of the crystalline to amorphous transition region in these materials, elongated pockets of amorphous material oriented parallel to the free surface are observed. Single crystal 6H-SiC and hot pressed and sintered 6H and 3C SiC were neutron irradiated at approximately 70°C to a dose of ˜2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC include a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystallization of the amorphized, single crystal 6H-SiC appears to occur in two stages. In the temperature range of ˜800-1000°C, crystallites nucleate and slowly grow. In the temperature range of 1125-1150°C spontaneous nucleation and rapid growth of crystallites occur. It is further noted that amorphized 6H (alpha) SiC recrystallizes to highly faulted fcc (beta) SiC.

  16. Isomer spectroscopy of neutron-rich 168Tb103

    DOE PAGES

    Gurgi, L. A.; Regan, P. H.; Söderström, P. -A.; ...

    2016-12-29

    In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified event-by-event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identifiedmore » using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3) fast-timing scintillation detectors from the FATIMA collaboration. This paper presents the internal decay of a metastable isomeric excited state in the odd-odd nucleus 168Tb, which corresponds to a single proton-neutron hole configuration in the valence maximum nucleus 170Dy. These data represent the first information on excited states in this nucleus, which is the most neutron-rich odd-odd isotope of terbium (Z = 65) studied to date. Here, Nilsson configurations associated with an axially symmetric, prolate-deformed nucleus are proposed for the 168Tb ground state the observed isomeric state by comparison with Blocked BCS-Nilsson calculations.« less

  17. Examination of experimental conditions for the production of proton-rich and neutron-rich hypernuclei

    NASA Astrophysics Data System (ADS)

    Rappold, C.; López-Fidalgo, J.

    2016-10-01

    After the demonstration of the feasibility of hypernuclear spectroscopy with heavy-ion beams, the HypHI Collaboration will next focus on the study of proton- and neutron-rich hypernuclei. The use of a fragment separator for the production and separation of rare-isotope beams is a crucial aspect to producing hypernuclei far from the stability line. Precise spectroscopy of exotic hypernuclei is planned to be carried out at the GSI and later at the FAIR facility with the FRS and Super-FRS fragment separators. A systematic study and an optimization analysis were performed to determine optimal experimental conditions for producing hypernuclei with high isospin. The optimal conditions are obtained based on theoretical models for the heavy-ion induced reaction and hypernuclei production. Experimental efficiencies for the production of exotic secondary beams were also taken into account via Monte Carlo simulations of the fragment separator. The developed methodology is presented to deduce the expected yields of Be8Λ and subsequently other proton-rich and neutron-rich hypernuclei.

  18. Structure of molten Al and eutectic Al-Si alloy studied by neutron diffraction

    SciTech Connect

    Dahlborg, U.; Kramer, Matthew J.; Besser, M.; Morris, J. R.; Calvo-Dahlborg, M.

    2012-11-24

    The structure of molten eutectic Al87.8Si12.2 alloy has been studied by neutron diffraction during a temperature cycle. For comparison measurements were performed on pure molten Al. The measurements show that the alloy after heating above the liquidus contains particles of two kinds, aluminum-rich and silicon-rich. The silicon-rich particles are partly dissolved after a further heating. Earlier published data obtained by the γ-ray absorption technique of the density of the molten eutectic Al–Si alloy had demonstrated the existence of two temperatures above the liquidus temperature: A dissolution temperature Td, at which the microstructure of the melt inherited from the ingot starts to dissolve and a branching temperature, Tb, at which the melt reaches a fully mixed state. The highest temperature that was possible to reach during the neutron experiments lies between Td and Tb. The obtained results support these conclusions that molten alloys after melting are inhomogeneous up to a temperature well above the liquidus. Moreover, the difference in shape between the static structure factors measured by neutron and X-ray diffraction on molten aluminum is observed and is found to be more accentuated and to extend to larger wavevectors than in earlier works.

  19. Study of weakening of shell N = 28 for neutron rich nuclei through particle number fluctuation and pairing energy

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Rupayan

    2017-03-01

    Evolution of shells has been studied through fluctuations of particle numbers, pairing energies of large number of isotopes and isotones of nuclei evaluated through Skyrme-Hartree-Fock theory after inclusion of optimized tensor interaction. For neutron rich isotopes of Mg, Si, S and Ar no indication of shell closure at N = 28 has been observed. Calculations show occurrence of a doubly shell closed nucleus 114 Fl 184 .

  20. Irradiation By Neutrons And Annealing of SiGe Alloys

    NASA Technical Reports Server (NTRS)

    Vandersande, Jan W.; Mccormack, Joseph; Zoltan, Andrew

    1992-01-01

    Heat treatment restores thermoelectric performance having deteriorated under irradiation by neutrons. Discovery suggests SiGe materials used in radioisotope thermoelectric generators and other applications up to fluences of 5.4 X 10(to the 19th power)cm(to the negative 2nd power) and operating at temperatures of 600 to 1,000 degrees C.

  1. Use of Neutron Transfer Reactions to Indirectly Determine Neutron Capture Cross Sections on Neutron-Rich Nuclei

    SciTech Connect

    McCleskey, M.; Mukhamedzhanov, A. M.; Tribble, R. E.; Simmons, E.; Spiridon, A.; Banu, A.; Roeder, B.; Goldberg, V.; Trache, L.; Chen, X. F.; Lui, Y.-W.

    2010-03-01

    {sup 14}C(n,gamma){sup 15}C is being used as a test case in the development of an indirect method to determine neutron capture cross sections on neutron-rich unstable nuclei at astrophysical energies. Our approach makes use of two reactions: one peripheral used to find the asymptotic normalization coefficient (ANC) and a second non-peripheral reaction to determine the spectroscopic factor. The ANC for {sup 15}C has been determined using a HI neutron transfer reaction with a 12 MeV/nucleon {sup 14}C beam on a {sup 13}C target. The spectroscopic factor will be determined using {sup 14}C(d,p) in forward kinematics with an incident deuteron energy of 60 MeV. Both experiments were performed using the MDM high-resolution spectrometer at Texas A and M University.

  2. Synthesis of New Neutron Rich Heavy Nuclei:. AN Experimentalist's View

    NASA Astrophysics Data System (ADS)

    Loveland, W.

    2014-09-01

    I attempt to experimentally evaluate the prospects of synthesizing new neutronrich superheavy nuclei. I consider three possible synthetic paths to neutronrich superheavy nuclei: (a) the use of neutron-rich radioactive beams. (b) the use of damped collisions and (c) the use of multi-nucleon transfer reactions. I consider the prospects of synthesizing new n-rich isotopes of Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB and SPIRAL2. For the damped collision path, I present the results of a study of a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au (trans-target) fragments and the depletion of yields of target-like fragments by fission and fragment emission. The data are compared to predictions of Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility of multi-nucleon transfer reactions with radioactive beams.

  3. Liquid-drop model for extremely neutron rich nuclei

    SciTech Connect

    Fisher, J.C.

    1998-08-01

    Nuclear energy levels are characterized in part by their isospin quantum numbers. Ordinary nuclides are well described by an independent-particle model with ground-state isospins equal to the minimum possible value T{sub min} = abs(A/2 {minus} Z). It has been suggested that extremely neutron rich nuclei constitute a second branch of the table of isotopes whose ground states have the maximum possible isospin T{sub max} = A/2 and that neutral members of the T{sub max} branch (i.e., polyneutrons) serve as mediating particles for the new class of nuclear reactions discovered by Fleischmann and Pons. The energetics of the new reactions have been qualitatively described by a liquid-drop model. Recent measurements of the mass spectrum of reaction products produced in the new reactions make possible a refinement of the model, providing an explanation for gaps of instability separating ranges of stability in the mass spectrum.

  4. New Band Structures in Aapprox110 Neutron-Rich Nuclei

    SciTech Connect

    Zhu, S. J.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Yeoh, E. Y.; Xiao, Z. G.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Li, K.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.; Qi, B.; Meng, J.

    2010-05-12

    The high spin states of neutron-rich nuclei in Aapprox110 region have been carefully investigated by measuring prompt gamma-gamma-gamma coincident measurements populated in the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. Many new collective bands have been discovered. In this proceeding paper, we introduce some interesting new band structures recently observed by our cooperative groups, that is, the one-phonon- and two-phonon gamma-vibrational bands in odd-A {sup 103}Nb, {sup 105}Mo and {sup 107}Tc, the chiral doublet bands in even-even {sup 106}Mo, {sup 110}Ru and {sup 112}Ru, and the pseudospin partner bands with in {sup 108}Tc. The characteristics of these band structures have been discussed.

  5. Beta decay rates of neutron-rich nuclei

    SciTech Connect

    Marketin, Tomislav; Huther, Lutz; Martínez-Pinedo, Gabriel

    2015-10-15

    Heavy element nucleosynthesis models involve various properties of thousands of nuclei in order to simulate the intricate details of the process. By necessity, as most of these nuclei cannot be studied in a controlled environment, these models must rely on the nuclear structure models for input. Of all the properties, the beta-decay half-lives are one of the most important ones due to their direct impact on the resulting abundance distributions. Currently, a single large-scale calculation is available based on a QRPA calculation with a schematic interaction on top of the Finite Range Droplet Model. In this study we present the results of a large-scale calculation based on the relativistic nuclear energy density functional, where both the allowed and the first-forbidden transitions are studied in more than 5000 neutron-rich nuclei.

  6. Soft Dipole Modes of Neutron-Rich Nuclei

    NASA Astrophysics Data System (ADS)

    Csoto, A.; Gibson, B. F.; Afnan, I. R.

    1996-10-01

    We explore the open question of whether valance neutrons in ``halo nuclei'' can oscillate against the core to create a ``soft dipole'' mode. It has been suggested that such a dipole state would be situated at a few MeV of excitation energy, in contrast to usual dipole excitations at higher energies. The existence of a soft dipole mode, at least in ^11Li, appears to be supported by certain theoretical models and experimental data.footnote A. C. Hayes, Comments in Nuclear and Particle Physics 22, 27 (1996) However, this conclusion is based upon the behavior of specific observables at real energies. To clearly establish the existence of such resonant states, one should locate the corresponding complex poles of the S-matrix. We study ^6He and ^11Li in a three-body model based upon separable potentials that describe the known physics of the underlying two-body interactions. We solve the resulting Faddeev equations, continued into the complex energy plane, to search for the low lying excited states of these neutron-rich light nuclei.

  7. Cluster emissions with ? daughter from neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Kumar, Satish; Batra, J. S.; Gupta, Raj K.

    1996-02-01

    Cluster emissions from neutron-rich 0954-3899/22/2/006/img2, and 0954-3899/22/2/006/img3 nuclei are studied within the preformed cluster model of Malik and Gupta. Q-value estimates of the decays selected on the basis of shell effects in binding energies and their relative preformation probabilities show that these nuclei are stable (Q<0) against 0954-3899/22/2/006/img4 and 0954-3899/22/2/006/img5 decays and all the metastable (Q>0) decays are of non-alpha-like heavy clusters. The most probable decays (minimum half-life times) are the ones with a doubly magic 0954-3899/22/2/006/img6 nucleus as the daughter nucleus, arising due to the WKB penetrability. Compared to the presently measurable alpha-like cluster decays of the corresponding neutron-deficient parents into a 0954-3899/22/2/006/img7 daughter nucleus, these decays are suppressed by many orders of magnitude.

  8. Production of heavy and superheavy neutron-rich nuclei in neutron capture processes

    NASA Astrophysics Data System (ADS)

    Zagrebaev, V. I.; Karpov, A. V.; Mishustin, I. N.; Greiner, Walter

    2011-10-01

    The neutron capture process is considered as an alternative method for production of superheavy (SH) nuclei. Strong neutron fluxes might be provided by nuclear reactors and nuclear explosions in the laboratory frame and by supernova explosions in nature. All these cases are discussed in the paper. There are two gaps of short-lived nuclei (one is the well-known fermium gap and the other one is located in the region of Z=106-108 and N˜170) which impede the formation of SH nuclei by rather weak neutron fluxes realized at available nuclear reactors. We find that in the course of multiple (rather “soft”) nuclear explosions these gaps may be easily bypassed, and thus, a measurable amount of the neutron-rich long-living SH nuclei located at the island of stability may be synthesized. Existing pulsed reactors do not allow one to bypass these gaps. We formulate requirements for the pulsed reactors of the next generation that could be used for production of long-living SH nuclei. Natural formation of SH nuclei (in supernova explosions) is also discussed. The yield of SH nuclei relative to lead is estimated to be about 10-12, which is not beyond the experimental sensitivity for a search of SH elements in cosmic rays.

  9. IBM-1 calculations towards the neutron-rich nucleus {sup 106}Zr

    SciTech Connect

    Lalkovski, Stefan

    2009-04-15

    The neutron-rich N=66 isotonic and A=106 isobaric chains, covering regions with varying types of collectivity, are interpreted in the framework of the interacting boson model. Level energies and electric quadrupole transition probabilities are compared with available experimental information. The calculations for the known nuclei in the two chains are extrapolated toward the neutron-rich nucleus {sup 106}Zr.

  10. Production and identification of new, neutron-rich nuclei in the {sup 208}Pb region

    SciTech Connect

    Rykaczewski, K.; Kurpeta, J.; Plochocki, A.; Karny, M.; Szerypo, J.; Evensen, A.-H.; Kugler, E.; Lettry, J.; Ravn, H.; Duppen, P. van; Andreyev, A.; Huyse, M.; Woehr, A.; Jokinen, A.; Aeystoe, J.; Nieminen, A.; Huhta, M.; Ramdhane, M.; Walter, G.; Hoff, P.

    1998-12-21

    The recently developed methods allowing the experimental studies on new neutron-rich nuclei beyond doubly-magic {sup 208}Pb are briefly described. An identification of new neutron-rich isotopes {sup 215}Pb and {sup 217}Bi, and new decay properties of {sup 216}Bi studied by means of a pulsed release element selective technique at PS Booster-ISOLDE are reported.

  11. Spectroscopy of the neutron-rich actinide nucleus 240U following multinucleon-transfer reactions

    NASA Astrophysics Data System (ADS)

    Birkenbach, B.; Vogt, A.; Geibel, K.; Recchia, F.; Reiter, P.; Valiente-Dobón, J. J.; Bazzacco, D.; Bowry, M.; Bracco, A.; Bruyneel, B.; Corradi, L.; Crespi, F. C. L.; de Angelis, G.; Désesquelles, P.; Eberth, J.; Farnea, E.; Fioretto, E.; Gadea, A.; Gengelbach, A.; Giaz, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Hess, H.; John, P. R.; Jolie, J.; Judson, D. S.; Jungclaus, A.; Korten, W.; Lenzi, S.; Leoni, S.; Lunardi, S.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Mijatović, T.; Montagnoli, G.; Montanari, D.; Napoli, D.; Pellegri, L.; Pollarolo, G.; Pullia, A.; Quintana, B.; Radeck, F.; Rosso, D.; Şahin, E.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Stefanini, A. M.; Steinbach, T.; Stezowski, O.; Szilner, S.; Szpak, B.; Theisen, Ch.; Ur, C.; Vandone, V.; Wiens, A.

    2015-10-01

    Background: Nuclear structure information for the neutron-rich actinide nuclei is important since it is the benchmark for theoretical models that provide predictions for the heaviest nuclei. Purpose: γ -ray spectroscopy of neutron-rich heavy nuclei in the actinide region.

  12. Laser synthesis of carbon-rich SiC nanoribbons

    NASA Astrophysics Data System (ADS)

    Salama, I. A.; Quick, N. R.; Kar, A.

    2003-06-01

    A nanosecond pulsed laser direct-write and doping (LDWD) technique is used for the fabrication of carbon-rich silicon carbide nanoribbons heterostructure in a single crystal 4H-SiC wafer. Characterization by high-resolution transmission electron microscope and selected area electron diffraction pattern revealed the presence of nanosize crystalline ribbons with hexagonal graphite structure in the heat-affected zone below the decomposition temperature isotherm in the SiC epilayer. The nanoribbons exist in three layers each being approximately 50-60 nm thick, containing 15-17 individual sheets. The layers are self-aligned on the (0001) plane of the SiC epilayer with their c axis at 87° to the incident laser beam. The LDWD technique permits synthesis of heterostructured nanoribbons in a single step without additional material or catalyst, and effectively eliminates the need for nanostructure handling and transferring processes.

  13. Electroluminescence and Photoluminescence from Scored Si-Rich SiO2 Film/p-Si Structure

    NASA Astrophysics Data System (ADS)

    Ran, Guang-Zhao; Sun, Yong-Ke; Chen, Yuan; Dai, Lun; Cui, Xiao-Ming; Zhang, Bo-Rui; Qiao, Yong-Ping; Ma, Zhen-Chang; Zong, Wan-Hua; Qin, Guo-Gang

    2003-02-01

    Electroluminescence (EL) is observed from the Au/Si-rich SiO2 film/p-Si diodes, in which the Si-rich SiO2 films are scored deliberately by a diamond tip. The EL intensity of the scored diode annealed at 800°C is about 6 times of that of the unscored counterpart. The EL spectrum of the unscored diode could be decomposed into two Gaussian luminescence bands with peaks at about 1.83 and 2.23 eV, while for the EL spectrum of the scored diode, an additional Gaussian band at about 3.0 eV appears, and the 1.83-eV peak increases significantly in intensity. The photoluminescence (PL) spectrum of an unscored Si-rich SiO2 film has only one band peaking at about 1.48 eV, whereas the PL spectrum of the scored one has two bands at about 1.48 and 1.97 eV. We consider that the high-density defect regions produced by the scoring provide new luminescence centres and become some types of nonradiative centres in the Si oxide layer, which thus result in changes of the EL and PL spectra.

  14. Enterphase Integrity of Neutron Irradiated SiC Composites

    SciTech Connect

    Lara-Curzio, E.; Snead, L.L.

    1999-11-30

    SiC/SiC composites were fabricated from Hi-Nicalon{trademark} fibers with carbon, porous SiC and multilayer SiC interphases. These materials were then irradiated in the High Flux Beam Reactor with fast neutrons at 260 and 900-1060 degrees C to a dose of 1.1X10{sup 25} n/m{sup 2} corresponding to 1.1 displacements per atom (dpa). Results are presented for bend strength of both non-irradiated and irradiated materials. Within the interphases studied the multilayer SiC interphase material showed the least degradation (8-20%) in ultimate bend stress, while porous SiC underwent the greatest degradation ({approximately}35%). The Fiber matrix interphases are studied with TEM for both nonirradiated and irradiated materials. While no irradiation induced microstructural evolution of the interphase was observed, debonding of the interphase from the fiber was observed for all cases. This debonding is attributed to tensile stresses developed at the interface due to densification of the Hi-Nicalon{trademark} fiber. Residual stress analysis of the fiber matrix interface indicates that the irradiation-induced densification of Hi-Nicalon{trademark} and the volumetric expansion of the CVD SiC matrix cause tensile stresses well in excess of those which can be withstood by these, or any other viable SiC composite interphase.

  15. Effect of neutron irradiation on fracture resistance of advanced SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Ozawa, Kazumi; Katoh, Yutai; Nozawa, Takashi; Snead, Lance L.

    2011-10-01

    In order to identify the neutron irradiation effects on fracture resistance of advanced SiC/SiC composites, unloading-reloading single edge notched bend tests were conducted and an analytical model based on non-linear fracture mechanics was applied. As a result of the analysis, energy release rate contributed by macro-crack initiation of 3.1 kJ/m 2 for both unirradiated and irradiated advanced SiC/SiC composites (Hi-Nicalon Type-S (0°/90° plain woven)/multilayer/chemically vapor infiltration) is estimated. This result indicates no significant degradation in fracture resistance after neutron irradiation to 5.9 × 10 25 n/m 2 at 800 °C.

  16. Enhanced light emission from Si nanocrystals produced using SiOx/SiO2 multilayered silicon-rich oxides

    NASA Astrophysics Data System (ADS)

    Yoon, Jong-Hwan

    2015-07-01

    The light emission from Si nanocrystals (NCs) produced in SiO2 by annealing of SiOx/SiO2 multilayered silicon-rich oxide (SRO) is examined as a function of the SiOx layer thickness. Multilayered SRO structures are shown to produce a significant increase in emission intensities with a large redshift of spectra as compared with a single-layer SRO film. A multilayered SRO film with ∼6-nm thick SiO1.45 layers exhibits a 13-fold increase in the emission intensity with a redshift of ∼70 nm relative to a single-layer SiO1.45 SRO film with a thickness equivalent to the total SiO1.45 layer thickness in the multilayered film. The transmission electron microscopy analyses indicate that the enhancement of the emission intensity with the redshift of spectrum is caused by the enhanced aggregation of phase separated Si atoms in the former SiOx layers due to the hindering of interlayer diffusion of Si by the neighboring SiO2 layers.

  17. Neutron radiation damage and recovery studies of SiPMs

    NASA Astrophysics Data System (ADS)

    Tsang, T.; Rao, T.; Stoll, S.; Woody, C.

    2016-12-01

    We characterized the performance of Silicon Photomultipliers (SiPMs) before and after exposure of up to 1012 neutron/cm2 dosage. We show that the typical orders of magnitude increase of dark current upon neutron irradiation can be suppressed by operating it at a lower temperature and single-photoelectron detection capability can be restored. The required operating temperature depends on the dosage received. Furthermore, after high temperature thermal annealing, there is compelling evidence that the extrinsic dark current is lowered by orders of magnitude and single-photon detection performance are to some extent recovered at room temperature. Our experimental findings might have widespread implications for extending the functionality and the useful lifetime of current and future large scale SiPM detectors deployed in ionization radiation environment.

  18. Neutron radiation damage and recovery studies of SiPMs

    SciTech Connect

    Tsang, T.; Rao, T.; Stoll, S.; Woody, C.

    2016-12-01

    We characterized the performance of Silicon Photomultipliers (SiPMs) before and after exposure of up to 1012 neutron/cm2 dosage. We show that the typical orders of magnitude increase of dark current upon neutron irradiation can be suppressed by operating it at a lower temperature and single-photoelectron detection capability can be restored. The required operating temperature depends on the dosage received. Furthermore, after high temperature thermal annealing, there is compelling evidence that the extrinsic dark current is lowered by orders of magnitude and single-photon detection performance are to some extent recovered at room temperature. Our experimental findings might have widespread implications for extending the functionality and the useful lifetime of current and future large scale SiPM detectors deployed in ionization radiation environment.

  19. Beta Decay Study of Neutron-rich Magnesium

    NASA Astrophysics Data System (ADS)

    Ash, John; Rajabali, Mustafa; Griffin Collaboration

    2015-10-01

    Within the ``island of inversion'' around the N = 20 shell gap, isotopes of magnesium, and aluminum deviate from the expected closed-shell structure. Particles promoted across the N = 20 shell gap result in a lower energy deformed ground state configuration rather than the expected spherical configuration. An experiment was conducted at TRIUMF laboratory in the summer of 2015 to study the decay of ``island of inversion'' isotopes 33 , 34 , 35Mg and the structure of the respective daughter nuclei. The isotopes of interest were produced by a proton beam from TRIUMF's 500 MeV cyclotron impacting on a UCx target. The magnesium decays populated states along the decay chain in Al, Si, P, and S isotopes. The new GRIFFIN spectrometer in the ISAC-I facility was used to detect the gamma rays. Two sets of scintillators, one for detecting the beta particles (SCEPTAR) and the other for detecting beta-delayed neutrons (DESCANT), were also used in conjunction with GRIFFIN. The GRIFFIN data were energy calibrated and partially analyzed for this project. New algorithms were developed for the analysis. Preliminary results for new transitions detected in 34Mg as well as the half lives obtained will be presented in their current form. This research was supported by the Tennessee Tech research office.

  20. Transition probabilities in neutron-rich Se,8684

    NASA Astrophysics Data System (ADS)

    Litzinger, J.; Blazhev, A.; Dewald, A.; Didierjean, F.; Duchêne, G.; Fransen, C.; Lozeva, R.; Sieja, K.; Verney, D.; de Angelis, G.; Bazzacco, D.; Birkenbach, B.; Bottoni, S.; Bracco, A.; Braunroth, T.; Cederwall, B.; Corradi, L.; Crespi, F. C. L.; Désesquelles, P.; Eberth, J.; Ellinger, E.; Farnea, E.; Fioretto, E.; Gernhäuser, R.; Goasduff, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Hackstein, M.; Hess, H.; Ibrahim, F.; Jolie, J.; Jungclaus, A.; Kolos, K.; Korten, W.; Leoni, S.; Lunardi, S.; Maj, A.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Mijatovic, T.; Million, B.; Möller, O.; Modamio, V.; Montagnoli, G.; Montanari, D.; Morales, A. I.; Napoli, D. R.; Niikura, M.; Pollarolo, G.; Pullia, A.; Quintana, B.; Recchia, F.; Reiter, P.; Rosso, D.; Sahin, E.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Stefanini, A. M.; Stezowski, O.; Szilner, S.; Theisen, Ch.; Valiente Dobón, J. J.; Vandone, V.; Vogt, A.

    2015-12-01

    Reduced quadrupole transition probabilities for low-lying transitions in neutron-rich Se,8684 are investigated with a recoil distance Doppler shift (RDDS) experiment. The experiment was performed at the Istituto Nazionale di Fisica Nucleare (INFN) Laboratori Nazionali di Legnaro using the Cologne Plunger device for the RDDS technique and the AGATA Demonstrator array for the γ -ray detection coupled to the PRISMA magnetic spectrometer for an event-by-event particle identification. In 86Se the level lifetime of the yrast 21+ state and an upper limit for the lifetime of the 41+ state are determined for the first time. The results of 86Se are in agreement with previously reported predictions of large-scale shell-model calculations using Ni78-I and Ni78-II effective interactions. In addition, intrinsic shape parameters of lowest yrast states in 86Se are calculated. In semimagic 84Se level lifetimes of the yrast 41+ and 61+ states are determined for the first time. Large-scale shell-model calculations using effective interactions Ni78-II, JUN45, jj4b, and jj4pna are performed. The calculations describe B (E 2 ;21+→01+) and B (E 2 ;61+→41+) fairly well and point out problems in reproducing the experimental B (E 2 ;41+→21+) .

  1. Intruder configurations in neutron-rich {sup 34}P

    SciTech Connect

    Ollier, J.; Chapman, R.; Liang, X.; Labiche, M.; Spohr, K.-M.; Davison, M.; De Angelis, G.; Axiotis, M.; Kroell, T.; Napoli, D.R.; Martinez, T.; Bazzacco, D.; Farnea, E.; Lunardi, S.; Smith, A.G.; Haas, F.

    2005-03-01

    Extensions to the yrast and near-yrast decay sequences of the neutron-rich nucleus {sub 15}{sup 34}P{sub 19} have been established through an analysis of the {gamma} deexcitation of fragments produced in deep-inelastic processes which occur when 230-MeV {sup 36}S ions interact with a thick target of {sup 176}Yb. The highly sensitive GASP array of escape-suppressed Ge detectors was used to measure the resulting {gamma}-ray deexcitations of both projectilelike and targetlike fragments. Previously unobserved excited states in {sup 34}P were observed at 3351, 6236, 2320, and (4723) keV. Several states above an excitation energy of 2.3 MeV involve intruder configurations from the f{sub 7/2} shell. The investigation of negative parity intruder states on the periphery of the 'island of inversion' has an important role to play in our understanding of the evolution of nuclear structure as the island of inversion is approached.

  2. Isomer spectroscopy of neutron-rich $$^{165,167}$$Tb

    DOE PAGES

    Gurgi, L. A.; Regan, P. H.; Soderstrom, P. -A.; ...

    2017-01-01

    We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165,167Tb100,102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the μs regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 72–[523] single quasi-proton Nilsson configurationmore » to rotational states built on the 32–[411] single quasi-proton ground state. Lastly, these data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170Dy doubly-midshell nucleus is approached.« less

  3. Isomer spectroscopy of neutron-rich $^{165,167}$Tb

    SciTech Connect

    Gurgi, L. A.; Regan, P. H.; Soderstrom, P. -A.; Watanabe, H.; Walker, P. M.; Podolyak, Zs.; Nishimura, S.; Berry, T. A.; Doornenbal, P.; Lorusso, G.; Isobe, T.; Baba, H.; Xu, Z. Y.; Sakurai, H.; Sumikama, T.; Catford, W. N.; Bruce, A. M.; Browne, F.; Lane, G. J.; Kondev, F. G.; Odahara, A.; Wu, J.; Liu, H. L.; Xu, F. R.; Korkulu, Z.; Lee, P.; Liu, J. J.; Phong, V. H.; Yagi, A.; Zhang, G. X.; Alharbi, T.; Carroll, R. J.; Chae, K. Y.; Dombradi, Zs.; Estrade, A.; Fukuda, N.; Griffin, C.; Ideguchi, E.; Inabe, N.; Kanaoka, H.; Kojouharov, I.; Kubo, T.; Kubono, S.; Kurz, N.; Kuti, I.; Lalkovski, S.; Lee, E. J.; Lee, C. S.; Lotay, G.; Moon, C. B.; Nishizuka, I.; Nita, C. R.; Patel, Z.; Roberts, O. J.; Schaffner, H.; Shand, C. M.; Suzuki, H.; Takeda, H.; Terashima, S.; Vajta, Zs.; Kanaya, S.; Valiente-Dobon, J. J.

    2017-01-01

    We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165,167Tb100,102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the μs regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 72[523] single quasi-proton Nilsson configuration to rotational states built on the 32[411] single quasi-proton ground state. Lastly, these data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170Dy doubly-midshell nucleus is approached.

  4. Multiquasiparticle states in the neutron-rich nucleus 174Tm

    NASA Astrophysics Data System (ADS)

    Hughes, R. O.; Lane, G. J.; Dracoulis, G. D.; Byrne, A. P.; Nieminen, P.; Watanabe, H.; Carpenter, M. P.; Chowdhury, P.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; Seweryniak, D.; Zhu, S.

    2013-07-01

    Deep inelastic and transfer reactions with an 820-MeV, 136Xe beam and various ytterbium and lutetium targets have been employed to study high-spin structures in the neutron-rich thulium isotopes beyond 171Tm. Results in the doubly odd nucleus, 174Tm, include the identification of numerous new two- and four-quasiparticle intrinsic states including several isomers below 1 MeV, and the observation of the Kπ=4- ground state rotational band populated via direct decay from a τ=153(10)-μs, Kπ=14- isomer at 2092 keV. The 398-keV, M1 transition linking the isomer and ground state band is abnormally fast for a highly forbidden, ΔK=10 decay. This relative enhancement is explained in terms of mixing of the 13- level with the nearby 13- member of a Kπ=8- rotational band, with an interaction strength of V ≈ 1.4 keV. Multiquasiparticle calculations are compared with the observed states.

  5. Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, Masayuki

    2015-03-01

    I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E 1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of 142Sn and the neutron capture of 141Sn .

  6. {beta}{sup -}-delayed spectroscopy of neutron-rich tantalum nuclei: Shape evolution in neutron-rich tungsten isotopes

    SciTech Connect

    Alkhomashi, N.; Regan, P. H.; Podolyak, Zs.; Pietri, S.; Garnsworthy, A. B.; Steer, S. J.; Farrelly, G.; Cullen, I. J.; Gelletly, W.; Walker, P. M.; Benlliure, J.; Caserejos, E.; Estevez, M. E.; Morales, A. I.; Casten, R. F.; Gerl, J.; Wollersheim, H. J.; Gorska, M.; Kojouharov, I.; Schaffner, H.

    2009-12-15

    The low-lying structure of {sup 188,190,192}W has been studied following {beta} decays of the neutron-rich mother nuclei {sup 188,190,192}Ta produced following the projectile fragmentation of a 1-GeV-per-nucleon {sup 208}Pb primary beam on a natural beryllium target at the GSI Fragment Separator. The {beta}-decay half-lives of {sup 188}Ta, {sup 190}Ta, and {sup 192}Ta have been measured, with {gamma}-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion {beta}-{gamma} correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in {sup 188}W, {sup 190}W, and {sup 192}W, which highlight a change in nuclear shape at {sup 190}W compared with that of lighter W isotopes. This evolution of ground-state structure along the W isotopic chain is discussed as evidence for a possible proton subshell effect for the A{approx}190 region and is consistent with maximization of the {gamma}-softness of the nuclear potential around N{approx}116.

  7. Laser induced sponge-like Si in Si-rich oxides for photovoltaics.

    PubMed

    Gundogdu, S; Ozen, E Sungur; Hübner, R; Heinig, K H; Aydinli, A

    2013-10-07

    We show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3rd generation thin-film solar cells. Well passivated by the SiO₂ dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar⁺ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon.

  8. 26Si excited states via one-neutron removal from a 27Si radioactive ion beam

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, A. A.; Amthor, A. M.; Bazin, D.; Becerril, A. D.; Gade, A.; Galaviz, D.; Glasmacher, T.; Kahl, D.; Lorusso, G.; Matos, M.; Ouellet, C. V.; Pereira, J.; Schatz, H.; Smith, K.; Wales, B.; Weisshaar, D.; Zegers, R. G. T.

    2012-04-01

    A study of 26Si states by neutron removal from a fast radioactive beam of 27Si has been performed. A beam of 27Si of energy 84.3 MeV/nucleon impinged on a polypropylene foil (C3H6) of 180 mg/cm2 thickness. Deexcitation γ rays were detected with a highly segmented germanium detector array, in coincidence with the 26Si recoils, and the corresponding 26Si level energies were determined. In comparing our results to two previous γ-ray spectroscopic studies of 26Si level structures, we find good agreement with a recent measurement of the 12C(16O,2nγ)26Si reaction. Our results support the use of excitation energies from that study in helping determine the important resonance energies for the thermonuclear 25Al(p,γ)26Si reaction rate. We do not observe a bound state at 4093 keV reported in an earlier study of the 24Mg(3He,nγ)26Si reaction.

  9. Efimov physics around the neutron-rich 60Ca isotope.

    PubMed

    Hagen, G; Hagen, P; Hammer, H-W; Platter, L

    2013-09-27

    We calculate the neutron-60Ca S-wave scattering phase shifts using state of the art coupled-cluster theory combined with modern ab initio interactions derived from chiral effective theory. Effects of three-nucleon forces are included schematically as density dependent nucleon-nucleon interactions. This information is combined with halo effective field theory in order to investigate the 60Ca-neutron-neutron system. We predict correlations between different three-body observables and the two-neutron separation energy of 62Ca. This provides evidence of Efimov physics along the calcium isotope chain. Experimental key observables that facilitate a test of our findings are discussed.

  10. Production and identification of new, neutron-rich nuclei in the [sup 208]Pb region

    SciTech Connect

    Rykaczewski, K. ); Szerypo, J.; Evensen, A.-H.; Kugler, E.; Lettry, J.; Ravn, H. ); Kurpeta, J.; Pkochocki, A.; Karny, M.; Szerypo, J. ); Szerypo, J. ); Andreyev, H.; Huyse, M.; Wo uml; hr, A. ); Aystuml, J.; Nieminen, A.; Huhta, M. ); Walter, G. ) Hoff, P. )

    1998-12-01

    The recently developed methods allowing the experimental studies on new neutron-rich nuclei beyond doubly-magic [sup 208]Pb are briefly described. An identification of new neutron-rich isotopes [sup 215]Pb and [sup 217]Bi, and new decay properties of [sup 216]Bi studied by means of a pulsed release element selective technique at PS Booster-ISOLDE are reported. [copyright] [ital 1998 American Institute of Physics.

  11. Production and identification of new, neutron-rich nuclei in the {sup 208}Pb region

    SciTech Connect

    Rykaczewski, K.; Szerypo, J.; Evensen, A.-H.; Kugler, E.; Lettry, J.; Ravn, H.; Kurpeta, J.; Pkochocki, A.; Karny, M.; Szerypo, J.; Szerypo, J.; Andreyev, H.; Huyse, M.; Wo¨ hr, A.; Aystuml, J.; Nieminen, A.; Huhta, M.; Walter, G. Hoff, P.

    1998-12-01

    The recently developed methods allowing the experimental studies on new neutron-rich nuclei beyond doubly-magic {sup 208}Pb are briefly described. An identification of new neutron-rich isotopes {sup 215}Pb and {sup 217}Bi, and new decay properties of {sup 216}Bi studied by means of a pulsed release element selective technique at PS Booster-ISOLDE are reported. {copyright} {ital 1998 American Institute of Physics.}

  12. Neutron-proton effective mass splitting in neutron-rich matter and its impacts on nuclear reactions

    NASA Astrophysics Data System (ADS)

    Li, Bao-An; Chen, Lie-Wen

    2015-04-01

    The neutron-proton effective mass splitting in neutron-rich nucleonic matter reflects the spacetime nonlocality of the isovector nuclear interaction. It affects the neutron/proton ratio during the earlier evolution of the Universe, cooling of proto-neutron stars, structure of rare isotopes and dynamics of heavy-ion collisions. While there is still no consensus on whether the neutron-proton effective mass splitting is negative, zero or positive and how it depends on the density as well as the isospin-asymmetry of the medium, significant progress has been made in recent years in addressing these issues. There are different kinds of nucleon effective masses. In this mini-review, we focus on the total effective masses often used in the non-relativistic description of nuclear dynamics. We first recall the connections among the neutron-proton effective mass splitting, the momentum dependence of the isovector potential and the density dependence of the symmetry energy. We then make a few observations about the progress in calculating the neutron-proton effective mass splitting using various nuclear many-body theories and its effects on the isospin-dependence of in-medium nucleon-nucleon cross-sections. Perhaps, our most reliable knowledge so far about the neutron-proton effective mass splitting at saturation density of nuclear matter comes from optical model analyses of huge sets of nucleon-nucleus scattering data accumulated over the last five decades. The momentum dependence of the symmetry potential from these analyses provide a useful boundary condition at saturation density for calibrating nuclear many-body calculations. Several observables in heavy-ion collisions have been identified as sensitive probes of the neutron-proton effective mass splitting in dense neutron-rich matter based on transport model simulations. We review these observables and comment on the latest experimental findings.

  13. Excitation dependent photoluminescence study of Si-rich a-SiNx:H thin films

    NASA Astrophysics Data System (ADS)

    Kumar Bommali, Ravi; Preet Singh, Sarab; Rai, Sanjay; Mishra, P.; Sekhar, B. R.; Vijaya Prakash, G.; Srivastava, P.

    2012-12-01

    We report photoluminescence (PL) investigations on Si-rich amorphous hydrogenated silicon nitride (a-SiNx:H) thin films of different compositions, using three different excitation lasers, viz., 325 nm, 410 nm, and 532 nm. The as-deposited films contain amorphous Si quantum dots (QDs) as evidenced in high resolution transmission electron microscopy images. The PL spectral shape is in general seen to change with the excitation used, thus emphasizing the presence of multiple luminescence centres in these films. It is found that all the spectra so obtained can be deconvoluted assuming Gaussian contributions from defects and quantum confinement effect. Further strength to this assignment is provided by low temperature (300 °C) hydrogen plasma annealing of these samples, wherein a preferential enhancement of the QD luminescence over defect luminescence is observed.

  14. Structure and reactions of light neutron rich nuclei

    SciTech Connect

    Esbensen, H.

    1993-01-01

    Radioactive beam experiments have made it possible to study the structure of nuclei at the neutron drip line. Pair correlations play a crucial role in such nuclei and characteristic features include an extended neutron halo density and a large dipole strength near threshold. The most detailed studies have been performed for [sup 11]Li. I will present a 3-body model that explains the main features of the data obtained for this nucleus.

  15. Structure and reactions of light neutron rich nuclei

    SciTech Connect

    Esbensen, H.

    1993-04-01

    Radioactive beam experiments have made it possible to study the structure of nuclei at the neutron drip line. Pair correlations play a crucial role in such nuclei and characteristic features include an extended neutron halo density and a large dipole strength near threshold. The most detailed studies have been performed for {sup 11}Li. I will present a 3-body model that explains the main features of the data obtained for this nucleus.

  16. Evaluation of Damage Tolerance of Advanced SiC/SiC Composites after Neutron Irradiation

    NASA Astrophysics Data System (ADS)

    Ozawa, Kazumi; Katoh, Yutai; Nozawa, Takashi; Hinoki, Tatsuya; Snead, Lance L.

    2011-10-01

    Silicon carbide composites (SiC/SiC) are attractive candidate materials for structural and functional components in fusion energy systems. The effect of neutron irradiation on damage tolerance of the nuclear grade SiC/SiC composites (plain woven Hi-Nicalon™ Type-S reinforced CVI matrix composites multilayer interphase and unidirectional Tyranno™-SA3 reinforced NITE matrix with carbon mono-layer interphase) was evaluated by means of miniaturized single-edged notched beam test. No significant changes in crack extension behavior and in the load-loadpoint displacement characteristics such as the peak load and hysteresis loop width were observed after irradiation to 5.9 × 1025 n/m2 (E > 0.1 MeV) at 800°C and to 5.8 × 1025 n/m2 at 1300°C. By applying a global energy balance analysis based on non-linear fracture mechanics, the energy release rate for these composite materials was found to be unchanged by irradiation with a value of 3±2 kJ/m2. This has led to the conclusion that, for these fairly aggressive irradiation conditions, the effect of neutron irradiation on the fracture resistance of these composites appears insignificant.

  17. Nuclear structure investigation of some neutron-rich halo nuclei

    NASA Astrophysics Data System (ADS)

    Abdullah, Ahmed N.

    The ground state proton, neutron and matter densities, the corresponding rms radii and charge form factors of a dripline nuclei 6He, 11Li, 12Be and 14Be have been studied via a three-body model of (Core + n + n). The core-neutron interaction takes the form of Woods-Saxon (WS) potential. The two valence neutrons of 6He, 11Li and 12Be interact by the realistic interaction of ZBMII while those of 14Be interact via the realistic interaction of VPNP. The core and valence (halo) density distributions are described by the single-particle wave functions of the WS potential. The calculated results are discussed and compared with the experimental data. The long tail performance is clearly noticed in the calculated neutron and matter density distributions of these nuclei. The structure of the two valence neutrons in 6He, 11Li and 12Be is found to be mixed configurations with dominant (1p1/2)2 while that for 14Be is mixed configurations with dominant (2s1/2)2. The analysis of the present study supports the halo structure of these nuclei.

  18. Nuclear Structure Between N = 20 and N = 28: Beta-Decay in the Neutron-Rich Mg and Al Isotopes

    NASA Astrophysics Data System (ADS)

    Crawford, Heather; NSCL Experiment E14063 Team

    2015-10-01

    The structure of nuclei in the vicinity of expected nuclear shell closures away from stability has been, and continues to be, a cornerstone for nuclear structure study. The confirmation of certain ``magic numbers'' in exotic nuclei provides insight into the evolution of nucleon configurations with isospin, but perhaps even more light is shed into the structure of the atomic nucleus when expected shell closures are found to be weakened, or entirely disappear. Two instances where this has been the case are the N = 20 and N = 28 neutron shell closures in the neutron-rich Mg, Si and S nuclei. However, a question which is only beginning to be answered is the nature of the transitional nuclei between N = 20 and 28. Recent experimental work in the Mg isotopes has suggested a chain of prolate-deformed nuclei at Z = 12, but the nature of the Al and Si isotopes just above remains a question. An experiment was conducted at NSCL to study the β-decay of neutron-rich Na, Mg, Al and Si isotopes to provide additional, and in some cases, first information on the level structures of the daughter isotopes in the region between N = 20 and N = 28. First results from this work will be presented, and the implications for nuclear structural evolution in this region discussed. This work was supported by the NSF under Grant No. PHY-1068217 (NSCL) and by the U. S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-05CH11231 (LBNL).

  19. Stellar (n, gamma) cross sections of neutron-rich nuclei

    SciTech Connect

    Marganiec, J.; Domingo Pardo, C.; Kaeppeler, F.

    2010-03-01

    The present measurements were performed by means of the activation technique. Neutrons were produced at the Karlsruhe Van de Graaff accelerator via the {sup 7}Li(p,n){sup 7}Be reaction. For proton energies just above threshold, one obtains a neutron spectrum similar to a Maxwellian distribution for kT = 25 keV. This quasi-stellar neutron spectrum allowed us to measure the Maxwellian averaged cross sections directly. The experimental results of {sup 174,176}Yb, {sup 184,186}W, {sup 190,192}Os, {sup 196,198}Pt, and {sup 202}Hg were extrapolated from kT = 25 keV to lower and higher temperatures.

  20. β-Delayed Gamma Spectroscopy of Neutron-Rich Mg Isotopes in and around the Island of Inversion

    NASA Astrophysics Data System (ADS)

    Richard, Andrea; Crawford, Heather; NSCL E14063 Collaboration

    2016-09-01

    The question of the immutability of ''magic numbers'' and structure of exotic nuclei near to shell closures has long been an area of interest. The neutron-rich Mg isotopes around N=20 and N=28 are examples of regions where the expected spherical shell gaps have narrowed or have disappeared entirely. The ``Island of Inversion,'' centered around 32Mg, is a region where a narrowed N=20 shell gap and collective np-nh excitations result in nuclei with deformed ground states. The N=28 region also exhibits a narrowed shell gap and large deformation. The nature of the Mg nuclei between these two shell closures, however, has only recently been studied. Accessing nuclei between N=20 and N=28 provides information about the evolution of single particle states, and the evolution of structure with the addition of neutrons can be indirectly probed. An experiment was performed in March 2015 at the NSCL to study the β-decay of neutron-rich Na, Mg, Al, and Si isotopes between N=20 and N=28. The details of the experiment and preliminary level schemes will be discussed along with the implications for the nuclear structure. This work was supported in part by the U.S. DOE through Grant No. DE-FG02-88ER40387 (OU) and Contract No. DE-AC02-05CH11231 (LBNL).

  1. Production of neutron-rich transcalifornium nuclei in 238U-induced transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Long; Su, Jun; Xie, Wen-Jie; Zhang, Feng-Shou

    2016-11-01

    In order to produce more unknown neutron-rich transcalifornium nuclei, the collisions of 238U with the targets 248Cm, 249Cf, and 250Cm are investigated within the framework of the dinuclear system model. The production cross sections of unknown neutron-rich nuclei with Z =99 -104 in these reactions are predicted. The influences of N /Z ratios and charge numbers of the targets on the production cross sections are studied. It is found that high N /Z ratios of 248Cm and 250Cm targets enhance the production cross sections of neutron-rich transcalifornium nuclei. However, due to high charge number of the target 249Cf the predicted production cross sections of unknown neutron-rich nuclei with Z =104 in the reaction 238U+249Cf are higher than those in 238U+248Cm . We also have studied the entrance angular momentum effects on production probabilities of transfer products in the reaction 238U+248Cm . It is found that the formation probabilities of the final neutron-rich products increase first and then decrease with the increasing J .

  2. (30)Si mole fraction of a silicon material highly enriched in (28)Si determined by instrumental neutron activation analysis.

    PubMed

    D'Agostino, Giancarlo; Di Luzio, Marco; Mana, Giovanni; Oddone, Massimo; Pramann, Axel; Prata, Michele

    2015-06-02

    The latest determination of the Avogadro constant, carried out by counting the atoms in a pure silicon crystal highly enriched in (28)Si, reached the target 2 × 10(-8) relative uncertainty required for the redefinition of the kilogram based on the Planck constant. The knowledge of the isotopic composition of the enriched silicon material is central; it is measured by isotope dilution mass spectrometry. In this work, an independent estimate of the (30)Si mole fraction was obtained by applying a relative measurement protocol based on Instrumental Neutron Activation Analysis. The amount of (30)Si isotope was determined by counting the 1266.1 keV γ-photons emitted during the radioactive decay of the radioisotope (31)Si produced via the neutron capture reaction (30)Si(n,γ)(31)Si. The x((30)Si) = 1.043(19) × 10(-6) mol mol(-1) is consistent with the value currently adopted by the International Avogadro Coordination.

  3. Boron-rich benzene and pyrene derivatives for the detection of thermal neutrons

    NASA Astrophysics Data System (ADS)

    Yemam, Henok A.; Mahl, Adam; Koldemir, Unsal; Remedes, Tyler; Parkin, Sean; Greife, Uwe; Sellinger, Alan

    2015-09-01

    A synthetic methodology is developed to generate boron rich aromatic small molecules based on benzene and pyrene moieties for the detection of thermal neutrons. The prepared aromatic compounds have a relatively high boron content up to 7.4 wt%, which is important for application in neutron detection as 10B (20% of natural abundance boron) has a large neutron induced reaction cross-section. This is demonstrated by preparing blends of the synthesized molecules with fluorescent dopants in poly(vinyltoluene) matrices resulting in comparable scintillation light output and neutron capture as state-of-the art commercial scintillators, but with the advantage of much lower cost. The boron-rich benzene and pyrene derivatives are prepared by Suzuki conditions using both microwave and traditional heating, affording yields of 40-93%. This new procedure is simple and straightforward, and has the potential to be scaled up.

  4. Goodness of isospin in neutron rich systems from the fission fragment distribution

    NASA Astrophysics Data System (ADS)

    Garg, Swati; Jain, Ashok Kumar

    2017-09-01

    We present the results of our calculations for the relative yields of neutron-rich fission fragments emitted in 208Pb (18O, fission) reaction by using the concept of the conservation of isospin and compare with the experimental data. We take into account a range of isospin values allowed by the isospin algebra and assume that the fission fragments are formed in isobaric analog states. We also take into account the neutron multiplicity data for various neutron-emission channels in each partition, and use them to obtain the weight factors in calculating the yields. We then calculate the relative yields of the fission fragments. Our calculated results are able to reproduce the experimental trends reasonably well. This is the first direct evidence of the isospin conservation in neutron-rich systems and may prove a very useful tool in their studies.

  5. Exotic neutron-rich medium-mass nuclei with realistic nuclear forces

    NASA Astrophysics Data System (ADS)

    Tsunoda, Naofumi; Otsuka, Takaharu; Shimizu, Noritaka; Hjorth-Jensen, Morten; Takayanagi, Kazuo; Suzuki, Toshio

    2017-02-01

    We present the first application of the newly developed extended Kuo-Krenciglowa (EKK) theory of the effective nucleon-nucleon interaction to shell-model studies of exotic nuclei, including those where conventional approaches with fitted interactions encounter difficulties. This EKK theory enables us to derive an interaction that is suitable for several major shells (s d +p f in this work). By using such an effective interaction obtained from the Entem-Machleidt QCD-based χ N3LO interaction and the Fujita-Miyazawa three-body force, the energies, E 2 properties, and spectroscopic factors of low-lying states of neutron-rich Ne, Mg, and Si isotopes are nicely described, as the first shell-model description of the "island of inversion" without fit of the interaction. The long-standing question as to how particle-hole excitations occur across the s d -p f magic gap is clarified with distinct differences from the conventional approaches. The shell evolution is shown to appear similarly to earlier studies.

  6. Shape Evolution in Neutron-Rich Ru Nuclei

    NASA Astrophysics Data System (ADS)

    Söderström, P.-A.; Lorusso, G.; Watanabe, H.; Nishimura, S.; Doornenbal, P.; Browne, F.; Bruce, A. M.; Daido, R.; Fang, Y.; Gey, G.; Jung, H. S.; Nishizuka, I.; Patel, Z.; Rice, S.; Sinclair, L.; Sumikama, T.; Taprogge, J.; Vajta, Zs.; Wu, J.; Xu, Z. Y.; Baba, H.; Benzoni, G.; Carroll, R. J.; Chae, K. Y.; Crespi, F. C. L.; Fukuda, N.; Gernhäuser, R.; Ideguchi, E.; Inabe, N.; Isobe, T.; Jungclaus, A.; Kameda, D.; Kim, G. D.; Kim, Y.-K.; Kojouharov, I.; Kondev, F. G.; Kubo, T.; Kurz, N.; Kwon, Y. K.; Lalkovski, S.; Lane, G. J.; Li, Z.; Lozeva, R.; Montaner-Piza, A.; Moschner, K.; Naqvi, F.; Niikura, M.; Nishibata, H.; Odahara, A.; Orlandi, R.; Podolyak, Zs.; Regan, P. H.; Roberts, O. J.; Sakurai, H.; Schaffner, H.; Simpson, G. S.; Steiger, K.; Suzuki, H.; Takeda, H.; Tanaka, M.; Wendt, A.; Werner, V.; Wieland, O.; Yagi, A.; Yoshinaga, K.

    Recent experimental work has been carried out at the RIBF using the EURICA HPGe detector array. In this contribution, we discuss the recently published results on the shape evolution of the even-even isotopes 116,118Ru and present an outlook of β-delayed γ-ray spectroscopy of the odd-neutron nuclei and possibilities for life-time measurements of excited states.

  7. Studies of neutron-rich nuclei using the CPT mass spectrometer at CARIBU

    NASA Astrophysics Data System (ADS)

    Chaudhuri, A.; Bertone, P. F.; Buchinger, F.; Caldwell, S.; Clark, J. A.; Crawford, J. E.; Deibel, C. M.; Gulick, S.; Lascar, D.; Levand, A. F.; Li, G.; Savard, G.; Segel, R. E.; Sharma, K. S.; Sternberg, M. G.; Sun, T.; Van Schelt, J.

    2011-09-01

    The nucleosynthetic path of the astrophysical r-process and the resulting elemental abundances depend on neutron-separation energies which can be determined from the masses of the nuclei along the r-process reaction path. Due to the current lack of experimental data, mass models are often used. The mass values provided by the mass models are often too imprecise or disagree with each other. Therefore, direct high-precision mass measurements of neutron-rich nuclei are necessary to provide input parameters to the calculations and help refine the mass models. The Californium Rare Isotope Breeder Upgrade (CARIBU) facility of Argonne National Laboratory will provide experiments with beams of short-lived neutron-rich nuclei. The Canadian Penning Trap (CPT) mass spectrometer has been relocated to the CARIBU low-energy beam line to extend measurements of the neutron-rich nuclei into the mostly unexplored region along the r-process path. This will allow precise mass measurements (~ 10 keV/c2) of more than a hundred very neutron-rich isotopes that have not previously been measured.

  8. RECENT RESULTS OF FUSION INDUCED BY NEUTRON-RICH RADIOACTIVE BEAMS STUDIED AT HRIBF

    SciTech Connect

    Liang, J Felix

    2013-01-01

    The reaccelerated fission-fragment beams at HRIBF provide a unique opportunity for studying the mechanisms of fusion involving nuclei with large neutron excess. The fusion excitation functions for neutron-rich ra- dioactive 132Sn incident on 40Ca and 58Ni targets have been measured to explore the role of transfer couplings in sub-barrier fusion enhancement. Evaporation residue cross sections for 124,126,127,128Sn+64Ni were measured to study the dependence of fusion probability on neutron excess.

  9. Exotic structure in light neutron-rich nuclei

    SciTech Connect

    Itagaki, N.; Zhao, P. W.; Meng, J.; Matsuno, H.; Suhara, T.

    2015-10-15

    In this presentation I discussed two subjects. One is the persistence of threefold symmetry in the ground state of {sup 12}C. Recently D{sub 3h} symmetry has been established in {sup 12}C, which reflects the geometric symmetry of the three α particles. Although the spin-orbit interaction plays a significant role and this interaction breaks the α clusters, we show that threefold symmetry of {sup 12}C is still there. We use AQCM approach and discuss that inclusion of spin-orbit interaction, which is absent in the conventional microscopic α cluster models, is possible keeping the threefold symmetry. The second subject is the appearance of rod shape in C isotopes, which has been investigated in the framework of the cranking covariant density functional theory. The relationship between the stability of such states and the spin and isospin degrees of freedom is discussed; adding valence neutrons and rotating the system. These two effects stabilize the rod shape, and in addition, their coherent effect has been found; the σ-orbits (parallel to the symmetry axis) of the valence neutrons, which enhances the rod shape, is lowered by the rotation of the system, and this σ-orbit pulls down the single particle energies of protons with linear configuration owing to the proton-neutron interaction effect.

  10. Ground-state properties of neutron-rich Mg isotopes

    NASA Astrophysics Data System (ADS)

    Watanabe, S.; Minomo, K.; Shimada, M.; Tagami, S.; Kimura, M.; Takechi, M.; Fukuda, M.; Nishimura, D.; Suzuki, T.; Matsumoto, T.; Shimizu, Y. R.; Yahiro, M.

    2014-04-01

    We analyze recently measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics (AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by fine tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of deformation parameter is predicted by AMD. Large deformation is seen from 31Mg with N =19 to a drip-line nucleus 40Mg with N =28, indicating that both the N =20 and 28 magicities disappear. N dependence of neutron skin thickness is also predicted by AMD.

  11. Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

    SciTech Connect

    Jiang, Xiaofan; Ma, Zhongyuan Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

    2014-09-28

    Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

  12. Production of Neutron-Rich Bi Isotopes by Electric Fields

    SciTech Connect

    Baranov, D. S.; Baranova, O. D.

    2010-04-30

    The short time (approx10 minutes) high voltage electrolysis of nitrate bismuth solution was performed. After electrolysis about 30 mg of electrolyte have been dried up on a thin polyethylene film. The sample obtained was placed into the detecting system (Si detector and plastic detector). Alpha-radioactivity of the sample was measured. The results showed that alpha-radioactivity increased about 100 times to the base level. The radioactivity decreasing was about 2 times for 50 minutes. Some signals from the Si detector was accompanied by a signal from the electron detector (22 events). The signal from the plastic detector for all the events the electron recorded preceded the Si detector signal with delay less than 1.4 musec. The conclusion was made that beta-decay of nuclei {sup 212}Bi and the subsequent alpha-decay of nuclei {sup 212}Po were recorded. The effect was reproduced in 28 experiments. The possible explanation of the phenomenon was given.

  13. One- and two neutron decay of light neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Thoennessen, Michael

    2014-09-01

    Direct reactions with radioactive beams have been used very successfully to populate and measure nuclei beyond the neutron dripline and neutron unbound excited states of nuclei close to the neutron dripline. The use of different reactions (for example neutron removal and proton removal) to populate the same final nucleus can be used to selectively populate different states. Recent results from the MoNA-LISA setup at the NSCL, including 10He, 10,11Li, and 12,13Be will be presented. Direct reactions with radioactive beams have been used very successfully to populate and measure nuclei beyond the neutron dripline and neutron unbound excited states of nuclei close to the neutron dripline. The use of different reactions (for example neutron removal and proton removal) to populate the same final nucleus can be used to selectively populate different states. Recent results from the MoNA-LISA setup at the NSCL, including 10He, 10,11Li, and 12,13Be will be presented. This work was supported in part by the NSF, Grant PHY-11-02511.

  14. Super-high density Si quantum dot thin film utilizing a gradient Si-rich oxide multilayer structure.

    PubMed

    Kuo, Kuang-Yang; Huang, Pin-Ruei; Lee, Po-Tsung

    2013-05-17

    A gradient Si-rich oxide multilayer (GSRO-ML) deposition structure is proposed to achieve super-high density Si quantum dot (QD) thin film formation while preserving QD size controllability for better photovoltaic properties. Our results indicate that the Si QD thin film using a GSRO-ML structure can efficiently increase the QD density and control the QD size. Its optical properties clearly promise the capability of effective bandgap engineering even though these QDs are closely formed. The Si QD thin film using a GSRO-ML structure obviously reveals better electro-optical properties than those using a [silicon dioxide/silicon-rich oxide] multilayer ([SiO2/SRO]-ML) structure owing to the better optical absorption and carrier transport properties. Therefore, we successfully demonstrate that our proposed GSRO-ML structure has great potential for application in solar cells integrating Si QD thin films.

  15. Development of high sensitivity 4H-SiC detectors for fission neutron pulse shape measurements.

    PubMed

    Wu, Jian; Jiang, Yong; Li, Meng; Zeng, Lina; Li, Junjie; Gao, Hui; Zou, Dehui; Bai, Zhongxiong; Ye, Cenming; Liang, Wenfeng; Dai, Shaofeng; Lu, Yi; Rong, Ru; Du, Jinfeng; Fan, Xiaoqiang

    2017-08-01

    4H-silicon carbide (4H-SiC) detectors are well suited for measurements of fission neutron pulse shape for their compact size, excellent radiation resistance, and hydrogen free composition. The aim of this study is to improve the 4H-SiC detector's sensitivity to fission neutron pulses. 4H-SiC detectors with varied epilayer thicknesses are fabricated and then tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). The sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is increased by 139.8%, with the enlargement of epilayer thickness from 20 μm to 120 μm. By employing the proton-recoil method, the sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is further increased by 11.6%. With enhanced sensitivity to fission neutron pulses, 4H-SiC detectors are promising devices for high intensity neutron pulse measurements.

  16. Development of high sensitivity 4H-SiC detectors for fission neutron pulse shape measurements

    NASA Astrophysics Data System (ADS)

    Wu, Jian; Jiang, Yong; Li, Meng; Zeng, Lina; Li, Junjie; Gao, Hui; Zou, Dehui; Bai, Zhongxiong; Ye, Cenming; Liang, Wenfeng; Dai, Shaofeng; Lu, Yi; Rong, Ru; Du, Jinfeng; Fan, Xiaoqiang

    2017-08-01

    4H-silicon carbide (4H-SiC) detectors are well suited for measurements of fission neutron pulse shape for their compact size, excellent radiation resistance, and hydrogen free composition. The aim of this study is to improve the 4H-SiC detector's sensitivity to fission neutron pulses. 4H-SiC detectors with varied epilayer thicknesses are fabricated and then tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). The sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is increased by 139.8%, with the enlargement of epilayer thickness from 20 μm to 120 μm. By employing the proton-recoil method, the sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is further increased by 11.6%. With enhanced sensitivity to fission neutron pulses, 4H-SiC detectors are promising devices for high intensity neutron pulse measurements.

  17. Optimization of Thermal Neutron Converter in SiC Sensors for Spectral Radiation Measurements

    SciTech Connect

    Krolikowski, Igor; Cetnar, Jerzy; Issa, Fatima; Ferrone, Raffaello; Ottaviani, Laurent; Szalkai, Dora; Klix, Axel; Vermeeren, Ludo; Lyoussi, Abdalla; Saenger, Richard

    2015-07-01

    Optimization of the neutron converter in SiC sensors is presented. The sensors are used for spectral radiation measurements of thermal and fast neutrons and optionally gamma ray at elevated temperature in harsh radiation environment. The neutron converter, which is based on 10B, allows to detect thermal neutrons by means of neutron capture reaction. Two construction of the sensors were used to measure radiation in experiments. Sensor responses collected in experiments have been reproduced by the computer tool created by authors, it allows to validate the tool. The tool creates the response matrix function describing the characteristic of the sensors and it was used for detailed analyses of the sensor responses. Obtained results help to optimize the neutron converter in order to increase thermal neutron detection. Several enhanced construction of the sensors, which includes the neutron converter based on {sup 10}B or {sup 6}Li, were proposed. (authors)

  18. Single-Neutron Structure of Neutron-Rich Nuclei near N=50 and N=82

    SciTech Connect

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, S. D.; Bardayan, Daniel W; Blackmon, Jeff C; Adekola, Aderemi S; Chae, K. Y.; Chipps, K.; Erikson, Luke; Gaddis, A. L.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; Kaplan, Ron; Krolas, W.; Liang, J Felix; Livesay, Jake; Ma, Zhanwen; Matei, Catalin; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Patterson, N. P.; Paulauskas, Stanley; Shapira, Dan; Shriner, Jr., John F; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Thomas, J. S.; Wilson, Gemma L

    2009-01-01

    The 82Ge, 84Se, 132Sn, 130Sn, and 134Te (d,p) reactions have been measured with {approx}4-5-MeV-A rare isotope beams and CD2 targets at the HRIBF at ORNL. Energies and spectroscopic strengths have been measured for excitations in 83Ge and 85Se. Direct neutron capture calculations on 82Ge are presented. Preliminary results for single-neutron excitations in 131Sn, 133Sn, and 135Te are reported.

  19. Bands and Isomers in Neutron-Rich Rare-Earth Nuclei in PHF Model

    NASA Astrophysics Data System (ADS)

    Praharaj, C. R.; Ghorui, S. K.; Naik, Z.; Sahu, B. B.

    Rotational structures of neutron-rich Gd and Dy nuclei in the REE peak region are studied with deformed Hartee-Fock (HF) and angular momentum (J) projection model. Spectra of ground band and a few more excited, positive and negative parity bands have been studied up to high spin values. Some 4-quasiparticle K-isomeric bands and their electromagnetic properties are predicted.

  20. Total absorption spectroscopy of neutron-rich nuclei around the A = 100 mass region

    NASA Astrophysics Data System (ADS)

    Dombos, Alexander; Algora, Alejandro; Baumann, Thomas; Brett, Jaclyn; Crider, Benjamin; Ginter, Tom; Hager, Ulrike; Kwan, Elaine; Liddick, Sean; Marks, Braden; Naqvi, Farheen; Ong, Wei Jia; Pereira, Jorge; Prokop, Christopher; Quinn, Stephen; Simon, Anna; Scriven, Dustin; Spyrou, Artemis; Sumithrarachchi, Chandana; Deyoung, Paul

    2015-10-01

    Accurate modeling of the r-process requires knowledge of properties related to the β-decay of neutron-rich nuclei, such as β-decay half-lives and β-delayed neutron emission probabilities. These properties are related to the β-decay strength distribution, which can provide a sensitive constraint on theoretical models. Total absorption spectroscopy is a powerful technique to accurately measure quantities needed to calculate the β-decay strength distribution. In an effort to improve models of the r-process, the total absorption spectra of neutron-rich nuclei in the mass region around A = 100 were recently measured using the Summing NaI(Tl) (SuN) detector at the NSCL in the first ever total absorption spectroscopy measurement performed in a fragmentation facility. Total absorption spectra will be presented and the extracted β-decay feeding intensities will be compared to theoretical calculations.

  1. Shape Evolution in Neutron-Rich Krypton Isotopes Beyond N =60 : First Spectroscopy of Kr,10098

    NASA Astrophysics Data System (ADS)

    Flavigny, F.; Doornenbal, P.; Obertelli, A.; Delaroche, J.-P.; Girod, M.; Libert, J.; Rodriguez, T. R.; Authelet, G.; Baba, H.; Calvet, D.; Château, F.; Chen, S.; Corsi, A.; Delbart, A.; Gheller, J.-M.; Giganon, A.; Gillibert, A.; Lapoux, V.; Motobayashi, T.; Niikura, M.; Paul, N.; Roussé, J.-Y.; Sakurai, H.; Santamaria, C.; Steppenbeck, D.; Taniuchi, R.; Uesaka, T.; Ando, T.; Arici, T.; Blazhev, A.; Browne, F.; Bruce, A.; Carroll, R.; Chung, L. X.; Cortés, M. L.; Dewald, M.; Ding, B.; Franchoo, S.; Górska, M.; Gottardo, A.; Jungclaus, A.; Lee, J.; Lettmann, M.; Linh, B. D.; Liu, J.; Liu, Z.; Lizarazo, C.; Momiyama, S.; Moschner, K.; Nagamine, S.; Nakatsuka, N.; Nita, C.; Nobs, C. R.; Olivier, L.; Orlandi, R.; Patel, Z.; Podolyák, Zs.; Rudigier, M.; Saito, T.; Shand, C.; Söderström, P. A.; Stefan, I.; Vaquero, V.; Werner, V.; Wimmer, K.; Xu, Z.

    2017-06-01

    We report on the first γ -ray spectroscopy of low-lying states in neutron-rich Kr,10098 isotopes obtained from Rb,10199(p ,2 p ) reactions at ˜220 MeV /nucleon . A reduction of the 21+ state energies beyond N =60 demonstrates a significant increase of deformation, shifted in neutron number compared to the sharper transition observed in strontium and zirconium isotopes. State-of-the-art beyond-mean-field calculations using the Gogny D1S interaction predict level energies in good agreement with experimental results. The identification of a low-lying (02+, 22+) state in Kr 98 provides the first experimental evidence of a competing configuration at low energy in neutron-rich krypton isotopes consistent with the oblate-prolate shape coexistence picture suggested by theory.

  2. TOF-Bρ Mass Measurement of Neutron Rich Nuclei at the NSCL

    NASA Astrophysics Data System (ADS)

    Estradé, Alfredo; Matoš, Milan; Amthor, Matthew A.; Bazin, Daniel; Becerril, Ana D.; Elliot, Thom J.; Gade, Alexandra; Galaviz, Daniel; Lorusso, Giuseppe; Pereira, Jorge; Portillo, Mauricio; Rogers, Andrew; Schatz, Hendrik; Shapira, Dan; Smith, Edward; Stolz, Andreas; Wallace, Mark S.

    2007-10-01

    Experimental knowledge of nuclear masses of exotic nuclei is important for understanding nuclear structure far from the valley of β-stability, and as a direct input into astrophysical models. In the case of astrophysical processes involving neutron rich nuclei, such as nucleosynthesis during the r-process and the evolution of matter in the crust of an accreting neutron star, we are mostly limited to using theoretical mass models. The time of flight (TOF) mass measurement technique allows measuring very short-lived nuclei. It has been effectively applied using the fast fragment beams produced at the A1900 fragment separator at the National Superconducting Cyclotron Lab (NSCL) to reach masses very far from stability. We describe a recent mass measurement experiment in the neutron rich Fe region performed at the NSCL, and present preliminary results.

  3. Coupled cluster calculations of neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Hagen, Gaute

    2016-09-01

    In this talk I will present recent highlights from ab initio computations of atomic nuclei using coupled-cluster methods with state-of-the-art interactions from chiral effective field theory (EFT). The recent progress in computing nuclei from scratch is based on new optimizations of interactions from chiral EFT, and ab initio methods with a polynomial computational cost together with available super computing resources. The physics advancements I will discuss include: (i) accurate nuclear binding energies and radii of light and medium-mass nuclei, (ii) the neutron distribution and electric dipole polarizability of the nucleus 48Ca, (iii) and the structure of the rare nucleus 78Ni from first principles. All these quantities are currently targeted by precision measurements worldwide.

  4. β -decay properties of neutron-rich rare-earth isotopes

    NASA Astrophysics Data System (ADS)

    Sarriguren, P.

    2017-01-01

    In this paper, β -decay properties of even-even neutron-rich isotopes in the rare-earth mass region are studied within a microscopic theoretical approach based on a proton-neutron quasiparticle random-phase approximation. The underlying mean field is constructed self-consistently from a deformed Hartree-Fock calculation with Skyrme interactions and pairing correlations to which particle-hole and particle-particle residual interactions are added. Nuclei in this mass region participate in the astrophysical rapid neutron capture process and are directly involved in the generation of the rare-earth peak in the isotopic abundance pattern centered at A ≃160 . The energy distributions of the Gamow-Teller strength as well as the β -decay half-lives and the β -delayed neutron-emission probabilities are discussed and compared with the available experimental information and with calculations based on different approaches.

  5. Emission Dependent on composition of Si-rich-SiNX Films obtained by PECVD

    NASA Astrophysics Data System (ADS)

    Jaramillo Gomez, J. A.; Torchynska, T. V.; Casas Espinola, J. L.; Bentosa Gutiérrez, J. A.; Khomenkova, L.; Slaoui, A.

    2017-02-01

    Silicon-rich silicon nitride films with different stoichiometry were grown on silicon substrate using the plasma-enhanced chemical vapor deposition. The excess silicon content in the films was monitored via a variation of the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Morphology and luminescence properties of the films were studied by means of atomic force microscopy (AFM) and photoluminescence (PL) methods. High-temperature annealing was employed to produce the silicon nanocrystals in the films and to enhance the photoluminescence in the range of 1.6-3.0 eV. The PL spectrum was found to be complex due to the contribution of several radiative channels in emission process. It was determined that their competition leads to the non-monotonous variation of total PL peak position with the increase of the Si excess content. It was observed that the shape of PL spectra depends on an excitation wavelength. The ways to control the PL emission is proposed based on the discussion of the PL mechanism.

  6. Theoretical study of triaxial shapes of neutron-rich Mo and Ru nuclei

    SciTech Connect

    Zhang, C. L.; Bhat, G. H.; Nazarewicz, W.; Sheikh, J. A.; Shi, Yue

    2015-09-10

    Here, whether atomic nuclei can possess triaxial shapes at their ground states is still a subject of ongoing debate. According to theory, good prospects for low-spin triaxiality are in the neutron-rich Mo-Ru region. Recently, transition quadrupole moments in rotational bands of even-mass neutron-rich isotopes of molybdenum and ruthenium nuclei have been measured. The new data have provided a challenge for theoretical descriptions invoking stable triaxial deformations. The purpose of this study is to understand experimental data on rotational bands in the neutron-rich Mo-Ru region, we carried out theoretical analysis of moments of inertia, shapes, and transition quadrupole moments of neutron-rich even-even nuclei around 110Ru using self-consistent mean-field and shell model techniques. Methods: To describe yrast structures in Mo and Ru isotopes, we use nuclear density functional theory (DFT) with the optimized energy density functional UNEDF0. We also apply triaxial projected shell model (TPSM) to describe yrast and positive-parity, near-yrast band structures. As a result, our self-consistent DFT calculations predict triaxial ground-state deformations in 106,108Mo and 108,110,112Ru and reproduce the observed low-frequency behavior of moments of inertia. As the rotational frequency increases, a negative-gamma structure, associated with the aligned ν(h11/2)2 pair, becomes energetically favored. The computed transition quadrupole moments vary with angular momentum, which reflects deformation changes with rotation; those variations are consistent with experiment. The TPSM calculations explain the observed band structures assuming stable triaxial shapes. Lastly, the structure of neutron-rich even-even nuclei around Ru-110 is consistent with triaxial shape deformations. Our DFT and TPSM frameworks provide a consistent and complementary description of experimental data.

  7. Shape changes in neutron rich N = 43 isotones

    NASA Astrophysics Data System (ADS)

    Sethi, Jasmine; Forney, A.; Walters, W. B.; Harker, J.; Chiara, C. J.; Stefanescu, I.; Janssens, R. V. F.; Zhu, S.; Carpenter, M. P.

    2016-09-01

    et al. Nuclei in the transitional region with 28 < Z < 50 and 40 < N < 50 are very sensitive to shape changes with addition of individual nucleons due to close-lying neutron orbitals in the fpg model space. A systematic comparison of the structure of N = 43 isotones, focussing on new results on 75Ge and 73Zn will be presented. Both nuclei were populated in deep inelastic scattering reactions, 76Ge+208Pb and 76Ge+238 U , at 25 % above the Coulomb barrier, using Gammasphere and ATLAS facility at ANL. A number of new transitions and levels have been identified in both nuclei. The experimental results and their comparison to the theoretical calculations will be presented. This work is supported by the U.S. Department of Energy, Office of Nuclear Physics under Contract Numbers DE-AC02-06CH11357 and DE- AC02-05CH11231 and under Grant Numbers DE-FG02-94ER40834 and by the Polish Ministry of Science Grant Numbers 1P03B05929 and NN202103333. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility.

  8. Size dependent optical properties of Si quantum dots in Si-rich nitride/Si{sub 3}N{sub 4} superlattice synthesized by magnetron sputtering

    SciTech Connect

    So, Yong-Heng; Huang, Shujuan; Conibeer, Gavin; Green, Martin A.; Gentle, Angus

    2011-03-15

    A spectroscopic ellipsometry compatible approach is reported for the optical study of Si quantum dots (QDs) in Si-rich nitride/silicon nitride (SRN/Si{sub 3}N{sub 4}) superlattice, which based on Tauc-Lorentz model and Bruggeman effective medium approximation. It is shown that the optical constants and dielectric functions of Si QDs are strongly size dependent. The suppressed imaginary dielectric function of Si QDs exhibits a single broad peak analogous to amorphous Si, which centered between the transition energies E{sub 1} and E{sub 2} of bulk crystalline Si and blue shifted toward E{sub 2} as the QD size reduced. A bandgap expansion observed by the TL model when the size of Si QD reduced is in good agreement with the PL measurement. The bandgap expansion with the reduction of Si QD size is well supported by the first-principles calculations based on quantum confinement.

  9. Isospin quartic term in the kinetic energy of neutron-rich nucleonic matter

    NASA Astrophysics Data System (ADS)

    Cai, Bao-Jun; Li, Bao-An

    2015-07-01

    The energy of a free gas of neutrons and protons is well known to be approximately isospin parabolic with a negligibly small quartic term of only 0.45 MeV at the saturation density of nuclear matter ρ0=0.16 fm-3 . Using an isospin-dependent single-nucleon momentum distribution including a high (low) momentum tail (depletion) with its shape parameters constrained by recent high-energy electron scattering and medium-energy nuclear photodisintegration experiments as well as the state-of-the-art calculations of the deuteron wave function and the equation of state of pure neutron matter near the unitary limit within several modern microscopic many-body theories, we show for the first time that the kinetic energy of interacting nucleons in neutron-rich nucleonic matter has a significant quartic term of 7.18 ±2.52 MeV. Such a large quartic term has broad ramifications in determining the equation of state of neutron-rich nucleonic matter using observables of nuclear reactions and neutron stars.

  10. Neutron imaging of hydrogen-rich fluids in geomaterials and engineered porous media: A review

    NASA Astrophysics Data System (ADS)

    Perfect, E.; Cheng, C.-L.; Kang, M.; Bilheux, H. Z.; Lamanna, J. M.; Gragg, M. J.; Wright, D. M.

    2014-02-01

    Recent advances in visualization technologies are providing new discoveries as well as answering old questions with respect to the phase structure and flow of hydrogen-rich fluids, such as water and oil, within porous media. Magnetic resonance and x-ray imaging are sometimes employed in this context, but are subject to significant limitations. In contrast, neutrons are ideally suited for imaging hydrogen-rich fluids in abiotic non-hydrogenous porous media because they are strongly attenuated by hydrogen and can "see" through the solid matrix in a non-destructive fashion. This review paper provides an overview of the general principles behind the use of neutrons to image hydrogen-rich fluids in both 2-dimensions (radiography) and 3-dimensions (tomography). Engineering standards for the neutron imaging method are examined. The main body of the paper consists of a comprehensive review of the diverse scientific literature on neutron imaging of static and dynamic experiments involving variably-saturated geomaterials (rocks and soils) and engineered porous media (bricks and ceramics, concrete, fuel cells, heat pipes, and porous glass). Finally some emerging areas that offer promising opportunities for future research are discussed.

  11. Theoretical study of triaxial shapes of neutron-rich Mo and Ru nuclei

    DOE PAGES

    Zhang, C. L.; Bhat, G. H.; Nazarewicz, W.; ...

    2015-09-10

    Here, whether atomic nuclei can possess triaxial shapes at their ground states is still a subject of ongoing debate. According to theory, good prospects for low-spin triaxiality are in the neutron-rich Mo-Ru region. Recently, transition quadrupole moments in rotational bands of even-mass neutron-rich isotopes of molybdenum and ruthenium nuclei have been measured. The new data have provided a challenge for theoretical descriptions invoking stable triaxial deformations. The purpose of this study is to understand experimental data on rotational bands in the neutron-rich Mo-Ru region, we carried out theoretical analysis of moments of inertia, shapes, and transition quadrupole moments of neutron-richmore » even-even nuclei around 110Ru using self-consistent mean-field and shell model techniques. Methods: To describe yrast structures in Mo and Ru isotopes, we use nuclear density functional theory (DFT) with the optimized energy density functional UNEDF0. We also apply triaxial projected shell model (TPSM) to describe yrast and positive-parity, near-yrast band structures. As a result, our self-consistent DFT calculations predict triaxial ground-state deformations in 106,108Mo and 108,110,112Ru and reproduce the observed low-frequency behavior of moments of inertia. As the rotational frequency increases, a negative-gamma structure, associated with the aligned ν(h11/2)2 pair, becomes energetically favored. The computed transition quadrupole moments vary with angular momentum, which reflects deformation changes with rotation; those variations are consistent with experiment. The TPSM calculations explain the observed band structures assuming stable triaxial shapes. Lastly, the structure of neutron-rich even-even nuclei around Ru-110 is consistent with triaxial shape deformations. Our DFT and TPSM frameworks provide a consistent and complementary description of experimental data.« less

  12. Sponge-like Si-SiO2 nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

    NASA Astrophysics Data System (ADS)

    Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

    2013-09-01

    Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

  13. Sponge-like Si-SiO{sub 2} nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

    SciTech Connect

    Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

    2013-09-23

    Sponge-like Si nanostructures embedded in SiO{sub 2} were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO{sub 2} nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

  14. Evidence for octupole excitations in the odd-odd neutron-rich nucleus {sup 142}Cs

    SciTech Connect

    Liu, S. H.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Ma, W. C.; Daniel, A. V.; Ter-Akopian, G. M.

    2010-05-15

    High-spin states in the neutron-rich nucleus {sup 142}Cs are reinvestigated from a study of the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. A new level scheme is built and spin-parities are assigned to levels based on angular correlation measurements and systematics. The new structure of {sup 142}Cs is proposed to be related to octupole correlations. The electric dipole moment of {sup 142}Cs is measured and a dramatic decrease of the dipole moments with increasing neutron numbers in the Cs isotopic chain is found.

  15. Decay spectroscopy of neutron-rich rare-earth isotopes and collectivity around double midshell

    SciTech Connect

    Watanabe, Hiroshi

    2015-10-15

    Neutron-rich rare-earth isotopes with A ≈ 170, which locate near the middle of the major shells for both proton and neutron between the doubly magic nuclei {sup 132}Sn and {sup 208}Pb, have been investigated by means of decay spectroscopy techniques at the RIBF facility at RIKEN. The nuclei of interest were produced by in-flight fission of a high-intensity {sup 238}U beam at 345 MeV/u. In this contribution, scientific motivations, the details of experimental procedures, and some prospects of the data analysis are reported.

  16. Thermal effects on the Fission Barrier of neutron-rich nuclei

    SciTech Connect

    Minato, Futoshi; Hagino, Kouichi

    2008-11-11

    We discuss the fission barrier height of neutron-rich nuclei in a r-process site at highly excited state, which is resulted from the beta-decay or the neutron-capture processes. We particularly investigate the sensitivity of the fission barrier height to the temperature, including the effect of pairing phase transition from superfluid to normal fluid phases. To this end, we use the finite-temperature Skyrme-Hartree-Fock-Bogolubov method with a zero-range pairing interaction. We also discuss the temperature dependence of the fission decay rate.

  17. High-accuracy mass measurements of neutron-rich Kr isotopes

    SciTech Connect

    Delahaye, P.; Kellerbauer, A.; Audi, G.; Lunney, D.; Blaum, K.; George, S.; Carrel, F.; Herfurth, F.; Yazidjian, C.; Herlert, A.; Schweikhard, L.; Kluge, H.-J.

    2006-09-15

    The atomic masses of the neutron-rich krypton isotopes {sup 84,86-95}Kr have been determined with the tandem Penning trap mass spectrometer ISOLTRAP with uncertainties ranging from 20 to 220 ppb. The masses of the short-lived isotopes {sup 94}Kr and {sup 95}Kr were measured for the first time. The masses of the radioactive nuclides {sup 89}Kr and {sup 91}Kr disagree by 4 and 6 standard deviations, respectively, from the present Atomic-Mass Evaluation database. The resulting modification of the mass surface with respect to the two-neutron separation energies as well as implications for mass models and stellar nucleosynthesis are discussed.

  18. Decay spectroscopy of neutron-rich rare-earth isotopes and collectivity around double midshell

    NASA Astrophysics Data System (ADS)

    Watanabe, Hiroshi

    2015-10-01

    Neutron-rich rare-earth isotopes with A ≈ 170, which locate near the middle of the major shells for both proton and neutron between the doubly magic nuclei 132Sn and 208Pb, have been investigated by means of decay spectroscopy techniques at the RIBF facility at RIKEN. The nuclei of interest were produced by in-flight fission of a high-intensity 238U beam at 345 MeV/u. In this contribution, scientific motivations, the details of experimental procedures, and some prospects of the data analysis are reported.

  19. Beta decay of very neutron-rich110Mo studied at the new IGISOL facility

    NASA Astrophysics Data System (ADS)

    Lhersonneau, G.; Honkanen, A.; Huhta, M.; Jauho, P. P.; Jokinen, A.; Leino, M.; Oinonen, M.; Ollikainen, E.; Parmonen, J. M.; Aysto, J.

    1994-06-01

    The decay of the new activity110Mo (t1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles, β-γ-t and γ- y-t coincidences were recorded. The decay scheme suggests Iπ=2+ for the ground state of the daughter nucleus110Tc. Three 1+ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.

  20. Studies of neutron-rich nuclei far from stability at TRISTAN

    SciTech Connect

    Gill, R.L.

    1984-01-01

    The ISOL facility, TRISTAN, is a user facility located at Brookhaven National Laboratory's High Flux Beam Reactor. Short-lived, neutron-rich nuclei, far from stability, are produced by thermal neutron fission of /sup 235/U. An extensive array of experimental end stations are available for nuclear structure studies. These studies are augmented by a variety of long-lived ion sources suitable for use at a reactor facility. Some recent results at TRISTAN are presented as examples of using an ISOL facility to study series of nuclei, whereby an effective means of conducting nuclear structure investigations is available.

  1. beta-decay properties of neutron-rich Zr and Mo isotopes

    SciTech Connect

    Sarriguren, P.; Pereira, J.

    2010-06-15

    Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron emission are investigated in neutron-rich Zr and Mo isotopes within a deformed quasiparticle random-phase approximation. The approach is based on a self-consistent Skyrme Hartree-Fock mean field with pairing correlations and residual separable particle-hole and particle-particle forces. Comparison with recent measurements of half-lives stresses the important role that nuclear deformation plays in the description of beta-decay properties in this mass region.

  2. Neutron Generation from Laser-Accelerated Ion Beams: Use of Alternative Deuteron-Rich Targets for Improved Neutron Yield and Control of Neutron Spectra

    NASA Astrophysics Data System (ADS)

    Albright, B. J.; Yin, L.; Favalli, A.

    2016-10-01

    Laser-ion-beam generation in the break-out afterburner (BOA) acceleration regime has been modeled for several deuteron-rich solid-density targets using the VPIC particle-in-cell code. Monte Carlo modeling of the transport of these beams in a beryllium converter in a pitcher-catcher neutron source configuration shows significant increases in neutron yields may be achievable through judicious choices of laser target material. Additionally, species-separation dynamics in some target materials during the BOA ion acceleration phase can be exploited to control the shapes of the neutron spectra. Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Funding provided by the Los Alamos National Laboratory Directed Research and Development Program.

  3. Symmetry energy and surface properties of neutron-rich exotic nuclei

    SciTech Connect

    Gaidarov, M. K.; Antonov, A. N.; Sarriguren, P.; Moya de Guerra, E.

    2014-07-23

    The symmetry energy, the neutron pressure and the asymmetric compressibility of spherical Ni, Sn, and Pb and deformed Kr and Sm neutron-rich even-even nuclei are calculated within the coherent density fluctuation model using the symmetry energy as a function of density within the Brueckner energy-density functional. The correlation between the thickness of the neutron skin and the characteristics related with the density dependence of the nuclear symmetry energy is investigated for isotopic chains of these nuclei in the framework of the deformed self-consistent mean-field Skyrme HF+BCS method. The mass dependence of the nuclear symmetry energy and the neutron skin thickness are also studied together with the role of the neutron-proton asymmetry. The studied correlations reveal a smoother behavior in the case of spherical nuclei than for deformed ones. We also notice that the neutron skin thickness obtained for {sup 208}Pb with SLy4 force is found to be in a good agreement with the recent data. In addition to the interest that this study may have by itself, we give some numerical arguments in proof of the existence of peculiarities of the studied quantities in Ni and Sn isotopic chains that are not present in the Pb chain.

  4. Effect of neutron irradiation on charge collection efficiency in 4H-SiC Schottky diode

    NASA Astrophysics Data System (ADS)

    Wu, Jian; Jiang, Yong; Lei, Jiarong; Fan, Xiaoqiang; Chen, Yu; Li, Meng; Zou, Dehui; Liu, Bo

    2014-01-01

    The charge collection efficiency (CCE) in 4H-SiC Schottky diode is studied as a function of neutron fluence. The 4H-SiC diode was irradiated with fast neutrons of a critical assembly in Nuclear Physics and Chemistry Institute and CCE for 3.5 MeV alpha particles was then measured as a function of the applied reverse bias. It was found from our experiment that an increase of neutron fluence led to a decrease of CCE. In particular, CCE of the diode was less than 1.3% at zero bias after an irradiation at 8.26×1014 n/cm2. A generalized Hecht's equation was employed to analyze CCE in neutron irradiated 4H-SiC diode. The calculations nicely fit the CCE of 4H-SiC diode irradiated at different neutron fluences. According to the calculated results, the extracted electron μτ product (μτ)e and hole μτ product (μτ)h of the irradiated 4H-SiC diode are found to decrease by increasing the neutron fluence.

  5. Stellar Origin of 15N-rich Presolar SiC Grains of Type AB: Supernovae with Explosive Hydrogen Burning

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Nittler, Larry R.; Pignatari, Marco; O'D. Alexander, Conel M.; Wang, Jianhua

    2017-06-01

    We report C, N, and Si isotopic data for 59 highly 13C-enriched presolar submicron- to micron-sized SiC grains from the Murchison meteorite, including eight putative nova grains (PNGs) and 29 15N-rich (14N/15N ≤ solar) AB grains, and their Mg-Al, S, and Ca-Ti isotope data when available. These 37 grains are enriched in 13C, 15N, and 26Al with the PNGs showing more extreme enhancements. The 15N-rich AB grains show systematically higher 26Al and 30Si excesses than the 14N-rich AB grains. Thus, we propose to divide the AB grains into groups 1 (14N/15N < solar) and 2 (14N/15N ≥ solar). For the first time, we have obtained both S and Ti isotopic data for five AB1 grains and one PNG and found 32S and/or 50Ti enhancements. Interestingly, one AB1 grain had the largest 32S and 50Ti excesses, strongly suggesting a neutron-capture nucleosynthetic origin of the 32S excess and thus the initial presence of radiogenic 32Si (t 1/2 = 153 years). More importantly, we found that the 15N and 26Al excesses of AB1 grains form a trend that extends to the region in the N-Al isotope plot occupied by C2 grains, strongly indicating a common stellar origin for both AB1 and C2 grains. Comparison of supernova models with the AB1 and C2 grain data indicates that these grains came from supernovae that experienced H ingestion into the He/C zones of their progenitors.

  6. Framework stabilization of Si-rich LTA zeolite prepared in organic-free media.

    PubMed

    Conato, Marlon T; Oleksiak, Matthew D; Peter McGrail, B; Motkuri, Radha K; Rimer, Jeffrey D

    2015-01-07

    Zeolite HOU-2 (LTA type) is prepared with the highest silica content (Si/Al = 2.1) reported for Na-LTA zeolites without the use of an organic structure-directing agent. The rational design of Si-rich zeolites has the potential to improve their thermal stability for applications in catalysis, gas storage, and selective separations.

  7. Framework Stabilization of Si-Rich LTA Zeolite Prepared in Organic-Free Media

    SciTech Connect

    Conato, Marlon T.; Oleksiak, Matthew D.; McGrail, B. Peter; Motkuri, Radha K.; Rimer, Jeffrey D.

    2014-10-16

    Zeolite HOU-2 (LTA type) is prepared with the highest silica content (Si/Al = 2.1) reported for Na-LTA zeolites without the use of an organic structure-directing agent. The rational design of Si-rich zeolites has the potential to improve their thermal stability for applications in catalysis, gas storage, and selective separations.

  8. Diffraction of slow neutrons by holographic SiO{sub 2} nanoparticle-polymer composite gratings

    SciTech Connect

    Klepp, J.; Fally, M.; Pruner, C.; Tomita, Y.; Plonka-Spehr, C.; Geltenbort, P.; Ivanov, S.; Manzin, G.; Andersen, K. H.; Kohlbrecher, J.; Ellabban, M. A.

    2011-07-15

    Diffraction experiments with holographic gratings recorded in SiO{sub 2} nanoparticle-polymer composites have been carried out with slow neutrons. The influence of parameters such as nanoparticle concentration, grating thickness, and grating spacing on the neutron-optical properties of such materials has been tested. Decay of the grating structure along the sample depth due to disturbance of the recording process becomes an issue at grating thicknesses of about 100 microns and larger. This limits the achievable diffraction efficiency for neutrons. As a solution to this problem, the Pendelloesung interference effect in holographic gratings has been exploited to reach a diffraction efficiency of 83% for very cold neutrons.

  9. Neutron multiplicity distributions for neutron-rich projectile fragments at the NSCL

    NASA Astrophysics Data System (ADS)

    Mazza, Maria; Christ, Peter; Stephenson, Sharon; MoNA Collaboration

    2016-09-01

    Projectile fragmentation is one of the mechanisms used at nuclear science facilities around the world for the production of rare isotope beams. The study of the projectile fragmentation mechanism informs beam simulation codes, but relatively few studies of the fragmentation process have been done, especially at intermediate energies. The MoNA Collaboration used an 86 MeV/u 32Mg beam on a natural beryllium target at the National Superconducting Cyclotron Laboratory to produce neutron multiplicities distributions in coincidence with charged fragments for isotopes ranging from 29Na to 20F. Particle identification for the isotopes from fluorine, neon, and sodium will be presented, as well as preliminary neutron multiplicities distributions. Supported by NSF Grants 1203357, 1613429 and HHMI Grant 52007540.

  10. Fission and Properties of Neutron-Rich Nuclei - Proceedings of the Second International Conference

    NASA Astrophysics Data System (ADS)

    Hamilton, J. H.; Phillips, W. R.; Carter, H. K.

    The Table of Contents for the book is as follows: * Preface * Structure of Elementary Matter: Cold Valleys and Their Importance in Fission, Fusion and for Superheavy Nuclei * Tunnelling Phenomena in Nuclear Physics * Heavy Nuclei Studies Using Transfer Reactions * Isomeric Properties of Nuclei Near 78Ni * Investigation of Light Actinide Nuclei at Yale and Beyond * U-Projectile Fission at Relativistic Energies * Cluster Description of Cold Fission Modes in 252Cf * Neutron-pair Transfer Theory for Pear-shaped Ba Fission Fragments * New RMFA Parameters of Normal and Exotic Nuclei * Study of Fission Fragments from 12C+238U Reactions: Prompt and Delayed Spectroscopy * γ-Ray Angular Correlations in 252Cf and 248Cm Fission Fragments * Fragment Angular Momentum and Descent Dynamics in 252Cf Spontaneous Fission * The Experimental Investigation of Neutron-Rich Nuclei * High-Spin Structure of Some Odd-Z Nuclei with A ≈ 100 From Heavy-Ion Induced Fission * Coexistence of Symmetric and Asymmetric Nuclear Shapes and 10Be Ternary Fission * Octupole Effects in the Lanthanides * High Spin Structure of the 113-1l6Cd Isotopes Produced by Heavy-Ion Induced Fission Reaction * Temperature-Dependent Fission Barriers and Mass Distributions for 239U * Strength Distributions for Gamow Teller Transitions in Very Weakly Bound Systems * High Spin Fragmentation Spectroscopy * Search for a Four-Neutron Transfer From 8He to 4He * Microsecond Isomers in Fission Fragments in the Vicinity of the Doubly Magic 132Sn * Recent On-Line NMR/on Nuclear Magnetic Dipole Moments Near 132Sn: Meson Exchange Current Effects at the Shell Closure and Shell Model Treatment of Variation with Proton and Neutron Number * High-spin K-Isomers Beyond the Fusion Limit * High Energy Neutron Induced Fission: Charge Yield Distributions and Search and Spectroscopy of New Isomers * Hartree-Fock Mean-Field Models Using Separable Interactions * Variation of Fission Characteristics Over the Nuclear Chart * Investigation of

  11. How Rice (Oryza sativa L.) Responds to Elevated As under Different Si-Rich Soil Amendments.

    PubMed

    Teasley, William A; Limmer, Matthew A; Seyfferth, Angelia L

    2017-09-19

    Several strategies exist to mitigate As impacts on rice and each has its set of trade-offs with respect to yield, inorganic As content in grain, and CH4 emissions. The addition of Si to paddy soil can decrease As uptake by rice but how rice will respond to elevated As when soil is amended with Si-rich materials is unresolved. Here, we evaluated yield impacts and grain As content and speciation in rice exposed to elevated As in response to different Si-rich soil amendments including rice husk, rice husk ash, and CaSiO3 in a pot study. We found that As-induced yield losses were alleviated by Husk amendment, partially alleviated by Ash amendment, and not affected by CaSiO3 amendment. Furthermore, Husk was the only tested Si-amendment to significantly decrease grain As concentrations. Husk amendment was likely effective at decreasing grain As and improving yield because it provided more plant-available Si, particularly during the reproductive and ripening phases. Both Husk and Ash provided K, which also played a role in yield improvement. This study demonstrates that while Si-rich amendments can affect rice uptake of As, the kinetics of Si dissolution and nutrient availability can also affect As uptake and toxicity in rice.

  12. Effects of neutron irradiation on dimensional stability and on mechanical properties of SiC/SiC composites

    SciTech Connect

    Youngblood, G.E.; Henager, C.H. Jr.; Senor, J.

    1995-04-01

    The objective of this work is to assess the development and the performance of continuous fiber SiC{sub f}/SiC composites as a structural material for advanced fusion reactor application. The dimensional stability and some mechanical properties of two similar 2D 0-90{degree} weave SiC{sub f}/SiC composites made with Nacalon{trademark} ceramic-grade fiber were characterized and compared after neutron irradiation to those properties for {beta}-SiC. The major difference between these two composites was that one had a thin (150 nm) and the other a thick (1000 nm) graphite interface layer. The irradiation conditions consisted of relatively high doses (4.3 to 26 dpa-SiC) at high temperature (430-1200{degree}C).

  13. Charge-exchange modes of excitation in deformed neutron-rich nuclei

    SciTech Connect

    Yoshida, Kenichi

    2015-10-15

    Gamow-Teller (GT) mode of excitation and β-decay properties of deformed neutron-rich even-N Zr isotopes are investigated in a self-consistent Skyrme energy-density-functional approach, in which the Hartree-Fock-Bogoliubov equation is solved in the coordinate space and the proton-neutron Quasiparticle-RPA equation is solved in the quasiparticle basis. It is found that a stronger collectivity is generated for the GT giant resonance as an increase in the neutron number. Furthermore, we find that the T = 0 pairing enhances the low-lying GT strengths cooperatively with the T = 1 pairing correlation depending on the microscopic structure of the low-lying mode and the shell structure around the Fermi levels, and that the enhanced strength shortens the β-decay half-lives by at most an order of magnitude.

  14. Synthesis of neutron-rich transuranic nuclei in fissile spallation targets

    NASA Astrophysics Data System (ADS)

    Mishustin, Igor; Malyshkin, Yury; Pshenichnov, Igor; Greiner, Walter

    2015-04-01

    A possibility of synthesizing neutron-rich superheavy elements in spallation targets of Accelerator Driven Systems (ADS) is considered. A dedicated software called Nuclide Composition Dynamics (NuCoD) was developed to model the evolution of isotope composition in the targets during a long-time irradiation by intense proton and deuteron beams. Simulation results show that transuranic elements up to 249Bk can be produced in multiple neutron capture reactions in macroscopic quantities. However, the neutron flux achievable in a spallation target is still insufficient to overcome the so-called fermium gap. Further optimization of the target design, in particular, by including moderating material and covering it by a reflector could turn ADS into an alternative source of transuranic elements in addition to nuclear fission reactors.

  15. Impact of Triaxiality on the Structure of Neutron-Rich Rhenium Isotopes

    SciTech Connect

    Reed, M. W.; Lane, G. L.; Dracoulis, G. D.; Kondev, F. G.; Carpenter, M. P.; Chowdhury, P.; Hota, S. S.; Hughes, R. O.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J.; Palalani, N; Seweryniak, D.; Watanabe, H.; Zhu, S.; Jiang, W.G.; Xu, F.R.

    2016-01-10

    A number of 3-quasiparticle isomers have been found and characterised in the odd-mass, neutron-rich, Re-187, Re-189 and Re-191 nuclei, the latter being four neutrons beyond stability. The decay of the isomers populates states in the rotational bands built upon the 9/2(-)[514] Nilsson orbital. These bands exhibit a degree of signature splitting that increases with neutron number. This splitting taken together with measurements of the M1/E2 mixing ratios and with the changes observed in the energy of the gamma-vibrational band coupled to the 9/2(-)[514] state, suggests an increase in triaxiality, with gamma values of 5 degrees, 18 degrees and 25 degrees deduced in the framework of a particle-rotor model. (C) 2015 Published by Elsevier B.V.

  16. Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Bottoni, S.; Leoni, S.; Fornal, B.; Raabe, R.; Rusek, K.; Benzoni, G.; Bracco, A.; Crespi, F. C. L.; Morales, A. I.; Bednarczyk, P.; Cieplicka-Oryńczak, N.; Królas, W.; Maj, A.; Szpak, B.; Callens, M.; Bouma, J.; Elseviers, J.; De Witte, H.; Flavigny, F.; Orlandi, R.; Reiter, P.; Seidlitz, M.; Warr, N.; Siebeck, B.; Hellgartner, S.; Mücher, D.; Pakarinen, J.; Vermeulen, M.; Bauer, C.; Georgiev, G.; Janssens, R. V. F.; Balabanski, D.; Sferrazza, M.; Kowalska, M.; Rapisarda, E.; Voulot, D.; Lozano Benito, M.; Wenander, F.

    2015-08-01

    An exploratory experiment performed at REX-ISOLDE to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions 7Li(98Rb,α xn ) and 7Li(98Rb,t xn ) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be described well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.

  17. Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei

    DOE PAGES

    Bottoni, S.; Leoni, S.; Fornal, B.; ...

    2015-08-27

    An exploratory experiment performed at REX-ISOLDE to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions 7Li(98Rb,αxn) and 7Li(98Rb,txn) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be describedmore » well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.« less

  18. New data on excited states in very neutron rich nickel isotopes

    NASA Astrophysics Data System (ADS)

    Go, Shintaro; Grzywacz, Robert; Kolos, Karolina; Alshudifat, Mohammad; Taylor, Steven; Xiao, Yongchi; Gross, Carl; Batchelder, Jon; Rykaczewski, Krzysztof; Mazzocchi, Chiara; Korgul, Agnieszka; Lis, Aleksandra; Rajabari, Mustafa; Paulauskas, Stanley; Liddick, Sean; Prokop, Christopher; Baumann, Thomas; Ginter, Tom

    2015-10-01

    The vicinity of 78Ni still remains elusive. Several experimental studies show evidence that 78Ni is a doubly magic nucleus, but deformed phenomena have been reported in this region. Spectroscopic studies around the region are of interest to clarify the shell evolution toward 78Ni. Beta decay studies of neutron-rich Co isotopes have been performed at the NSCL. The isotopes were produced in the fragmentation of the 140 MeV/u 82Se beam. These isotopes were implanted in a planar Germanium DSSD. The measurement of gamma-rays using clover detectors revealed excited states in neutron-rich Ni isotopes at high excitation energies. Preliminary results will be presented.

  19. Nuclear structure in the neutron-rich doubly magic sup 78 Ni region

    SciTech Connect

    Hill, J.C.; Wohn, F.K.; Winger, J.A.; Warburton, E.K.; Gill, R.L.; Schuhmann, R.B.; Brookhaven National Lab., Upton, NY; Clark Univ., Worcester, MA )

    1989-01-01

    The magic numbers Z=28 and N=50 imply that very neutron-rich {sup 78}Ni, which has not yet been observed, is doubly magic. The {sup 78}Ni region was investigated by studying the N=50 isotones and neutron-rich Zn isotopes. Results on the level structure of {sup 83}As, {sup 74}Zn, and {sup 76}Zn populated in the decays of {sup 83}Ge, {sup 74}Cu, and {sup 76}Cu are presented. The parent nuclides were produced and mass separated using the TRISTAN facility on-line to the High-Flux Beam Reactor at Brookhaven. The systematics of the N=50 isotones and even-A Zn isotopes are discussed and compared with shell-model calculations involving active nucleons outside of a {sup 78}Ni and {sup 66}Ni core, respectively. The extent to which the {sup 78}Ni region can be considered doubly magic is assessed. 43 refs., 7 figs.

  20. Isospin effects on fragmentation in the asymmetric reactions induced by neutron-rich targets

    SciTech Connect

    Sharma, Arun

    2016-05-06

    To understand the isospin effects in terms of fragment’s yield in the asymmetric reactions induced by neutron-rich targets, we perform a theoretical study using isospin-dependent quantum molecular dynamics (IQMD) model. Simulations are carried out for reactions of {sup 16}O+Br{sup 80,84,92} and {sup 16}O+Ag{sup 108,113,122}. We envision that fragments’s yield in the asymmetric collisions induced by neutron-rich targets is better candidate to study isospin effects via symmetry energy and nucleon-nucleon (nn) cross-sections. Also, pronounced effects of symmetry energy and cross-sections can be found at lower and higher beam energies, respectively.

  1. Low-lying structure and shape evolution in neutron-rich Se isotopes

    NASA Astrophysics Data System (ADS)

    Chen, S.; Doornenbal, P.; Obertelli, A.; Rodríguez, T. R.; Authelet, G.; Baba, H.; Calvet, D.; Château, F.; Corsi, A.; Delbart, A.; Gheller, J.-M.; Giganon, A.; Gillibert, A.; Lapoux, V.; Motobayashi, T.; Niikura, M.; Paul, N.; Roussé, J.-Y.; Sakurai, H.; Santamaria, C.; Steppenbeck, D.; Taniuchi, R.; Uesaka, T.; Ando, T.; Arici, T.; Blazhev, A.; Browne, F.; Bruce, A. M.; Caroll, R.; Chung, L. X.; Cortés, M. L.; Dewald, M.; Ding, B.; Flavigny, F.; Franchoo, S.; Górska, M.; Gottardo, A.; Jungclaus, A.; Lee, J.; Lettmann, M.; Linh, B. D.; Liu, J.; Liu, Z.; Lizarazo, C.; Momiyama, S.; Moschner, K.; Nagamine, S.; Nakatsuka, N.; Nita, C. R.; Nobs, C.; Olivier, L.; Orlandi, R.; Patel, Z.; Podolyak, Zs.; Rudigier, M.; Saito, T.; Shand, C.; Söderström, P.-A.; Stefan, I.; Vaquero, V.; Werner, V.; Wimmer, K.; Xu, Z.

    2017-04-01

    Neutron-rich 88,90,92,94Se isotopes were studied via in-beam γ -ray spectroscopy after nucleon removal reactions at intermediate energies at the Radioactive Isotope Beam Factory. Based on γ -γ coincidence analysis, low-lying excitation level schemes are proposed for these nuclei, including the 21+, 41+ states and 22+ states at remarkably low energies. The low-lying 22+ states, along with other features, indicate triaxiality in these nuclei. The experimental results are in good overall agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, which suggests both triaxial degree of freedom and shape coexistence playing important roles in the description of intrinsic deformations in neutron-rich Se isotopes.

  2. Charge Radius Changes Of Even-even Neutron-Rich Tellurium Isotopes

    SciTech Connect

    Sifi, R.; Le Blanc, F.; Barre, N.; Ducourtieux, M.; Essabaa, S.; Lau, C.; Oms, J.; Roussiere, B.; Sauvage, J.; Cabaret, L.; Pinard, J.; Crawford, J.; Lee, J. K. P.; Genevey, J.; Huber, G.; Kowalska, M.; Seliverstov, M.; Le Scornet, G.; Stroke, H.

    2006-04-26

    Laser spectroscopy based on resonant ionization of laser-desorbed atoms has been used to study the neutron-rich tellurium isotopes with the COMPLIS facility at ISOLDE-CERN. The isotope shift and the hyperfine structure of several neutron-rich Te isotopes: 120-136Te and 123m-133mTe have been measured. From the hyperfine structure and the isotope shift we can extract the magnetic and quadrupole moments and the change in the mean square charge radius respectively. The mean square charge radii of the even-even isotopes have been deduced and their comparison with the known data for the other elements near Z=50 is presented. The experimental {delta} is compared with that obtained from the relativistic mean field calculations.

  3. Nucleon effective E-mass in neutron-rich matter from the Migdal–Luttinger jump

    DOE PAGES

    Cai, Bao-Jun; Li, Bao-An

    2016-03-25

    The well-known Migdal-Luttinger theorem states that the jump of the single-nucleon momentum distribution at the Fermi surface is equal to the inverse of the nucleon effective E-mass. Recent experiments studying short-range correlations (SRC) in nuclei using electron-nucleus scatterings at the Jefferson National Laboratory (JLAB) together with model calculations constrained significantly the Migdal-Luttinger jump at saturation density of nuclear matter. We show that the corresponding nucleon effective E-mass is consequently constrained to M-0(*,E)/M approximate to 2.22 +/- 0.35 in symmetric nuclear matter (SNM) and the E-mass of neutrons is smaller than that of protons in neutron-rich matter. Moreover, the average depletionmore » of the nucleon Fermi sea increases (decreases) approximately linearly with the isospin asymmetry delta according to kappa(p/n) approximate to 0.21 +/- 0.06 +/- (0.19 +/- 0.08)delta for protons (neutrons). These results will help improve our knowledge about the space-time non-locality of the single-nucleon potential in neutron-rich nucleonic matter Useful in both nuclear physics and astrophysics. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).« less

  4. Dipole response in neutron-rich nuclei with new Skyrme interactions

    NASA Astrophysics Data System (ADS)

    Zheng, H.; Burrello, S.; Colonna, M.; Baran, V.

    2016-07-01

    We investigate the isoscalar and isovector E 1 response of neutron-rich nuclei, within a semiclassical transport model employing effective interactions for the nuclear mean field. In particular, we adopt the recently introduced SAMi-J Skyrme interactions, whose parameters are specifically tuned to improve the description of spin-isospin properties of nuclei. Our analysis evidences a relevant degree of isoscalar-isovector mixing of the collective excitations developing in neutron-rich systems. Focusing on the low-lying strength emerging in the isovector response, we show that this energy region essentially corresponds to the excitation of isoscalar-like modes, which also contribute to the isovector response owing to their mixed character. Considering effective interactions which mostly differ in the isovector channels, we observe that these mixing effects increase with the slope L of the symmetry energy at saturation density, leading to a larger strength in the low-energy region of the isovector response. This result appears connected to the increase, with L , of the neutron-proton asymmetry at the surface of the considered nuclei, i.e., to the neutron skin thickness.

  5. Production of neutron-rich nuclei with Z =60 -73 in reactions induced by Xe isotopes

    NASA Astrophysics Data System (ADS)

    Zhu, Long; Zhang, Feng-Shou; Wen, Pei-Wei; Su, Jun; Xie, Wen-Jie

    2017-08-01

    The multinucleon transfer reactions 124,136,144Xe +238U , Xe,144136+160Gd , Xe,144136+170Er , and Xe,144136+186W are investigated within the framework of the dinuclear system model. The charge equilibration effects on the production cross sections of exotic nuclei are studied. The neutron-deficient projectile 124Xe is favorable to produce transtarget neutron-deficient nuclei, while Xe,144136 shows great advantages of cross sections for producing neutron-rich nuclei in the proton pick-up channel. Furthermore, the influence of entrance angular momentum on the charge equilibration process is investigated. It is found that in a low angular momentum channel the more profound reconstruction of initial nuclei is noticed rather than peripheral collisions. We predict the production cross sections of several neutron-rich nuclei in the reactions Xe,144136+160Gd , Xe,144136+170Er , and Xe,144136+186W . It is found that many unknown nuclei can be produced at the level of μ b to mb.

  6. Response of a Si-diode-based device to fast neutrons.

    PubMed

    Spurný, Frantisek

    2005-02-01

    Semiconductor devices based on a Si-detector are frequently used for charged particle's detection; one application being in the investigation of cosmic radiation fields. From the spectra of energy deposition events in such devices, the total energy deposited by the radiation in silicon can be derived. This contribution presents the results of studies concerning the response of this type of detector to fast neutrons. First, the spectrum of energy deposition was established in fast neutron radiation fields with average energies from 0.5 to 50 MeV. It was found that these spectra vary significantly with the neutron energy. The comparison with the spectra registered in photon beams permitted an estimation of the part of energy deposited that could be attributed to neutrons. It was found that this part increases rapidly with neutron energy. The possibilities to use this type of detector for neutron detection and dosimetry for radiation protection are analysed and discussed.

  7. Structure of Light Neutron-rich Nuclei Studied with Transfer Reactions

    SciTech Connect

    Wuosmaa, A. H.

    2015-01-01

    Transfer reactions have been used for many years to understand the shell structure of nuclei. Recent studies with rare-isotope beams extend this work and make it possible to probe the evolution of shell structure far beyond the valley of stability, requiring measurements in inverse kinematics. We present a novel technical approach to measurements in inverse kinematics, and apply this method to different transfer reactions, each of which probes different properties of light, neutron-rich nuclei.

  8. Characterizing the effect of neutron-richness on the reaction dynamics in chromium and tungsten systems

    NASA Astrophysics Data System (ADS)

    Hammerton, Kalee Michelle

    Superheavy elements are primarily formed through heavy-ion fusion reactions [1, 2, 3]. Formation of a fully equilibrated compound nucleus is a critical step in the heavy-ion fusion reaction mechanism but can be hindered by orders of magnitude by quasifission, a process in which the dinuclear system breaks apart prior to full equilibration [1, 4, 5, 6, 7, 8]. To provide a complete description of heavy-ion fusion it is important to characterize the quasifission process. The interplay between the fusion-fission and quasifission reaction channels was explored by measuring mass distributions in eight different combinations of Cr +W reactions, with varying neutron-richness, at the Australian National University. The reactions were measured in two energy regimes: one at center-of-mass energies (Ec.m.) 13% above the Bass interaction barrier [9] and one at 52.0 MeV of excitation energy in the compound nucleus (E*CN). For the systems measured at the higher energies at Ec.m./ V Bass = 1.13 the dependence on the neutron-richness is clear and an increase in the neutron-richness of the entrance channel decreases the likelihood of quasifission [10]. However, for the reactions at E*CN = 52.0 MeV, the dependence is less clear and additional factors are shown to play a vital role, especially the influence of deformation on the effective fusion barrier. The present work demonstrates that quasifission is an important process in competition with fusion in reactions with intermediate mass projectiles, particularly with more neutron-rich systems.

  9. Reflection Asymmetric Shapes in the Neutron-Rich 140,143Ba Isotopes

    NASA Astrophysics Data System (ADS)

    Zhu Sheng-jiang (S, J. Zhu; Wang, Mu-ge; J, H. Hamilton; A, V. Ramayya; B, R. S. Babu; W, C. Ma; Long, Gui-lu; Deng, Jing-kang; Zhu, Ling-yan; Li, Ming; T, N. Ginter; J, Komicki; J, D. Cole; R, Aryaeinejad; Y, K. Dardenne; M, W. Drigert; J, O. Rasmussen; Ts, Yu Oganessian; M, A. Stoyer; S, Y. Chu; K, E. Gregorich; M, F. Mohar; S, G. Prussin; I, Y. Lee; N, R. Johnson; F, K. McGowan

    1997-08-01

    Level schemes for the neutron-rich 140,143Ba nuclei have been determined by study of prompt γ-rays in spontaneous fission of 252Cf. The level pattern and enhanced E1 transitions between π = + and π = - bands show reflection asymmetric shapes with simplex quantum number s = +1 in 140Ba and s = ±i in 143Ba, respectively. The octupole deformation stability with spin variation has been discussed.

  10. Structure of neutron-rich nuclei around the N = 50 shell-gap closure

    NASA Astrophysics Data System (ADS)

    Faul, T.; Duchêne, G.; Thomas, J.-C.; Nowacki, F.; Huyse, M.; Van Duppen, P.

    2010-04-01

    The structure of neutron-rich nuclei in the vicinity of 78Ni have been investigated via the β-decay of 71,73,75Cu isotopes (ISOLDE, CERN). Experimental results have been compared with shell-model calculations performed with the ANTOINE code using a large (2p3/21f5/22p1/21g9/2) valence space and a 56/28Ni28 core.

  11. Structural and optical characterization of pure Si-rich nitride thin films

    PubMed Central

    2013-01-01

    The specific dependence of the Si content on the structural and optical properties of O- and H-free Si-rich nitride (SiNx>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) Si-N stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiNx<0.8. Besides, quantum confinement effects on the Raman peaks of crystalline Si-np, which were observed by HRTEM, were evidenced for Si-np average sizes between 3 and 6 nm. A contrario, visible photoluminescence (PL) was only observed for SiNx>0.9, demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiNx>0.9 could be then due to a size effect of Si-np but having an amorphous phase. PMID:23324447

  12. Production of very neutron-rich nuclei with a {sup 76}Ge beam

    SciTech Connect

    Tarasov, O. B.; Portillo, M.; Baumann, T.; Bazin, D.; Ginter, T. N.; Hausmann, M.; Pereira, J.; Stolz, A.; Amthor, A. M.; Gade, A.; Nettleton, A.; Sherrill, B. M.; Thoennessen, M.; Inabe, N.; Kubo, T.; Morrissey, D. J.

    2009-09-15

    Production cross sections for neutron-rich nuclei from the fragmentation of a {sup 76}Ge beam at 132 MeV/u were measured. The longitudinal momentum distributions of 34 neutron-rich isotopes of elements 13{<=}Z{<=}27 were scanned using a novel experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei, including 15 isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 17{<=}Z{<=}25 ({sup 50}Cl, {sup 53}Ar, {sup 55,56}K, {sup 57,58}Ca, {sup 59,60,61}Sc, {sup 62,63}Ti, {sup 65,66}V, {sup 68}Cr, and {sup 70}Mn). A one-body Q{sub g} systematics is used to describe the production cross sections based on thermal evaporation from excited prefragments. Some of the fragments near {sup 58}Ca show anomalously large production cross sections.

  13. A Si-PIN-stack detector for 14 MeV pulsed neutrons measurement

    NASA Astrophysics Data System (ADS)

    Zhang, Xianpeng; Ouyang, Xiaoping; Chen, Yanli; Zhang, Zhongbing; Tian, Geng; Chen, Liang; Liu, Jinliang

    2012-11-01

    We have developed a high-sensitivity fast neutron stack detector for use in the current mode by introducing a readout circuit that is capable of operating with a single detector's time response, while its neutron sensitivity, statistics, and n-γ sensitivity ratio are greatly improved compared to the single detector. The neutron stack detector sandwiches large-area Si-PIN semiconductor detectors and 2-mm-thick polyethylene disks used as the n-p converter and sensitivity enhancement medium. A neutron stack detector composed of 9 ∅80 mm×0.8 mm Si-PIN detectors has been built and used to measure a pulsed 14 MeV neutron flux of dense plasma focus devices (DPF). We have acquired its sensitivity to 14 MeV neutrons and 1.25 MeV γ-rays, the n-γ sensitivity ratio, and time response experimentally or theoretically. The study shows that this neutron stack detector can be applied for the diagnosis of DPF and neutron tubes. The results of this investigation also suggest a general model for developing high-sensitivity detectors based on a single radiation detector of another type.

  14. Recent progress in the studies of neutron-rich and high-$Z$ systems within the covariant density functional theory

    SciTech Connect

    Afanasjev, Anatoli V.; Agbemava, S. E.; Ray, D.; Ring, P.

    2017-01-01

    Here, the analysis of statistical and systematic uncertainties and their propagation to nuclear extremes has been performed. Two extremes of nuclear landscape (neutron-rich nuclei and superheavy nuclei) have been investigated. For the first extreme, we focus on the ground state properties. For the second extreme, we pay a particular attention to theoretical uncertainties in the description of fission barriers of superheavy nuclei and their evolution on going to neutron-rich nuclei.

  15. Proton beam characterisation of a prototype thin-tile plastic scintillator detector with SiPM readout for use in fast-neutron tracker

    NASA Astrophysics Data System (ADS)

    Preston, R.; Jakubek, J.; Prokopovich, D.; Uher, J.

    2012-02-01

    We present details of the construction and characterisation of a prototype thin-tile plastic scintillation detector for use in a multi-layer Fast Neutron Tracker. Scintillation light is read out using solid-state silicon photomultiplier detectors (SiPMs). The Tracker consists of alternating scintillator and Timepix detector layers. The scintillator tile provides a hydrogen-rich target, in which impinging fast neutrons produce recoil protons. The energies lost by protons in the plastic scintillator are measured and recoil protons exiting the scintillator are tracked in the Timepix detector. The combination of signals from the scintillator and Timepix provides information to reconstruct the energy or direction of the impinging neutron, using calculations based on the kinematics of the elastic neutron scattering. Three prototype scintillation detectors were constructed, using either a pair of 3 × 3 mm sensitive area SPMMicro3035 SiPMs from SensL or a pair of MAPD-3n SiPMs from Zecotek. The detector performances were characterised using a mono-energetic proton beam. An absolute energy calibration was measured at 3, 4 and 5 MeV proton energies with good linearity. The best measured energy resolution was 29.8% at 5 MeV. Spatial uniformity was assessed by measuring the response across the detector face. Finally, the tile detector's ability to provide a trigger for Timepix acquisition in the stack configuration was demonstrated for single and double neutron recoil events using a DT neutron source. The SiPM-based design was found to be well-suited for the application of the multi-layer fast neutron tracker.

  16. Allowed and unique first-forbidden stellar electron emission rates of neutron-rich copper isotopes

    NASA Astrophysics Data System (ADS)

    Majid, Muhammad; Nabi, Jameel-Un; Daraz, Gul

    2017-06-01

    The allowed charge-changing transitions are the most common weak interaction processes of spin-isospin form that play a crucial role in several nuclear/astrophysical processes. The first-forbidden (FF) transition becomes important, in the circumstances where allowed Gamow-Teller (GT) transitions are unfavored, specifically for neutron-rich nuclei due to phase space considerations. In this paper deformed proton-neutron quasi-particle random phase approximation (pn-QRPA) model is applied, for the first time, for the estimation of allowed GT and unique first-forbidden (U1F) transitions (|Δ J| = 2) of neutron rich copper isotopes in mass range 72 ≤ A ≤ 82 under stellar conditions. We compared our computed terrestrial β-decay half-life values with previous calculations and experimental results. It was concluded that the pn-QRPA calculation is in good accordance with measured data. Our study suggests that the addition of rank (0 and 1) operators in FF transitions can further improve the comparison which remain unattended at this stage. The deformed pn-QRPA model was employed for the estimation of GT and U1F stellar electron emission (β--decay) rates over wide range of stellar temperature (0.01 GK-30 GK) and density (10-10^{11} g/cm3) domains for astrophysical applications. Our study shows that, in high density and low temperature regions, the contribution of U1F rates to total electron emission rates of neutron-rich copper nuclei is negligible.

  17. Determination of europium content in Li2SiO3(Eu) by neutron activation analysis using Am-Be neutron source.

    PubMed

    Naik, Yeshwant; Tapase, Anant Shamrao; Mhatre, Amol; Datrik, Chandrashekhar; Tawade, Nilesh; Kumar, Umesh; Naik, Haladhara

    2016-12-01

    Circulardiscs of Li2SiO3 doped with europium were prepared and a new activation procedure for the neutron dose estimation in a breeder blanket of fusion reactor is described. The amount of europium in the disc was determined by neutron activation analysis (NAA) using an isotopic neutron source. The average neutron absorption cross section for the reaction was calculated using neutron distribution of the Am-Be source and available neutron absorption cross section data for the (151)Eu(n,γ)(152m)Eu reaction, which was used for estimation of europium in the pallet. The cross section of the elements varies with neutron energy, and the flux of the neutrons in each energy range seen by the nuclei under investigation also varies. Neutron distribution spectrum of the Am-Be source was worked out prior to NAA and the effective fractional flux for the nuclear reaction considered for the flux estimation was also determined.

  18. Spectroscopy of 36Mg: interplay of normal and intruder configurations at the neutron-rich boundary of the "island of inversion".

    PubMed

    Gade, A; Adrich, P; Bazin, D; Bowen, M D; Brown, B A; Campbell, C M; Cook, J M; Ettenauer, S; Glasmacher, T; Kemper, K W; McDaniel, S; Obertelli, A; Otsuka, T; Ratkiewicz, A; Siwek, K; Terry, J R; Tostevin, J A; Utsuno, Y; Weisshaar, D

    2007-08-17

    We report on the first spectroscopy study of the very neutron-rich nucleus (36)(12)Mg24 using the direct two-proton knockout reaction 9Be(38Si,36Mg+gamma)X at 83 MeV/nucleon. The energy of the first excited 2+ state of 36Mg, E(2+(1)=660(6) keV, was measured. The magnitude of the partial cross sections to the ground state and the 2+(1) state is indicative of strong intruder admixtures in the lowest-lying states as suggested by Monte Carlo shell-model calculations.

  19. Direct Mass Measurements of Fluorine Through Chlorine Neutron-Rich Nuclei.

    NASA Astrophysics Data System (ADS)

    Zhou, Xiao-Gang

    1991-02-01

    Mass measurements have been made of the neutron -rich isotopes of fluorine through chlorine at the Los Alamos Meson Physics Facility. The masses of 34 neutron-rich isotopes are reported. Ten of these measurements represent first-time mass determinations of these species. The nuclei of interest are produced in fragmentation reaction. A transport line is used to capture a small fraction of the ions and transport them into the time-of-flight isochronous (TOFI) spectrometer. The TOFI spectrometer is isochronously designed, such that the transit time of the ion passing through the spectrometer is independent of the ion velocity, and only depends on its mass-to-charge ratio. A gas ionization counter located at the exit of the TOFI spectrometer is used to identify the ion atomic number and to measure the total energy. Three fast timing detectors are placed in the middle of the transport line, entrance, and exit of the TOFI spectrometer to determine the ion velocity and the M/Q ratio. We calculate each ion's charge state by using velocity, total energy, and M/Q ratio. With A, Z, Q assigned to each ion, we fit M/Q linearly to the known masses to obtain a high precision M/Q calibration. The masses of unknown nuclei are calculated through the M/Q calibration. The final results are generated by taking a weighted average for all runs and charge states. These results have confirmed the anomaly of enhanced binding found in neutron-rich Na and Mg isotopes and also suggest that the binding energies for those nuclei are less than that originally reported. The masses of several F through Al isotopes are compared with the shell model calculations. These comparisons demonstrate that the anomaly can be understood in terms of one or two neutron promotions from the sd shell to the fp shell. The results for some neutron-rich isotopes of P through Cl are compared to several mass models and good agreement in all cases is found.

  20. Microscopic dynamics simulations of heavy-ion fusion reactions induced by neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Ou, Li; Zhang, Yingxun; Li, Zhuxia

    2014-06-01

    The heavy-ion fusion reactions induced by neutron-rich nuclei are investigated with the improved quantum molecular dynamics (ImQMD) model. With a subtle consideration of the neutron skin thickness of nuclei and the symmetry potential, the stability of nuclei and the fusion excitation functions of heavy-ion fusion reactions O16 + Ge76, O16 + Sm154, Ca40 + Zr96, and Sn132 + Ca40 are systematically studied. The fusion cross sections of these reactions at energies around the Coulomb barrier can be well reproduced by using the ImQMD model. The corresponding slope parameter of the symmetry energy adopted in the calculations is L ≈78 MeV and the surface energy coefficient is gsur=18±1.5 MeV fm2. In addition, it is found that the surface-symmetry term significantly influences the fusion cross sections of neutron-rich fusion systems. For sub-barrier fusion, the dynamical fluctuations in the densities of the reaction partners and the enhanced surface diffuseness at neck side result in the lowering of the fusion barrier.

  1. Decay Pattern of Pygmy States Observed in Neutron-Rich Ne26

    NASA Astrophysics Data System (ADS)

    Gibelin, J.; Beaumel, D.; Motobayashi, T.; Blumenfeld, Y.; Aoi, N.; Baba, H.; Elekes, Z.; Fortier, S.; Frascaria, N.; Fukuda, N.; Gomi, T.; Ishikawa, K.; Kondo, Y.; Kubo, T.; Lima, V.; Nakamura, T.; Saito, A.; Satou, Y.; Scarpaci, J.-A.; Takeshita, E.; Takeuchi, S.; Teranishi, T.; Togano, Y.; Vinodkumar, A. M.; Yanagisawa, Y.; Yoshida, K.

    2008-11-01

    Coulomb excitation of the exotic neutron-rich nucleus Ne26 on a Pb208 target was measured at 58MeV/u in order to search for low-lying E1 strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the Ne25+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of B(E1)=0.49±0.16e2fm2 is deduced, corresponding to 4.9±1.6% of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.

  2. MCNPX Monte Carlo simulations of particle transport in SiC semiconductor detectors of fast neutrons

    NASA Astrophysics Data System (ADS)

    Sedlačková, K.; Zat'ko, B.; Šagátová, A.; Pavlovič, M.; Nečas, V.; Stacho, M.

    2014-05-01

    The aim of this paper was to investigate particle transport properties of a fast neutron detector based on silicon carbide. MCNPX (Monte Carlo N-Particle eXtended) code was used in our study because it allows seamless particle transport, thus not only interacting neutrons can be inspected but also secondary particles can be banked for subsequent transport. Modelling of the fast-neutron response of a SiC detector was carried out for fast neutrons produced by 239Pu-Be source with the mean energy of about 4.3 MeV. Using the MCNPX code, the following quantities have been calculated: secondary particle flux densities, reaction rates of elastic/inelastic scattering and other nuclear reactions, distribution of residual ions, deposited energy and energy distribution of pulses. The values of reaction rates calculated for different types of reactions and resulting energy deposition values showed that the incident neutrons transfer part of the carried energy predominantly via elastic scattering on silicon and carbon atoms. Other fast-neutron induced reactions include inelastic scattering and nuclear reactions followed by production of α-particles and protons. Silicon and carbon recoil atoms, α-particles and protons are charged particles which contribute to the detector response. It was demonstrated that although the bare SiC material can register fast neutrons directly, its detection efficiency can be enlarged if it is covered by an appropriate conversion layer. Comparison of the simulation results with experimental data was successfully accomplished.

  3. Searching for isovector signatures in the neutron-rich oxygen and calcium isotopes

    NASA Astrophysics Data System (ADS)

    Chen, Wei-Chia; Piekarewicz, Jorge

    2015-04-01

    We search for potential isovector signatures in the neutron-rich oxygen and calcium isotopes within the framework of a relativistic mean-field theory with an exact treatment of pairing correlations. To probe the isovector sector we calibrate a few relativistic density functionals using the same isoscalar constraints but with one differing isovector assumption. It is found that under certain conditions, the isotopic chain in oxygen can be made to terminate at the experimentally observed 24 O isotope. In the case of the calcium isotopes, the drip line is predicted to be reached beyond 60 Ca. To produce such behavior, the resulting symmetry energy must be soft, with predicted values for the symmetry energy and its slope at saturation density being J = (30 . 92 +/- 0 . 47) MeV and L = (51 . 0 +/- 1 . 5) MeV, respectively. As a consequence, the neutron-skin thickness of 208 Pb is rather small: Rskin208 = (0 . 161 +/- 0 . 011) fm. This same model, labelled FSUGarnet , predicts R1 . 4 = (13 . 1 +/- 0 . 1) km for the radius of a ``canonical'' 1.4M⊙ neutron star, yet is also able to support a two-solar-mass neutron star.

  4. Pygmy dipole mode in deformed neutron-rich Mg isotopes close to the drip line

    NASA Astrophysics Data System (ADS)

    Yoshida, Kenichi

    2009-10-01

    We investigate the microscopic structure of the low-lying isovector-dipole excitation mode in neutron-rich Mg36,38,40 close to the drip line by means of the deformed quasiparticle random-phase approximation employing the Skyrme and the local pairing energy-density functionals. It is found that the low-lying bump structure above the neutron emission-threshold energy develops when the drip line is approached, and that the isovector dipole strength at Ex<10 MeV exhausts about 6.0% of the classical Thomas-Reiche-Kuhn dipole sum rule in Mg40. We obtained the collective dipole modes at around 8-10 MeV in Mg isotopes, that consist of many two-quasiparticle excitations of the neutron. The transition density clearly shows an oscillation of the neutron skin against the isoscalar core. We found significant coupling effects between the dipole and octupole excitation modes due to the nuclear deformation. It is also found that the responses for the compressional dipole and isoscalar octupole excitations are much enhanced in the lower energy region.

  5. Optimization of the optical properties of Er-doped Si-rich SiO 2/SiO 2 multilayers obtained by reactive magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Gourbilleau, F.; Dufour, C.; Madelon, R.; Rizk, R.

    2006-05-01

    The effects of annealing time and of Si nanocluster (Si-nc) size on the coupling rate to Er ions were investigated through studies made on multilayers (MLs) consisting in about 20 periods of Er-doped Si-rich SiO 2/SiO 2. These MLs were deposited by reactive magnetron sputtering at 650 °C and subsequently annealed at 900 °C. A steep increase of the PL emission is observed for short annealing time while a trend of some saturation occurs for longer treatment time. Besides, the Er lifetime continuously increases with the annealing time. For Si-rich layer thickness or Si-nc larger than about 5 nm, the rate of energy transfer is lowered because of the weak confinement of carriers and the loss of resonant excitation of Er through the upper levels (second, third, etc.). The latter is liable to prevent the energy back transfer process, while the weak confinement reduces strongly the probability of no phonon radiative recombination that governs the transfer excitation rate from Si-nc to Er ions.

  6. Single-neutron excitations in neutron-rich Ge83 and Se85

    NASA Astrophysics Data System (ADS)

    Thomas, J. S.; Arbanas, G.; Bardayan, D. W.; Blackmon, J. C.; Cizewski, J. A.; Dean, D. J.; Fitzgerald, R. P.; Greife, U.; Gross, C. J.; Johnson, M. S.; Jones, K. L.; Kozub, R. L.; Liang, J. F.; Livesay, R. J.; Ma, Z.; Moazen, B. H.; Nesaraja, C. D.; Shapira, D.; Smith, M. S.; Visser, D. W.

    2007-10-01

    The H2(Ge82,p)Ge83 and H2(Se84,p)Se85 reactions were studied with radioactive beams of Ge82 and Se84 at beam energies of Ebeam=330 and 380 MeV, respectively. Excitation energies, proton angular distributions, and asymptotic normalization coefficients have been determined for the lowest lying states of Ge83 and Se85. Spectroscopic factors have also been extracted under normal assumptions of the bound-state potential properties in the distorted waves Born approximation analysis. However, the peripheral character of the measurements leads to large uncertainties in this extraction. Shell-model calculations have been performed in the region above Ni78, comparing the single-particle properties of the even-Z,N=51 nuclei up to Zr91 and including Ge83 and Se85. Direct-semidirect neutron capture calculations to Ge83 and Se85 have also been performed using the spectroscopic input from these (d,p) reaction measurements.

  7. Isomers of Pm Isotopes on the Neutron-Rich Frontier of the Deformed Z ~ 60 Region

    NASA Astrophysics Data System (ADS)

    Yokoyama, Rin; Ideguchi, Eiji; Simpson, Gary; Tanaka, Mana; Nishimura, Shunji; Doornnbal, Pieter; Söderström, Pär-Anders; Lorusso, Giuseppe; Xu, Zhengyu; Wu, Jin; Sumikama, Toshiyuki; Aoi, Nori; Baba, Hidetada; Bello, Frank; Browne, Frank; Daido, Rie; Fang, Yifan; Fukuda, Naoki; Gey, Guillaume; Go, Shintaro; Inabe, Naohiro; Isobe, Tadaaki; Kameda, Daisuke; Kobayashi, Kazuma; Kobayashi, Motoki; Komatsubara, Tetsuro; Kubo, Toshiyuki; Kuti, Istvan; Li, Zhihuan; Matsushita, Masafumi; Michimasa, Shin'ichiro; Moon, Chang-Bum; Nishibata, Hiroki; Nishizuka, Ippei; Odahara, Atsuko; Patel, Zena; Rice, Simon; Sahin, Eda; Sinclair, Laura; Suzuki, Hiroshi; Takeda, Hiroyuki; Taprogge, Jan; Vajta, Zsolt; Watanabe, Hiroshi; Yagi, Ayumi

    Neutron-rich Pm (Z = 61) isotopes were studied by delayed γ-ray spectroscopy at RIBF, Riken Nishina Center using the in-flight fission of 345 MeV/u 238U beam. An array of cluster-type Ge detectors, EURICA, was used to measure the delayed γ rays from stopped ions. Isomers were observed in 158Pm, 159Pm and 161Pm with half-lives of >16, 4.64(21), and 0.88(10) µs respectively. Preliminary level schemes for 159Pm and 161Pm were constructed in this study. They have ground-state bands similar to those of 153Pm and 155Pm. The isomeric state of 161Pm could be interpreted as a two quasi-particle excitation of neutrons with configuration of ν 7/2[633] otimes ν 1/2[521] as other Kπ = 4 - isomers observed systematically in other N = 100 isotones.

  8. Nuclear shape transitions in neutron-rich medium-mass nuclei

    SciTech Connect

    Sarriguren, P.; Rodriguez-Guzman, R.; Robledo, L. M.

    2012-10-20

    We study the isotopic evolution of the ground-state nuclear shapes in neutron-rich Kr, Rb, Sr, Y, Zr, Nb, and Mo isotopic chains. Both even-even and odd-A nuclei are included in the analysis. For the latter we also study the systematics of their one-quasiparticle low-lying configurations. The theoretical approach is based on a selfconsistent Hartree-Fock-Bogoliubov formalism with finite range Gogny energy density functionals. Neutron separation energies, charge radii, and the spin-parity of the ground states are calculated and compared with available data. Shape-transition signatures are identified around N= 60 isotones as discontinuities in both charge radii isotopic shifts and spin-parities of the ground states. The nuclear deformation including triaxiality is shown to play a relevant role in the understanding of the bulk and spectroscopic features of the ground and low-lying one-quasiparticle states.

  9. Promises and Challenges of Two-Step Targets for Production of Neutron-rich RIBs

    SciTech Connect

    Talbert, W.L.; Drake, D.M.; Hsu, H.-H.; Wilson, M.T.

    2003-08-26

    Development of a prototype two-step target to produce neutron-rich RIBs is presented, with particular emphasis on thermal analysis under high-power operation. The two-step target is an attractive concept for production of fission-product activities without interference by high-energy spallation reactions which occur in direct production targets. In this concept, a high-energy production beam interacts with a primary target of refractory metal, depositing beam energy in the primary target and producing low-energy neutrons that cause fissions in a surrounding secondary target of mixed UC2 and excess C. Thermal analysis of the composite target presents challenges in cooling the primary target while maintaining the secondary target at temperatures suitable for release of the fission products. The effects of fission energy deposition in the secondary target are discussed, along with the complexities resulting from the thermally insulating character of the secondary target material.

  10. Identification of a quasiparticle band in very neutron-rich {sup 104}Zr

    SciTech Connect

    Yeoh, E. Y.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Xiao, Z. G.; Zhu, S. J.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Liu, Y. X.; Sun, Y.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.

    2010-08-15

    The high spin levels of a very neutron-rich {sup 104}Zr nucleus have been reinvestigated by measuring the prompt {gamma} rays in the spontaneous fission of {sup 252}Cf. The ground-state band has been confirmed. A new sideband has been identified with a band-head energy at 1928.7 keV. The projected shell model is employed to investigate the band structure of {sup 104}Zr. The results of calculated levels are in good agreement with the experimental data, and suggest that the new band in {sup 104}Zr may be based on the neutron {nu}5/2{sup -}[532] x {nu}3/2{sup +}[411] configuration.

  11. β and β -n decay of the neutron-rich

    NASA Astrophysics Data System (ADS)

    Korgul, A.; Rykaczewski, K. P.; Grzywacz, R. K.; Bingham, C. R.; Brewer, N. T.; Gross, C. J.; Ciemny, A. A.; Jost, C.; Karny, M.; Madurga, M.; Mazzocchi, C.; Mendez, A. J.; Miernik, K.; Miller, D.; Padgett, S.; Paulauskas, S. V.; Piersa, M.; Stracener, D. W.; Stryjczyk, M.; Wolińska-Cichocka, M.; Zganjar, E. F.

    2016-06-01

    The β -decay properties of the very neutron-rich neutron emission was observed. The shell-model calculations and apparent β transition intensities were used to guide the spin assignment to the

  12. Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields

    SciTech Connect

    Nakada, H.

    2010-05-15

    Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the spherical Hartree-Fock calculations with semi-realistic NN interactions. Specific ingredients of the effective interaction, particularly the tensor force, often play a key role in the Z dependence of the neutron shell structure. Such examples are found in N=32 and N=40; N=32 becomes magic or submagic in {sup 52}Ca while its magicity is broken in {sup 60}Ni, and N=40 is submagic (though not magic) in {sup 68}Ni but not in {sup 60}Ca. Comments are given on the doubly magic nature of {sup 78}Ni. We point out that the loose binding can lead to a submagic number N=58 in {sup 86}Ni, assisted by the weak pair coupling.

  13. Proton-hole states in the N=30 neutron-rich {sup 49}K isotope.

    SciTech Connect

    Broda, R.; Wrzesinski, J.; Gadea, A.; Marginean, N.; Fornal, B.; Carpenter, M. P.; Janssens, R. V. F.; Zhu, S.

    2010-09-22

    Excited states in the N=30 neutron-rich isotope {sup 49}K have been studied using multinucleon transfer reactions with thin targets and the PRISMA-CLARA spectrometer combined with thick-target {gamma}-coincidence data from Gammasphere. The d{sub 3/2} proton-hole state is located 92 keV above the s{sub 1/2} ground state, and the proton-particle f{sub 7/2} state is suggested at 2104 keV. Three other levels are established as involving the coupling to 2{sup +} of two neutrons above the N=28 shell. The measured or estimated lifetimes served to reinforce the interpretation of the observed level structure, which is found to be in satisfactory agreement with shell-model calculations.

  14. Spectroscopy of Moderately Neutron-rich Nuclei with the CLARA-PRISMA Setup

    SciTech Connect

    Gadea, A.; Marginean, N.; De Angelis, G.; Napoli, D. R.; Corradi, L.; Stefanini, A. M.; Fioretto, E.; Axiotis, M.; Behera, B. R.; Latina, A.; Rusu, C.; Zhimin, W.; Valiente-Dobon, J.; Pokrovskiy, I.; Della Vedova, F.; Farnea, E.; Lenzi, S. M.; Bazzacco, D.; Beghini, S.; Ur, C.

    2006-04-26

    Deep-inelastic and multi-nucleon transfer reactions can be used to populate nuclei with relatively large neutron excess. Recently, at the Laboratori Nazionali di Legnaro, a setup consisting on an efficient {gamma}-ray detection system CLARA coupled to the large acceptance magnetic spectrometer PRISMA, capable of tracking the trajectories of the reaction products, has been assembled. During the first year of activity, the experiments performed with the CLARA-PRISMA setup, have been focused mainly on the nuclear structure of neutron-rich nuclei. In particular, nuclei around N=20, N=50 and lying in the A{approx}60 transitional region with N<40, have been investigated. In this contribution, results of these experiments will be reported.

  15. Beta-decay study of neutron rich isotopes of Bromine and Krypton

    SciTech Connect

    Miernik, Krzysztof A; Gross, Carl J; Grzywacz, Robert Kazimierz; Madurga, M; Mendez, II, Anthony J; Miller, D.; Padgett, S; Paulauskas, Stanley V; Rykaczewski, Krzysztof Piotr; Stracener, Daniel W; Wolinska-Cichocka, Marzena; Zganjar, E. F.; Batchelder, J. C.; Brewer, N.T.; Cartegni, L.; Fijalkowska, Aleksandra G; Hamilton, J. H.; Hwang, J. K.; Ilyushkin, S.; Jost, Carola U; Karny, M.; Korgul, A.; Krolas, W.; Liu, S.H.; Ramayya, A. V.; Surman, Rebecca; Winger, J. A.; Wolinska-Cichocka, M

    2013-01-01

    Short lived neutron rich nuclei including 93 Br, 93 Kr and 94 Kr were produced in proton induced fission of 238 U at the HRIBF in Oak Ridge. Their beta decay was studied by means of a high resolution on line mass separator and beta gamma spectroscopy methods. The half life of 93Br T1/2 = 152(8) ms and delayed branching ratio of Pn = 53-8+11 may be compared to the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half life of 94Kr T1/2 = 227(14) ms and B delayed branching ratio of Pn = 1.9+0.6 0.2 % of 93Kr are in very good agreement with literature values. The decay properties of 93Br include four new gamma transitions following beta delayed neutron emission.

  16. Nuclear shape and structure in neutron-rich {sup 110,111}Tc

    SciTech Connect

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

    2006-08-15

    The high-spin nuclear structure of Tc isotopes is extended to more neutron-rich regions based on the measurements of prompt {gamma} rays from the spontaneous fission of {sup 252}Cf at the Gammasphere. The high-spin level scheme of N=67 neutron-rich {sup 110}Tc (Z=43) is established for the first time, and that of {sup 111}Tc is extended and expanded. The ground band of {sup 111}Tc reaches the band-crossing region, and the new observation of the weakly populated {alpha}=-1/2 member of the band provides important information on signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band crossing of the ground band of {sup 111}Tc is due to alignment of a pair of h{sub 11/2} neutrons. The best fit to signature splitting, branching ratios, and excitations of the ground band of {sup 111}Tc by the rigid triaxial rotor plus particle model calculations result in a shape of {epsilon}{sub 2}=0.32 and {gamma}=-26 deg. for this nucleus. Its triaxiality is larger than that of {sup 107,109}Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated K+2 satellite band provides strong evidence for the large triaxiality of {sup 111}Tc. In {sup 110}Tc, the four lowest-lying levels observed are very similar to those in {sup 108}Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a {delta}I=1 band are observed. This band of {sup 110}Tc is very analogous to the {delta}I=1 bands in {sup 106,108}Tc, but it has greater and reversal signature splitting at higher spins.

  17. Si-rich Silicon Nitride for Nonlinear Signal Processing Applications.

    PubMed

    Lacava, Cosimo; Stankovic, Stevan; Khokhar, Ali Z; Bucio, T Dominguez; Gardes, F Y; Reed, Graham T; Richardson, David J; Petropoulos, Periklis

    2017-12-01

    Nonlinear silicon photonic devices have attracted considerable attention thanks to their ability to show large third-order nonlinear effects at moderate power levels allowing for all-optical signal processing functionalities in miniaturized components. Although significant efforts have been made and many nonlinear optical functions have already been demonstrated in this platform, the performance of nonlinear silicon photonic devices remains fundamentally limited at the telecom wavelength region due to the two photon absorption (TPA) and related effects. In this work, we propose an alternative CMOS-compatible platform, based on silicon-rich silicon nitride that can overcome this limitation. By carefully selecting the material deposition parameters, we show that both of the device linear and nonlinear properties can be tuned in order to exhibit the desired behaviour at the selected wavelength region. A rigorous and systematic fabrication and characterization campaign of different material compositions is presented, enabling us to demonstrate TPA-free CMOS-compatible waveguides with low linear loss (~1.5 dB/cm) and enhanced Kerr nonlinear response (Re{γ} = 16 Wm(-1)). Thanks to these properties, our nonlinear waveguides are able to produce a π nonlinear phase shift, paving the way for the development of practical devices for future optical communication applications.

  18. Heavy Ion Reactions with Neutron-Rich Beams - Proceedings of the Riken International Workshop

    NASA Astrophysics Data System (ADS)

    Yamaji, S.; Ishihara, M.; Takigawa, N.

    1993-11-01

    The Table of Contents for the book is as follows: * Preface * Opening Address * Fusion I * Heavy Ion Fusion at Subbarrier Energies: Progress and Questions * Angular Momentum in Heavy Ion Subbarrier Interaction * Fusion II * High Precision Fusion Excitation Function Measurements: What Can We Learn from Them? * Transfer Reactions for 16O + 144,152Sm near the Coulomb Barrier * Fusion III * Recent Theoretical Developments in the Study of Subbarrier Fusion * Direct Reaction Approach to Heavy Ion Scattering and Fusion at Energies near Coulomb Barrier * Fusion IV * Roles of Multi-Step Transfer in Fusion Process Induced by Heavy Ion Reactions * Special Session * RIKEN Accelerator Research Facility (RARF) * Fission I * Bimodal Nature of Nuclear Fission * Systematics of Isotope Production Rates: Mass Excess Dependence of Fission Products * Semiclassical Methods for the Multi-Dimensional Quantum Decay * Dynamics of Di-Nucleus Systems: Molecular Resonances * Fission II * The Competition Between Fusion-Fission and Deeply Inelastic Reactions in the Medium Mass Systems * Unstable Nuclei I * Coulomb Dissociation and Momentum Distributions for 11Li → 9Li+n+n Breakup Reactions * Unstable Nuclei II * Elastic Scattering and Fragmentation of Halo Nuclei * Secondary Reactions of Neutron-Rich Nuclei at Intermediate Energies * Life Time of Soft Dipole Excitation * Unstable Nuclei III * Shell Structure of Exotic Unstable Nuclei * Properties of Unstable Nuclei Within the Relativistic Many-Body Theory * Fusion with Unstable Nuclei * Barrier Distributions for Heavy Ion Fusion * Heavy Ion Reactions with Neutron-Rich Beams * Heavy Ion Fusion with Neutron-Rich Beams * Superheavy Elements * Study of α Decays Following 40Ar Bombardment on 238U * Production of Superheavy Elements via Fusion: What is Limiting Us? * Panel Session * Comments * List of Participants

  19. d{sub 5/2} proton hole strength in neutron-rich {sup 43}P: Shell structure and nuclear shapes near N=28

    SciTech Connect

    Riley, L. A.; Baugher, T. R.; Hosier, K. E.; Adrich, P.; Bazin, D.; Diget, C. A.; Weisshaar, D.; Brown, B. A.; Cook, J. M.; Gade, A.; Garland, D. A.; Glasmacher, T.; Ratkiewicz, A.; Siwek, K. P.; Cottle, P. D.; Kemper, K. W.; Otsuka, T.; Rae, W. D. M.; Tostevin, J. A.; Utsuno, Y.

    2008-07-15

    We report on the use of the one-proton knockout reaction from {sup 44}S to determine the location of d{sub 5/2} proton strength in neutron-rich {sup 43}P. The results are used to test two shell-model frameworks with different pictures of the evolution of single-proton energies along the N=28 isotones near the neutron dripline. We observe a concentration of d{sub 5/2} proton hole strength near 1 MeV in excitation energy. This result favors the recent shell-model interaction of Utsuno et al. [Eur. Phys. J. Spec. Top. 150, 187 (2007)] and provides additional evidence for an oblate shape for {sup 42}Si.

  20. Si Memory Chip as a Sensitive Neutron Detector

    SciTech Connect

    William Quam

    2008-03-01

    A novel neutron detector is based on semiconductor technology. A boron-containing film is an integral part of the semiconductor device and is in physical contact with the charge-storage medium (CSM). The CSM is a proprietary cell design known as MirrorBit{trademark}, which is different from conventional memory designs such as SRAM or DRAM. The design doubles the resolution and sensitivity in the array. This enables a highly effective detection of the secondary particles, {sup 7}Li and {sup 4}He, produced due to neutron capture by {sup 10}B in the device. Other approaches using semiconductor materials for neutron detection have employed single-diode detectors that require off-system preamplifiers to filter and condition the signal. There are several advantages to this non-volatile detector, one being that it requires no power for detection and retains the signal until reset. Further, this detector, a semiconductor chip, can be seamlessly integrated into other systems. Finally, the semiconductor manufacturing process on which the detector is based will allow for a high-volume and low-cost alternative to current detectors. MirrorBit{trademark} chips were exposed to neutron flux and the signals recorded. Detailed results from this experiment will be described in this presentation.

  1. Coulomb breakup of neutron-rich 29,30Na isotopes near the island of inversion

    NASA Astrophysics Data System (ADS)

    Rahaman, A.; Datta, Ushasi; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Carlson, B. V.; Catford, W. N.; Chakraborty, S.; Chartier, M.; Cortina-Gil, D.; De Angelis, G.; Diaz Fernandez, P.; Emling, H.; Ershova, O.; Fraile, L. M.; Geissel, H.; Gonzalez-Diaz, D.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Langer, C.; Le Bleis, T.; Leifels, Y.; Marganiec, J.; Münzenberg, G.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Plag, R.; Reifarth, R.; Ricciardi, M. V.; Rigollet, C.; Rossi, D.; Scheidenberger, C.; Scheit, H.; Simon, H.; Taylor, J. T.; Togano, Y.; Typel, S.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Winfield, J. S.; Yakorev, D.; Zoric, M.

    2017-04-01

    First results are reported on the ground state configurations of the neutron-rich 29,30Na isotopes, obtained via Coulomb dissociation (CD) measurements. The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a 208Pb target at energies of 400–430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive CD cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from 29Na and 30Na, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of 29Na (3/{2}+) and 30Na ({2}+) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are 28Na{}{gs}({1}+)\\otimes {ν }s,d and 29Na{}{gs}(3/{2}+)\\otimes {ν }s,d, respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd–pf shell gap in 30Na.

  2. Decay of the neutron-rich isotope 171Ho and the identification of 169Dy

    NASA Astrophysics Data System (ADS)

    Chasteler, R. M.; Nitschke, J. M.; Firestone, R. B.; Vierinen, K. S.; Wilmarth, P. A.

    1990-10-01

    Neutron-rich rare-earth isotopes were produced in multinucleon transfer reactions between 170Er ions and natW targets. On-line mass separation was used together with β- and γ-ray spectroscopy in these studies. At mass A=169, the heaviest known dysprosium isotope, 39(8) s,169Dy, was identified. It was observed to β- decay to the ground state of 169Ho or through a level at 1578 keV. In the A=171 mass chain, a partial decay scheme for 55(3)-s 171Ho was determined.

  3. Experimental study of the β decay of the very neutron-rich nucleus 85Ge

    NASA Astrophysics Data System (ADS)

    Korgul, A.; Rykaczewski, K. P.; Grzywacz, R. K.; Bingham, C. R.; Brewer, N. T.; Gross, C. J.; Jost, C.; Karny, M.; Madurga, M.; Mazzocchi, C.; Mendez, A. J.; Miernik, K.; Miller, D.; Padgett, S.; Paulauskas, S. V.; Piersa, M.; Stracener, D. W.; Stryjczyk, M.; Wolińska-Cichocka, M.; Zganjar, E. F.

    2017-04-01

    The β -decay properties of the very neutron-rich nucleus 85Ge, produced in the proton-induced fission of 238U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 52 33 85As populated in 85Geβ γ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N =52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N =52 isotone 81Cu.

  4. Evolution of collectivity in neutron-rich nuclei in the Sn132 region

    NASA Astrophysics Data System (ADS)

    Kshetri, Ritesh; Sarkar, M. Saha; Sarkar, S.

    2006-09-01

    Motivated by the observed regularity in the energy spectra and the structure of the shell model wave functions for the levels of Te137 and I137, a few weakly and moderately deformed neutron-rich odd-A nuclei above the doubly magic nucleus Sn132 were studied using the particle rotor model (PRM). The calculated energy spectra and branching ratios agree reasonably well with the most recent experimental data. In a few cases ambiguity in level ordering was resolved and spin-parities were assigned to the levels. Observed octupole correlation in some of these nuclei is discussed in the light of the present results.

  5. Nuclear structure of the odd-odd N=85 neutron-rich nucleus {sup 140}Cs

    SciTech Connect

    Liu, S. H.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Luo, Y. X.; Rasmussen, J. O.; Daniel, A. V.; Ter-Akopian, G. M.; Zhu, S. J.; Ma, W. C.

    2010-03-15

    High-spin excited states in the neutron-rich nucleus {sup 140}Cs were re-investigated from the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. Seven new transitions at low and moderate spin and 13 at high spin were observed in {sup 140}Cs and the level scheme of {sup 140}Cs was extended to 3794 keV with a new sideband. Spins and parities were assigned to levels based on angular correlation measurements and the systematics in the N=85 isotones.

  6. Isomeric Decay Studies in Neutron-Rich N ≈ 126 Nuclei

    NASA Astrophysics Data System (ADS)

    Steer, S. J.; Podolyák, Zs.; Pietri, S.; Górska, M.; Farrelly, G. F.; Regan, P. H.; Rudolph, D.; Garnsworthy, A. B.; Hoischen, R.; Gerl, J.; Wollersheim, H. J.; Grawe, H.; Maier, K. H.; Becker, F.; Bednarczyk, P.; Cáceres, L.; Doornenbal, P.; Geissel, H.; GrȨBOSZ, J.; Kelic, A.; Kojouharov, I.; Kurz, N.; Montes, F.; Prokopowicz, W.; Saito, T.; Schaffner, H.; Tashenov, S.; Heinz, A.; Kurtukian-Nieto, T.; Benzoni, G.; Pfützner, M.; Jungclaus, A.; Balabanski, D. L.; Brandau, C.; Brown, A.; Bruce, A. M.; Catford, W. N.; Cullen, I. J.; Dombrádi, Zs.; Estevez, M. E.; Gelletly, W.; Ilie, G.; Jolie, J.; Jones, G. A.; Kmiecik, M.; Kondev, F. G.; Krücken, R.; Lalkovski, S.; Liu, Z.; Maj, A.; Myalski, S.; Schwertel, S.; Shizuma, T.; Walker, P. M.; Werner-Malento, E.; Wieland, O.

    Heavy neutron-rich nuclei were populated via relativistic energy fragmentation of a E/A = 1 GeV 208Pb beam. The nuclei of interest were selected and identified by a fragment separator and then implanted in a passive plastic stopper. Delayed γ rays following internal isomeric decays were detected by the RISING array. Experimental information was obtained on a number of nuclei with Z = 73-80 (Ta-Hg), providing new information both on the prolate-oblate transitional region as well as on the N = 126 closed shell nuclei.

  7. Structure of neutron-rich nuclei around the N = 50 shell-gap closure

    SciTech Connect

    Faul, T.; Duchene, G.; Nowacki, F.; Thomas, J.-C.; Huyse, M.; Van Duppen, P.

    2010-04-26

    The structure of neutron-rich nuclei in the vicinity of {sup 78}Ni have been investigated via the beta-decay of {sup 71,73,75}Cu isotopes (ISOLDE, CERN). Experimental results have been compared with shell-model calculations performed with the ANTOINE code using a large (2p{sub 3/2}1 f{sub 5/2}2 p{sub 1/2}1 g{sub 9/2}) valence space and a (56/28)Ni{sub 28} core.

  8. Shape coexistence in neutron-rich strontium isotopes at N = 60

    NASA Astrophysics Data System (ADS)

    Clément, E.; Zielińska, M.

    2017-08-01

    The structure of neutron-rich {}{96,98}Sr nuclei was investigated by low-energy Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr with low configuration mixing. They are discussed in the context of systematics of quadrupole moments and transition probabilities in the N = 60 region.

  9. A Systematic Study of β- Decay of Neutron-Rich Rh and Ag Isotopes

    NASA Astrophysics Data System (ADS)

    Wang, Y.-B.; Dendooven, P.; Huikari, J.; Jokinen, A.; Kolhinen, V. S.; Lhersonneau, G.; Nieminen, A.; Nummela, S.; Penttilä, H.; Peräjärvi, K.; Rinta-Antila, S.; Szerypo, J.; Wang, J. C.; ńystö, J.

    2006-11-01

    Beta decay of neutron-rich even-mass 114-118Rh and 116-120Ag isotopes has been studied using on-line mass-separated sources that were produced by applying 25 MeV proton induced symmetric fission of natural uranium at the IGISOL facility. The β-γ and γ-γ coincidence spectroscopy is employed in all cases that enables for the construction of the decay scheme and for the deduction of the decay properties. Systematics for two-quasineutron states in 114,116,118Pd and for three-phonon multiplet in 114,116,118Cd are presented and discussed.

  10. Collective Band Structures in the Neutron-Rich 107,109Ru Nuclei

    NASA Astrophysics Data System (ADS)

    Zhu, Sheng-jiang; Gan, Cui-yun; J, Hamilton H.; A, Ramayya V.; B, Babu R. S.; M, Sakhaee; W, Ma C.; Long, Gui-lu; Deng, Jing-kang; Zhu, Ling-yan; Li, Ming; Yang, Li-ming; J, Komicki; J, Cole D.; R, Aryaeinejad; Y, Dardenne K.; M, Drigert W.; J, Rasmussen O.; M, Stoyer A.; S, Chu Y.; K, Gregorich E.; M, Mohar F.; S, Prussin G.; I, Lee Y.; N, Johnson R.; F, McGowan K.

    1998-11-01

    The levels in neutron-rich odd-A 107,109Ru nuclei have been investigated by using γ-γ- and γ-γ-γ-coincidence studies of the prompt γ-rays from the spontaneous fission of 252Cf. The ground state bands and the negative parity bands are identified and expanded in both nuclei. Triaxial rotor plus particle model calculations indicate the ground state bands originate from ν(d5/2 + g7/2) quasiparticle configurations and the negative parity bands are from νh11/2 orbital.

  11. Reinvestigation of s=+/- i octupole bands in neutron-rich 141Xe

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Zhu, S. J.; Hamilton, J. H.; Chen, Y. J.; Wang, E. H.; Ramayya, A. V.; Xiao, Z. G.; Li, H. J.; Luo, Y. X.; Rasmussen, J. O.; Ter-Akopian, G. M.; Oganessian, Yu Ts

    2017-09-01

    High-spin level structures in neutron-rich 141Xe nucleus have been reinvestigated by measuring the triple fold and four-fold γ coincidence data obtained in the spontaneous fission of 252Cf. Several new levels and transitions are identified. The previously proposed s=+/- i octupole bands have been significatively updated and expanded. The systematic characteristics of the octupole deformation and octupole correlations are discussed. Reflection asymmetric shell model calculations for the s=+/- i octupole bands of 141Xe are in good agreement with the experimental data.

  12. Application of the generator coordinate method to neutron-rich Se and Ge isotopes

    NASA Astrophysics Data System (ADS)

    Higashiyama, Koji; Yoshinaga, Naotaka

    2014-03-01

    The quantum-number projected generator coordinate method (GCM) is applied to the neutron-rich Se and Ge isotopes, where the monopole and quadrupole pairing plus quadrupole-quadrupole interaction is employed as an effective interaction. The energy spectra obtained by the GCM are compared to both the shell model results and the experimental data. The GCM reproduces well the energy levels of high-spin states as well as the low-lying states. The structure of the low-lying collective states is analyzed through the GCM wave functions.

  13. Collectivity at N=40 in neutron-rich {sup 64}Cr

    SciTech Connect

    Gade, A.; Baugher, T.; Brown, B. A.; McDaniel, S.; Ratkiewicz, A.; Stroberg, S. R.; Walsh, K. A.; Janssens, R. V. F.; Carpenter, M. P.; Hoffman, C. R.; Kay, B. P.; Lauritsen, T.; Zhu, S.; Bazin, D.; Grinyer, G. F.; Weisshaar, D.; Winkler, R.; Chiara, C. J.; Deacon, A. N.; Freeman, S. J.

    2010-05-15

    {sup 9}Be-induced inelastic scattering of {sup 62,64,66}Fe and {sup 60,62,64}Cr was performed at intermediate beam energies. Excited states in {sup 64}Cr were measured for the first time. Energies and population patterns of excited states in these neutron-rich Fe and Cr nuclei are compared and interpreted in the framework of large-scale shell-model calculations in different model spaces. Evidence for increased collectivity and for distinct structural changes between the neighboring Fe and Cr isotopic chains near N=40 is presented.

  14. Collectivity at N = 40 in neutron-rich {sup 64}Cr.

    SciTech Connect

    Gade, A.; Janssens, R. V. F.; Baugher, T.; Bazin, D.; Brown, B. A.; Carpenter, M. P.; Chiara, C. J.; Deacon, A. N.; Freeman, S. J.; Grinyer, G. F.; Hoffman, C. R.; Kay, B. P.; Kondev, F. G.; Lauritsen, T.; McDaniel, S.; Meierbachtol, K.; Ratkiewicz, A.; Stroberg, S. R.; Walsh, K. A.; Weisshaar, D.; Zhu, S.; Winkler, R.; Michigan State Univ.; Univ. of Maryland; Univ. of Manchester

    2010-05-01

    9Be-induced inelastic scattering of 62,64,66Fe and 60,62,64Cr was performed at intermediate beam energies. Excited states in 64Cr were measured for the first time. Energies and population patterns of excited states in these neutron-rich Fe and Cr nuclei are compared and interpreted in the framework of large-scale shell-model calculations in different model spaces. Evidence for increased collectivity and for distinct structural changes between the neighboring Fe and Cr isotopic chains near N=40 is presented.

  15. Experimental study of the β decay of the very neutron-rich nucleus Ge85

    DOE PAGES

    Korgul, A.; Rykaczewski, Krzysztof Piotr; Grzywacz, Robert Kazimierz; ...

    2017-04-04

    The β -decay properties of the very neutron-rich nucleus 85Ge, produced in the proton-induced fission of 238U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 33 85As52 populated in 85Geβ γ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N =52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N =52 isotone 81Cu.

  16. Maser emission of the most abundant SiO isotopomers in O-rich stars

    NASA Astrophysics Data System (ADS)

    Rizzo, J. R.; García Miró, C.; Cernicharo, J.

    2015-05-01

    SiO maser emission constitutes one of the most puzzling cases in spectroscopy. The overall inversion of the rotational transitions in each vibrational ladder is rather well understood. However, there are a number of anomalies in specific rotational transitions that are still unexplained. O-rich stars are probably the most powerful maser emitters known to date, and therefore the best candidates to model the SiO maser emission at different rotational and vibrational levels. In order to properly tackle the SiO excitation problem, it is vital to simultaneously observe a large number of SiO (and isotopomers) lines in a large and varied sample of sources. We profit the availability of new wideband backends to carry out a deep survey of ^{28}SiO, ^{29}SiO, and ^{30}SiO maser emission, in a sample of 67 evolved O-rich stars. The survey was done using the DSS-54 antenna at the Madrid Deep Space Communications complex in Robledo, and the IRAM 30m radio telescope at Pico Veleta. A total of 61 lines were observed, including rotational transitions from J=1→0 to J=5→4, for vibrational levels from 0 to 6. In this contribution, overall results of the survey are presented.

  17. Laser Phase Separation of Si Rich Oxides: The Role of Composition

    NASA Astrophysics Data System (ADS)

    Sungur Ozen, Emel; Aydinli, Atilla; Gundogdu, Sinan

    2012-02-01

    Continuous-wave laser annealing of Si-rich oxide thin films with varying Si content were performed in order to obtain Si nanocrystals (Sinc) embedded in silica. The composition, irradiation times and power densities were investigated as well as the role of hydrogen in phase separation. Sinc in SiO2 appear to be very promising for the realization of optical function as light emission or optical memory. Nanocrystaline Si finds also important utility in photovoltaics thanks to quantum confinement in the nanostructures offering a wider bandgap material which, in a tandem configuration, can allow a better use of the solar spectrum. Conventional techniques utilize high-temperature processing to obtain Si-SiO2 phase separation. These processes are not compatible with mass production methods. An alternative approach capable of avoiding high temperature processing is the laser annealing of SiOx films. The structural effect due to annealing were investigated by Raman and photoluminescence spectroscopy. It has been shown that the size and amount of Sinc depends both on the oxygen content and on the laser power density. PECVD grown hydrogenated SiOx films were compared with sputtered films without hydrogen to identify its role for the phase separation.

  18. Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si

    SciTech Connect

    Myers, S. M.; Cooper, P. J.; Wampler, W. R.

    2008-08-15

    Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed.

  19. Performance of a 4H-SiC Schottky diode as a compact sized detector for neutron pulse form measurements

    NASA Astrophysics Data System (ADS)

    Wu, Jian; Li, Meng; Jiang, Yong; Li, Junjie; Zhang, Yi; Gao, Hui; Liu, Xiaobo; Du, Jinfeng; Zou, Dehui; Fan, Xiaoqiang; Gan, Lei; Peng, Cheng; Lu, Yi; Lei, Jiarong

    2015-01-01

    4H-silicon carbide (4H-SiC) detectors are desirable for neutron pulse form measurement for their compact size, excellent radiation resistance and hydrogen free composition. The aim of this study is to investigate the use of a 4H-SiC detector to measure the pulse form of a neutron burst. A 4H-SiC detector is fabricated and tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). Important parameters such as the breeding period and the FWHM of the neutron pulse are derived from the experimental result of the 4H-SiC detector. These parameters agree well with those from a plastic scintillator detector. The divergences are only 0.5%, demonstrating that the 4H-SiC detector can yield a high fidelity time profile of the CFBR II pulse. The difference in peak centroid of alpha spectra is negligible for the 4H-SiC detector even after 18 reactor pulses (a neutron fluence of 8.41×1012 cm-2), confirming the excellent radiation hardness of the 4H-SiC detector in pulsed neutron field. This study therefore indicates that 4H-SiC detectors can be usable as a compact sized detector to measure neutron pulses.

  20. Neutron absorption of Al-Si-Mg-B{sub 4}C composite

    SciTech Connect

    Abdullah, Yusof Yusof, Mohd Reusmaazran; Ibrahim, Anis Syukriah; Daud, Abdul Razak

    2016-01-22

    Al-Si-Mg-B{sub 4}C composites containing 2-8 wt% of B{sub 4}C were prepared by stir casting technique. Homogenization treatment was carried out at temperatures of 540°C for 4 houra and followed by ageing at 180°C for 2 houra. Microstructure and phase identification were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Neutron absorption study was investigated using neutron source Am/Be{sup 241}. The result indicated that higher B{sub 4}C content improved the neutron absorption property. Meanwhile homogeneity of the composite was increased by ageing processes. This composite is potential to be used as neutron shielding material especially for nuclear reactor application.

  1. Neutron absorption of Al-Si-Mg-B4C composite

    NASA Astrophysics Data System (ADS)

    Abdullah, Yusof; Ibrahim, Anis Syukriah; Daud, Abdul Razak; Yusof, Mohd Reusmaazran

    2016-01-01

    Al-Si-Mg-B4C composites containing 2-8 wt% of B4C were prepared by stir casting technique. Homogenization treatment was carried out at temperatures of 540°C for 4 houra and followed by ageing at 180°C for 2 houra. Microstructure and phase identification were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Neutron absorption study was investigated using neutron source Am/Be241. The result indicated that higher B4C content improved the neutron absorption property. Meanwhile homogeneity of the composite was increased by ageing processes. This composite is potential to be used as neutron shielding material especially for nuclear reactor application.

  2. Lattice HFB calculations for nuclei far from stability: neutron-rich sulfur and tin isotopes

    NASA Astrophysics Data System (ADS)

    Oberacker, Volker; Umar, Sait; Teran, Edgar

    2002-10-01

    We have developed a new Hartree-Fock-Bogoliubov (HFB) code to study ground state and pairing properties of nuclei near the neutron and proton drip lines. The unique feature of our code is that it takes into account the strong coupling to high energy continuum states (up to an equivalent s.p. energy of about 60 MeV). We solve the HFB equations for deformed, axially symmetric even-even nuclei on a two-dimensional lattice using high accuracy Basis-Spline methods (Galerkin and collocation schemes). The effective N-N interaction in the p-h channel is of Skyrme-type (SLy4), and in the p-p and h-h channel it is a (modified) delta interaction. We present results for binding energies, 2-neutron separation energies, Fermi levels, pairing gaps, normal densities and pairing densities, and other observables. In particular, we will discuss neutron-rich sulfur (S-48,S-52) and tin (Sn-150) isotopes. [1] E. Teran, V.E. Oberacker and A.S. Umar, "Axially symmetric Hartree-Fock-Bogoliubov Calculations for Nuclei Near the Drip-Lines; nucl-th/0205042 * Research supported by U.S. DOE grant DE-FG02-96ER40963, and by the National Energy Research Scientific Computing Center (NERSC)

  3. Structure of Neutron-rich Calcium Isotopes and Roles of Three-body Interaction

    SciTech Connect

    Suzuki, T.; Otsuka, T.

    2011-10-28

    Structure of neutron-rich calcium isotopes are studied by shell model calculations with the inclusion of three-body interactions. The three-body force induces repulsive contributions to the monopole terms of the valence neutron-neutron interaction Ground state energies of the isotopes, which have deviations from the experimental values near drip-lines only with the microscopic two-body interaction, are found to be well reproduced up to the observed ones when the three-body interaction is included. The excitation energies of the 2{sub 1}{sup +} state in {sup 48}Ca and {sup 54}Ca are found to be enhanced with the inclusion of the three-body interaction. The three-body force thus plays a key role for the magicity of {sup 48}Ca and {sup 54}Ca. The magnetic dipole (M1) strength in {sup 48}Ca, which is fragmented in case with the microscopic two-body interaction only, is found to be concentrated and pushed up to higher excitation energy when the three-body interarction is included. An important role of the multipole components is pointed out for the concentration of the strength.

  4. Impact of new data for neutron-rich heavy nuclei on theoretical models for r-process nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Kajino, Toshitaka; Mathews, Grant J.

    2017-08-01

    Current models for the r process are summarized with an emphasis on the key constraints from both nuclear physics measurements and astronomical observations. In particular, we analyze the importance of nuclear physics input such as beta-decay rates; nuclear masses; neutron-capture cross sections; beta-delayed neutron emission; probability of spontaneous fission, beta- and neutron-induced fission, fission fragment mass distributions; neutrino-induced reaction cross sections, etc. We highlight the effects on models for r-process nucleosynthesis of newly measured β-decay half-lives, masses, and spectroscopy of neutron-rich nuclei near the r-process path. We overview r-process nucleosynthesis in the neutrino driven wind above the proto-neutron star in core collapse supernovae along with the possibility of magneto-hydrodynamic jets from rotating supernova explosion models. We also consider the possibility of neutron star mergers as an r-process environment. A key outcome of newly measured nuclear properties far from stability is the degree of shell quenching for neutron rich isotopes near the closed neutron shells. This leads to important constraints on the sites for r-process nucleosynthesis in which freezeout occurs on a rapid timescale.

  5. Impact of new data for neutron-rich heavy nuclei on theoretical models for r-process nucleosynthesis.

    PubMed

    Kajino, Toshitaka; Mathews, Grant J

    2017-08-01

    Current models for the r process are summarized with an emphasis on the key constraints from both nuclear physics measurements and astronomical observations. In particular, we analyze the importance of nuclear physics input such as beta-decay rates; nuclear masses; neutron-capture cross sections; beta-delayed neutron emission; probability of spontaneous fission, beta- and neutron-induced fission, fission fragment mass distributions; neutrino-induced reaction cross sections, etc. We highlight the effects on models for r-process nucleosynthesis of newly measured β-decay half-lives, masses, and spectroscopy of neutron-rich nuclei near the r-process path. We overview r-process nucleosynthesis in the neutrino driven wind above the proto-neutron star in core collapse supernovae along with the possibility of magneto-hydrodynamic jets from rotating supernova explosion models. We also consider the possibility of neutron star mergers as an r-process environment. A key outcome of newly measured nuclear properties far from stability is the degree of shell quenching for neutron rich isotopes near the closed neutron shells. This leads to important constraints on the sites for r-process nucleosynthesis in which freezeout occurs on a rapid timescale.

  6. Isospin and kinematical properties of heavy residues from the multifragmentation of neutron-rich systems

    NASA Astrophysics Data System (ADS)

    Souliotis, G. A.; Veselsky, M.; Botvina, A. S.; Keksis, A.; Martin, E.; Shetty, D. V.; Yennello, S. J.

    2004-05-01

    The yields and velocity distributions of isotopically resolved projectile residues from the reactions of 86Kr(25MeV/nucleon) with 64Ni,58Ni,124Sn,112Sn and 208Pb, as well as 124Sn(20MeV/u) with 124Sn are studied in this work [1,2]. Special attention is given to residues produced at excitation energies near the multifragmentation threshold ( ˜2-3MeV/nucleon). Both the isospin and the kinematical properties of the observed residues are well described by a hybrid approach consisting of a deep inelastic transfer model for the dynamical stage of the collision and the statistical multifragmentation model (SMM) for the de-excitation stage [3]. The present version of SMM features a fully microcanonically-based partition of fragmentation space and a detailed treatment of Coulomb interaction (including the interaction of fragments with target `spectators'). Apart from a nuclear reaction standpoint, the present study also addresses, both experimentally and theoretically, the practical issue of the production of very neutron-rich rare isotopes in multifragmentation of neutron-rich systems. [1] G.A. Souliotis et al., Phys. Rev. C 68 024605 (2003). [2] G.A. Souliotis et al., Nucl. Instrum. Methods B 204 166 (2003). [3] A.S. Botvina et al. Phys. Rev. C 65 044610 (2002) and references therein.

  7. New neutron-rich isotope production in 154Sm+160Gd

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Guo, Lu

    2016-09-01

    Deep inelastic scattering in 154Sm+160Gd at energies above the Bass barrier is for the first time investigated with two different microscopic dynamics approaches: improved quantum molecular dynamics (ImQMD) model and time dependent Hartree-Fock (TDHF) theory. No fusion is observed from both models. The capture pocket disappears for this reaction due to strong Coulomb repulsion and the contact time of the di-nuclear system formed in head-on collisions is about 700 fm/c at an incident energy of 440 MeV. The isotope distribution of fragments in the deep inelastic scattering process is predicted with the simulations of the latest ImQMD-v2.2 model together with a statistical code (GEMINI) for describing the secondary decay of fragments. More than 40 extremely neutron-rich unmeasured nuclei with 58 ≤ Z ≤ 76 are observed and the production cross sections are at the order of μb to mb. The multi-nucleon transfer reaction of Sm+Gd could be an alternative way to synthesize new neutron-rich lanthanides which are difficult to be produced with traditional fusion reactions or fission of actinides.

  8. Shell Evolution in the Neutron-Rich Cu and Zn Isotopes

    NASA Astrophysics Data System (ADS)

    Belarge, Joe; Bazin, Daniel; Gade, Alexandra; Ayyad, Yassid; Bender, Peter; Elder, Robert; Elman, Brandon; Iwasaki, Hiro; Kobayashi, Nobuyuki; Loelius, Charles; Longfellow, Brenden; Lunderberg, Eric; Morfouace, Pierre; Sullivan, Chris; Weisshaar, Dirk; Whitmore, Kenneth

    2016-09-01

    Recent shell model calculations predict a gradual reduction of the Z=28 shell gap in Ni isotopes as the ν 1g9 / 2 orbital is filled from 68Ni to 78Ni [Otsuka et al. PRL 95, 232502]. These predictions can be experimentally tested by measuring the spectroscopic strength of a given orbital in an isotopic chain. The neutron-rich Cu isotopes, with one proton outside of a filled π 1f7 / 2 orbital, are some of the best candidates to exhibit the effects of the underlying structure evolution in this region. The high luminosity provided by fast beam, thick target experiments performed at the NSCL, coupled with the high resolution, high efficiency gamma-ray array GRETINA, provide a unique opportunity to study the neutron-rich Cu isotopes. The current experiment aims to measure the strength of 2p-1h excitations in 69-77Cu, populated through one proton knockout from 70-78Zn beams on a Be target, thereby probing the effective single particle energy and spectroscopic strength of the π 1f7 / 2 orbital. Results from the ongoing analysis will be presented.

  9. Spectroscopy of neutron-rich nuclei populated through binary heavy-ion collisions

    SciTech Connect

    Lunardi, S.

    2009-05-04

    Neutron-rich nuclei from A = 50 to A = 80 have been studied through multi-nucleon transfer reactions by bombarding {sup 208}Pb and {sup 238}U targets with beams of {sup 48}Ca, {sup 64}Ni, {sup 70}Zn and {sup 82}Se. The gamma-array CLARA coupled to the large-acceptance magnetic spectrometer PRISMA gave unambiguous identification of prompt {gamma} rays belonging to each nucleus. The existence of the N = 32 sub-shell closure has been corroborated through the study of odd V isotopes, whereas a sizable gap at N = 34 has been evidenced from the spectroscopy of {sup 51}Ca and {sup 52}Sc. The evolution of the N = 50 shell closure far from stability has been studied down to Z = 31. With the {sup 48}Ca beam we have applied for the first time the Recoil Distance Dopple Shift technique to measure lifetimes of neutron-rich nuclei populated in multi-nucleon transfer reactions. Effective charges in the fp shell above {sup 48}Ca have been derived. The first implementation of the tracking array AGATA (the so called 'Demon-strator') will be soon coupled to the PRISMA spectrometer at Legnaro. The future prospects with the use of the Demonstrator are also presented.

  10. Residue Coulomb Interaction Among Isobars and Its Influence in Symmetry Energy of Neutron-Rich Fragment

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Wang; Wang, Shan-Shan; Zhang, Yan-Li; Zhao, Yi-Long; Wei, Hui-Ling

    2015-09-01

    The residue Coulomb interaction (RCI), which affects the result of symmetry-energy coefficient of neutron-rich nucleus in isobaric yield ratio (IYR) method, is difficult to be determined. Four RCI approximations are investigated: (i) The M1-RCI adopting the ac/T (the ratio of Coulomb energy coefficient to temperature) determined from the IYR of mirror-nucleus fragments; (ii) The M2-RCI by fitting the difference between IYRs; (iii) The M3-RCI adopting the standard Coulomb energy at a temperature T = 2 MeV; and (iv) Neglecting the RCI among isobars. The M1-, M2- and M3-RCI are no larger than 0.4. In particular, the M2-RCI is very close to zero. The effects of RCI in asym/T of fragment are also studied. The M1- and M4-asym/T are found to be the lower and upper limitations of asym/T, respectively. The M2-asym/T overlaps the M4-asym/T, which indicates that the M2-RCI is negligible in the IYR method, and the RCI among the three isobars can be neglected. The relative consistent low values of M3-asym/T (7.5 ± 2.5) are found in very neutron-rich isobars. Supported by the Program for Science & Technology Innovation Talents in Universities of Henan Province (13HASTIT046), and Young Teacher Project in Henan Normal University (HNU), China

  11. Recent activities for β-decay half-lives and β-delayed neutron emission of very neutron-rich isotopes

    SciTech Connect

    Dillmann, Iris; Abriola, Daniel; Singh, Balraj

    2014-05-02

    Beta-delayed neutron (βn) emitters play an important, two-fold role in the stellar nucleosynthesis of heavy elements in the 'rapid neutron-capture process' (r process). On one hand they lead to a detour of the material β-decaying back to stability. On the other hand, the released neutrons increase the neutron-to-seed ratio, and are re-captured during the freeze-out phase and thus influence the final solar r-abundance curve. A large fraction of the isotopes inside the r-process reaction path are not yet experimentally accessible and are located in the (experimental) 'Terra Incognita'. With the next generation of fragmentation and ISOL facilities presently being built or already in operation, one of the main motivation of all projects is the investigation of these very neutron-rich isotopes. A short overview of one of the planned programs to measure βn-emitters at the limits of the presently know isotopes, the BRIKEN campaign (Beta delayed neutron emission measurements at RIKEN) will be given. Presently, about 600 β-delayed one-neutron emitters are accessible, but only for a third of them experimental data are available. Reaching more neutron-rich isotopes means also that multiple neutron-emission becomes the dominant decay mechanism. About 460 β-delayed two-, three-or four-neutron emitters are identified up to now but for only 30 of them experimental data about the neutron branching ratios are available, most of them in the light mass region below A=30. The International Atomic and Energy Agency (IAEA) has identified the urgency and picked up this topic recently in a 'Coordinated Research Project' on a 'Reference Database for Beta-Delayed Neutron Emission Data'. This project will review, compile, and evaluate the existing data for neutron-branching ratios and half-lives of β-delayed neutron emitters and help to ensure a reliable database for the future discoveries of new isotopes and help to constrain astrophysical and theoretical models.

  12. The thermoluminescence response of doped SiO2 optical fibres subjected to fast neutrons.

    PubMed

    Hashim, S; Bradley, D A; Saripan, M I; Ramli, A T; Wagiran, H

    2010-01-01

    This paper describes a preliminary study of the thermoluminescence (TL) response of doped SiO(2) optical fibres subjected to (241)AmBe neutron irradiation. The TL materials, which comprise Al- and Ge-doped silica fibres, were exposed in close contact with the (241)AmBe source to obtain fast neutron interactions through use of measurements obtained with and without a Cd filter (the filter being made to entirely enclose the fibres). The neutron irradiations were performed for exposure times of 1-, 2-, 3-, 5- and 7-days in a neutron tank filled with water. In this study, use was also made of the Monte Carlo N-particle (MCNP) code version 5 (V5) to simulate the neutron irradiations experiment. It was found that the commercially available Ge-doped and Al-doped optical fibres show a linear dose response subjected to fast neutrons from (241)AmBe source up to seven days of irradiations. The simulation performed using MCNP5 also exhibits a similar pattern, albeit differing in sensitivity. The TL response of Ge-doped fibre is markedly greater than that of the Al-doped fibre, the total absorption cross section for Ge in both the fast and thermal neutrons region being some ten times greater than that of Al.

  13. Isomer spectroscopy of neutron-rich 168Tb103

    SciTech Connect

    Gurgi, L. A.; Regan, P. H.; Söderström, P. -A.; Watanabe, H.; Walker, P. M.; Podolyák, Zs.; Nishimura, S.; Berry, T. A.; Doornenbal, P.; Lorusso, G.; Isobe, T.; Baba, H.; Xu, Z. Y.; Sakurai, H.; Sumikama, T.; Catford, W. N.; Bruce, A. M.; Browne, F.; Lane, G. J.; Kondev, F. G.; Odahara, A.; Wu, J.; Liu, H. L.; Xu, F. R.; Korkulu, Z.; Lee, P.; Liu, J. J.; Phong, V. H.; Yag, A.; Zhang, G. X.; Alharbi, T.; Carroll, R. J.; Chae, K. Y.; Dombradi, Zs.; Estrade, A.; Fukuda, N.; Griffin, C.; Ideguchi, E.; Inabe, N.; Kanaoka, H.; Kojouharov, I.; Kubo, T.; Kubono, S.; Kurz, N.; Kuti, I.; Lalkovski, S.; Lee, E. J.; Lee, C. S.; Lotay, G.; Moon, C. -B.; Nishizuka, I.; Nita, C. R.; Patel, Z.; Roberts, O. J.; Schaffner, H.; Shand, C. M.; Suzuki, H.; Takeda, H.; Terashima, S.; Vajta, Zs.; Yoshida, S.; Valiente-Dòbon, J. J.

    2016-12-29

    In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified event-by-event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3) fast-timing scintillation detectors from the FATIMA collaboration. This paper presents the internal decay of a metastable isomeric excited state in the odd-odd nucleus 168Tb, which corresponds to a single proton-neutron hole configuration in the valence maximum nucleus 170Dy. These data represent the first information on excited states in this nucleus, which is the most neutron-rich odd-odd isotope of terbium (Z = 65) studied to date. Here, Nilsson configurations associated with an axially symmetric, prolate-deformed nucleus are proposed for the 168Tb ground state the observed isomeric state by comparison with Blocked BCS-Nilsson calculations.

  14. Nuclear shape and structure in neutron-rich 110,111Tc

    SciTech Connect

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

    2006-02-02

    The structure of Tc nuclei is extended to the moreneutron-rich regions based on measurements of prompt gamma rays from thespontaneous fission of 252Cf at Gammasphere. The level scheme of N=67neutron-rich (Z=43) 110Tc is established for the first time and that of111Tc is expanded. The ground-state band of 111Tc reaches theband-crossing region and the new observation of the weakly populatedalpha = -1/2 member of the band provides important information ofsignature splitting. The systematics of band crossings in the isotopicand isotonic chains and a CSM calculation suggest that the band crossingof the gs band of 111Tc is due to alignment of a pair of h11/2 neutrons.The best fit to signature splitting, branching ratios, and excitations ofthe ground-state band of 111Tc by RTRP model calculations result in ashape of epsilon2 = 0.32 and gamma = -26 deg. for this nucleus. Itstriaxiality is larger than that of 107Tc, to indicate increasingtriaxiality with increasing neutron number. The identification of theweakly-populated "K+2 satellite" band provides strong evidence for thelarge triaxiality of 111Tc. In 110Tc the four lowest-lying levelsobserved are very similar to those in 108Tc. At an excitation of 478.9keV above the lowest state observed, ten states of a delta I = 1 band areobserved. This band is very analogous to the delta I = 1 bands in106,108Tc, but it has greater signature splitting at higherspins.

  15. 26Si Excited States via One-Neutron Removal from 27Si Using Radioactive Beam

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, A. A.; Amthor, A. M.; Bazin, D.; Becerril, A. D.; Gade, A.; Galaviz, D.; Glasmacher, T.; Kahl, D.; Lorusso, G.; Matos, M.; Ouellet, C. V.; Pereira, J.; Schatz, H.; Smith, K. M.; Wales, B.; Weisshaar, D.; Zegers, R. G. T.

    2013-03-01

    A measurement of the p(27Si, d)26Si reaction has been performed to study levels of 26Si, with connections to the stellar 25Al(p, γ)26Si reaction rate. A beam of adioactive 27Si of energy 84.3 MeV/A was impinged on a polypropylene foil (CH2) of 180 mg/cm2 in thickness. De-excitation γ-rays were detected with a highly-segmented germanium detector array, in coincidence with the 26Si recoils. Our results are an independent measurement of states used in the energy calibration of other experiments on 26Si structure. They also suggest that the spin-parity of the Ex(26Si) = 6454 keV (Er = 940 keV) state should be 4+ instead of the previously adopted assignment of 0+.

  16. Onset of collectivity in Neutron-Rich iron isotopes: Toward a new island of inversion?

    SciTech Connect

    Ljungvall, J.

    2011-10-28

    The lifetimes of the first excited 2{sup +} states in {sup 62}Fe and {sup 64}Fe have been measured for the first time using the recoil-distance Doppler shift technique, at GANIL. A {sup 238}U beam of 6.5 AMeV impinged on {sup 64}Ni target, and the target like products were slowed down by a degrader foil positioned at micrometer distance downstream of the target and identified in the VAMOS spectrometer on an event-by-event basis. The lifetimes were then determined from the intensities of the degraded and fully Doppler shifted components of the 2{sup +}{yields}0{sup +} transition detected in EXOGAM detectors positioned at backward angles.The resulting lifetimes show a steep increase of the B(E2) values of the first excited 2{sup +} state from {sup 62}Fe to {sup 64}Fe. A comparison with shell model calculations shows that the onset of collectivity is related to the occupation of neutron intruder orbitals. The large B(E2) value for {sup 64}Fe is only reproduced if the valence space includes both the neutron g{sub 9/2} and d{sub 5/2} orbitals. The transition from spherical {sup 68}Ni to more proton-deficient N 40 isotones has some similarity with the island of inversion around {sup 32}Mg. The developing quadrupole collectivity can in both cases be related to the occupation of neutron intruder orbitals which are at the same time quasi-SU(3) partners: (f{sub 7/2}, p{sub 3/2}) for {sup 32}Mg and (g{sub 9/2}, d{sub 5/2}) for the neutron-rich Fe.

  17. Lithium Transport in an Amorphous LixSi Anode Investigated by Quasi-elastic Neutron Scattering

    DOE PAGES

    Sacci, Robert L.; Lehmann, Michelle L.; Diallo, Souleymane O.; ...

    2017-04-27

    Here, we demonstrate the room temperature mechanochemical synthesis of highly defective LixSi anode materials and characterization of the Li transport. We probed the Li+ self-diffusion using quasi-elastic neutron scattering (QENS) to measure the Li self-diffusion in the alloy. Li diffusion was found to be significantly greater (3.0 × 10–6 cm2 s–1) than previously measured crystalline and electrochemically made Li–Si alloys; the energy of activation was determined to be 0.20 eV (19 kJ mol–1). Amorphous Li–Si structures are known to have superior Li diffusion to their crystalline counterparts; therefore, the isolation and stabilization of defective Li–Si structures may improve the utilitymore » of Si anodes for Li-ion batteries.« less

  18. Discovery of Highly Excited Long-Lived Isomers in Neutron-Rich Hafnium and Tantalum Isotopes through Direct Mass Measurements

    SciTech Connect

    Reed, M. W.; Cullen, I. J.; Walker, P. M.; Deo, A. Y.; Kempley, R. S.; Swan, T. P. D.; Litvinov, Yu. A.; Winckler, N.; Blaum, K.; Bosch, F.; Dimopoulou, C.; Farinon, F.; Heil, M.; Knoebel, R.; Kozhuharov, C.; Kurcewicz, J.; Kuzminchuk, N.; Litvinov, S.; Nociforo, C.; Nolden, F.

    2010-10-22

    A study of cooled {sup 197}Au projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides {sup 183,184,186}Hf and {sup 186,187}Ta. The results support the prediction of a strongly favored isomer region near neutron number 116.

  19. Dineutron correlations in quasi-two-dimensional systems in a simplified model, and possible relation to neutron-rich nuclei

    SciTech Connect

    Kanada-En'yo, Yoshiko; Hinohara, Nobuo; Suhara, Tadahiro; Schuck, Peter

    2009-05-15

    Two-neutron correlation in the {sup 1}S channel in quasi-two-dimensional (2D) neutron systems at zero temperature is studied by means of the BCS theory with finite-range effective nuclear forces. The dineutron correlation in low density neutron systems confined in an infinite slab is investigated in a simplified model that neutron motion of one direction is frozen. When the slab is thin enough, two neutrons form a tightly bound dineutron with a small size in the quasi-2D system, and a Bose dineutron gas is found in low density limit. With increase of Fermi momentum, the neutron system changes from the Bose-gas phase to the superfluid Cooper pair phase. The density dependence of the neutron pairing shows the BCS-BEC crossover phenomena at finite low-density region. In the transition region, the size shrinking of neutron pair and enhancement of pairing gap are found. The relation to dineutron correlation at surface of neutron-rich nuclei is also discussed.

  20. Stability of SiC and its Composites at High Neutron Fluence

    SciTech Connect

    Katoh, Yutai; Nozawa, Takashi; Snead, Lance Lewis; Ozawa, Kazumi; Tanigawa, H.

    2011-01-01

    High purity chemically vapor-deposited (CVD) silicon carbide (SiC) and near-stoichiometric SiC fiber, chemically vapor-infiltrated (CVI) SiC matrix composite were evaluated following neutron irradiation to {approx}28 dpa at 300 and 650 C and to {approx}41 dpa at 800 C, respectively. The irradiated swelling, thermal conductivity, and elastic modulus indicated no additional changes in these properties at high fluences after saturation at low fluences. With a statistically meaningful sample population, no change in flexural strength of CVD SiC was observed after 300 C irradiation. A slight decrease in strength was observed after 650 C irradiation but was attributed to an experimental artifact; specifically, a reaction between samples and the capsule components. The Hi-Nicalon{trademark} Type-S, CVI SiC composite retained the pre-irradiation strength and the non-linear fracture mode. The electrical resistivity measurement revealed a relatively minor effect of irradiation. Overall, irradiation-insensitivity of the high purity SiC ceramics and composite to neutron irradiation to doses 30-40 dpa at temperatures 300-800 C was demonstrated.

  1. Threshold resistance switching in silicon-rich SiO x thin films

    NASA Astrophysics Data System (ADS)

    Chen, Da; Huang, Shi-Hua

    2016-11-01

    Si-rich SiO x and amorphous Si clusters embedded in SiO x films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment. The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films, which was caused by the formation of clusters due to the local overheating under a large electric field. Besides, the I-V characteristics of the threshold switching showed a dependence on the annealing temperature and the SiO x thickness. In particular, formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiO x film, while for the 78 nm-SiO x film, adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable. This study demonstrates the importance of investigation of both switching modes in resistance random access memory. Project supported by the Open Project Program of Surface Physics Laboratory (National Key Laboratory) of Fudan University, China (Grant No. KF2015_02), the Open Project Program of National Laboratory for Infrared Physics, Chinese Academy of Sciences (Grant No. M201503), Zhejiang Provincial Science and Technology Key Innovation Team, China (Grant No. 2011R50012), and Zhejiang Provincial Key Laboratory, China (Grant No. 2013E10022).

  2. Positron annihilation spectroscopy investigation of vacancy defects in neutron-irradiated 3 C -SiC

    NASA Astrophysics Data System (ADS)

    Hu, Xunxiang; Koyanagi, Takaaki; Katoh, Yutai; Wirth, Brian D.

    2017-03-01

    Positron annihilation spectroscopy characterization results for neutron-irradiated 3 C -SiC are described here, with a specific focus on explaining the size and character of vacancy clusters as a complement to the current understanding of the neutron irradiation response of 3 C -SiC. Positron annihilation lifetime spectroscopy was used to capture the irradiation temperature and dose dependence of vacancy defects in 3 C -SiC following neutron irradiation from 0.01 to 31 dpa in the temperature range from 380°C to 790°C . The neutral and negatively charged vacancy clusters were identified and quantified. The results suggest that the vacancy defects that were measured by positron annihilation spectroscopy technique contribute very little to the transient swelling of SiC. In addition, coincidence Doppler broadening measurement was used to investigate the chemical identity surrounding the positron trapping sites. It was found that silicon vacancy-related defects dominate in the studied materials and the production of the antisite defect CSi may result in an increase in the probability of positron annihilation with silicon core electrons.

  3. Positron annihilation spectroscopy investigation of vacancy defects in neutron-irradiated 3C -SiC

    DOE PAGES

    Hu, Xunxiang; Koyanagi, Takaaki; Katoh, Yutai; ...

    2017-03-10

    We described positron annihilation spectroscopy characterization results for neutron-irradiated 3 C -SiC, with a specific focus on explaining the size and character of vacancy clusters as a complement to the current understanding of the neutron irradiation response of 3 C -SiC. Positron annihilation lifetime spectroscopy was used to capture the irradiation temperature and dose dependence of vacancy defects in 3 C -SiC following neutron irradiation from 0.01 to 31 dpa in the temperature range from 380C °to 790C .° The neutral and negatively charged vacancy clusters were identified and quantified. The results suggest that the vacancy defects that were measuredmore » by positron annihilation spectroscopy technique contribute very little to the transient swelling of SiC. Additionally, we used coincidence Doppler broadening measurement to investigate the chemical identity surrounding the positron trapping sites.Finally, we found that silicon vacancy-related defects dominate in the studied materials and the production of the antisite defect CSi may result in an increase in the probability of positron annihilation with silicon core electrons.« less

  4. Direct mass measurements of neutron-rich 86Kr projectile fragments and the persistence of neutron magic number N=32 in Sc isotopes

    NASA Astrophysics Data System (ADS)

    Xu, Xing; Wang, Meng; Zhang, Yu-Hu; Xu, Hu-Shan; Shuai, Peng; Tu, Xiao-Lin; Yuri, A. Litvinov; Zhou, Xiao-Hong; Sun, Bao-Hua; Yuan, You-Jin; Xia, Jia-Wen; Yang, Jian-Cheng; Klaus, Blaum; Chen, Rui-Jiu; Chen, Xiang-Cheng; Fu, Chao-Yi; Ge, Zhuang; Hu, Zheng-Guo; Huang, Wen-Jia; Liu, Da-Wei; Lam, Yi-Hua; Ma, Xin-Wen; Mao, Rui-Shi; Uesaka, T.; Xiao, Guo-Qing; Xing, Yuan-Ming; Yamaguchi, T.; Yamaguchi, Y.; Zeng, Qi; Yan, Xin-Liang; Zhao, Hong-Wei; Zhao, Tie-Cheng; Zhang, Wei; Zhan, Wen-Long

    2015-10-01

    In this paper, we present direct mass measurements of neutron-rich 86Kr projectile fragments conducted at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. The new mass excesses of 52-54Sc nuclides are determined to be -40492(82), -38928(114), -34654(540) keV, which show a significant increase of binding energy compared to the reported ones in the Atomic Mass Evaluation 2012 (AME12). In particular, 53Sc and 54Sc are more bound by 0.8 MeV and 1.0 MeV, respectively. The behavior of the two neutron separation energy with neutron numbers indicates a strong sub-shell closure at neutron number N=32 in Sc isotopes. Supported by 973 Program of China (2013CB834401), the NSFC (U1232208, U1432125, 11205205, 11035007) and the Helmholtz-CAS Joint Research Group (HCJRG-108)

  5. Production of neutron-rich Ca, Sn, and Xe isotopes in transfer-type reactions with radioactive beams

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Lacroix, D.

    2010-12-15

    The production cross sections of neutron-rich isotopes {sup 52,54,56,58,60}Ca, {sup 136,138,140,142}Sn, and {sup 146,148,150,152}Xe are predicted for future experiments in the diffusive multinucleon transfer reactions {sup 86,90,92,94}Kr, {sup 124,130,132,134}Sn, {sup 136,140,142,146}Xe, and {sup 138,144,146}Ba+{sup 48}Ca with stable and radioactive beams at incident energies close to the Coulomb barrier. Because of the small cross sections, the production of neutron-rich isotopes requires the optimal choice of projectile-target combinations and bombarding energies.

  6. K-isomers in Hf nuclei at and beyond the neutron-rich edge of {beta}-stability.

    SciTech Connect

    Chowdhury, P.; Alarcao, R. D.; Seabury, E. H.; Walker, P. M.; Wheldon, C.; Ahmad. I.; Carpenter, M. P.; Hackman, G.; Janssens, R. V. F.; Khoo, T. L.; Nisius, D.; Reiter, P.

    1999-03-30

    New high-K isomers are populated in {sup 180,181,182}Hf nuclei via inelastic excitation and transfer reactions, using pulsed {sup 238}U beams on Hf targets. The new data explore K-hindrances for different multipolarities and the role of residual spin-spin interactions for multi-quasiparticle (qp) configurations at the neutron-rich edge of the {beta}-stability line. The mapping of 4-qp K-isomers in the A {approx} 180 region is extended into neutron-rich territory.

  7. Production cross sections of heavy neutron-rich nuclei approaching the nucleosynthesis r-process path around A =195

    NASA Astrophysics Data System (ADS)

    Kurtukian-Nieto, T.; Benlliure, J.; Schmidt, K.-H.; Audouin, L.; Becker, F.; Blank, B.; Casarejos, E.; Farget, F.; Fernández-Ordóñez, M.; Giovinazzo, J.; Henzlova, D.; Jurado, B.; Pereira, J.; Yordanov, O.

    2014-02-01

    In the present work we were able to synthesize and measure with high accuracy the production cross sections of more than 190 heavy neutron-rich nuclei by the in-flight fragmentation of relativistic 208Pb projectiles, 26 of which were produced for the first time. This work has shown that the N =126 region far below the doubly magic 208Pb has become accessible experimentally and represents a step further towards the study of heavy neutron-rich nuclei approaching the r-process waiting point at A =195.

  8. Elastic Scattering of Neutron-Rich Helium Isotopes from Polarized Protons at 71 MeV/A

    NASA Astrophysics Data System (ADS)

    Sakaguchi, S.; Uesaka, T.; Kawabata, T.; Wakui, T.; Aoi, N.; Hashimoto, Y.; Ichikawa, Y.; Itoh, K.; Itoh, M.; Iwasaki, H.; Kawahara, T.; Kondo, Y.; Kuboki, H.; Maeda, Y.; Nakamura, T.; Nakao, T.; Nakayama, Y.; Okamura, H.; Sakai, H.; Sasamoto, Y.; Sasano, M.; Satou, Y.; Sekiguchi, K.; Shimamura, T.; Shimizu, Y.; Shinohara, M.; Suda, K.; Suzuki, D.; Takahashi, Y.; Tamii, A.; Yako, K.; Yamaguchi, M.

    2011-09-01

    The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He and 8He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic field of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potentials for 6He and 8He are characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics reflect a diffused density distribution of the neutron-rich isotopes.

  9. A γ-ray detector with a silicon photomultiplier (SiPM) readout for neutron diffraction experiments at spallation neutron sources

    NASA Astrophysics Data System (ADS)

    Festa, G.; Pietropaolo, A.; Reali, E.; Grazzi, F.; Schooneveld, E. M.

    2010-03-01

    Standard detectors for neutron diffraction experiments are typically 3He filled proportional counters. Indeed, in the near future the 3He availability will be greatly reduced, so the R&D activity on alternative neutron counters is a very important issue to be addressed. Scintillator detectors could be considered as one of these alternatives. In this context, a prototype thermal neutron counter composed of a yttrium-aluminium-perovskite scintillator crystal coupled to a silicon photomultiplier (SiPM) and a standard photomultiplier tube (PMT) was used in time of flight neutron diffraction experiments on the INES spectrometer at the ISIS spallation neutron source. Neutron detection was realized by attaching the crystal to a natural cadmium sheet, used as a (n, γ) converter. Results show that the SiPM-based readout detection system has promising performances with respect to that based on a standard PMT. Diffraction patterns recorded with the 3He tubes' neutron counters in use on INES allowed a comparative assessment of the SiPM-based device for time of flight neutron diffraction experiments, with respect to the standard detection technique.

  10. Neutron activation analysis of the 30Si content of highly enriched 28Si: proof of concept and estimation of the achievable uncertainty

    NASA Astrophysics Data System (ADS)

    D'Agostino, G.; Mana, G.; Oddone, M.; Prata, M.; Bergamaschi, L.; Giordani, L.

    2014-06-01

    We investigated the use of neutron activation to estimate the 30Si mole fraction of the ultra-pure silicon material highly enriched in 28Si for the measurement of the Avogadro constant. Specifically, we developed a relative method based on instrumental neutron activation analysis and using a natural-Si sample as a standard. To evaluate the achievable uncertainty, we irradiated a 6 g sample of a natural-Si material and modelled experimentally the signal that would be produced by a sample of the 28Si-enriched material of similar mass and subjected to the same measurement conditions. The extrapolation of the expected uncertainty from the experimental data indicates that a measurement of the 30Si mole fraction of the 28Si-enriched material might reach a 4% relative combined standard uncertainty.

  11. Dimensional isotropy of 6H and 3C SiC under neutron irradiation

    DOE PAGES

    Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki; ...

    2016-01-16

    This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstrated equivalent swelling behavior.more » Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ~0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ~7.8% volume expansion in SiC was observed prior to amorphization. Above ~0.9 × 1025 n/m2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm3. As a result, the as-amorphized density was the same at the 2 × 1025 and 2 × 1026 n/m2 (E > 0.1 MeV) dose levels.« less

  12. Dimensional isotropy of 6H and 3C SiC under neutron irradiation

    SciTech Connect

    Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki; Terrani, Kurt A.; Specht, Eliot D.

    2016-01-16

    This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstrated equivalent swelling behavior. Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ~0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ~7.8% volume expansion in SiC was observed prior to amorphization. Above ~0.9 × 1025 n/m2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm3. As a result, the as-amorphized density was the same at the 2 × 1025 and 2 × 1026 n/m2 (E > 0.1 MeV) dose levels.

  13. Photoelectron diffraction study of the Si -rich 3C-SiC(001)-(3×2) structure

    NASA Astrophysics Data System (ADS)

    Tejeda, A.; Dunham, D.; García de Abajo, F. J.; Denlinger, J. D.; Rotenberg, E.; Michel, E. G.; Soukiassian, P.

    2004-07-01

    The structure of the Si -rich 3C-SiC(001)-(3×2) surface reconstruction is determined using soft x-ray photoelectron diffraction. Photoelectrons are detected along a full hemispherical sector for different photon energies. A comparison between the experimental data and multiple scattering calculations of the competing models favors a modified version of the two-adlayer asymmetric dimer model. An R -factor analysis has been employed to refine this model. We determine the interlayer spacings of the last six atomic layers and find a corrugation of (0.25±0.10) Å for the atoms in the outermost dimer. Atoms in the second layer dimerize as well, forming rows of long and short dimers.

  14. Neutron-rich isotope production using the uranium carbide multi-foil SPES target prototype

    NASA Astrophysics Data System (ADS)

    Scarpa, D.; Biasetto, L.; Corradetti, S.; Manzolaro, M.; Andrighetto, A.; Carturan, S.; Prete, G.; Zanonato, P.; Stracener, D. W.

    2011-03-01

    In the framework of the R&D program for the SPES (Selective Production of Exotic Species) project of the Istituto Nazionale di Fisica Nucleare (INFN), production yields of neutron-rich isotopes have been measured at the Holifield Radioactive Ion Beam Facility (HRIBF, Oak Ridge National Laboratory, USA). This experiment makes use of the multi-foil SPES target prototype composed of 7 uranium carbide discs, with excess of graphite (ratio C/ U = 4 . 77 isotopes of medium mass (between 72 and 141amu), produced via proton-induced fission of uranium using a 40MeV proton beam, have been collected and analyzed for the target heated at 2000 ° C target temperature.

  15. Stellar electron capture rates on neutron-rich nuclei and their impact on stellar core collapse

    NASA Astrophysics Data System (ADS)

    Raduta, Ad. R.; Gulminelli, F.; Oertel, M.

    2017-02-01

    During the late stages of gravitational core-collapse of massive stars, extreme isospin asymmetries are reached within the core. Due to the lack of microscopic calculations of electron-capture (EC) rates for all relevant nuclei, in general simple analytic parametrizations are employed. We study here several extensions of these parametrizations, allowing for a temperature, electron density, and isospin dependence as well as for odd-even effects. The latter extra degrees of freedom considerably improve the agreement with large-scale microscopic rate calculations. We find, in particular, that the isospin dependence leads to a significant reduction of the global EC rates during core collapse with respect to fiducial results, where rates optimized on calculations of stable f p -shell nuclei are used. Our results indicate that systematic microscopic calculations and experimental measurements in the N ≈50 neutron-rich region are desirable for realistic simulations of the core collapse.

  16. Alpha decay and cluster decay of some neutron-rich actinide nuclei

    NASA Astrophysics Data System (ADS)

    Carmel Vigila Bai, G. M.; Agnes, R. Nithya

    2017-03-01

    Nuclei in the actinide region are good in exhibiting cluster radioactivity. In the present work, the half-lives of α-decay and heavy cluster emission from certain actinide nuclei have been calculated using cubic plus Yukawa plus exponential model (CYEM). Our model has a cubic potential for the overlapping region which is smoothly connected by a Yukawa plus exponential potential for the region after separation. The computed half-lives are compared with those of other theoretical models and are found to be in good agreement with each other. In this work, we have also studied the deformation effects on half-lives of cluster decay. These deformation effects lower the half-life values and it is also found that the neutron-rich parent nuclei slow down the cluster decay process. Geiger-Nuttal plots for various clusters are found to be linear and most of the emitted clusters are α-like nuclei.

  17. Observation of isoscalar and isovector dipole excitations in neutron-rich 20O

    NASA Astrophysics Data System (ADS)

    Nakatsuka, N.; Baba, H.; Aumann, T.; Avigo, R.; Banerjee, S. R.; Bracco, A.; Caesar, C.; Camera, F.; Ceruti, S.; Chen, S.; Derya, V.; Doornenbal, P.; Giaz, A.; Horvat, A.; Ieki, K.; Inakura, T.; Imai, N.; Kawabata, T.; Kobayashi, N.; Kondo, Y.; Koyama, S.; Kurata-Nishimura, M.; Masuoka, S.; Matsushita, M.; Michimasa, S.; Million, B.; Motobayashi, T.; Murakami, T.; Nakamura, T.; Ohnishi, T.; Ong, H. J.; Ota, S.; Otsu, H.; Ozaki, T.; Saito, A.; Sakurai, H.; Scheit, H.; Schindler, F.; Schrock, P.; Shiga, Y.; Shikata, M.; Shimoura, S.; Steppenbeck, D.; Sumikama, T.; Syndikus, I.; Takeda, H.; Takeuchi, S.; Tamii, A.; Taniuchi, R.; Togano, Y.; Tscheuschner, J.; Tsubota, J.; Wang, H.; Wieland, O.; Wimmer, K.; Yamaguchi, Y.; Yoneda, K.; Zenihiro, J.

    2017-05-01

    The isospin characters of low-energy dipole excitations in neutron-rich unstable nucleus 20O were investigated, for the first time in unstable nuclei. Two spectra obtained from a dominant isovector probe (20O + Au) and a dominant isoscalar probe (20O + α) were compared and analyzed by the distorted-wave Born approximation to extract independently the isovector and isoscalar dipole strengths. Two known 1- states with large isovector dipole strengths at energies of 5.36(5) MeV (11-) and 6.84(7) MeV (12-) were also excited by the isoscalar probe. These two states were found to have different isoscalar dipole strengths, 2.70(32)% (11-) and 0.67(12)% (12-), respectively, in exhaustion of the isoscalar dipole-energy-weighted sum rule. The difference in isoscalar strength indicated that they have different underlying structures.

  18. g-Factors of Isomeric States in the Neutron-Rich Nuclei

    SciTech Connect

    Georgiev, G.; Neyens, G.; Hass, M.; Balabanski, Dimiter Loukanov; Bingham, Carrol R; Borcea, C.; Coulier, N.; Coussenment, R.; Daugas, J. M.; De France, Gilles M; Gorska, M.; Grawe, Hubert H; Grzywacz, Robert Kazimierz; Lewitowicz, Marek; Mach, Henryk A; Matea, I.; de Oliveira Santos, F.; Page, R. D.; Pfutzner, Marek; Penionzhkevich, Yu. E.; Podolyak, Zsolt F; Regan, Patrick H; Rykaczewski, Krzysztof Piotr; Sawicka, M.; Smirnova, N. A.; Sobolev, Yu.; Stanoiu, M.; Teughels, S.; Vyvey, K.

    2004-02-01

    We report the results from the first experiment to measure gyromagnetic factors of {micro}s isomers in neutron-rich nuclei produced by intermediate-energy projectile-fragmentation reactions. The Time Dependent Perturbed Angular Distribution (TDPAD) method was applied in combination with the heavy-ion-gamma correlation technique. The nuclides in the vicinity of {sup 68}Ni were produced and spin-oriented following the fragmentation of a {sup 76}Ge, 61.4 MeV/ u beam at GANIL. The results obtained, |g|({sup 69 m}Cu) = 0.225(25) and |g|({sup 67 m}Ni) = 0.125(6) provide another indication of the importance of proton excitation across the Z = 28 shell gap for the description of these states.

  19. Triaxiality of neutron-rich 84,86,88Ge from low-energy nuclear spectra

    NASA Astrophysics Data System (ADS)

    Lettmann, M.; Werner, V.; Pietralla, N.; Doornenbal, P.; Obertelli, A.; Rodríguez, T. R.; Sieja, K.; Authelet, G.; Baba, H.; Calvet, D.; Château, F.; Chen, S.; Corsi, A.; Delbart, A.; Gheller, J.-M.; Giganon, A.; Gillibert, A.; Lapoux, V.; Motobayashi, T.; Niikura, M.; Paul, N.; Roussé, J.-Y.; Sakurai, H.; Santamaria, C.; Steppenbeck, D.; Taniuchi, R.; Uesaka, T.; Ando, T.; Arici, T.; Blazhev, A.; Browne, F.; Bruce, A.; Caroll, R. J.; Chung, L. X.; Cortés, M. L.; Dewald, M.; Ding, B.; Flavigny, F.; Franchoo, S.; Górska, M.; Gottardo, A.; Jungclaus, A.; Lee, J.; Linh, B. D.; Liu, J.; Liu, Z.; Lizarazo, C.; Momiyama, S.; Moschner, K.; Nagamine, S.; Nakatsuka, N.; Nita, C.; Nobs, C. R.; Olivier, L.; Patel, Z.; Podolyák, Zs.; Rudigier, M.; Saito, T.; Shand, C.; Söderström, P.-A.; Stefan, I.; Vaquero, V.; Wimmer, K.; Xu, Z.

    2017-07-01

    γ -ray transitions between low-spin states of the neutron-rich 84,86,88Ge were measured by means of in-flight γ -ray spectroscopy at 270 MeV/u. Excited 61+,41,2 + , and 21,2 + states of Ge,8684 and 41+ and 21,2 + states of 88Ge were observed. Furthermore, a candidate for a 31+ state of 86Ge was identified. This state plays a key role in the discussion of ground-state triaxiality of 86Ge, along with other features of its low-energy level scheme. A new region of triaxially deformed nuclei is proposed in the Ge isotopic chain.

  20. First total-absorption spectroscopy measurement on the neutron-rich Cu isotopes

    NASA Astrophysics Data System (ADS)

    Naqvi, F.; Spyrou, A.; Liddick, S. N.; Larsen, A. C.; Guttormsen, M.; Bleuel, D. L.; Campo, L. C.; Couture, A.; Crider, B. P.; Dombos, A. C.; Ginter, T.; Lewis, R.; Mosby, S.; Perdikakis, G.; Prokop, C. P.; Quinn, S. J.; Renstrom, T.; Rubio, B.; Siem, S.

    2015-10-01

    The first beta-decay studies of 73-71Cu isotopes using the Total Absorption Spectroscopy (TAS) will be reported. The Cu isotopes have one proton outside the Z = 28 shell and hence are good candidates to probe the single-particle structure in the region.Theories predict weakening of the Z = 28 shell gap due to the tensor interaction between the valence πν single-particle orbitals. Comparing the beta-decay strength distributions in the daughter Zn isotopes to the theoretical calculations will provide a stringent test of the predictions. The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) employing the TAS technique with the Summing NaI(Tl) detector, while beta decays were measured in the NSCL beta-counting system. The experimentally obtained total absorption spectra for the neutron-rich Cu isotopes will be presented and the implications of the extracted beta-feeding intensities will be discussed.

  1. Spectroscopy of neutron-rich {sup 59-63}Mn isotopes

    SciTech Connect

    Valiente-Dobon, J. J.; Vedova, F. Della; Gadea, A.; Napoli, D. R.; Corradi, L.; De Angelis, G.; Fioretto, E.; Guiot, B.; Orlandi, R.; Sahin, E.; Singh, R. P.; Stefanini, A. M.; Lenzi, S. M.; Lunardi, S.; Aydin, S.; Mengoni, D.; Montagnoli, G.; Scarlassara, F.; Freeman, S. J.; Smith, J. F.

    2008-08-15

    The neutron-rich Mn isotopes from A=59 to 63 have been studied through multi-nucleon transfer reactions by bombarding a {sup 238}U target with a beam of {sup 70}Zn at an energy of E{sub lab}=460 MeV. Prompt {gamma} rays measured by the CLARA array have been identified unambiguously for each nucleus, using coincidence relationships with ions detected in the high-acceptance magnetic spectrometer PRISMA. The new data extends the knowledge of the low-lying level structure of Mn isotopes, which is discussed in terms of the systematics of the region. Results are compared with large-scale shell-model calculations using different effective interactions and valence spaces.

  2. Cluster structure of neutron-rich 10Be and 14C via resonant alpha scattering

    NASA Astrophysics Data System (ADS)

    Suzuki, D.; Ahn, T.; Bazin, D.; Becchetti, F. D.; Beceiro-Novo, S.; Fritsch, A.; Kolata, J. J.; Mittig, W.; AT-TPC Collaboration

    2017-09-01

    Neutron-rich ^{10} Be and ^{14} C nuclei were studied via resonant α scattering of radioactive 6 He and ^{10} Be beams, respectively, produced by the TwinSol facility at the University of Notre Dame. The Prototype Active-Target Time-Projection Chamber (pAT-TPC) was used as a thick gaseous α target to induce resonant scattering and as a device to track reacted particles inside the target, providing continuous excitation functions and angular distributions over a wide range of energies and angles. The experimental results indicate a melting phenomenon of α clusters in the 4+ rotational member of the ^{10} Be ground state and a linear chain alignment of three α clusters in ^{14} C excited states, as recently predicted by an anti-symmetrized molecular dynamics calculation.

  3. Shell quenching in Ni78: A hint from the structure of neutron-rich copper isotopes

    NASA Astrophysics Data System (ADS)

    Sieja, K.; Nowacki, F.

    2010-06-01

    Recent progress in experimental techniques allows us to study very exotic systems like neutron-rich nuclei in the vicinity of Ni78. The spectroscopy of this region can nowadays be studied theoretically in the large scale shell model calculations. In this work, we perform a shell model study of odd copper nuclei with N=40-50, in a large valence space with the Ca48 core, using a realistic interaction derived from the CD-Bonn potential. We present the crucial importance of the proton core excitations for the description of spectra and magnetic moments, which are for the first time correctly reproduced in theoretical calculations. Shell evolution from Ni68 to Ni78 is discussed in detail. A weakening of the Z=28 gap when approaching the N=50 shell closure, suggested by the experimental evidence, is confirmed in the calculations.

  4. Enhanced Quadrupole Collectivity at N=40: The Case of Neutron-Rich Fe Isotopes

    SciTech Connect

    Rother, W.; Dewald, A.; Fransen, C.; Hackstein, M.; Jolie, J.; Pissulla, Th.; Zell, K.-O.; Iwasaki, H.; Baugher, T.; Brown, B. A.; Gade, A.; Glasmacher, T.; McDaniel, S.; Ratkiewicz, A.; Voss, P.; Walsh, K. A.; Lenzi, S. M.; Ur, C. A.; Starosta, K.; Bazin, D.

    2011-01-14

    The transition rates for the 2{sub 1}{sup +} states in {sup 62,64,66}Fe were studied using the recoil distance Doppler-shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N=40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N=40 as governed by the number of valence protons with respect to Z{approx_equal}30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell-model calculations with a new effective interaction developed for the fpgd valence space.

  5. Enhanced quadrupole collectivity at N = 40: the case of neutron-rich Fe isotopes.

    PubMed

    Rother, W; Dewald, A; Iwasaki, H; Lenzi, S M; Starosta, K; Bazin, D; Baugher, T; Brown, B A; Crawford, H L; Fransen, C; Gade, A; Ginter, T N; Glasmacher, T; Grinyer, G F; Hackstein, M; Ilie, G; Jolie, J; McDaniel, S; Miller, D; Petkov, P; Pissulla, Th; Ratkiewicz, A; Ur, C A; Voss, P; Walsh, K A; Weisshaar, D; Zell, K-O

    2011-01-14

    The transition rates for the 2(1)+ states in (62,64,66)Fe were studied using the recoil distance Doppler-shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell-model calculations with a new effective interaction developed for the fpgd valence space.

  6. Systematic study of neutron-rich rare isotope production in peripheral heavy-ion collisions below the Fermi energy

    NASA Astrophysics Data System (ADS)

    Fountas, P. N.; Souliotis, G. A.; Veselsky, M.; Bonasera, A.

    2014-12-01

    Detailed calculations of the yields of projectilelike fragments (with focus on the neutron-rich isotopes) are presented for the interaction of 86Kr (15 MeV/nucleon) with 64Ni, 58Ni, and 124Sn, 112Sn, as well as 86Kr (25 MeV/nucleon) with 124Sn and compared with our recently published experimental data for these reactions. The calculations are based on a two-step approach: the dynamical stage of the collision was described with the microscopic constrained molecular dynamics (CoMD) model, as well as the phenomenological deep-inelastic transfer (DIT) model and its modified (DITm) version. The deexcitation of the hot projectile fragments was performed with the statistical multifragmentation model (SMM) and the binary-decay model gemini, which provided nearly similar results for the neutron-rich products from the reactions studied. An overall good agreement of the calculations with the experimental results, especially for near-projectile isotopes was observed using both the CoMD model and the DITm model for the dynamical stage. The successful description of the production of neutron-rich isotopes with the CoMD model is of particular importance, due to the predictive power of the microscopic approach that essentially does not depend on the reaction dynamics. Our studies to date suggest that peripheral heavy-ion collisions at this energy range (i.e., well above the Coulomb barrier, but below the Fermi energy), if induced by neutron-rich rare-isotope beams of adequate intensity may offer a unique route to access extremely neutron-rich rare isotopes toward the astrophysical r -process path and the presently uncharted neutron drip line.

  7. New K isomers in the neutron-rich N =100 isotones 162Sm, 163Eu, and 164Gd

    NASA Astrophysics Data System (ADS)

    Yokoyama, R.; Go, S.; Kameda, D.; Kubo, T.; Inabe, N.; Fukuda, N.; Takeda, H.; Suzuki, H.; Yoshida, K.; Kusaka, K.; Tanaka, K.; Yanagisawa, Y.; Ohtake, M.; Sato, H.; Shimizu, Y.; Baba, H.; Kurokawa, M.; Nishimura, D.; Ohnishi, T.; Iwasa, N.; Chiba, A.; Yamada, T.; Ideguchi, E.; Fujii, T.; Nishibata, H.; Ieki, K.; Murai, D.; Momota, S.; Sato, Y.; Hwang, J. W.; Kim, S.; Tarasov, O. B.; Morrissey, D. J.; Sherrill, B. M.; Simpson, G.; Praharaj, C. R.

    2017-03-01

    Very neutron-rich Z ˜60 isotopes produced by in-flight fission of a 345 MeV/nucleon 238U beam at the RI Beam Factory, RIKEN Nishina Center, have been studied by delayed γ -ray spectroscopy. New isomers were discovered in the neutron-rich N =100 isotones 162Sm, 163Eu, and 164Gd. Half-lives, γ -ray energies, and relative intensities of these isomers were obtained. Level schemes were proposed for these nuclei and the first 2+ and 4+ states were assigned for the even-even nuclei. The first 2+ and 4+ state energies decrease as the proton numbers get smaller. The energies and the half-lives of the new isomers are very similar to those of 4- isomers known in less neutron-rich N =100 isotones 168Er and 170Yb. A deformed Hartree-Fock with angular momentum projection model suggests Kπ=4- two-quasiparticle states with ν 7 /2 [633 ]⊗ν 1 /2 [521 ] configurations with similar excitation energy. The results suggest that neutron-rich N =100 nuclei are well deformed and the deformation gets larger as Z decreases to 62. The onset of K isomers with the same configuration at almost the same energy in N =100 isotones indicates that the neutron single-particle structures of neutron-rich isotones down to Z =62 do not change significantly from those of the Z =70 stable nuclei. Systematics of the excitation energies of new isomers can be explained without the predicted N =100 shell gap.

  8. Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Suhara, T.; Kanada-En'yo, Y.

    2016-12-01

    We present a review of recent works on clustering phenomena in unstable nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in these decades have uncovered novel types of clustering phenomena brought about by the excess neutrons. Among them, this review focuses on the molecule-like structure of unstable nuclei. One of the earliest discussions on the clustering in unstable nuclei was made for neutron-rich Be and B isotopes. AMD calculations predicted that the ground state clustering is enhanced or reduced depending on the number of excess neutrons. Today, the experiments are confirming this prediction as the change of the proton radii. Behind this enhancement and reduction of the clustering, there are underlying shell effects called molecular and atomic orbits. These orbits form covalent and ionic bonding of the clusters analogous to the atomic molecules. It was found that this "molecular-orbit picture" reasonably explains the low-lying spectra of Be isotopes. The molecular-orbit picture is extended to other systems having parity asymmetric cluster cores and to the three cluster systems. O and Ne isotopes are the candidates of the former, while the 3 α linear chains in C isotopes are the latter. For both subjects, many intensive studies are now in progress. We also pay a special attention to the observables which are the fingerprint of the clustering. In particular, we focus on the monopole and dipole transitions which are recently regarded as good probe for the clustering. We discuss how they have and will reveal the exotic clustering.

  9. SUPERBURST MODELS FOR NEUTRON STARS WITH HYDROGEN- AND HELIUM-RICH ATMOSPHERES

    SciTech Connect

    Keek, L.; Heger, A.; In 't Zand, J. J. M.

    2012-06-20

    Superbursts are rare day-long type I X-ray bursts due to carbon flashes on accreting neutron stars in low-mass X-ray binaries. They heat the neutron star envelope such that the burning of accreted hydrogen and helium becomes stable, and the common shorter X-ray bursts are quenched. Short bursts reappear only after the envelope cools down. We study multi-zone one-dimensional models of the neutron star envelope, in which we follow carbon burning during the superburst, and we include hydrogen and helium burning in the atmosphere above. We investigate the cases of both a solar-composition and a helium-rich atmosphere. This allows us to study for the first time a wide variety of thermonuclear burning behavior as well as the transitions between the different regimes in a self-consistent manner. For solar composition, burst quenching ends much sooner than previously expected. This is because of the complex interplay between the 3{alpha}, hot CNO, and CNO breakout reactions. Stable burning of hydrogen and helium transitions via marginally stable burning (mHz quasi-periodic oscillations) to less energetic bursts with short recurrence times. We find a short-lived bursting mode where weaker and stronger bursts alternate. Eventually the bursting behavior changes back to that of the pre-superburst bursts. Because of the scarcity of observations, this transition has not been directly detected after a superburst. Using the MINBAR burst catalog we identify the shortest upper limit on the quenching time for 4U 1636-536, and derive further constraints on the timescale on which bursts return.

  10. Configuration assignments to isomers in the neutron-rich 186Ta (Z =73 ) nucleus

    NASA Astrophysics Data System (ADS)

    Sood, P. C.; Gowrishankar, R.

    2014-12-01

    Though the neutron-rich odd-odd nucleus Ta18673113 was first produced in 1955, even after 60 years its ground state (g.s.) and both of its two other isomers remain undefined. We use the well-tested two-quasiparticle rotor model, which explicitly includes residual neutron-proton n -p interaction and other contributing factors, to evaluate the bandhead energies of the physically admissible low-lying two-particle structures in 186Ta with inputs from experimentally observed structures in neighboring isotopes and isotones to characterize these levels. Our analysis assigns Kπ = 5-{p :7 /2 [404 ]⊗n :3 /2 [512 ]} configuration to the 10.5 min 186Ta (g.s.) and the antiparallel-spin Kπ=2- of the same configuration to the 1.54 min isomer with Ex = 90(10) keV. We further assign Kπ=8-{p :7 /2 [404 ]⊗n :9 /2 [505 ]} configuration to the recently identified 3.0 min isomer with Ex=336 (20) keV. These assignments are shown to be consistent with all the available experimental data. Further, they are seen to fit nicely as another instance of highly hindered Δ I =3 isomeric transitions, and also of low-lying long-lived isomer triplets, frequently observed in numerous odd-odd Z =61 (2 )75 nuclides.

  11. First Results From GRIFFIN: Half-Lives of Neutron Rich 128-130Cd

    NASA Astrophysics Data System (ADS)

    Dunlop, Ryan; Griffin Collaboration

    2016-09-01

    Half-lives of N = 82 nuclei below doubly-magic 132Sn are key input parameters for any astrophysical r-process scenario and play an important role in the formation and shape of the second r-process abundance peak. Shell-model calculations for neutron-rich nuclei near the N = 82 neutron shell closure that are not yet experimentally accessible have been performed by adjusting the quenching of the Gamow-Teller (GT) operator to reproduce the 130Cd half-life. The calculated half-lives of other nuclei in the region are known to be systematically too long. Recently, a shorter half-life for 130Cd was measured by the EURICA collaboration that resolves this discrepancy by scaling the GT quenching by a constant factor for all of the nuclei in the region. Distinguishing between these discrepant half-life measurements for 130Cd is thus of critical importance. We have measured the half-lives of 128-130Cd using the high-efficiency GRIFFIN γ-ray spectrometer at TRIUMF, which improves the precision of the 128,129Cd half-lives, and confirms the shorter half-life of 130Cd recently reported by the EURICA collaboration. Details of the GRIFFIN experiments will be presented and the implications of the resulting half-lives discussed.

  12. Measurement of the isoscalar monopole response in the neutron-rich nucleus 68Ni.

    PubMed

    Vandebrouck, M; Gibelin, J; Khan, E; Achouri, N L; Baba, H; Beaumel, D; Blumenfeld, Y; Caamaño, M; Càceres, L; Colò, G; Delaunay, F; Fernandez-Dominguez, B; Garg, U; Grinyer, G F; Harakeh, M N; Kalantar-Nayestanaki, N; Keeley, N; Mittig, W; Pancin, J; Raabe, R; Roger, T; Roussel-Chomaz, P; Savajols, H; Sorlin, O; Stodel, C; Suzuki, D; Thomas, J C

    2014-07-18

    The isoscalar monopole response has been measured in the unstable nucleus (68)Ni using inelastic alpha scattering at 50A  MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 ± 1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9 ± 1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L = 0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

  13. Low-energy Coulomb excitation of neutron-rich zinc isotopes

    NASA Astrophysics Data System (ADS)

    van de Walle, J.; Aksouh, F.; Behrens, T.; Bildstein, V.; Blazhev, A.; Cederkäll, J.; Clément, E.; Cocolios, T. E.; Davinson, T.; Delahaye, P.; Eberth, J.; Ekström, A.; Fedorov, D. V.; Fedosseev, V. N.; Fraile, L. M.; Franchoo, S.; Gernhauser, R.; Georgiev, G.; Habs, D.; Heyde, K.; Huber, G.; Huyse, M.; Ibrahim, F.; Ivanov, O.; Iwanicki, J.; Jolie, J.; Kester, O.; Köster, U.; Kröll, T.; Krücken, R.; Lauer, M.; Lisetskiy, A. F.; Lutter, R.; Marsh, B. A.; Mayet, P.; Niedermaier, O.; Pantea, M.; Raabe, R.; Reiter, P.; Sawicka, M.; Scheit, H.; Schrieder, G.; Schwalm, D.; Seliverstov, M. D.; Sieber, T.; Sletten, G.; Smirnova, N.; Stanoiu, M.; Stefanescu, I.; Thomas, J.-C.; Valiente-Dobón, J. J.; Duppen, P. Van; Verney, D.; Voulot, D.; Warr, N.; Weisshaar, D.; Wenander, F.; Wolf, B. H.; Zielińska, M.

    2009-01-01

    At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2,21+→01+) values in Zn74-80, B(E2,41+→21+) values in Zn74,76 and the determination of the energy of the first excited 21+ states in Zn78,80. The zinc isotopes were produced by high-energy proton- (A=74,76,80) and neutron- (A=78) induced fission of U238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N=50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.

  14. High-spin structure and multiphonon {gamma} vibrations in very neutron-rich {sup 114}Ru

    SciTech Connect

    Yeoh, E. Y.; Wang, J. G.; Ding, H. B.; Gu, L.; Xu, Q.; Xiao, Z. G.; Zhu, S. J.; Hamilton, J. H.; Li, K.; Ramayya, A. V.; Hwang, J. K.; Liu, Y. X.; Liu, S. H.; Sheikh, J. A.; Bhat, G. H.; Luo, Y. X.; Rasmussen, J. O.; Lee, I. Y.; Ma, W. C.

    2011-05-15

    High-spin levels of the neutron-rich {sup 114}Ru have been investigated by measuring the prompt {gamma} rays in the spontaneous fission of {sup 252}Cf. The ground-state band and one-phonon {gamma}-vibrational band have been extended up to 14{sup +} and 9{sup +}, respectively. Two levels are proposed as the members of a two-phonon {gamma}-vibrational band. A back bending (band crossing) has been observed in the ground-state band at ({h_bar}/2{pi}){omega}{approx_equal} 0.40 MeV. Using the triaxial deformation parameters, the cranked shell model calculations indicate that this back bending in {sup 114}Ru should originate from the alignment of a pair of h{sub 11/2} neutrons. Triaxial projected shell model calculations for the {gamma}-vibrational band structures of {sup 114}Ru are in good agreement with the experimental data. However, when using the oblate deformation parameters, both of the above-calculated results are not in agreement with the experimental data.

  15. Measurement of the Isoscalar Monopole Response in the Neutron-Rich Nucleus Ni68

    NASA Astrophysics Data System (ADS)

    Vandebrouck, M.; Gibelin, J.; Khan, E.; Achouri, N. L.; Baba, H.; Beaumel, D.; Blumenfeld, Y.; Caamaño, M.; Càceres, L.; Colò, G.; Delaunay, F.; Fernandez-Dominguez, B.; Garg, U.; Grinyer, G. F.; Harakeh, M. N.; Kalantar-Nayestanaki, N.; Keeley, N.; Mittig, W.; Pancin, J.; Raabe, R.; Roger, T.; Roussel-Chomaz, P.; Savajols, H.; Sorlin, O.; Stodel, C.; Suzuki, D.; Thomas, J. C.

    2014-07-01

    The isoscalar monopole response has been measured in the unstable nucleus Ni68 using inelastic alpha scattering at 50A MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1±1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9±1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L =0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

  16. Gamma-ray spectroscopy of neutron-rich products of heavy-ion collisions

    SciTech Connect

    Carpenter, M.P.; Janssens, R.V.F.; Ahmad, I.

    1995-08-01

    Thick-target {gamma}{gamma} coincidence techniques are being used to explore the spectroscopy of otherwise hard-to-reach neutron-rich products of deep-inelastic heavy ion reactions. Extensive {gamma}{gamma} coincidence measurements were performed at ATLAS using pulsed beams of {sup 80}Se, {sup 136}Xe, and {sup 238}U on lead-backed {sup 122,124}Sn targets with energies 10-15% above the Coulomb barrier. Gamma-ray coincidence intensities were used to map out yield distributions with A and Z for even-even product nuclei around the target and around the projectile. The main features of the yield patterns are understandable in terms of N/Z equilibration. We had the most success in studying the decays of yrast isomers. Thus far, more than thirty new {mu}s isomers in the Z = 50 region were found and characterized. Making isotopic assignments for previously unknown {gamma}-ray cascades proves to be one of the biggest problems. Our assignments were based (a) on rare overlaps with radioactivity data, (b) on the relative yields with different beams, and (c) on observed cross-coincidences between {gamma} rays from light and heavy reaction partners. However, the primary products of deep inelastic collisions often are sufficiently excited for subsequent neutron evaporation, so {gamma}{gamma} cross-coincidence results require careful interpretation.

  17. Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Holt, J. D.; Menéndez, J.; Schwenk, A.

    2013-03-01

    We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in 21, 22, 23O , focusing on the role of three-nucleon forces, in the standard sd shell and an extended sdf_{7/2}p_{3/2} valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in 21O and 23O , which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.

  18. Shape coexistence in neutron-rich odd-mass S isotopes

    NASA Astrophysics Data System (ADS)

    Mijatovic, Tea; Kobayashi, Nobuyuki; Iwasaki, Hiro; Loelius, Charles; Whitmore, Kenneth; Elder, Robert; Gade, Alexandra; Bazin, Daniel; Weisshaar, Dirk; Bender, Peter; Belarge, Joe; Lunderberg, Eric; Elman, Brandon; Longfellow, Brenden; Dewald, Alfred; Haylett, Thoryn; Mathry, Michael; Heil, Sebastian

    2017-01-01

    Collective motions in atomic nuclei at low excitation energies have been characterized by the ground-state shape as a single basis. This picture can be altered in exotic nuclei with unusual proton-to-neutron ratios if the nuclear shape can change drastically at low spin. Recently, there has been an increasing interest for shape-coexistence phenomena in neutron-rich S isotopes and studies suggested fairly large collectivity in 40 , 42 , 44S isotopes. We will discuss the search for isomeric or long-lived states in 45S for which no excited states are known in the literature and the pursuit to fully characterize the band structure of the low-lying states in 43,45S, which provide key information to establish a comprehensive picture of the shape coexistence in this region. Direct model-independent measurements of the 43,45S excited states were realized by applying the Recoil Distance Method with the TRIPLEX Plunger in conjunction with GRETINA to fast rare isotope beams at the NSCL.

  19. Low-lying dipole resonance in neutron-rich Ne isotopes

    NASA Astrophysics Data System (ADS)

    Yoshida, Kenichi; van Giai, Nguyen

    2008-07-01

    Microscopic structure of the low-lying isovector dipole excitation mode in neutron-rich Ne26,28,30 is investigated by performing deformed quasiparticle-random-phase-approximation (QRPA) calculations. The particle-hole residual interaction is derived from a Skyrme force through a Landau-Migdal approximation. We obtain the low-lying resonance in Ne26 at around 8.6 MeV. It is found that the isovector dipole strength at Ex<10 MeV exhausts about 6.0% of the classical Thomas-Reiche-Kuhn dipole sum rule. This excitation mode is composed of several QRPA eigenmodes, one is generated by a ν(2s1/2-12p3/2) transition dominantly and the other mostly by a ν(2s1/2-12p1/2) transition. The neutron excitations take place outside of the nuclear surface reflecting the spatially extended structure of the 2s1/2 wave function. In Ne30, the deformation splitting of the giant resonance is large, and the low-lying resonance overlaps with the giant resonance.

  20. gamma-ray spectroscopy of neutron-rich {sup 40}S

    SciTech Connect

    Wang, Z. M.; Chapman, R.; Liang, X.; Burns, M.; Hodsdon, A.; Keyes, K.; Kumar, V.; Papenberg, A.; Smith, J. F.; Spohr, K. M.; Haas, F.; Caurier, E.; Curien, D.; Nowacki, F.; Azaiez, F.; Ibrahim, F.; Verney, D.; Behera, B. R.; Corradi, L.; Fioretto, E.

    2010-05-15

    Yrast states up to (6{sup +}) in the neutron-rich {sup 40}S nucleus have been studied using binary grazing reactions produced by the interaction of a 215 MeV beam of {sup 36}S ions with a thin {sup 208}Pb target. The novel experimental setup that combines the large acceptance magnetic spectrometer, PRISMA, and the high-efficiency gamma-ray detection array, CLARA, was used. A new gamma-ray transition at an energy of 1572 keV was observed and tentatively assigned to the (6{sup +})->(4{sup +}) transition. A comparison of experimental observations and the results of large-scale 0(Planck constant/2pi)omega sd-pf shell-model calculations indicates that one- and two-proton excitations from the 2s{sub 1/2} to the 1d{sub 3/2} orbitals play an important role in reproducing the {sup 40}S yrast level structure and the published B(E2;0{sub g.s.}{sup +}->2{sub 1}{sup +}) value. The structure of the yrast states of the even-A isotopes of sulfur is interpreted in terms of the configurations of valence protons and neutrons within the context of large-scale 0(Planck constant/2pi)omega sd-pf shell-model calculations.

  1. 6+ isomers in neutron-rich Sn isotopes beyond N =82 and effective interactions

    NASA Astrophysics Data System (ADS)

    Maheshwari, Bhoomika; Jain, Ashok Kumar; Srivastava, P. C.

    2015-02-01

    Recent observation of the 6+ seniority isomers and measurements of the B (E 2 ) values in the Sn-138134 isotopes lying close to the neutron drip line have raised some questions about the validity of the currently used effective interactions in the neutron-rich region. Simpson et al. [Phys. Rev. Lett. 113, 132502 (2014), 10.1103/PhysRevLett.113.132502] had to modify the diagonal and nondiagonal ν f7/2 2 two-body matrix elements of the V l k interaction by ˜150 keV in their shell model calculations in order to explain the data of 136Sn. In contrast, we are able to explain the observed energy levels and the B (E 2 ) values after marginal reduction of the same set of matrix elements by 25 keV in the RCDB (renormalized CD-Bonn) interaction. The observed mismatch in reproducing the data of 136Sn is due to the seniority mixing. Further, we do not find it necessary to consider the core excitations, and the RCDB interaction seems better suited to explain the data beyond N =82 magic number.

  2. Evolution of single-particle strength in neutron-rich 71Cu

    NASA Astrophysics Data System (ADS)

    Morfouace, P.; Franchoo, S.; Sieja, K.; Matea, I.; Nalpas, L.; Niikura, M.; Sánchez-Benítez, A. M.; Stefan, I.; Assié, M.; Azaiez, F.; Beaumel, D.; Boissinot, S.; Borcea, C.; Borcea, R.; Burgunder, G.; Cáceres, L.; De Séréville, N.; Dombrádi, Zs.; Elseviers, J.; Fernández-Domínguez, B.; Gillibert, A.; Giron, S.; Grévy, S.; Hammache, F.; Kamalou, O.; Lapoux, V.; Lefebvre, L.; Lepailleur, A.; Louchart, C.; Marquinez-Duran, G.; Martel, I.; Matta, A.; Mengoni, D.; Napoli, D. R.; Recchia, F.; Scarpaci, J.-A.; Sohler, D.; Sorlin, O.; Stanoiu, M.; Stodel, C.; Thomas, J.-C.; Vajta, Zs.

    2015-12-01

    The strength functions of the πf5/2, πp3/2 and πf7/2 orbitals in neutron-rich 71Cu were obtained in a 72Zn(d,3He)71Cu proton pick-up reaction in inverse kinematics using a radioactive beam of 72Zn at 38 MeV/u. A dedicated set-up was developed to overcome the experimental challenges posed by the low cross section of the reaction and the low energy of the outgoing 3He particles. The excitation-energy spectrum was reconstructed and spectroscopic factors were obtained after analysis of the angular distributions with the finite-range Distorted-Wave Born Approximation (DWBA). The results show that unlike for the πf5/2 orbital and contrary to earlier interpretation, the πf7/2 single-particle strength distribution is not appreciably affected by the addition of neutrons beyond N = 40.

  3. A SiO 2-1 SURVEY TOWARD GAS-RICH ACTIVE GALAXIES

    SciTech Connect

    Wang, Junzhi; Zhang, Jiangshui; Shi, Yong; Zhang, Zhiyu

    2013-12-01

    In order to study the feedback from active galactic nuclei (AGNs), we performed a survey of SiO J = 2-1 (v = 0) transition toward ten gas-rich active galaxies with the IRAM 30 m telescope. As the first survey of SiO in such galaxies, we detected SiO J = 2-1 (v = 0) emission in six galaxies above the 3σ level and one galaxy (NGC 3690) at the 2.7σ level. The detection rate is not related to the AGN type or to star formation activity. In comparison with M82, which is a pure star-forming galaxy without nuclear activity, our SiO detections could not be completely ascribed to being due to star formation activity. This suggests that the AGN feedback may be efficient in producing SiO molecules in such galaxies. Further surveys with large single-dish millimeter telescopes and interferometers are necessary for understanding the origin of SiO in galaxies with nuclear activity.

  4. Neutron-gamma discrimination via PSD plastic scintillator and SiPMs

    NASA Astrophysics Data System (ADS)

    Taggart, M. P.; Payne, C.; Sellin, P. J.

    2016-10-01

    The reduction in availability and inevitable increase in cost of traditional neutron detectors based on the 3He neutron capture reaction has resulted in a concerted effort to seek out new techniques and detection media to meet the needs of national nuclear security. Traditionally, the alternative has been provided through pulse shape discrimination (PSD) using liquid scintillators. However, these are not without their own inherent issues, primarily concerning user safety and ongoing maintenance. A potential system devised to separate neutron and gamma ray pulses utilising the PSD technique takes advantage of recent improvements in silicon photomultiplier (SiPM) technology and the development of plastic scintillators exhibiting the PSD phenomena. In this paper we present the current iteration of this ongoing work having achieved a Figure of Merit (FoM) of 1.39 at 1.5 MeVee.

  5. Influence of neutron irradiation on etching of SiC in KOH

    NASA Astrophysics Data System (ADS)

    Mokhov, E. N.; Kazarova, O. P.; Soltamov, V. A.; Nagalyuk, S. S.

    2017-07-01

    The effect of reactor neutron irradiation on the etch rate of SiC in potassium hydroxide has been studied. In the case of high irradiation doses (1019-1021 cm-2), the etch rate of silicon carbide has been shown to drastically rise, especially in the [0001]Si direction. This considerably mitigates the orientation anisotropy of polar face etching. After high-temperature annealing (up to 1200-1400°C), a higher etch rate of irradiated crystals persists. The results have been explained by the high concentration of radiation-induced (partially clustered) defects they contain.

  6. Defect-induced magnetism in neutron irradiated 6H-SiC single crystals.

    PubMed

    Liu, Yu; Wang, Gang; Wang, Shunchong; Yang, Jianhui; Chen, Liang; Qin, Xiubo; Song, Bo; Wang, Baoyi; Chen, Xiaolong

    2011-02-25

    Defect-induced magnetism is firstly observed in neutron irradiated SiC single crystals. We demonstrated that the intentionally created defects dominated by divacancies (V(Si)V(C)) are responsible for the observed magnetism. First-principles calculations revealed that defect states favor the formation of local moments and the extended tails of defect wave functions make long-range spin couplings possible. Our results confirm the existence of defect-induced magnetism, implying the possibility of tuning the magnetism of wide band-gap semiconductors by defect engineering. © 2011 American Physical Society

  7. Setup with Laser Ionization in Gas Cell for Production and Study of Neutron-Rich Heavy Nuclei

    NASA Astrophysics Data System (ADS)

    Zagrebaev, V. I.; Zemlyanoy, S. G.; Kozulin, E. M.; Kudryavtsev, Yu.; Fedosseev, V.; Bark, R.; Janas, Z.; Othman, H. A.

    2015-11-01

    The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N=126 is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleosynthesis. This area of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes widely used nowadays for the production of exotic nuclei. A new way was recently proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be significantly high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136Xe with 208Pb. A new setup is proposed to produce and study heavy neutron-rich nuclei located along the neutron closed shell N=126.

  8. Spectroscopic studies of neutron-deficient light nuclei: decay properties of 21Mg, 25Si and 26P

    NASA Astrophysics Data System (ADS)

    Thomas, J.-C.; Achouri, L.; ńystö, J.; Béraud, R.; Blank, B.; Canchel, G.; Czajkowski, S.; Dendooven, P.; Ensallem, A.; Giovinazzo, J.; Guillet, N.; Honkanen, J.; Jokinen, A.; Laird, A.; Lewitowicz, M.; Longour, C.; de Oliveira Santos, F.; Stanoiu, M.

    2003-09-01

    Neutron-deficient nuclei with Tz equals to -3/2 and -2 have been produced at the GANIL/LISE3 facility in fragmentation reactions of a 95 MeV/u 36Ar primary beam in a 12C target. For the first time, β-delayed proton and β-γ emission has been simultaneously observed in the decay of 21Mg, 25Si and 26P. The decay scheme of the latter is proposed and the Gamow-Teller strength distribution in its β decay is compared to shell-model calculations based on the USD interaction. The B(GT) values derived from the absolute measurement of the β-branching ratios are in agreement with the quenching factor of about 60% obtained for allowed Gamow-Teller transitions in this mass region. A precise half-life of 43.7 (6) ms was determined for 26P, the β-2p emission of which was studied. The expected contribution of spectroscopic studies of neutron-rich nuclei is discussed with respect to the mirror asymmetry phenomenon occuring in analogous β decays.

  9. Shape Evolution in Neutron-Rich Krypton Isotopes Beyond N=60: First Spectroscopy of ^{98,100}Kr.

    PubMed

    Flavigny, F; Doornenbal, P; Obertelli, A; Delaroche, J-P; Girod, M; Libert, J; Rodriguez, T R; Authelet, G; Baba, H; Calvet, D; Château, F; Chen, S; Corsi, A; Delbart, A; Gheller, J-M; Giganon, A; Gillibert, A; Lapoux, V; Motobayashi, T; Niikura, M; Paul, N; Roussé, J-Y; Sakurai, H; Santamaria, C; Steppenbeck, D; Taniuchi, R; Uesaka, T; Ando, T; Arici, T; Blazhev, A; Browne, F; Bruce, A; Carroll, R; Chung, L X; Cortés, M L; Dewald, M; Ding, B; Franchoo, S; Górska, M; Gottardo, A; Jungclaus, A; Lee, J; Lettmann, M; Linh, B D; Liu, J; Liu, Z; Lizarazo, C; Momiyama, S; Moschner, K; Nagamine, S; Nakatsuka, N; Nita, C; Nobs, C R; Olivier, L; Orlandi, R; Patel, Z; Podolyák, Zs; Rudigier, M; Saito, T; Shand, C; Söderström, P A; Stefan, I; Vaquero, V; Werner, V; Wimmer, K; Xu, Z

    2017-06-16

    We report on the first γ-ray spectroscopy of low-lying states in neutron-rich ^{98,100}Kr isotopes obtained from ^{99,101}Rb(p,2p) reactions at ∼220  MeV/nucleon. A reduction of the 2_{1}^{+} state energies beyond N=60 demonstrates a significant increase of deformation, shifted in neutron number compared to the sharper transition observed in strontium and zirconium isotopes. State-of-the-art beyond-mean-field calculations using the Gogny D1S interaction predict level energies in good agreement with experimental results. The identification of a low-lying (0_{2}^{+}, 2_{2}^{+}) state in ^{98}Kr provides the first experimental evidence of a competing configuration at low energy in neutron-rich krypton isotopes consistent with the oblate-prolate shape coexistence picture suggested by theory.

  10. On the synthesis of neutron-rich isotopes along the N = 126 shell in multinucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Beliuskina, O.; Heinz, S.; Zagrebaev, V.; Comas, V.; Heinz, C.; Hofmann, S.; Knöbel, R.; Stahl, M.; Ackermann, D.; Heßberger, F. P.; Kindler, B.; Lommel, B.; Maurer, J.; Mann, R.

    2014-10-01

    We performed experimental and theoretical studies of deep inelastic multinucleon transfer reactions in heavy-ion collisions at Coulomb barrier energies. Our goal was to investigate if deep inelastic transfer is superior to fragmentation reactions for producing neutron-rich isotopes in the astrophysically interesting region along the closed neutron shell N = 126 . Here, we will present our results obtained in reactions of 64Ni + 207Pb at 5.0 MeV/nucleon. The experiment was performed at the velocity filter SHIP at GSI Darmstadt. Several transfer products on the neutron-rich side were populated but new isotopes were not observed. A comparison of the measured transfer cross-sections and production yields with those from fragmentation reactions allowed for interesting conclusions.

  11. Isobaric yield ratios in heavy-ion reactions, and symmetry energy of neutron-rich nuclei at intermediate energies

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Wang; Wang, Fang; Ma, Yu-Gang; Jin, Chan

    2011-06-01

    The isobaric yield ratios of the fragments produced in the neutron-rich Ca48 and Ni64 projectile fragmentation are analyzed in the framework of a modified Fisher model. The correlations between the isobaric yield ratios (R) and the energy coefficients in the Weiszäcker-Beth semiclassical mass formula (the symmetry-energy term asym, the Coulomb-energy term ac, and the pairing-energy term ap) and the difference between the chemical potentials of the neutron and proton (μn-μp) are investigated. Simple correlations between (μn-μp)/T, ac/T, asym/T, and ap/T (where T is the temperature), and lnR are obtained. It is suggested that (μn-μp)/T, ac/T, asym/T, and ap/T of neutron-rich nuclei can be extracted using isobaric yield ratios for heavy-ion collisions at intermediate energies.

  12. Structural evolution and photoluminescence of annealed Si-rich nitride with Si quantum dots prepared by plasma enhanced chemical vapor deposition

    SciTech Connect

    Zeng, Xiangbin Liao, Wugang; Wen, Guozhi; Wen, Xixing; Zheng, Wenjun

    2014-04-21

    Silicon-rich nitride films were deposited by plasma enhanced chemical vapor deposition. Silicon quantum dots (Si QDs) were formed by post-thermal annealing processing verified using the High-Resolution Transmission Electron Microscope. The 1100 °C thermal annealing leads to the nucleation of silicon atoms, the growth of Si QDs, and the rearrangement of Si 2p and N 1s elements. The structural evolution of silicon-rich nitride thin film with post annealing promotes the formation of Si QDs and Si{sub 3}N{sub 4} matrix. We also investigated the effect of the NH{sub 3}-to-SiH{sub 4} ratio R on the photoluminescence (PL) of SiN{sub x} with Si QDs. We found that the broad blue luminescence originates from both quantum confined effect and radiative defects. The intensity of the PL was changed by adjusting the NH{sub 3} flow rate. The increase of R could limit the transformation of Si QDs from amorphous to crystalline status, meanwhile lead to the alteration of distribution of defect states. These can help to understand the annealing-dependent characteristics, the PL mechanisms of silicon-rich nitride and to optimize the fabrication process of Si QDs embedded in nitride.

  13. Characteristics of SiC neutron sensor spectrum unfolding process based on Bayesian inference

    SciTech Connect

    Cetnar, Jerzy; Krolikowski, Igor; Ottaviani, L.; Lyoussi, A.

    2015-07-01

    This paper deals with SiC detector signal interpretation in neutron radiation measurements in mixed neutron gamma radiation fields, which is called the detector inverse problem or the spectrum unfolding, and it aims in finding a representation of the primary radiation, based on the measured detector signals. In our novel methodology we resort to Bayesian inference approach. In the developed procedure the resultant spectra is unfolded form detector channels reading, where the estimated neutron fluence in a group structure is obtained with its statistical characteristic comprising of standard deviation and correlation matrix. In the paper we present results of unfolding process for case of D-T neutron source in neutron moderating environment. Discussions of statistical properties of obtained results are presented as well as of the physical meaning of obtained correlation matrix of estimated group fluence. The presented works has been carried out within the I-SMART project, which is part of the KIC InnoEnergy R and D program. (authors)

  14. CRYSTALLIZATION EXPERIMENTS OF SiO{sub 2}-RICH AMORPHOUS SILICATE: APPLICATION TO SiO{sub 2}-RICH CIRCUMSTELLAR DUST AND GEMS

    SciTech Connect

    Matsuno, Junya; Tsuchiyama, Akira; Koike, Chiyoe; Chihara, Hiroki; Imai, Yuta; Noguchi, Ryo; Ohi, Shugo

    2012-07-10

    Crystallization experiments of relatively SiO{sub 2}-rich amorphous silicates using the mean chemical composition of the silicate portions in GEMS (glass with embedded metal and sulfide), which is a major component in anhydrous interplanetary dust particles and a primitive material of the early solar system, were performed to understand the presence of crystalline silica around young stars and crystallization in GEMS. Olivine crystallized at {approx}900-1400 K, probably prior to pyroxene. Three different polymorphs of pyroxene, protopyroxene, orthopyroxene, and clinopyroxene, were identified at {>=}1000 K. Cristobalite, which is one of the silica polymorphs, crystallized only at high temperatures ({>=}1500 K). We obtained time-temperature-transformation (TTT) crystallization diagrams. These results suggest that crystallization of a silica polymorph is kinetically difficult in a day or so at {approx}900-1400 K even for the SiO{sub 2}-saturated composition, while the crystallization might be possible after metastable olivine crystallization if duration is long enough. The TTT diagram also indicates that the GEMS cooling timescale was {approx}10{sup 5} s if they condensed at 1000 K as amorphous silicates and annealed during cooling after the condensation.

  15. Crystallization Experiments of SiO2-rich Amorphous Silicate: Application to SiO2-rich Circumstellar Dust and GEMS

    NASA Astrophysics Data System (ADS)

    Matsuno, Junya; Tsuchiyama, Akira; Koike, Chiyoe; Chihara, Hiroki; Ohi, Shugo; Imai, Yuta; Noguchi, Ryo

    2012-07-01

    Crystallization experiments of relatively SiO2-rich amorphous silicates using the mean chemical composition of the silicate portions in GEMS (glass with embedded metal and sulfide), which is a major component in anhydrous interplanetary dust particles and a primitive material of the early solar system, were performed to understand the presence of crystalline silica around young stars and crystallization in GEMS. Olivine crystallized at ~900-1400 K, probably prior to pyroxene. Three different polymorphs of pyroxene, protopyroxene, orthopyroxene, and clinopyroxene, were identified at >=1000 K. Cristobalite, which is one of the silica polymorphs, crystallized only at high temperatures (>=1500 K). We obtained time-temperature-transformation (TTT) crystallization diagrams. These results suggest that crystallization of a silica polymorph is kinetically difficult in a day or so at ~900-1400 K even for the SiO2-saturated composition, while the crystallization might be possible after metastable olivine crystallization if duration is long enough. The TTT diagram also indicates that the GEMS cooling timescale was ~105 s if they condensed at 1000 K as amorphous silicates and annealed during cooling after the condensation.

  16. Krypton and xenon in Apollo 14 samples - Fission and neutron capture effects in gas-rich samples

    NASA Technical Reports Server (NTRS)

    Drozd, R.; Hohenberg, C.; Morgan, C.

    1975-01-01

    Gas-rich Apollo 14 breccias and trench soil are examined for fission xenon from the decay of the extinct isotopes Pu-244 and I-129, and some samples have been found to have an excess fission component which apparently was incorporated after decay elsewhere and was not produced by in situ decay. Two samples have excess Xe-129 resulting from the decay of I-129. The excess is correlated at low temperatures with excess Xe-128 resulting from neutron capture on I-127. This neutron capture effect is accompanied by related low-temperature excesses of Kr-80 and Kr-82 from neutron capture on the bromine isotopes. Surface correlated concentrations of iodine and bromine are calculated from the neutron capture excesses.

  17. Quadrupole transition strength in the (74)Ni nucleus and core polarization effects in the neutron-rich Ni isotopes.

    PubMed

    Marchi, T; de Angelis, G; Valiente-Dobón, J J; Bader, V M; Baugher, T; Bazin, D; Berryman, J; Bonaccorso, A; Clark, R; Coraggio, L; Crawford, H L; Doncel, M; Farnea, E; Gade, A; Gadea, A; Gargano, A; Glasmacher, T; Gottardo, A; Gramegna, F; Itaco, N; John, P R; Kumar, R; Lenzi, S M; Lunardi, S; McDaniel, S; Michelagnoli, C; Mengoni, D; Modamio, V; Napoli, D R; Quintana, B; Ratkiewicz, A; Recchia, F; Sahin, E; Stroberg, R; Weisshaar, D; Wimmer, K; Winkler, R

    2014-10-31

    The reduced transition probability B(E2;0(+)→2(+)) has been measured for the neutron-rich nucleus (74)Ni in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained B(E2;0(+)→2(+))=642(-226)(+216)  e(2) fm(4) value defines a trend which is unexpectedly small if referred to (70)Ni and to a previous indirect determination of the transition strength in (74)Ni. This indicates a reduced polarization of the Z=28 core by the valence neutrons. Calculations in the pfgd model space reproduce well the experimental result indicating that the B(E2) strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.

  18. Yield ratios and directed flows of light fragments from reactions induced by neutron-rich nuclei at intermediate energy

    NASA Astrophysics Data System (ADS)

    Yan, Ting-Zhi; Li, Long-Long; Wang, Rui-Feng; Yan, Ting-Feng

    2017-04-01

    The yield ratios of neutron/proton and 3H/3He and the directed flow per nucleon for these projectile-like fragments at large impact parameters are studied for 50Ca + 40Ca and 50Cr + 40Ca for comparison at 50 MeV/u using the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the yield ratios and the directed flows per nucleon are different for reactions induced by the neutron-rich nucleus 50Ca and the stable isobaric nucleus 50Cr, and depend on the hardness of the EOS. The ratios of neutron/proton and 3H/3He and the difference of directed flow per nucleon of neutron-proton are suggested to be possible observables to investigate the isospin effects. Supported by National Natural Science Foundation of China (11405025)

  19. Operando Lithium Dynamics in the Li-Rich Layered Oxide Cathode Material via Neutron Diffraction

    SciTech Connect

    Liu, Haodong; An, Ke; Venkatachalam, Subramanian; Qian, Danna; Zhang, Minghao; Meng, Ying Shirley

    2016-04-06

    Neutron diffraction under operando battery cycling is used to study the lithium and oxygen dynamics of high Li-rich Li(Lix/3Ni(3/8-3x/8)Co(1/4-x/4)Mn(3/8+7x/24)O2 (x = 0.6, HLR) and low Li-rich Li(Lix/3Ni(1/3-x/3)Co(1/3-x/3)Mn(1/3+x/3)O2 (x = 0.24, LLR) compounds that exhibit different degrees of oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show largely contrasting changes for the two cathodes where the LLR exhibits larger movement of oxygen and lattice contractions in comparison to the HLR that maintains relatively constant lattice parameters and oxygen position during the high voltage plateau until the end of charge. Density functional theory calculations show the presence of oxygen vacancy during the high voltage plateau; changes in the lattice parameters and oxygen position are consistent with experimental observations. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer, and transition metal layer is related to the different charge and discharge characteristics. At the beginning of charging, the lithium extraction predominately occurs within the lithium layer. The lithium extraction from the lithium layer slows down and extraction from the transition metal layer evolves at a faster rate once the high voltage plateau is reached.

  20. Operando Lithium Dynamics in the Li-Rich Layered Oxide Cathode Material via Neutron Diffraction

    DOE PAGES

    Liu, Haodong; An, Ke; Venkatachalam, Subramanian; ...

    2016-04-06

    Neutron diffraction under operando battery cycling is used to study the lithium and oxygen dynamics of high Li-rich Li(Lix/3Ni(3/8-3x/8)Co(1/4-x/4)Mn(3/8+7x/24)O2 (x = 0.6, HLR) and low Li-rich Li(Lix/3Ni(1/3-x/3)Co(1/3-x/3)Mn(1/3+x/3)O2 (x = 0.24, LLR) compounds that exhibit different degrees of oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show largely contrasting changes for the two cathodes where the LLR exhibits larger movement of oxygen and lattice contractions in comparison to the HLR that maintains relatively constant lattice parameters and oxygen position during the high voltage plateau until the end of charge. Density functional theory calculations show the presencemore » of oxygen vacancy during the high voltage plateau; changes in the lattice parameters and oxygen position are consistent with experimental observations. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer, and transition metal layer is related to the different charge and discharge characteristics. At the beginning of charging, the lithium extraction predominately occurs within the lithium layer. The lithium extraction from the lithium layer slows down and extraction from the transition metal layer evolves at a faster rate once the high voltage plateau is reached.« less

  1. Si-rich Fe-Ni grains in highly unequilibrated chondrites

    NASA Technical Reports Server (NTRS)

    Rambaldi, E. R.; Sears, D. W.; Wasson, J. T.

    1980-01-01

    Consideration is given to the Si contents of Fe-Ni grains in highly unequilibrated chondrites, which have undergone little metamorphosis and thus best preserve the record of processes in the solar nebula. Electron microprobe determinations of silicon content in grains of the Bishunpur chondrite are presented for the six Si-bearing Fe-Ni grains for which data could be obtained, five of which were found to be embedded in olivine chondrules. In addition, all grains are found to be Cr-rich, with Cr increased in concentration towards the grain edge, and to be encased in FeS shells which evidently preserved the Si that entered the FeNi at higher temperatures. A mechanism for the production of Si-bearing metal during the condensation of the cooling solar nebula is proposed which considers the metal to have condensed heterogeneously while the mafic silicates condensed homogeneously with amounts of required undercooling in the low-pressure regions where ordinary and carbonaceous chondrites formed, resulting in Si mole fractions of 0.003 at nebular pressures less than 0.000001 atm.

  2. Si-rich W silicide films composed of W-atom-encapsulated Si clusters deposited using gas-phase reactions of WF6 with SiH4.

    PubMed

    Okada, Naoya; Uchida, Noriyuki; Kanayama, Toshihiko

    2016-02-28

    We formed Si-rich W silicide films composed of Sin clusters, each of which encapsulates a W atom (WSi(n) clusters with 8 < n ≤ ∼ 12), by using a gas-phase reaction between WF6 and SiH4 in a hot-wall reactor. The hydrogenated WSi(n)H(x) clusters with reduced F concentration were synthesized in a heated gas phase and subsequently deposited on a substrate heated to 350-420 °C, where they dehydrogenated and coalesced into the film. Under a gas pressure of SiH4 high enough for the WSi(n)H(x) reactant to collide a sufficient number of times with SiH4 molecules before reaching the substrate, the resulting film was composed of WSi(n) clusters with a uniform n, which was determined by the gas temperature. The formed films were amorphous semiconductors with an optical gap of ∼0.8-1.5 eV and an electrical mobility gap of ∼0.05-0.12 eV, both of which increased as n increased from 8 to 12. We attribute this dependence to the reduction of randomness in the Si network as n increased, which decreased the densities of band tail states and localized states.

  3. Monte Carlo simulation and experimental studies of the production of neutron-rich medical isotopes using a particle accelerator

    NASA Astrophysics Data System (ADS)

    Necsoiu Rosencranz, Daniela

    The developments of nuclear medicine lead to an increasing demand for the production of radioisotopes with suitable nuclear and chemical properties. Furthermore, from the literature it is evident that the production of radioisotopes using charged-particle accelerators instead of nuclear reactors is gaining increasing popularity. The main advantages of producing medical isotopes with accelerators are carrier free radionuclides of short lived isotopes, improved handling, reduction of the radioactive waste, and lower cost of isotope fabrication. Proton-rich isotopes are the result of nuclear interactions between enriched stable isotopes and energetic protons. An interesting observation is that during the production of proton-rich isotopes, fast and intermediately fast neutrons from nuclear reactions such as (p,xn) are also produced as a by-product in the nuclear reactions. This observation suggests that it is perhaps possible to use these neutrons to activate secondary targets for the production of neutron-rich isotopes. The study of secondary radioisotope production with fast neutrons from (p,xn) reactions using a particle accelerator is the main goal of the research in this thesis. Yttrium-90 (90Y) is a good example of an isotope that can be made in combination with proton-rich isotope production. Traditionally, 90Y is obtained from a 90Sr/90Y generator. In order to produce a carrier free isotope, a chemical separation of 90Sr must be performed. The main disadvantage of 90Sr is a high toxicity level. 90Sr is well known to cause bone marrow suppressions, and it has a long half-life of 28.78 y. Therefore, special waste handling and storage conditions are required. In this study, 90Y has been produced with (p,xn) fast neutrons using the 90Zr(n,p)90Y reaction. Fast neutrons for the activation process were produced during proton irradiation of natural tungsten targets. The proton beam used was produced by a 33 MeV linear accelerator (LINAC). Since 90Y is a pure beta

  4. Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

    SciTech Connect

    Lillo, Thomas; Rooyen, Isabella Van

    2015-05-01

    Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory’s AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ~23 μm along a radial direction through the 35 μm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ~24 μm in the SiC layer. Also, Pd-rich, nano-precipitates (~10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not all

  5. Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

    NASA Astrophysics Data System (ADS)

    Lillo, T. M.; van Rooyen, I. J.

    2015-05-01

    Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory's AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ∼23 μm along a radial direction through the 35 μm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ∼24 μm in the SiC layer. Also, Pd-rich, nano-precipitates (∼10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not

  6. Shape Coexistence, Triaxiality, Chiral Bands in Neutron-Rich Nuclei and Hot Fission Mode

    NASA Astrophysics Data System (ADS)

    Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Zhu, S. J.; Luo, Y. X.; Rasmussen, J. O.; Gore, P. M.; Jones, E. F.; Fong, D.; Li, K.; Beyer, C. J.; Chaturvedi, L.; Xu, R. Q.; Yang, L. M.; Jiang, Z.; Zhang, Z.; Xiou, S. D.; Zhang, X. Q.; Ter-Akopian, G. M.; Daniel, A. V.; Oganessian, Yu.; Dimitrov, V.; Frauendorf, S.; Gelberg, A.; Kormicki, J.; Gilat, J.; Lee, I. Y.; Fallon, P.; Cole, J. D.; Drigert, M. W.; Stoyer, M. A.; Ginter, T. N.; Wu, S. C.; Donangelo, R.

    2005-09-01

    The structure of neutron-rich nuclei in the A=100 region have been investigated via prompt γ-γ-γ coincidences in the spontaneous fission of 252Cf at Gammasphere. New levels are observed in 93,95,97Sr, 99,101Y, 101,105Nb, 104,106Mo, 105,107,109Tc, 111,113Rh and 115,117Ag. The level structures show a clear evolution from spherical single particle structures seen in Sr, to symmetric, large prolate deformation in Y, to increasing triaxial shapes with increasing Z in Nb, Mo, Tc, Rh and Ag. Rigid triaxial-plus-rotor calculations were carried out for 107Tc and 111,113Rh. Best fits in 107Tc and 111,113Rb are for prolate β2 ~ 0.3 and γ increasing from -22.5° in 107Tc to near maximum triaxiality, γ = -28° in 111,113Rh. A K= 1/2 intruder band with symmetric deformation is found to coexist with the triaxial asymmetric bands in the Tc and Rh nuclei. In 106Mo, two sets of ΔI=1 bands have all the characteristics of chiral doublets. Tilted axis cranking calculations support the chiral assignment and indicate these form a new type of chiral band with a one and two phonon chiral vibrational nature associated essentially with the neutrons. These new type chiral doublets demonstrate the general nature of chirality in nuclei. Binary yields of Mo-Ba and Ru-Xe were determined with higher accuracy. The hot fission mode is seen only in Mo-Ba where it goes via a type of hyperdeformed shape for 144,145,146Ba with a 4.7% intensity.

  7. The impact of the intruder orbitals on the structure of neutron-rich Ag isotopes

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Biswas, S.; Rejmund, M.; Navin, A.; Lemasson, A.; Bhattacharyya, S.; Caamaño, M.; Clément, E.; de France, G.; Jacquot, B.

    2017-09-01

    The low-lying high-spin yrast band structure of neutron-rich 113 , 118- 121Ag has been established for the first time using prompt γ-ray spectroscopy of isotopically identified fission fragments produced in the 9Be(238U, fγ) fusion- and transfer-induced fission processes. The newly obtained level energies follow the systematics of the neighboring isotopes. The sequences of levels exhibit an energy inheritance from states in the corresponding Cd core. A striking constancy of a large signature splitting in odd-A Ag throughout the long chain of isotopes with 50 < N < 82 and a signature inversion in even-A Ag isotopes, which are indications of triaxiality, were evidenced. These observed features were reproduced by large-scale shell-model calculations with a spherical basis for the first time in the Ag isotopic chain, revealing microscopically their complex nature with severely broken seniority ordering. The essential features of the observed signature splitting were further examined in the light of simplified, two-orbital shell-model calculations including only two intruder orbitals πg9/2 and νh11/2 from two consecutive shells above Z = 50 and N = 82 for protons and neutrons respectively, resulting in the πg9/2-3 × νh11/2m configurations. The newly established bands were understood as fairly pure, built mainly on unique-parity intruder configurations and coupled to the basic states of the Cd core.

  8. Shape Coexistence in Neutron-Rich Nickel Isotopes around N = 40

    NASA Astrophysics Data System (ADS)

    Prokop, C. J.; e14039 Collaboration; e14057 Collaboration

    2015-10-01

    Shape coexistence is a fascinating phenomenon in atomic nuclei characterized by multiple states with different intrinsic shapes coexisting at similar excitation energies. In even-even nuclei, a hallmark of shape coexistence is low-energy 0+ states. In 68Ni, the Monte-Carlo Shell Model (MCSM) employing the A3DA interaction, utilizing the fpg9/2d5 / 2 model space for protons and neutrons, predicts triple shape coexistence with three 0+ states below 3 MeV. Transitioning to 70Ni, the energy of the prolate-deformed 0+ state is predicted to drop precipitously from 2511 to 1525 keV. This is due to strengthening of the attractive νg9 / 2 - πf5 / 2 and repulsive νg9 / 2 - πf7 / 2 monopole interactions of the tensor force altering the effective single-particle energies of the πf7 / 2 and πf5 / 2 single-particle states, thereby reducing the spherical Z = 28 shell gap. Recent beta-decay spectroscopy experiments at the National Superconducting Cyclotron Laboratory (NSCL) have discovered a new excited 0+ state at 1567 keV in 70Ni. This result supports MCSM predictions extending the picture of shape coexistence to 70Ni and demonstrates the importance of the tensor force for describing the nuclear structure of neutron-rich nuclei. Results of the latest NSCL experiments will be presented. Supported by NSF Contract No. PHY-1102511, by the DOE NNSA Award Nos. DE-NA0000979 and DE-FG52-08NA28552, the U.S DOE SC NP Contract No. DE-AC-06CH11357 and Grant Nos. DE-FG02-94ER40834 and DE-FG02-96ER40983, and U.S. ARL Coop. Agreement W911NF-12-2-0019.

  9. Extension of the nuclear mass surface for neutron-rich isotopes of argon through iron

    NASA Astrophysics Data System (ADS)

    Meisel, Zachary Paul

    Nuclear mass measurement has maintained an important position in the field of nuclear physics for a little over a century. Nuclear masses provide key evidence of the structural transformation of nuclei away from the valley of beta-stability and are essential input for many simulations of extreme astrophysical environments. However, obtaining these masses is often a challenging endeavor due to the low production cross sections and short half-lives of the exotic nuclei which are of particular interest. To this end, the time-of-flight mass measurement technique has been developed to obtain the masses of several nuclei at once to precisions of 1 part in 105 with virtually no half-life limitation. This dissertation contains a description of the experiment, analysis, and results of the second implementation of the time-of-flight nuclear mass measurement technique at the National Superconducting Cyclotron Laboratory. 18 masses were obtained for neutron-rich isotopes of argon through iron, where the masses of 48Ar, 49Ar, 56Sc, 57Sc, 64Cr, 67Mn, and 69Fe were measured for the first time. These newly obtained masses were applied to outstanding problems in nuclear structure and nuclear astrophysics, resulting in significant scientific advances. The measurement results for 48Ar and 49Ar, which were found to have atomic mass excesses of -22.28(31) MeV and -17.8(1.1) MeV, respectively, provide strong evidence for the closed shell nature of neutron number N = 28 in argon. It follows that argon is therefore the lowest even-Z element exhibiting the N = 28 closed shell. The masses of 64Cr, 67 Mn, and 69Fe, which were found to have atomic mass excesses of -33.48(44) MeV, -34.09(62) MeV, and -39.35(60) MeV, respectively, show signs of nuclear deformation occurring around the N = 40 subshell. In addition, we found 64Cr is substantially less bound than predicted by global mass models that are commonly used in nuclear astrophysics simulations, resulting in a significant reduction in the

  10. Stellar (n ,γ ) cross sections of neutron-rich nuclei: Completing the isotope chains of Yb, Os, Pt, and Hg

    NASA Astrophysics Data System (ADS)

    Marganiec, J.; Dillmann, I.; Domingo-Pardo, C.; Käppeler, F.

    2014-12-01

    The (n ,γ ) cross sections of the most neutron-rich stable isotopes of Yb, Os, Pt, and Hg have been determined in a series of activation measurements at the Karlsruhe 3.7 MV Van de Graaff accelerator, using the quasistellar neutron spectrum for k T =25 keV that can be produced with the 7Li(p ,n ) 7Be reaction. In this way, Maxwellian averaged cross sections could be directly obtained with only minor corrections. After irradiation the induced activities were counted with a HPGe detector via the strongest γ -ray lines. The stellar neutron capture cross sections of Yb,176174, Os,192190, Pt,198196, and Hg,204202, extrapolated to k T =30 keV, were found to be 157 ±6 mb, 114 ±8 mb, 278 ±11 mb, 160 ±7 mb, 171 ±19 mb, 94 ±4 mb, 62 ±2 mb, and 32 ±15 mb, respectively. In the case of 196Pt the partial cross section to the isomeric state at 399.5 keV could be determined as well. With these results the cross section data for long isotopic chains could be completed for a discussion of the predictive power of statistical model calculations towards the neutron-rich and proton-rich sides of the stability valley.

  11. Spectroscopy of {sup 36}Mg: Interplay of Normal and Intruder Configurations at the Neutron-Rich Boundary of the 'Island of Inversion'

    SciTech Connect

    Gade, A.; Bowen, M. D.; Brown, B. A.; Campbell, C. M.; Cook, J. M.; Glasmacher, T.; McDaniel, S.; Ratkiewicz, A.; Siwek, K.; Terry, J. R.; Adrich, P.; Bazin, D.; Ettenauer, S.; Obertelli, A.; Weisshaar, D.; Kemper, K. W.; Otsuka, T.; Tostevin, J. A.; Utsuno, Y.

    2007-08-17

    We report on the first spectroscopy study of the very neutron-rich nucleus {sub 12}{sup 36}Mg{sub 24} using the direct two-proton knockout reaction {sup 9}Be({sup 38}Si,{sup 36}Mg+{gamma})X at 83 MeV/nucleon. The energy of the first excited 2{sup +} state of {sup 36}Mg, E(2{sub 1}{sup +})=660(6) keV, was measured. The magnitude of the partial cross sections to the ground state and the 2{sub 1}{sup +} state is indicative of strong intruder admixtures in the lowest-lying states as suggested by Monte Carlo shell-model calculations.

  12. CARIBU: a new facility for the study of neutron-rich isotopes

    NASA Astrophysics Data System (ADS)

    Savard, G.; Pardo, R. C.; Baker, S.; Davids, C. N.; Levand, A.; Peterson, D.; Phillips, D. G.; Sun, T.; Vondrasek, R.; Zabransky, B. J.; Zinkann, G. P.

    2011-07-01

    The Californium Rare Ion Breeder Upgrade (CARIBU) to the ATLAS superconducting linac facility is currently being commissioned. It provides low-energy and re-accelerated beams of neutron-rich isotopes obtained from 252Cf fission. The fission products from a 252Cf source are stopped in a large high-intensity gas catcher, thermalized and extracted through an RFQ cooler, accelerated to 50 kV and mass separated in a high-resolution separator before being sent to either an ECR charge breeder for post-acceleration through the ATLAS linac or to a low-energy experimental area. This approach gives access to beams of very neutron-rich isotopes, many of which have not been available at low or Coulomb barrier energies previously. These beams provide unique opportunities for measurements along the r-process path. To take advantage of these unique possibility, the reaccelerated beams from CARIBU will be made available at the experimental stations of ATLAS to serve equipment such as Gammasphere, HELIOS and the reaction spectrometers. In addition, the Canadian Penning Trap (CPT) mass spectrometer has been moved to the CARIBU low-energy experimental area and a new injection line has been built. The new injection line consists of a RFQ buncher sitting on a 50 kV high-voltage platform that will accumulate the mass separated 50 kV radioactive beams, cool and extract them as a pulsed beam of 3 keV. This beam can be sent either to a tape station for diagnostics and tuning, or a cryogenic linear trap for preparation before transfer to the high-precision Penning trap where the mass measurements will take place. Initial CARIBU commissioning is proceeding with a 2 mCi source that will be replaced by a 100 mCi source as the commissioning proceeds. Final operation will use a 1 Ci source and attain yield in excess of 107 ions/sec for the most intense beams at low energy, an order of magnitude less for reaccelerated beams.

  13. Lifetime measurement of neutron-rich even-even molybdenum isotopes

    NASA Astrophysics Data System (ADS)

    Ralet, D.; Pietri, S.; Rodríguez, T.; Alaqeel, M.; Alexander, T.; Alkhomashi, N.; Ameil, F.; Arici, T.; Ataç, A.; Avigo, R.; Bäck, T.; Bazzacco, D.; Birkenbach, B.; Boutachkov, P.; Bruyneel, B.; Bruce, A. M.; Camera, F.; Cederwall, B.; Ceruti, S.; Clément, E.; Cortés, M. L.; Curien, D.; De Angelis, G.; Désesquelles, P.; Dewald, M.; Didierjean, F.; Domingo-Pardo, C.; Doncel, M.; Duchêne, G.; Eberth, J.; Gadea, A.; Gerl, J.; Ghazi Moradi, F.; Geissel, H.; Goigoux, T.; Goel, N.; Golubev, P.; González, V.; Górska, M.; Gottardo, A.; Gregor, E.; Guastalla, G.; Givechev, A.; Habermann, T.; Hackstein, M.; Harkness-Brennan, L.; Henning, G.; Hess, H.; Hüyük, T.; Jolie, J.; Judson, D. S.; Jungclaus, A.; Knoebel, R.; Kojouharov, I.; Korichi, A.; Korten, W.; Kurz, N.; Labiche, M.; Lalović, N.; Louchart-Henning, C.; Mengoni, D.; Merchán, E.; Million, B.; Morales, A. I.; Napoli, D.; Naqvi, F.; Nyberg, J.; Pietralla, N.; Podolyák, Zs.; Pullia, A.; Prochazka, A.; Quintana, B.; Rainovski, G.; Reese, M.; Recchia, F.; Reiter, P.; Rudolph, D.; Salsac, M. D.; Sanchis, E.; Sarmiento, L. G.; Schaffner, H.; Scheidenberger, C.; Sengele, L.; Singh, B. S. Nara; Singh, P. P.; Stahl, C.; Stezowski, O.; Thoele, P.; Valiente Dobon, J. J.; Weick, H.; Wendt, A.; Wieland, O.; Winfield, J. S.; Wollersheim, H. J.; Zielinska, M.; PreSPEC Collaboration

    2017-03-01

    Background: In the neutron-rich A ≈100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A =100 up to mass A =108 , and the results that were obtained. Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the γ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a γ -ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A =100 to A =108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: τ =29 .7-9.1+11.3 ps for the 4+ state of 108Mo and τ =3 .2-0.7+0.7 ps for the 6+ state of 102Mo. Conclusions: The reduced transition strengths B (E 2 ) , calculated from lifetimes measured in this experiment, compared to beyond

  14. Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust

    DOE PAGES

    Meisel, Z.; George, S.; Ahn, S.; ...

    2016-03-22

    Here, we present the mass excesses of 59-64Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N = 38. Additionally, we extend the S2n trend for chromium to N = 40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-artmore » shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g9/2 and d5/2 orbits for the neutron valence space. We employ our result for the mass of 64Cr in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A = 64 isobaric chain, resulting in a cooler than expected accreted neutron star crust. This reduced heating is found to be due to the >1-MeV reduction in binding for 64Cr with respect to values from commonly used global mass models.« less

  15. Electrical properties of amorphous and epitaxial Si-rich silicide films composed of W-atom-encapsulated Si clusters

    SciTech Connect

    Okada, Naoya; Uchida, Noriyuki; Kanayama, Toshihiko

    2015-03-07

    We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSi{sub n}) films and approximately 1-nm-thick crystalline WSi{sub n} epitaxial films (e-WSi{sub n}) on Si (100) substrates with composition n = 8–10, both composed of Si{sub n} clusters each of which encapsulates a W atom (WSi{sub n} clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSi{sub n} is a nearly intrinsic semiconductor, whereas e-WSi{sub n} is an n-type semiconductor with electron mobility of ∼8 cm{sup 2}/V s and high sheet electron density of ∼7 × 10{sup 12 }cm{sup −2}. According to the temperature dependence of the electrical properties, a-WSi{sub n} has a mobility gap of ∼0.1 eV and mid gap states in the region of 10{sup 19 }cm{sup −3} eV{sup −1} in an optical gap of ∼0.6 eV with considerable band tail states; e-WSi{sub n} has a donor level of ∼0.1 eV with sheet density in the region of 10{sup 12 }cm{sup −2} in a band gap of ∼0.3 eV. These semiconducting band structures are primarily attributed to the open band-gap properties of the constituting WSi{sub n} cluster. In a-WSi{sub n}, the random network of the clusters generates the band tail states, and the formation of Si dangling bonds results in the generation of mid gap states; in e-WSi{sub n}, the original cluster structure is highly distorted to accommodate the Si lattice, resulting in the formation of intrinsic defects responsible for the donor level.

  16. Structure And Decay Of Neutron-Rich Nuclides In The 115 {<=} A {<=} 138 Mass Range And r-Process Nucleosynthesis

    SciTech Connect

    Walters, W.B.; Stoyer, M.A.; Shergur, J.; Hoteling, N.; Ressler, J.J.; Rikovska, J.; Kratz, K.-L.; Woehr, A.; Pfeiffer, B.; Arndt, O.; Mantica, P.F.; Tomlin, B.; Schatz, H.; Montes, F.; Brown, B.A.; Seweryniak, D.; Ravn, H.; Fedoseyev, V.; Koester, U.; Wu, C.Y.

    2005-04-05

    The structure and decay of neutron-rich r-process nuclides has been studied by a variety of means that take advantage of enhanced selectivity to permit identification of exotic nuclides. New level structures are presented for 134,135Sb along with data for Ag isomers and Cd yrast structures. Some of the properties measured play an important role in calculations of the yields of elements and isotopes produced in r-process nucleosynthesis that takes place at high temperature in the presence of large densities of neutrons.

  17. Li dynamics in carbon-rich polymer-derived SiCN ceramics probed by NMR

    NASA Astrophysics Data System (ADS)

    Baek, Seung-Ho; Reinold, Lukas; Graczyk-Zajac, Magdalena; Riedel, Ralf; Hammerath, Franziska; Buechner, Bernd; Grafe, Hajo

    2014-03-01

    We report 7Li, 29Si, and 13C NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei at room temperature, we find that only the 13C spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature and Larmor frequency (ωL) dependences of the 7Li linewidth and spin-lattice relaxation rates T1-1 are described by an activated law with the activation energy EA of 0.31 eV and the correlation time τ0 in the high temperature limit of 1.3 ps. The 3 / 2 power law dependence of T1-1 on ωL which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the μs timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T1ρ-1 results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes.

  18. Silicon-rich SiO{sub 2}/SiO{sub 2} multilayers: A promising material for the third generation of solar cell

    SciTech Connect

    Gourbilleau, F.; Ternon, C.; Dufour, C.

    2009-07-01

    Si-rich-SiO{sub 2}(SRSO)/SiO{sub 2} multilayers (MLs) have been grown by reactive magnetron sputtering. The presence of silicon nanoclusters (Si-ncls) within the SRSO sublayer and annealing temperature influence optical absorption as well as photoluminescence. The optimized annealing temperature has been found to be 1100 deg. C, which allows the recovery of defects and thus enhances photoluminescence. Four MLs with Si-ncl size ranging from 1.5 to 8 nm have been annealed using the optimized conditions and then studied by transmission measurements. Optical absorption has been modeled so that a size effect in the linear absorption coefficient alpha (in cm{sup -1}) has been evidenced and correlated with TEM observations. It is demonstrated that amorphous Si-ncl absorption is fourfold higher than that of crystalline Si-ncls.

  19. Sensitizing properties of luminescence centers on the emission of Er3+ in Si-rich SiO2 film

    NASA Astrophysics Data System (ADS)

    Fu, Qianyu; Gao, Yuhan; Li, Dongsheng; Yang, Deren

    2016-05-01

    In this paper, we report on the luminescence-center (LC)-mediated excitation of Er3+ as a function of annealing temperature in Er-doped Si-rich SiO2 (SRO) films fabricated by electron beam evaporation. It is found that the annealing temperature has significant effects on the emission of Er3+ and the specific optical-active point-defects called LCs within Er-doped SRO films. Different luminescence centers generated by the evolution of microstructures during annealing process act as efficient sensitizers for Er3+ in the films when the annealing temperature is below 1100 °C. Moreover, the temperature dependence of the energy coupling between LCs and Er3+ demonstrates the effective phonon-mediated energy transfer process. In addition, when the annealing temperature reaches 1100 °C, the decreased density of activable erbium ions induced by the aggregation of Er will bring detrimental effects on the emission of Er3+. It is demonstrated that an appropriate annealing process can be designed to achieve efficiently enhanced emissions from Er3+ ions by optimizing the density of LCs and the coupling between Er3+ and LCs.

  20. Tritium generation and neutron measurements in Pd-Si under high deuterium gas pressure

    SciTech Connect

    Claytor, T.N.; Tuggle, D.G.; Menlove, H.O.

    1991-01-01

    This paper summarizes some of the methods applicable for low level tritium detection needed in the search for anomalous fusion in metal hydrides. It is also intended to further detail our tritium and neutron results that have been obtained with the Pd-Si-D system, originally presented at earlier workshops. A measure of reproducibility that was not evident in our previous work has been achieved partially due to the better detection sensitivity afforded by the use of low tritium deuterium and partially from the fact that the foil-wafer cells can be made with nearly identical electrical characteristics. This reproducibility has allowed us to narrow the optimum conditions for the experiment. While this experiment is rather different from the standard'' electrolytic cell or the Ti gas hydride experiment, similarities exist in that non equilibrium conditions are sought and the tritium generation levels are low and neutron emission is extremely weak. In contrast to many electrochemical cell experiments, the system used in these experiments is completely sealed during operation and uses no electrolyte. The major improvements to the experiment have been the use of vary low tritium deuterium for the hydriding and the replacement of the aluminum neutron counter tubes with ones of stainless steel. These changes have resulted in pronounced improvements to the detection systems since the background tritium level in the gas has been reduced by a factor of 300 and the neutron background has been decreased by a factor of 14. 16 refs., 8 figs., 1 tab.

  1. Radiation detector based on 4H-SiC used for thermal neutron detection

    NASA Astrophysics Data System (ADS)

    Zaťko, B.; Šagátová, A.; Sedlačková, K.; Boháček, P.; Sekáčová, M.; Kohout, Z.; Granja, C.; Nečas, V.

    2016-11-01

    In this work we have focused on detection of thermal neutrons generated by 239Pu-Be isotopic neutron source. A high quality liquid phase epitaxial layer of 4H-SiC was used as a detection region. The thickness of the layer was 70 μ m and the diameter of circular Au/Ni Schottky contact was 4.5 mm. Around the Schottky contact two guard rings were created. The detector structure was first examined as a detector of protons and alpha particles for energy calibration. Monoenergetic protons of energies from 300 keV up to 1.9 MeV were used for detector energy calibration and a good linearity was observed. The energy resolution of 35 keV was obtained for 1.9 MeV protons. The 6LiF conversion layer was applied on the detector Schottky contact. In the experiment we used different thicknesses of conversion layers from 5 μ m up to 35 μ m. Measured detected spectra show two parts corresponding to alpha particles detection in lower energy channels and 3H in higher energy channels. We have also performed simulations of thermal neutron detection using MCNPX (Monte Carlo N-particle eXtended) code. The detection efficiency and the detector response to thermal neutrons was calculated with respect to the 6LiF layer thickness. The detection efficiency calculation is found to be in good agreement with the experiment.

  2. Decay Spectroscopy of Neutron-Rich Cd Around the N = 82 Shell Closure

    NASA Astrophysics Data System (ADS)

    Bernier, Nikita; Dillmann, Iris; Kruecken, Reiner; Griffin Collaboration

    2016-09-01

    The neutron-rich region around A = 132 is of special interest for nuclear astrophysics and nuclear structure. This region is connected with the second r-process abundance peak at A 130 and the waiting-point nuclei around N = 82. For nuclear structure studies, the neighbours of the doubly-magic 132Sn (Z = 50, N = 82) are an ideal test ground for shell model predictions. The beta-decay of the N = 82 isotope 130Cd into 130In was first investigated a decade ago, but the information for states of the lighter indium isotopes (128,129In) is still limited. In the present experiment, a detailed gamma-spectroscopy of the beta-decay of 128-132Cd was achieved with the newly commissioned GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei) gamma-ray spectrometer, which is capable of measuring down to rates of 0.1 pps. The low-energy cadmium isotopes were implanted into a movable tape at the central focus of the array from the ISAC-I facility at TRIUMF. The beta-tagging was performed using the auxiliary beta-particle detector SCEPTAR. The required beta-gamma(-gamma) coincidence data in high statistics needed to fill the spectroscopic gaps described in literature were obtained. The ongoing analysis of these data will be presented. Work supported by the Natural Sciences and Engineering Research Council of Canada and the National Research Council of Canada.

  3. Isomer-delayed gamma-ray spectroscopy of neutron-rich 166Tb

    NASA Astrophysics Data System (ADS)

    Gurgi, L. A.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Walker, P. M.; Podolyák, Zs.; Nishimura, S.; Berry, T. A.; Doornenbal, P.; Lorusso, G.; Isobe, T.; Baba, H.; Xu, Z. Y.; Sakurai, H.; Sumikama, T.; Catford, W. N.; Bruce, A. M.; Browne, F.; Lane, G. J.; Kondev, F. G.; Odahara, A.; Wu, J.; Liu, H. L.; Xu, F. R.; Korkulu, Z.; Lee, P.; Liu, J. J.; Phong, V. H.; Yagi, A.; Zhang, G. X.; Alharbi, T.; Carroll, R. J.; Chae, K. Y.; Dombradi, Zs.; Estrade, A.; Fukuda, N.; Griffin, C.; Ideguchi, E.; Inabe, N.; Kanaoka, H.; Kojouharov, I.; Kubo, T.; Kubono, S.; Kurz, N.; Kuti, I.; Lalkovski, S.; Lee, E. J.; Lee, C. S.; Lotay, G.; Moon, C. B.; Nishizuka, I.; Nita, C. R.; Patel, Z.; Roberts, O. J.; Schaffner, H.; Shand, C. M.; Suzuki, H.; Takeda, H.; Terashima, S.; Vajta, Zs.; Kanaya, S.; Valiente-Dobòn, J. J.

    2017-09-01

    This short paper presents the identification of a metastable, isomeric-state decay in the neutron-rich odd-odd, prolate-deformed nucleus 166Tb. The nucleus of interest was formed using the in-flight fission of a 345 MeV per nucleon 238U primary beam at the RIBF facility, RIKEN, Japan. Gamma-ray transitions decaying from the observed isomeric states in 166Tb were identified using the EURICA gamma-ray spectrometer, positioned at the final focus of the BigRIPS fragments separator. The current work identifies a single discrete gamma-ray transition of energy 119 keV which de-excites an isomeric state in 166Tb with a measured half-life of 3.5(4) μs. The multipolarity assignment for this transition is an electric dipole and is made on the basis internal conversion and decay lifetime arguments. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in 166Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from the coupling of the v(1-/2)?[521] and ? π(3+/2) Nilsson orbitals.

  4. Precision mass measurements of neutron-rich nuclei, and limitations on the r-process environment

    NASA Astrophysics Data System (ADS)

    Van Schelt, Jonathon A.

    2012-05-01

    The masses of 65 neutron-rich nuclides and 6 metastable states from Z = 49 to 64 were measured at a typical precision of δm/m= 10-7 using the Canadian Penning Trap mass spectrometer at Argonne National Laboratory. The measurements are on fission fragments from 252Cf spontaneous fission sources, including those measurements made at the new Californium Rare Isotope Breeder Upgrade facility (CARIBU) and an earlier source. The measured nuclides lie on or approach the predicted path of the astrophysical r process. Where overlap exists, this data set is largely consistent with previous measurements from Penning traps, storage rings, and reaction energetics, but large systematic deviations are apparent in β-endpoint measurements. Simulations of the r process were undertaken to determine how quickly material can pass through the studied elements for a variety of conditions, placing limits on what temperatures densities allow passage on a desired timescale. The new masses produce manifold differences in effective lifetime compared to simulations performed with some model masses.

  5. Spectroscopy of neutron-rich nickel isotopes: Experimental results and microscopic interpretation

    NASA Astrophysics Data System (ADS)

    Girod, M.; Dessagne, Ph.; Bernas, M.; Langevin, M.; Pougheon, F.; Roussel, P.

    1988-06-01

    The spectroscopy of neutron-rich isotopes of 67Ni and 68Ni is studied using the quasi-elastic transfer reactions (14C,16O) and (14C,17O) on a 70Zn mass separated target. The structure of these exotic nuclei is investigated in the framework of a microscopic collective model based on the Hartree-Fock-Bogoliubov theory. Gogny's two-body effective interaction is used. Collective excited states of 68Ni are obtained by solving the Bohr Hamiltonian in which inertia parameters are calculated in the cranking approximation. Spin and parity assignments to observed excited levels are suggested on the basis of information deduced from this analysis. This assignment is further checked by comparing measured angular distributions to predictions. Predictions of the level structure of 70Ni and 78Ni isotopes are given. A more precise test of the 0+ wave functions is provided by the calculation of monopole operator of the 0+1-->0+2 transition in 68Ni. An impressive agreement is obtained between the measured and calculated half-life.

  6. Ground-state nuclear-moment measurement of neutron-rich sulfur isotopes

    NASA Astrophysics Data System (ADS)

    Ohtomo, Yuichi; Ichikawa, Yuichi; Shirai, Hazuki; Ueno, Hideki; Ishibashi, Youko; Suzuki, Takahiro; Furukawa, Takeshi; Yoshimi, Akihiro; Abe, Yasushi; Asahi, Koichiro; Daugasu, J. M.; Fujita, Tomomi; Hayasaka, Miki; Imamura, Kei; Kishi, Shota; Kojima, Shuichiro; Nagae, Daisuke; Nakao, Aiko; Sagayama, Tsubasa; Sakamoto, Yu; Sato, Tomoya

    2014-09-01

    Recently the erosion of N = 28 shell gap has been suggested from several spectroscopic experimental data on neutron-rich nuclei. In particular, 43S isotope is of much interest since shape coexistence is expected to occur which provides key information to understand the evolution of shell gaps far from the stability. The isomeric state of 43S at 320 keV is suggested to have a shape close to sphericity with spin-parity of 7/2, but both the spin-parity and deformed parameter of the ground-state have not been determined directly. In order to investigate mechanisms leading to such an anomalous nuclear structure, we aim at measuring the ground-state nuclear-moment for 41,43S. As the first step, the measurement of μ moment of 41S was performed using the technique of β-NMR method at the RIPS facility at RIKEN. In the presentation, the result of this work will be reported.

  7. E2 transition probabilities for decays of isomers observed in neutron-rich odd Sn isotopes

    SciTech Connect

    Iskra, Ł. W.; Broda, R.; Janssens, R. V.F.; Wrzesiński, J.; Chiara, C. J.; Carpenter, M. P.; Fornal, B.; Hoteling, N.; Kondev, F. G.; Królas, W.; Lauritsen, T.; Pawłat, T.; Seweryniak, D.; Stefanescu, I.; Walters, W. B.; Zhu, S.

    2015-01-01

    High-spin states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following ⁴⁸Ca + ²⁰⁸Pb, ⁴⁸Ca + ²³⁸U, and ⁶⁴Ni + ²³⁸U reactions. By exploiting delayed and cross-coincidence techniques, level schemes have been delineated in odd ¹¹⁹⁻¹²⁵Sn isotopes. Particular attention was paid to the occurrence of 19/2⁺ and 23/2⁺ isomeric states for which the available information has now been significantly extended. Reduced transition probabilities, B(E2), extracted from the measured half-lives and the established details of the isomeric decays exhibit a striking regularity. This behavior was compared with the previously observed regularity of the B(E2) amplitudes for the seniority ν = 2 and 3, 10⁺ and 27/2⁻ isomers in even- and odd-Sn isotopes, respectively.

  8. E2 transition probabilities for decays of isomers observed in neutron-rich odd Sn isotopes

    DOE PAGES

    Iskra, Ł. W.; Broda, R.; Janssens, R. V.F.; ...

    2015-01-01

    High-spin states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following ⁴⁸Ca + ²⁰⁸Pb, ⁴⁸Ca + ²³⁸U, and ⁶⁴Ni + ²³⁸U reactions. By exploiting delayed and cross-coincidence techniques, level schemes have been delineated in odd ¹¹⁹⁻¹²⁵Sn isotopes. Particular attention was paid to the occurrence of 19/2⁺ and 23/2⁺ isomeric states for which the available information has now been significantly extended. Reduced transition probabilities, B(E2), extracted from the measured half-lives and the established details of the isomeric decays exhibit a striking regularity. This behavior was compared with the previously observed regularity of the B(E2) amplitudesmore » for the seniority ν = 2 and 3, 10⁺ and 27/2⁻ isomers in even- and odd-Sn isotopes, respectively.« less

  9. Direct evidence of octupole deformation in neutron-rich 144Ba

    SciTech Connect

    Bucher, B.; Zhu, S.; Wu, C. Y.; Janssens, R. V. F.; Cline, D.; Hayes, A. B.; Albers, M.; Ayangeakaa, A. D.; Butler, P. A.; Campbell, C. M.; Carpenter, M. P.; Chiara, C. J.; Clark, J.; Crawford, H. L.; Cromaz, M.; David, H. M.; Gregor, E. T.; Kondev, F. G.; Harker, J.; Hoffman, C. R.; Kay, B. P.; Korichi, A.; Lauritsen, T.; Macchiavelli, A. O.; Pardo, R. C.; Richard, A.; Riley, M. A.; Savard, G.; Scheck, M.; Seweryniak, D.; Smith, M. K.; Wiens, A.; Vondrasek, R.

    2016-03-17

    Here, the neutron-rich nucleus 144Ba (t1/2 = 11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multistep Coulomb excitation of a post-accelerated 650-MeV 144Ba beam on a 1.0–mg/cm2 208Pb target. The measured value of the matrix element, < 31–∥M(E3)∥01+ >= 0.65(+17–23) eb3/2, corresponds to a reduced B(E3) transition probability of 48(+25–34) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

  10. Direct evidence of octupole deformation in neutron-rich 144Ba

    DOE PAGES

    Bucher, B.; Zhu, S.; Wu, C. Y.; ...

    2016-03-17

    Here, the neutron-rich nucleus 144Ba (t1/2 = 11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multistep Coulomb excitation of a post-accelerated 650-MeV 144Ba beam on a 1.0–mg/cm2 208Pb target. The measured value of the matrix element, < 31–∥M(E3)∥01+ >= 0.65(+17–23) eb3/2, corresponds to a reduced B(E3) transition probabilitymore » of 48(+25–34) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.« less

  11. One- and two-phonon γ -vibrational bands in neutron-rich 107Mo

    NASA Astrophysics Data System (ADS)

    Marcellino, J.; Wang, E. H.; Zachary, C. J.; Hamilton, J. H.; Ramayya, A. V.; Bhat, G. H.; Sheikh, J. A.; Dai, A. C.; Liang, W. Y.; Xu, F. R.; Hwang, J. K.; Brewer, N. T.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.

    2017-09-01

    Neutron-rich 107Mo has been reinvestigated by analyzing the large statistics γ -γ -γ and γ -γ -γ -γ coincidence data from the spontaneous fission of 252Cf at the Gammasphere detector array. Two new bands have been identified. The potential-energy surface calculations of this nucleus have been performed. The calculations show evidence for the 5 /2+[413 ] configuration of the ground-state band and 7 /2-[523 ] configuration for the 348-keV excited band, as assigned in previous work. The two bands newly established are proposed to be one- and two-phonon γ -vibrational bands built on the 7 /2-[523 ] Nilsson orbital, respectively, in the current paper. Triaxial projected shell-model (TPSM) calculations have been performed to explain the level structure and are found in fair agreement with experimental data. In particular, the TPSM study confirms the γ - and γ γ -vibrational structure for the two observed excited band structures. Systematics of the one- and two-phonon γ -vibrational bands in the A ˜100 Mo series is also discussed.

  12. Decay spectroscopy of neutron-rich 134Sb at the CARIBU facility

    NASA Astrophysics Data System (ADS)

    Kolos, Karolina; Scielzo, Nicholas; Padgett, Stephen; McCutchan, Elizabeth A.; Mitchell, Alan John; Lister, Christopher J.; Copp, Patrick; Clark, Jason A.; Carpenter, Mike P.; Savard, Guy; Zhu, Shaofei; Norman, Eric B.; Apbrahamian, Ani; Siegl, Kevin; Heckmaier, Elizabeth; Marley, Scott

    2016-09-01

    Neutron-rich 134Sb is one of a few isotopes (together with 92Rb, 96Y and 142Cs) that have a large branching ratio to decay to the ground state via a 0- ->0+ first-forbidden transition. Previous measurements have indicated that 97.5% of the decays of 134Sb ground state populate the ground state of 134Te directly. However, a recent experiment using an ion trap indicated that this number may be lower. In order to confirm the β-decay branching ratios, an experiment was carried out to measure the decay properties of 134Sb/134mSb using the X-Array (a highly efficient HPGe clover array) and SATURN (a plastic scintillators and tape-transport system) decay-spectroscopy station at the CARIBU radioactive ion-beam facility at Argonne National Laboratory. Results on the analysis will be presented. The U.S. DOE No. DE-AC52-07NA27344, DE-FG02-94ER40848, DE-AC02-98CH10886, DE-AC02-06CH11357, DE-NA-0000979. The NSF under Grant No. PHY-1203100 and the ARCD Project 120104176. This research used resources of ANL's ATLAS facility.

  13. β decay of neutron-rich 118Ag and 120Ag isotopes

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Rinta-Antila, S.; Dendooven, P.; Huikari, J.; Jokinen, A.; Kolhinen, V. S.; Lhersonneau, G.; Nieminen, A.; Nummela, S.; Penttilä, H.; Peräjärvi, K.; Szerypo, J.; Wang, J. C.; Äystö, J.

    2003-06-01

    β decays of on-line mass-separated neutron-rich 118Ag and 120Ag isotopes have been studied by using β-γ and γ-γ coincidence spectroscopy. Extended decay schemes to the 118,120Cd daughter nuclei have been constructed. The three-phonon quintuplet in 118Cd is completed by including a new level at 2023.0 keV, which is tentatively assigned the spin and parity of 2+4. The intruder band in 118Cd is proposed up to the 4+ level at 2322.4 keV. The measured β-decay half-life for the high-spin isomer of 120Ag is 0.40±0.03 s. Candidates for the three-phonon states, as well as the lowest members of the intruder band in 120Cd, are also presented. These data support the coexistence of quadrupole anharmonic vibration and proton particle-hole intruder excitations in 118,120Cd.

  14. Excited State Properties in Neutron-rich Nuclei near N = 40

    NASA Astrophysics Data System (ADS)

    Crider, B. P.; Prokop, C. J.; Liddick, S. N.; Chiara, C. J.; Ayangeakaa, A. D.; Carroll, J. J.; Chen, J.; David, H. M.; Go, S.; Grzywacz, R.; Harker, J.; Janssens, R. V. F.; Lauritsen, T.; Seweryniak, D.; Walters, W. B.

    2015-10-01

    The neutron-rich nuclei near N = 40 have recently been the focus of many experimental and theoretical efforts. In this region, the competing energy cost for promoting pairs of nucleons across either Z = 28 or N = 40 and the energy gain from residual nucleon-nucleon interactions gives rise to several low-energy 0+ states and is a hallmark of shape coexistence. Low-energy 0+ states have been observed in 68Ni, and predicted for other nuclei in the region. Recent theoretical calculations are able to reproduce the energies of known states in 68Ni and stress the importance of the tensor component of the monopole interaction. Yet, while energies of the levels are a useful comparison, a more stringent test is the reproduction of level lifetimes, where the predicted half-lives can vary by several orders of magnitude depending on the interaction. To further benchmark theoretical calculations in this region, a setup designed to measure level lifetimes has been constructed. A description of the array and preliminary results will be presented. This work was supported by the DOE NNSA Award No. DE-NA0000979, NSF Contract No. PHY1102511, DOE SC NP Contract No. DE-AC-06CH11357 and Grant No. DE-FG02-94ER40834.

  15. Resonant states of the neutron-rich Λ hypernucleus He7Λ

    NASA Astrophysics Data System (ADS)

    Hiyama, E.; Isaka, M.; Kamimura, M.; Myo, T.; Motoba, T.

    2015-05-01

    The structure of the neutron-rich Λ hypernucleus, He7Λ is studied within the framework of an α +Λ +n +n four-body cluster model. We predict second 3 /2+ and 5 /2+ states, corresponding to a 0 s Λ coupled to the second 2+ state of 6He, as narrow resonant states with widths of Γ ˜1 MeV to be at 0.03 and 0.07 MeV with respect to the α +Λ +n +n threshold. From a separate estimate of the differential cross section for the 7Li (γ ,K+) He7Λ reaction, we suggest a possibility to observe these states at the Thomas Jefferson National Accelerator Facility (JLab) in the future. We also calculate the second 2+ state of 6He as a resonant state within the framework of an α +n +n three-body cluster model. Our result is 2.81 MeV with Γ =4.63 MeV with respect to the α +n +n threshold. This energy position is ˜1 MeV higher, and with a much broader decay width, than the recent SPIRAL data. We suggest that an experiment at JLab to search for the second 3 /2+ and 5 /2+ states of He7Λ would provide an opportunity to confirm the second 2+ state of the core nucleus 6He.

  16. Direct Evidence of Octupole Deformation in Neutron-Rich ^{144}Ba.

    PubMed

    Bucher, B; Zhu, S; Wu, C Y; Janssens, R V F; Cline, D; Hayes, A B; Albers, M; Ayangeakaa, A D; Butler, P A; Campbell, C M; Carpenter, M P; Chiara, C J; Clark, J A; Crawford, H L; Cromaz, M; David, H M; Dickerson, C; Gregor, E T; Harker, J; Hoffman, C R; Kay, B P; Kondev, F G; Korichi, A; Lauritsen, T; Macchiavelli, A O; Pardo, R C; Richard, A; Riley, M A; Savard, G; Scheck, M; Seweryniak, D; Smith, M K; Vondrasek, R; Wiens, A

    2016-03-18

    The neutron-rich nucleus ^{144}Ba (t_{1/2}=11.5  s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multistep Coulomb excitation of a post-accelerated 650-MeV ^{144}Ba beam on a 1.0-mg/cm^{2} ^{208}Pb target. The measured value of the matrix element, ⟨3_{1}^{-}∥M(E3)∥0_{1}^{+}⟩=0.65(+17/-23) eb^{3/2}, corresponds to a reduced B(E3) transition probability of 48(+25/-34)  W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

  17. Astrophysical implication of low E(21+) in neutron-rich Sn isotopes

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Sarkar, M. Saha

    2009-10-01

    The observation and prediction of unusually depressed first excited 21+ states in even-A neutron-rich isotopes of semi-magic Sn above 132Sn provide motivations for reviewing the problems related to the nuclear astrophysics in general. In the present work, the β-decay rates of the exotic even Sn isotopes (134,136Sn) above the 132Sn core have been calculated as a function of temperature (T). In order to get the necessary ft values, B(GT) values corresponding to allowed Gamow Teller (GT-) β-decay have been theoretically calculated using shell model. The total decay rate shows decrease with increasing temperature as the ground state population is depleted and population of excited states with slower decay rates increases. The abundance at each Z value is inversely proportional to the decay constant of the waiting point nucleus for that particular Z. So the increase in half-life of isotopes of Sn, like 136Sn, might have substantial impact on the r-process nucleosynthesis.

  18. Isomer-delayed gamma-ray spectroscopy of neutron-rich 166Tb

    DOE PAGES

    Gurgi, L. A.; Regan, P. H.; Söderström, P. -A.; ...

    2017-09-13

    Here, this short paper presents the identification of a metastable, isomeric-state decay in the neutron-rich odd-odd, prolate-deformed nucleus 166Tb. The nucleus of interest was formed using the in-flight fission of a 345 MeV per nucleon 238U primary beam at the RIBF facility, RIKEN, Japan. Gamma-ray transitions decaying from the observed isomeric states in 166Tb were identified using the EURICA gamma-ray spectrometer, positioned at the final focus of the BigRIPS fragments separator. The current work identifies a single discrete gamma-ray transition of energy 119 keV which de-excites an isomeric state in 166Tb with a measured half-life of 3.5(4) μs. The multipolaritymore » assignment for this transition is an electric dipole and is made on the basis internal conversion and decay lifetime arguments. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in 166Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from the coupling of the v(1-/2)[521] and π(3+/2) Nilsson orbitals.« less

  19. Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers

    NASA Astrophysics Data System (ADS)

    Wraith, C.; Yang, X. F.; Xie, L.; Babcock, C.; Bieroń, J.; Billowes, J.; Bissell, M. L.; Blaum, K.; Cheal, B.; Filippin, L.; Garcia Ruiz, R. F.; Gins, W.; Grob, L. K.; Gaigalas, G.; Godefroid, M.; Gorges, C.; Heylen, H.; Honma, M.; Jönsson, P.; Kaufmann, S.; Kowalska, M.; Krämer, J.; Malbrunot-Ettenauer, S.; Neugart, R.; Neyens, G.; Nörtershäuser, W.; Nowacki, F.; Otsuka, T.; Papuga, J.; Sánchez, R.; Tsunoda, Y.; Yordanov, D. T.

    2017-08-01

    Collinear laser spectroscopy was performed on Zn (Z = 30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N = 33- 49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-A neutron-rich nuclei up to N = 50. Exactly one long-lived (>10 ms) isomeric state has been established in each 69-79Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell-model calculations in the f5pg9 and fpg9d5 model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder Iπ = 1 /2+ isomer in 79Zn is reproduced only if the νs1/2 orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction. The spin and moments of the low-lying isomeric state in 73Zn suggest a strong onset of deformation at N = 43, while the progression towards 79Zn points to the stability of the Z = 28 and N = 50 shell gaps, supporting the magicity of 78Ni.

  20. β-decay spectroscopy of neutron-rich 160,161,162Sm isotopes

    NASA Astrophysics Data System (ADS)

    Patel, Z.; Podolyák, Zs.; Walker, P. M.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Ideguchi, E.; Simpson, G. S.; Nishimura, S.; Browne, F.; Doornenbal, P.; Lorusso, G.; Rice, S.; Sinclair, L.; Sumikama, T.; Wu, J.; Xu, Z. Y.; Aoi, N.; Baba, H.; Bello Garrote, F. L.; Benzoni, G.; Daido, R.; Dombrádi, Zs.; Fang, Y.; Fukuda, N.; Gey, G.; Go, S.; Gottardo, A.; Inabe, N.; Isobe, T.; Kameda, D.; Kobayashi, K.; Kobayashi, M.; Komatsubara, T.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kuti, I.; Li, Z.; Liu, H. L.; Matsushita, M.; Michimasa, S.; Moon, C.-B.; Nishizuka, H.; Nishizuka, I.; Odahara, A.; Şahin, E.; Sakurai, H.; Schaffner, H.; Suzuki, H.; Takeda, H.; Tanaka, M.; Taprogge, J.; Vajta, Zs.; Xu, F. R.; Yagi, A.; Yokoyama, R.

    2016-09-01

    Neutron-rich 160,161,162Sm isotopes have been populated at the RIBF, RIKEN via β first time. β-coincident γ rays were observed in all three isotopes including γ rays from the isomeric decay of 160Sm and 162Sm. The isomers in 160Sm and 162Sm have previously been observed but have been populated via β decay for the first time. The isomeric state in 162Sm is assigned a {4^ - }v{{7 over 2}^ + }≤ft[ {633} right] otimes v{{1 over 2}^ - }≤ft[ {521} right] configuration based on the decay pattern. The level schemes of 160Sm and 162Sm are presented. The ground states in the parent nuclei 160Pm and 162Pm are both assigned a {6^ - }v{{7 over 2}^ + }≤ft[ {633} right] otimes π {{5 over 2}^ - }≤ft[ {532} right] configuration based on the population of states in the daughter nuclei. Blocked BCS calculations were performed to further investigate the spin-parities of the ground states in 160Pm, 161Pm, and 162Pm, and the isomeric state in 162Sm

  1. Exotic clusters in an unbound region of light neutron-rich systems

    NASA Astrophysics Data System (ADS)

    Ito, Makoto

    2009-10-01

    In light neutron-rich systems, many kinds of molecular structures are discussed from the view point of the clustering phenomena.In particular, much attention has been concentrated on Be isotopes. The molecular orbital (MO), such as &-circ; and &+circ; associated with the covalent binding of atomic molecules, have been shown to give a good description for the low-lying states of these isotopes. In their highly-excited states, furthermore, recent experiments revealed the existence of the interesting resonant states which dominantly decay to the ^6,8He fragments. In this report, we show the unified study of the exotic structures of ^12Be=α+α+4N in an unbound region and the α+^6,8He resonant scattering. We applied the generalized two-center cluster model in which the covalent MO and the atomic orbital (AO) configurations with ^xHe+^yHe could be described in a unified manner. First, we calculated the energy spectra below an α decay-threshold. The (π32^-)^2 (σ12^+)^2 configuration corresponding to ν(0p)^4(sd)^2 becomes the ground state, while (π3 2^-)^2(π12^-)^2 having a large overlap with ν(0p)^6 appears as the first excited state. The rotational band of the ground state reaches to the maximum spin of J^π = 8^+. This result means that the magicity of N=8 is broken in ^12Be due to the formation of (π3 2^-)^2(σ12^+)^2. Next, we solved the scattering problem of α+^8He and identified the several resonance poles. In the continuum region, we found the rotational bands having the AO configurations of α+^8He, ^6He+^6He, and ^5He+^7 He. Furthermore, a much more exotic band appears in the same energy region. In this band, two valence neutrons are localized at individual α-cores (the ^5He+^5He cluster), while the other two neutrons form the covalent &+circ;- bonding between two ^5He clusters; hence, it has a ``hybrid structure'' between the MO configuration and the AO one. In the J^π=0^+ state, it is strongly excited by the two-neutron transfer reaction, α+^8He

  2. RIR MAPLE procedure for deposition of carbon rich Si/C/H films

    NASA Astrophysics Data System (ADS)

    Dřínek, Vladislav; Strašák, Tomáš; Novotný, Filip; Fajgar, Radek; Bastl, Zdeněk

    2014-02-01

    We applied the resonant infrared matrix assisted pulsed laser evaporation (RIR MAPLE) technique to demonstrate a new approach to a controlled deposition of carbon rich amorphous Si/C/H film. In absence of radicals and accelerated species commonly generated in PECVD and sputtering setups, the RIR MAPLE method does not decompose precursor molecules. Moreover, unlike the standard MAPLE procedure, in which solvent molecules absorb laser energy from excimer or near infrared lasers, we applied the pulsed TEA CO2 laser to excite the dendrimer precursor molecules in a frozen target. In this manner we achieved just cross-linking of the starting precursor on substrates and the deposition of carbon rich Si/C/H film. The film was analyzed by Fourier Transformed Infrared (FTIR), UV/VIS, Raman and X-ray Photoelectron (XPS) spectroscopy and Atomic Force Microscopy (AFM) technique. According to analyses the film retained the precursor elemental composition free of graphitic (sp2) clusters. In course of reaction only the peripheral allyl groups containing C=C bonds were opened to achieve cross-linking. Whereas annealing to 300 °C was necessary for the elimination of =C-H1, 2 bonds in the films prepared at 200 °C, those bonds vanished completely for the films prepared at substrate temperature 255 °C. The film posseses a smooth surface with root mean square (RMS) parameter up to 10 nm within scanned distance 2.5 μm.

  3. Comparison of yields of neutron-rich nuclei in proton- and photon-induced 238U fission

    NASA Astrophysics Data System (ADS)

    Khan, F. A.; Bhowmick, Debasis; Basu, D. N.; Farooq, M.; Chakrabarti, Alok

    2016-11-01

    A comparative study of fission of actinides, especially 238U, by proton and bremsstrahlung photon is performed. The relative mass distribution of 238U fission fragments has been explored theoretically for both proton- and photon-induced fission. The integrated yield along with charge distribution of the products are calculated to find the neutron richness in comparison with the nuclei produced by the r process in nucleosynthesis. Some r -process nuclei in the intermediate-mass range for symmetric fission mode are found to be produced almost two orders of magnitude more for proton-induced fission than for photofission, although the rest of the neutron-rich nuclei in the asymmetric mode are produced in comparable proportion for both processes.

  4. New neutron-rich microsecond isomers observed among fission products of {sup 238}U at 80 MeV/nucleon

    SciTech Connect

    Folden, C. M. III; Ginter, T. N.; Hausmann, M.; Portillo, M.; Nettleton, A. S.; Amthor, A. M.; Sherrill, B. M.; Kubo, T.; Takeda, H.; Loveland, W.; Manikonda, S. L.; Morrissey, D. J.; Nakao, T.; Souliotis, G. A.; Strong, B. F.; Tarasov, O. B.

    2009-06-15

    Eight new isomeric states in neutron-rich nuclides have been discovered in fission fragments produced by the reaction of an 80 MeV/nucleon {sup 238}U beam with a {sup 9}Be target and separated in-flight using the A1900 fragment separator. The experiment was conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Gamma rays were detected in a high-purity germanium detector located at the focal plane within a time window of 20 {mu}s following ion implantation. In some cases the isomers were observed to decay into previously reported states, allowing us to assign the initial decay from the isomeric state. Among the outcomes, the results suggest that many studies on the nuclear structure of medium-mass neutron-rich nuclei are feasible at projectile fragmentation facilities using induced fission.

  5. -decay measurements for N > 40 Mn nuclei and inference of collectivity for neutron-rich Fe isotopes

    SciTech Connect

    Daugas, J; Delaroche, J. P.; Pfutzner, M.; Sawicka, M.; Becker, F.; Belier, G.; Bingham, C. R.; Borcea, C.; Bouchez, E.; Buta, A.; Dragulescu, E.; Georgiev, G.; Giovinazzo, J.; Grawe, H.; Grzywacz, R.; Hammache, F.; Libert, J.; Meot, V.; Negoita, F.; de Oliveira Santos, F.; Perru, O.; Roig, O.; Rykaczewski, Krzysztof Piotr; Saint-Laurent, M. G.; Sauvestre, J. E.; Sorlin, O.; Stanoiu, M.; Stefan, I.; Theisen, Ch.

    2011-01-01

    A decay spectroscopic study of the neutron-rich isotopes has been performed using fragmentation of a 86Kr primary beam. Fragments from this reaction have been selected by the LISE2000 spectrometer at the Grand Acc el erateur National d Ions Lourds (GANIL). Half-lives of 29 isotopes, including the first ones identified for 61Ti (15 4 ms), 64V (19 8 ms), and 71Fe (28 5 ms), have been determined and compared with model predictions. 67,68Mn -delayed rays were observed for the first time. The branching for the -delayed neutron emission was measured to be greater than 10(5)% in the 67Mn decay. The 67Fe isomeric level is firmly determined at higher energy than assigned in previous works. The excitation energies of the first (2+) and (4+) states of 68Fe are suggested to lie at 522(1) and 1389(1) keV, respectively, thus bringing confirmation of assignments based on in-beam -ray spectroscopy. Beyond-mean-field calculations with the Gogny D1S force have been performed for even-mass nuclei through the Fe isotopic chain. Not only 68Fe but most of the neutron-rich Fe isotopes with neutron numbers below N = 50 are interpreted as soft rotors. The calculated mean occupancy of the neutron g9/2 and d5/2 orbitals in correlated ground states is steadily growing with increasing neutron number throughout the isotopic chain. Interpretation of 67Fe data is based upon the present calculations for the 66Fe and 68Fe even cores.

  6. Nuclear Structure of Radioactive Neutron-Rich Nuclei with 4pi Detector Arrays

    SciTech Connect

    Wu, C Y; Becker, J A; Cline, D

    2005-05-10

    In-beam studies of {gamma}-ray spectroscopy of radioactive neutron-rich nuclei using the 4{pi} TIGRESS array at TRIUMF requires a ''tag'' to improve the selectivity of the detected {gamma} rays in the high {gamma}-ray background produced by radioactive beams and the need for Doppler-shift correction. We propose development of two types of large solid angle auxiliary charged particle detectors to be used in conjunction with TRIGRESS in order to provide the required tag. The initial phase of detector development will focus on research involving light-mass radioactive beams with Z {le} 20. Gas avalanche detectors, such as CHICO, are not the ideal detector for lighter ions. Therefore, a new detector system, called Bambino, is being developed that is based on commercially available CD type position-sensitive silicon detectors. Three CD-S2 detectors, with a thickness of 140 {micro}m, have been ordered from Micron Semiconductor Ltd. A split spherical target chamber will be built in Rochester to accommodate two of those CD detectors in both forward and backward directions. These detectors will be placed 3 cm from the target, providing an angular coverage from 20.1{sup o} to 49.4{sup o} for the forward hemisphere and from 130.6{sup o} to 159.9{sup o} for the backward hemisphere. The detectors will us ten 8-channels preamplifiers, from Swan Research, that will be mechanically mounted on both the entrance and exit beam pipes. The work on both the internal and external cables connecting the detectors to the preamplifiers, vacuum feedthrough etc. is in progress. In addition, a vacuum chamber has been ordered from Kurt J. Lesker Company for testing these detectors. Bambino should be ready by the spring 2006. The second phase will involve the development of a next generation CHICO-like gas avalanche detector for experiments involving heavier radioactive beams. CHICO, a highly segmented parallel-plate avalanche counter, has proven to be very successful when used in conjunction

  7. Blue--green to near-IR switching electroluminescence from Si-rich silicon oxide/nitride bilayer structures

    NASA Astrophysics Data System (ADS)

    Berencén, Y.; Jambois, O.; Ramírez, J. M.; Rebled, J. M.; Estradé, S.; Peiró, F.; Domínguez, C.; Rodríguez, J. A.; Garrido, B.

    2011-07-01

    Blue--green to near-IR switching electroluminescence (EL) has been achieved in a metal-oxide-semiconductor light emitting device, where the dielectric has been replaced by a Si-rich silicon oxide/nitride bilayer structure. To form Si nanostructures, the layers were implanted with Si ions at high energy, resulting in a Si excess of 19%, and subsequently annealed at 1000°C. Transmission electron microscopy and EL studies allowed ascribing the blue--green emission to the Si nitride related defects and the near-IR band with the emission of the Si-nanoclusters embedded into the SiO2 layer. Charge transport analysis is reported and allows for identifying the origin of this two-wavelength switching effect.

  8. Development of STJ for neutron detector on Si-LBO hybrid substrate by surface-activated room-temperature bonding

    NASA Astrophysics Data System (ADS)

    Endo, S.; Fujii, G.; Ukibe, M.; Takagi, H.; Ohkubo, M.; Naruse, M.; Myoren, H.; Otani, C.; Taino, T.

    2017-07-01

    We have been developing superconducting tunnel junctions (STJs) for neutron detector on a Si-Li2B4O7 (LBO) hybrid substrate. An active area of each STJ was limited by dicing in order to obtain high spatial resolution. The Si-LBO hybrid substrate was bonded by a surface-activated room-temperature bonding. In this bonding method, the Si and LBO surfaces were sputter-etched by high energy Ar ion beam and bonded in a vacuum. We fabricated STJs on the Si-LBO hybrid substrate and measured their current-voltage characteristic. Their leakage currents (I leak) were < 10 nA, and so we succeeded in fabricating STJs on the Si-LBO hybrid substrate, which can be expected to operate as neutron detectors with high performance.

  9. High-spin isomers in neutron-rich nuclei studied with the TARDIS-array at IGISOL

    NASA Astrophysics Data System (ADS)

    Lhersonneau, G.; Butler, P. A.; Cocks, J. F. C.; Honkanen, A.; Huhta, M.; Jones, P. M.; Jokinen, A.; Julin, R.; Juutinen, S.; Lampinen, A.; Müller, D.; Mäkelä, E.; Oinonen, M.; Parmonen, J. M.; Piiparinen, M.; Savelius, A.; Smith, J. F.; Törmänen, S.; Virtanen, A.; Äystö, J.

    1996-02-01

    A 12 Compton-suppressed detector array TARDIS has been placed around the collection spot of the IGISOL separator, with the aim of studying decays of high-spin isomers in neutron-rich isotopes produced by fission. An experiment on 97Y shows that the detection limit is improved by more than one order of magnitude with respect to previous measurements at research reactors with conventional detector setups.

  10. Possibility of production of neutron-rich Zn and Ge isotopes in multinucleon transfer reactions at low energies

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Sargsyan, V. V.; Scheid, W.

    2010-02-15

    The production cross sections of new neutron-rich {sup 84,86}Zn and {sup 90,92}Ge isotopes beyond N=50 are estimated for the first time in the multinucleon transfer reactions {sup 48}Ca + {sup 238}U and {sup 48}Ca + {sup 244}Pu. The production of new isotopes in reactions with a {sup 48}Ca beam is discussed for future experiments.

  11. The effect of neutron irradiation on the mechanical properties of C/SiC composites

    SciTech Connect

    Shih, Chunghao; Katoh, Yutai; Snead, Lance Lewis; Steinbeck, John

    2013-01-01

    The effects of neutron irradiation to 3.5 and 9.5 dpa at 730 C on a 2D plain woven carbon fiber reinforced polymer derived SiC matrix composite are presented. For both fluences, the irradiation caused in-plane contraction and trans-plane expansion. Irradiation also caused substantial reduction in composite flexural strength (54%) and increase in flexural tangent modulus (+85%). The extents of dimensional/ mechanical property changes were greater for the higher fluence irradiated samples. Those changes suggest the instability of the polymer derived SiC matrix following irradiation. The nature of the mechanical property changes suggest increased clamping stress between the fiber and the matrix. The composite property changes are explained in terms of irradiation effects on composite constituents and are compared with carbon fiber reinforced carbon matrix composite as a reference material.

  12. The effect of neutron irradiation on the mechanical properties of C/SiC composites

    NASA Astrophysics Data System (ADS)

    Shih, Chunghao; Katoh, Yutai; Snead, Lance L.; Steinbeck, John

    2013-08-01

    The effects of neutron irradiation to 3.5 and 9.5 dpa at 730 °C on a 2D plain woven carbon fiber reinforced polymer derived SiC matrix composite are presented. For both fluences, the irradiation caused in-plane contraction and trans-plane expansion. Irradiation also caused substantial reduction in composite flexural strength (-54%) and increase in flexural tangent modulus (+85%). The extents of dimensional/mechanical property changes were greater for the higher fluence irradiated samples. Those changes suggest the instability of the polymer derived SiC matrix following irradiation. The nature of the mechanical property changes suggest increased clamping stress between the fiber and the matrix. The composite property changes are explained in terms of irradiation effects on composite constituents and are compared with carbon fiber reinforced carbon matrix composite as a reference material.

  13. Effect of a Si-rich layer on olivine carbonation under in-situ conditions

    NASA Astrophysics Data System (ADS)

    Johnson, N. C.; Thomas, B.; Rosenbauer, R. J.; Maher, K.; Brown, G. E.

    2011-12-01

    Mineral carbonation, a geochemical reaction between Mg-, Fe-, and Ca-silicate minerals and dissolved carbon dioxide (CO2), results in the long-term, stable storage of CO2 as carbonate minerals. Although the reaction is thermodynamically favored and occurs naturally, the kinetics are typically slow at temperatures < 100°C and thus limit industrial applications of the process. This study presents the results of a series of batch reactions designed to further understand the kinetics and mechanism of olivine carbonation in a three-phase system (water, solid, and supercritical CO2) at conditions relevant to in-situ¬ carbonation (60°C, 100 bar CO2 pressure, water:solid of 20:1 to 50:1, pH 3-6 ). Twin Sisters (OR) olivine ((Mg0.85 Fe0.15)2SiO4) was chosen as the reactive silicate mineral because olivines are abundant and undergo carbonation in nature. The carbonation of olivine in the presence of water and supercritical CO2 proceeds via dissolution of the starting mineral and CO2, followed by precipitation of secondary phases. Two secondary phases are relevant to this study. The first is Mg-carbonate (magnesite, MgCO3), the desired reaction product because it sequesters CO2 for geologic time scales. The second is amorphous silica (SiO2), a side-product that increases the total volume of solids in the system but does not interact with CO2. Because the solubility of silica is much less than that of Mg-carbonate at <100°C, silica reaches thermodynamic saturation first. The present study shows that the rate of olivine dissolution depends on the saturation state of amorphous silica and decreases by up to two orders of magnitude (from 10-11 to 10-13 mol cm-2 s-1) as saturation is approached. This observed effect is likely due to formation of a Si-rich layer on olivine grain surfaces after exposure to acidic solution, observed by x-ray photoelectron spectroscopy. The initial olivine dissolution is incongruent over the timeframe of several hours as shown by solution

  14. Neutron Transfer Reactions on Neutron-Rich N=50 and N=82 Nuclei Near the r-Process Path

    SciTech Connect

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, S. D.; Thomas, J. S.; Arbanas, Goran; Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Chae, K. Y.; Chipps, K.; Dean, David Jarvis; Erikson, Luke; Gaddis, A. L.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; Johnson, Micah; Kapler, R.; Krolas, W.; Liang, J Felix; Livesay, Jake; Ma, Zhanwen; Matei, Catalin; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Paulauskas, Stanley V; Shapira, Dan; ShrinerJr., J. F.; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Wilson, Gemma L

    2009-01-01

    Neutron transfer (d,p) reaction studies on the N = 50 isotones, 82Ge and 84Se, and A{approx}130 nuclei, 130,132Sn and 134Te, have been measured. Direct neutron capture cross sections for 82Ge and 84Se (n,?) have been calculated and are combined with Hauser-Feshbach expectations to estimate total (n,?) cross sections. The A{approx}130 studies used an early implementation of the ORRUBA array of position-sensitive silicon strip detectors for reaction proton measurements. Preliminary excitation energy and angular distribution results from the A{approx}130 measurements are reported.

  15. The Use of the Photofission of 238U for a Neutron-Rich Radioactive Ion Beams Generation

    NASA Astrophysics Data System (ADS)

    Szöllős, O.; Kliman, J.

    2003-10-01

    The fission fragments yield for photofission of 238U, induced by bremsstrahlung photons with endpoint energies of 25 and 50MeV was evaluated to estimate the possibility of producing the neutron-rich nuclei. The systematics coming from A.C. Wahl's Zp model 1 for charge distribution of fission fragments were used. Results for xenon and krypton isotopes are compared with experimental data 2 obtained on the DRIBs 3 (Dubna Radioactive Ion Beams) facility for neutron-rich nuclei production in Flerov Laboratory. The fission rate and fission density in production target for metallic uranium and UCx compounds were simulated with Geant4 4 simulation toolkit to design the target geometry, The fission rate dependence on material of the electron stopping target was examined, At nominal beam values on microtron MT-25 (Ie = 20μA, Ee = 25MeV) up to 2.1011 fissions/s could be achieved. Then the production rate of neutron-rich isotopes reaching order of 109s-1. The induced activity in the production target depending on an irradiation time was calculated for radiation protection purposes and target safety estimation. The cumulation of actinide nuclei was also calculated.

  16. Precision Mass Measurements of Short-Lived, Neutron-Rich, R-Process Nuclei About the N=82 Waiting Point

    NASA Astrophysics Data System (ADS)

    Lascar, Daniel David

    This thesis details the precision mass measurements of 33 neutron-rich ground-state nuclei and isomeric states that approach or lie on the proposed rapid neutron capture process (r-process) path. For many of the nuclei measured the work presented here will be the rst direct mass measurements of these nuclei, including 130In, 137Sb, 133I, and 134I. The measurements were made using the Canadian Penning Trap mass spectrometer (CPT), located at the ATLAS heavy ion-linac at Argonne National Laboratory. Ground states and isomers have been measured with the CPT at fractional precisions (δm/m) between 10-7, and 10-8. The nuclei were produced at the new CAlifornium Rare Isotope Breeder Upgrade (CARIBU) to ATLAS. Because nuclear masses are required for measuring neutron separation energies, and neutron separation energies are important inputs in r-process network calculations, precision mass measurements are critical for advancing our knowledge of the r-process. This thesis will give the astrophysical motivation for making these mass measurements, the theoretical background behind ion trapping and mass measurements using ion traps, an explanation of the CPT apparatus, the mass measurements themselves, and the results of those measurements as they pertain to r-process network calculations. Results of these mass measurements show significant shifts in the r-process path over a range of temperatures and neutron densities.

  17. Nuclear-decay studies of neutron-rich rare-earth nuclides

    SciTech Connect

    Chasteler, R.M. . Dept. of Chemistry Lawrence Berkeley Lab., CA )

    1990-04-26

    Neutron-rich rare-earth nuclei were produced in multinucleon transfer reactions of {sup 170}Er and {sup 176}Yb projectiles on {sup nat}W targets at the Lawrence Berkeley Laboratory SuperHILAC and their radioactive decays properties studied at the on-line mass separation facility OASIS. Two unknown isotopes, {sup 169}Dy (t {sub 1/2} {equals} 39 {plus minus} 8 s) and {sup 174}Er(t{sub 1/2} {equals} 3.3 {plus minus} 0.2 m) were discovered and their decay characteristics determined. The decay schemes for two previously identified isotopes, {sup 168}Dy (t{sub 1/2} {equals} 8.8 {plus minus} 0.3 m) and {sup 171}Ho (t{sub 1/2} {equals} 55 {plus minus} 3 s), were characterized. Evidence for a new isomer of 3.0 m {sup 168}Ho{sup g}, {sup 168}Ho{sup m} (t{sub 1/2} {equals} 132 {plus minus} 4 s) which decays by isomeric transition (IT) is presented. Beta particle endpoint energies were determined for the decay of {sup 168}Ho{sup g}, {sup 169}Dy, {sup 171}Ho, and {sup 174}Er, the resulting Q{beta}-values are: 2.93 {plus minus} 0.03, 3.2 {plus minus} 0.3, 3.2 {plus minus} 0.6, and 1.8 {plus minus} 0.2 MeV, respectively. These values were compared with values calculated using recent atomic mass formulae. Comparisons of various target/ion source geometries used in the OASIS mass separator facility for these multinucleon transfer reactions were performed. 73 refs., 40 figs., 11 tabs.

  18. Lifetimes in neutron-rich Nd isotopes measured by Doppler profile method

    SciTech Connect

    Ahmad, I.; Lister, C.J.; Morss, L.R.

    1995-08-01

    Lifetimes of the rotational levels in neutron-rich even-even Nd isotopes were deduced from the analysis of the Doppler broadened line shapes. The experiment was performed at Daresbury with the Eurogam array, which at that time consisted of 45 Compton-suppressed Ge detectors and 5 Low-Energy Photon Spectrometers. The source was in the form of a 7-mm pellet which was prepared by mixing 5-mg; {sup 248}Cm and 65-mg KCl and pressing it under high pressure. Events for which three or more detectors fired were used to construct a cubic data array whose axes represented the {gamma}-ray energies and the contents of each channel the number of events with that particular combination of {gamma}-ray energies. From this cubic array, one-dimensional spectra were generated by placing gates on peaks on the other two axes. Gamma-ray spectra of even-even Nd isotopes were obtained by gating on the transitions in the complimentary Kr fragments. The gamma peaks de-exciting states with I {>=} 12 h were found to be broader than the instrumental line width due to the Doppler effect. The line shapes of they-ray peaks were fitted separately with a simple model for the feeding of the states and assuming a rotational band with constant intrinsic quadruple moment and these are shown in Fig. I-27. The quadrupole moments thus determined were found to be in good agreement with the quadrupole moments measured previously for lower spin states. Because of the success of this technique for the Nd isotopes, we intend to apply this technique to the new larger data set collected with the Eurogam II array. The results of this study were published.

  19. Growth of hexagonal boron nitride on (111) Si for deep UV photonics and thermal neutron detection

    NASA Astrophysics Data System (ADS)

    Ahmed, K.; Dahal, R.; Weltz, A.; Lu, J.-Q.; Danon, Y.; Bhat, I. B.

    2016-09-01

    Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of 1350 °C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm-1 with a full width at half maximum of 25 cm-1, corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors.

  20. Light-toned salty soils and coexisting Si-rich species discovered by the Mars Exploration Rover Spirit in Columbia Hills

    NASA Astrophysics Data System (ADS)

    Wang, Alian; Bell, J. F.; Li, Ron; Johnson, J. R.; Farrand, W. H.; Cloutis, E. A.; Arvidson, R. E.; Crumpler, L.; Squyres, S. W.; McLennan, S. M.; Herkenhoff, K. E.; Ruff, S. W.; Knudson, A. T.; Chen, Wei; Greenberger, R.

    2008-12-01

    Light-toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light-toned soils are hydrous and sulfate-rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter-scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne-Penny, a well-mixed nature for light-toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light-toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Si-rich nodules and soils were observed near the major exposures of S-rich soils. They possess a characteristic feature in Pancam visible near-infrared (Vis-NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si-rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.

  1. Light-toned salty soils and co-existing Si-rich species discovered by the Mars Exploration Rover Spirit in Columbia Hills

    USGS Publications Warehouse

    Wang, Alian; Bell, J.F.; Li, Ron; Johnson, J. R.; Farrand, W. H.; Cloutis, E.A.; Arvidson, R. E.; Crumpler, L.; Squyres, S. W.; McLennan, S.M.; Herkenhoff, K. E.; Ruff, S.W.; Knudson, A.T.; Chen, Wei; Greenberger, R.

    2008-01-01

    Light-toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light-toned soils are hydrous and sulfate-rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter-scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne-Penny, a well-mixed nature for light-toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light-toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Si-rich nodules and soils were observed near the major exposures of S-rich soils. They possess a characteristic feature in Pancam visible near-infrared (Vis-NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si-rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.

  2. Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust

    SciTech Connect

    Meisel, Z.; George, S.; Ahn, S.; Bazin, D.; Brown, B. A.; Browne, J.; Carpino, J. F.; Chung, H.; Cyburt, R. H.; Estrade, A.; Famiano, M.; Gade, A.; Langer, C.; Matos, M.; Mittig, W.; Montes, F.; Morrissey, D. J.; Pereira, J.; Schatz, H.; Schatz, J.; Scott, M.; Shapira, Dan; Sieja, K.; Smith, K.; Stevens, J.; Tan, W.; Tarasov, O.; Towers, S.; Wimmer, K.; Winkelbauer, J. R.; Yurkon, J.; Zegers, R. G. T.

    2016-03-22

    Here, we present the mass excesses of 59-64Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N = 38. Additionally, we extend the S2n trend for chromium to N = 40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-art shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g9/2 and d5/2 orbits for the neutron valence space. We employ our result for the mass of 64Cr in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A = 64 isobaric chain, resulting in a cooler than expected accreted neutron star crust. This reduced heating is found to be due to the >1-MeV reduction in binding for 64Cr with respect to values from commonly used global mass models.

  3. Crossover from skin mode to proton-neutron mode in E1 excitations of neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Nakada, H.; Inakura, T.; Sawai, H.

    2013-03-01

    The character of the low-energy E1 excitations is investigated by analyzing transition densities obtained from the RPA calculations in the doubly magic nuclei. We propose a decomposition method of the E1 excitations into the pn mode (i.e., oscillation between protons and neutrons) and the skin mode (i.e., oscillation of the neutron skin against the inner core) via the transition densities, by which their mixing is handled in a straightforward manner. Crossover behavior of the E1 excitations is found, from the skin mode at low energy to the pn mode at higher energy. The ratio of the skin-mode strength to the full strength turns out to be insensitive to the nuclides and to the effective interactions in the energy region of the crossover. Depending on the excitation energy, the observed low-energy E1 excitations are not necessarily dominated by the skin mode, as exemplified for 90Zr.

  4. Characterization of the Fe-rich corner of Al-Fe-Si-Ti.

    PubMed

    Marker, Martin C J; Duarte, Liliana I; Leinenbach, Christian; Richter, Klaus W

    2013-08-01

    The quaternary system Al-Fe-Si-Ti was studied in the iron-rich corner for sections at 50, 60 and 70 at.% Fe at 900 °C. Isothermal phase equilibria were investigated by a combination of optical microscopy, X-ray powder diffraction (XRD) followed by Rietveld refinement and Electron Probe Microanalysis (EPMA). Phase boundaries of the phases, in particular of the Laves phase (Fe2Ti) and of the extended phase field of A2/B2/D03, were investigated. Selected samples containing the Laves phase and the B2 phase were characterized by microhardness measurements at different compositions throughout the quaternary homogeneity range of the phases.

  5. Surface properties of neutron-rich exotic nuclei: A source for studying the nuclear symmetry energy

    SciTech Connect

    Gaidarov, M. K.; Antonov, A. N.; Sarriguren, P.; Moya de Guerra, E.

    2011-09-15

    We study the correlation between the thickness of the neutron skin in finite nuclei and the nuclear symmetry energy for isotopic chains of even-even Ni, Sn, and Pb nuclei in the framework of the deformed self-consistent mean-field Skyrme HF + BCS method. The symmetry energy, the neutron pressure, and the asymmetric compressibility in finite nuclei are calculated within the coherent density fluctuation model using the symmetry energy as a function of density within the Brueckner energy density functional. The mass dependence of the nuclear symmetry energy and the neutron-skin thickness are also studied together with the role of the neutron-proton asymmetry. A correlation between the parameters of the equation of state (symmetry energy and its density slope) and the neutron skin is suggested in the isotopic chains of Ni, Sn, and Pb nuclei.

  6. Magnetic ordering in UCoNiSi2 and UCoCuSi2 studied by ac-susceptibility and neutron-diffraction measurements

    NASA Astrophysics Data System (ADS)

    Kuznietz, Moshe; Pinto, Haim; Melamud, Mordechai

    1994-05-01

    Polycrystalline samples of intermediate solid solutions of the UM2Si2 compounds (M=Co,Ni,Cu), namely UCoNiSi2 and UCoCuSi2, were prepared and were found to have body-centered tetragonal ThCr2Si2-type crystallographic structure. In UCoNiSi2 ac susceptibility indicates a single antiferromagnetic (AF) transition at TN=115±5 K, confirmed by neutron-diffraction observation of the AF-I structure down to 10 K (with uranium moments of 1.6±0.2μB, along the tetragonal c axis). In UCoCuSi2 ac susceptibility indicates ferromagnetic transition at TC=107±5 K, and implies an AF transition at lower temperature, confirmed by the AF-I structure, observed in neutron diffraction below T0=95±5 K down to 10 K (with uranium moments of 1.6±0.1μB, along the c axis). The magnetic properties are discussed in comparison with UM2X2 and U(M,M')2X2 materials (X=Si,Ge).

  7. Superior magnetic softness at elevated temperature of Si-rich Fe-based nanocrystalline alloy

    NASA Astrophysics Data System (ADS)

    Shi, Rui-min; Wang, Zhi; Jia, Yun-yun; Wen, Zhuan-ping; Wang, Bo-wen; Zhang, Tao

    2012-10-01

    An excellent high-temperature magnetic softness was observed in a Si-rich nanocrystalline Fe74.5Cu1Nb2Si17.5B5 alloy. The Curie temperatures of amorphous and crystal phases, TCA* and TCcry, for this alloy were detected to be 365 °C and 580 °C, respectively. For the 480 °C-annealed alloy, the initial permeability μi drops to nearly zero just above TCA*; however, for the 540 °C-annealed alloy, the μi of about 10 000 at f = 10 kHz has no perceivable decline in this temperature range and can hold up to more than 400 °C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported. The origin of the high temperature magnetic softness was interpreted by the enhancement effect of Curie temperature in residual amorphous matrix.

  8. Isobaric yield ratios in heavy-ion reactions, and symmetry energy of neutron-rich nuclei at intermediate energies

    SciTech Connect

    Ma Chunwang; Wang Fang; Ma Yugang; Jin Chan

    2011-06-15

    The isobaric yield ratios of the fragments produced in the neutron-rich {sup 48}Ca and {sup 64}Ni projectile fragmentation are analyzed in the framework of a modified Fisher model. The correlations between the isobaric yield ratios (R) and the energy coefficients in the Weiszaecker-Beth semiclassical mass formula (the symmetry-energy term a{sub sym}, the Coulomb-energy term a{sub c}, and the pairing-energy term a{sub p}) and the difference between the chemical potentials of the neutron and proton ({mu}{sub n}-{mu}{sub p}) are investigated. Simple correlations between ({mu}{sub n}-{mu}{sub p})/T, a{sub c}/T, a{sub sym}/T, and a{sub p}/T (where T is the temperature), and lnR are obtained. It is suggested that ({mu}{sub n}-{mu}{sub p})/T, a{sub c}/T, a{sub sym}/T, and a{sub p}/T of neutron-rich nuclei can be extracted using isobaric yield ratios for heavy-ion collisions at intermediate energies.

  9. Non destructive examination of UN / U-Si fuel pellets using neutrons (preliminary assessment)

    SciTech Connect

    Bourke, Mark Andrew; Vogel, Sven C.; Voit, Stewart Lancaster; Mcclellan, Kenneth James; Losko, Adrian S.; Tremsin, Anton

    2016-03-31

    Tomographic imaging and diffraction measurements were performed on nine pellets; four UN/ U Si composite formulations (two enrichment levels), three pure U3Si5 reference formulations (two enrichment levels) and two reject pellets with visible flaws (to qualify the technique). The U-235 enrichments ranged from 0.2 to 8.8 wt.%. The nitride/silicide composites are candidate compositions for use as Accident Tolerant Fuel (ATF). The monophase U3Si5 material was included as a reference. Pellets from the same fabrication batches will be inserted in the Advanced Test Reactor at Idaho during 2016. The goal of the Advanced Non-destructive Fuel Examination work package is the development and application of non-destructive neutron imaging and scattering techniques to ceramic and metallic nuclear fuels. Data reported in this report were collected in the LANSCE run cycle that started in September 2015 and ended in March 2016. Data analysis is ongoing; thus, this report provides a preliminary review of the measurements and provides an overview of the characterized samples.

  10. Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiNx:H films

    PubMed Central

    2011-01-01

    In this study, a wide range of a-SiNx:H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH3 and SiH4. The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si3N4/SRSN/SiO2/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices. PMID:21711712

  11. Observation of new neutron-rich Mn, Fe, Co, Ni, and Cu isotopes in the vicinity of 78Ni

    NASA Astrophysics Data System (ADS)

    Sumikama, T.; Nishimura, S.; Baba, H.; Browne, F.; Doornenbal, P.; Fukuda, N.; Franchoo, S.; Gey, G.; Inabe, N.; Isobe, T.; John, P. R.; Jung, H. S.; Kameda, D.; Kubo, T.; Li, Z.; Lorusso, G.; Matea, I.; Matsui, K.; Morfouace, P.; Mengoni, D.; Napoli, D. R.; Niikura, M.; Nishibata, H.; Odahara, A.; Sahin, E.; Sakurai, H.; Söderström, P.-A.; Stefan, G. I.; Suzuki, D.; Suzuki, H.; Takeda, H.; Taniuchi, R.; Taprogge, J.; Vajta, Zs.; Watanabe, H.; Werner, V.; Wu, J.; Xu, Z. Y.; Yagi, A.; Yoshinaga, K.

    2017-05-01

    Neutron-rich nuclei in the vicinity of 78Ni were produced using a 238U beam at the RIKEN Radioactive Isotope Beam Factory. The particle-identification plot for the in-flight fission fragments highlights the first observation of eight new isotopes: 73Mn, 76Fe, Co,7877, 80,81,82Ni, and 83Cu. Although the β -decay half-lives of 77Co and 80Ni were recently reported by Xu et al. [Phys. Rev. Lett. 113, 032505 (2014)], 10.1103/PhysRevLett.113.032505 using data from the same experiment, the current work provides the first direct, quantitative evidence for the existence of these isotopes. The experimental production cross sections are reproduced in a satisfactory manner by theoretical predictions. An odd-even staggering of the cross sections was observed, and the effect appears to become more pronounced for the most exotic nuclei that were investigated. The staggering effect was interpreted as an increase of the neutron-evaporation probability for odd-N isotopes, owing to the decrease of the neutron-separation energy, Sn. The predicted cross section for 80Ni is significantly overestimated, which may be related to a weak binding of the neutron pair above the N =50 shell closure.

  12. Exploring the extended density-dependent Skyrme effective forces for normal and isospin-rich nuclei to neutron stars

    SciTech Connect

    Agrawal, B.K.; Dhiman, Shashi K.; Kumar, Raj

    2006-03-15

    We parametrize the recently proposed generalized Skyrme effective force (GSEF) containing extended density dependence. The parameters of the GSEF are determined by the fit to several properties of the normal and isospin-rich nuclei. We also include in our fit a realistic equation of state for the pure neutron matter up to high densities so that the resulting Skyrme parameters can be suitably used to model the neutron star with the 'canonical' mass ({approx}1.4M{sub {center_dot}}). For the appropriate comparison, we generate a parameter set for the standard Skyrme effective force (SSEF) using exactly the same set data as employed to determine the parameters of the GSEF. We find that the GSEF yields larger values for the neutron skin thickness which are closer to the recent predictions based on the isospin diffusion data. The Skyrme parameters so obtained are employed to compute the strength function for the isoscalar giant monopole, dipole, and quadrupole resonances. It is found that in the case of GSEF, because of the larger value of the nucleon effective mass, the values of centroid energies for the isoscalar giant resonances are in better agreement with the corresponding experimental data than those obtained using the SSEF. We also present results for some of the key properties associated with the neutron star of canonical mass and for the one with the maximum mass.

  13. B(E2)↑ Measurements for Radioactive Neutron-Rich Ge Isotopes: Reaching the N=50 Closed Shell

    NASA Astrophysics Data System (ADS)

    Padilla-Rodal, E.; Galindo-Uribarri, A.; Baktash, C.; Batchelder, J. C.; Beene, J. R.; Bijker, R.; Brown, B. A.; Castaños, O.; Fuentes, B.; del Campo, J. Gomez; Hausladen, P. A.; Larochelle, Y.; Lisetskiy, A. F.; Mueller, P. E.; Radford, D. C.; Stracener, D. W.; Urrego, J. P.; Varner, R. L.; Yu, C.-H.

    2005-03-01

    The B(E2;0+1→2+1) values for the radioactive neutron-rich germanium isotopes 78,80Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction.

  14. β-decay of neutron-rich Z∼60 nuclei and the origin of rare earth elements

    SciTech Connect

    Wu, J.; Nishimura, S.; Lorusso, G.; Baba, H.; Doornenbal, P.; Isobe, T.; Söderström, P. A.; Sakurai, H.; Xu, Z. Y.; Browne, F.; Daido, R.; Fang, Y. F.; Yagi, A.; Nishibata, H.; Odahara, A.; Yamamoto, T.; Ideguchi, E.; Aoi, N.; Tanaka, M.; Collaboration: EURICA Collaboration; and others

    2014-05-02

    A large fraction of the rare-earth elements observed in the solar system is produced in the astrophysical rapid neutron capture process (r-process). However, current stellar models cannot completely explain the relative abundance of these elements partially because of nuclear physics uncertainties. To address this problem, a β-decay spectroscopy experiment was performed at RI Beam Factory (RIBF) at RIKEN, aimed at studying a wide range of very neutron-rich nuclei with Z∼60 that are progenitors of the rare-earth elements with mass number A∼460. The experiment provides a test of nuclear models as well as experimental inputs for r-process calculations. This contribution presents the experimental setup and some preliminary results of the experiment.

  15. Extremely Metal-poor Stars. The Carbon-rich, Neutron Capture Element--poor Object CS 22957-027

    NASA Astrophysics Data System (ADS)

    Norris, John E.; Ryan, Sean G.; Beers, Timothy C.

    1997-11-01

    Analysis of high-resolution spectra of the carbon-rich, metal-poor giant CS 22957-027 yields [Fe/H] = -3.38, [C/Fe] = 2.2, 12C/13C = 10, [N/Fe] = 2.0, [Sr/Fe] = -0.6, and [Ba/Fe] = -1.0. This combination of large C and N overabundances and the absence of heavy neutron capture element enrichment differs from that normally found in C-rich metal-poor stars, which are all usually enhanced in these elements. Any explanation in terms of the canonical binary mass transfer origin of CH stars or of supernovae ejecta requires a decoupling of the processes that produce the C and neutron capture element overabundances. An alternative possibility is that the heavy element abundances are typical of the halo interstellar medium from which CS 22957-027 formed and the C and N overabundances result from processes internal to the star itself. One candidate process is helium core flash induced mixing in low-mass, zero heavy element stars as predicted by Hollowell et al. CS 22957-027 exhibits strong features of 13CH at ~4019.0 A, which coincide with Th II 4019.12 A. This should be borne in mind when using the Th/Eu ratio in metal-poor, C-rich stars such as CS 22892-052 as a Galactic chronometer.

  16. Mechanical properties of SiC composites neutron irradiated under light water reactor relevant temperature and dose conditions

    NASA Astrophysics Data System (ADS)

    Koyanagi, Takaaki; Katoh, Yutai

    2017-10-01

    Silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites are being actively investigated for use in accident-tolerant core structures of light water reactors (LWRs). Owing to the limited number of irradiation studies previously conducted at LWR-coolant temperature, this study examined SiC/SiC composites following neutron irradiation at 230-340 °C to 2.0 and 11.8 dpa in the High Flux Isotope Reactor. The investigated materials were chemical vapor infiltrated (CVI) SiC/SiC composites with three different reinforcement fibers. The fiber materials were monolayer pyrolytic carbon (PyC) -coated Hi-Nicalon™ Type-S (HNS), Tyranno™ SA3 (SA3), and SCS-Ultra™ (SCS) SiC fibers. The irradiation resistance of these composites was investigated based on flexural behavior, dynamic Young's modulus, swelling, and microstructures. There was no notable mechanical properties degradation of the irradiated HNS and SA3 SiC/SiC composites except for reduction of the Young's moduli by up to 18%. The microstructural stability of these composites supported the absence of degradation. In addition, no progressive swelling from 2.0 to 11.8 dpa was confirmed for these composites. On the other hand, the SCS composite showed significant mechanical degradation associated with cracking within the fiber. This study determined that SiC/SiC composites with HNS or SA3 SiC/SiC fibers, a PyC interphase, and a CVI SiC matrix retain their properties beyond the lifetime dose for LWR fuel cladding at the relevant temperature.

  17. Mechanical properties of SiC composites neutron irradiated under light water reactor relevant temperature and dose conditions

    DOE PAGES

    Koyanagi, Takaaki; Katoh, Yutai

    2017-07-04

    Silicon carbide (SiC) fiber–reinforced SiC matrix (SiC/SiC) composites are being actively investigated for use in accident-tolerant core structures of light water reactors (LWRs). Owing to the limited number of irradiation studies previously conducted at LWR-coolant temperature, this paper examined SiC/SiC composites following neutron irradiation at 230–340 °C to 2.0 and 11.8 dpa in the High Flux Isotope Reactor. The investigated materials were chemical vapor infiltrated (CVI) SiC/SiC composites with three different reinforcement fibers. The fiber materials were monolayer pyrolytic carbon (PyC) -coated Hi-Nicalon™ Type-S (HNS), Tyranno™ SA3 (SA3), and SCS-Ultra™ (SCS) SiC fibers. The irradiation resistance of these composites wasmore » investigated based on flexural behavior, dynamic Young's modulus, swelling, and microstructures. There was no notable mechanical properties degradation of the irradiated HNS and SA3 SiC/SiC composites except for reduction of the Young's moduli by up to 18%. The microstructural stability of these composites supported the absence of degradation. In addition, no progressive swelling from 2.0 to 11.8 dpa was confirmed for these composites. On the other hand, the SCS composite showed significant mechanical degradation associated with cracking within the fiber. Finally, this study determined that SiC/SiC composites with HNS or SA3 SiC/SiC fibers, a PyC interphase, and a CVI SiC matrix retain their properties beyond the lifetime dose for LWR fuel cladding at the relevant temperature.« less

  18. Sensitivity of the moment of inertia of neutron stars to the equation of state of neutron-rich matter

    SciTech Connect

    Fattoyev, F. J.; Piekarewicz, J.

    2010-08-15

    The sensitivity of the stellar moment of inertia to the neutron-star matter equation of state is examined using accurately calibrated relativistic mean-field models. We probe this sensitivity by tuning both the density dependence of the symmetry energy and the high-density component of the equation of state, properties that are at present poorly constrained by existing laboratory data. Particularly attractive is the study of the fraction of the moment of inertia contained in the solid crust. Analytic treatments of the crustal moment of inertia reveal a high sensitivity to the transition pressure at the core-crust interface. This may suggest the existence of a strong correlation between the density dependence of the symmetry energy and the crustal moment of inertia. However, no correlation was found. We conclude that constraining the density dependence of the symmetry energy - through, for example, the measurement of the neutron skin thickness in {sup 208}Pb - will place no significant bound on either the transition pressure or the crustal moment of inertia.

  19. MSL SAM-Like Evolved Gas Analyses of Si-rich Amorphous Materials

    NASA Technical Reports Server (NTRS)

    McAdam, Amy; Knudson, Christine; Sutter, Brad; Andrejkovicova, Slavka; Archer, P. Douglas; Franz, Heather; Eigenbrode, Jennifer; Morris, Richard; Ming, Douglas; Sun, Vivian; Wilhelm, Mary Beth; Mahaffy, Paul

    2016-01-01

    Chemical and mineralogical analyses of several samples from Murray Formation mudstones and Stimson Formation sandstones by the Mars Science Laboratory (MSL) revealed the presence of Si-rich amorphous or poorly ordered materials. It is possible to identify the presence of high-SiO2 vs. lower SiO2 amorphous materials (e.g., basaltic glasses), based on the position of the resulting wide diffraction features in XRD patterns from the Chemistry and Mineralogy (CheMin) instrument, but it is not possible to distinguish between several candidate high-SiO2 amorphous materials such as opal-A or rhyolitic glass. In the Buckskin (BS) sample from the upper Murray Formation, and the Big Sky (BY) and Greenhorn (GH) samples from the Stimson Formation, analyses by the Sample Analysis at Mars (SAM) instrument showed very broad H2O evolutions during sample heating at temperatures >450-500degC which had not been observed from previous samples. BS also had a significant broad evolution <450-500degC. We have undertaken a laboratory study targeted at understanding if the data from SAM can be used to place constraints on the nature of the amorphous phases. SAM-like evolved gas analyses have been performed on several opal and rhyolitic glass samples. Opal-A samples exhibited wide <500degC H2O evolutions, with lesser H2O evolved above 500degC. H2O evolution traces from rhyolitic glasses varied, having either two broad H2O peaks, <300degC and >500degC, or a broad peak centered around 400degC. For samples that produced two evolutions, the lower temperature peak is more intense than the higher temperature peak, a trend also exhibited by opal-A. This trend is consistent with data from BS, but does not seem consistent with data from BY and GH which evolved most of their H2O >500degC. It may be that dehydration of opal-A and/or rhyolitic glass can result in some preferential loss of lower temperature H2O, to produce traces that more closely resemble BY and GH. This is currently under investigation

  20. Boron doped Si rich oxide/SiO{sub 2} and silicon rich nitride/SiN{sub x} bilayers on molybdenum-fused silica substrates for vertically structured Si quantum dot solar cells

    SciTech Connect

    Lin, Ziyun Wu, Lingfeng; Jia, Xuguang; Zhang, Tian; Puthen-Veettil, Binesh; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-07-28

    Vertically structured Si quantum dots (QDs) solar cells with molybdenum (Mo) interlayer on quartz substrates would overcome current crowding effects found in mesa-structured cells. This study investigates the compatibility between boron (B) doped Si QDs bilayers and Mo-fused silica substrate. Both Si/SiO{sub 2} and Si/SiN{sub x} based QDs bilayers were studied. The material compatibility under high temperature treatment was assessed by examining Si crystallinity, microstress, thin film adhesion, and Mo oxidation. It was observed that the presence of Mo interlayer enhanced the Si QDs size confinement, crystalline fraction, and QDs size uniformity. The use of B doping was preferred compared to phosphine (PH{sub 3}) doping studied previously in terms of better surface and interface properties by reducing oxidized spots on the film. Though crack formation due to thermal mismatch after annealing remained, methods to overcome this problem were proposed in this paper. Schematic diagram to fabricate full vertical structured Si QDs solar cells was also suggested.

  1. Exploring Light Neutron Rich Nuclei via the ({sup 7}Li,{sup 7}Be) Reaction

    SciTech Connect

    Cavallaro, M.; Cappuzzello, F.; Cunsolo, A.; Foti, A.; Orrigo, S. E. A.; Rodrigues, M. R. D.; Borello-Lewin, T.; Lenske, H.; Petrascu, H.; Winfield, J. S.

    2008-11-11

    A systematic study of the nuclei that can be described as an integer number of {alpha} particles plus three neutrons via the ({sup 7}Li,{sup 7}Be) reaction at about 8 MeV/u has shown the presence of Bound States Embedded in the Continuum in the energy spectra. These are experimental signatures of the dynamical correlations of an easily polarizable core with a single-particle state of the valence neutron.

  2. Neutron transition strengths of 2{sub 1}{sup +} states in the neutron-rich oxygen isotopes determined from inelastic proton scattering

    SciTech Connect

    Nguyen Dang Chien; Khoa, Dao T.

    2009-03-15

    A coupled-channel analysis of the {sup 18,20,22}O(p,p{sup '}) data has been performed to determine the neutron transition strengths of the 2{sub 1}{sup +} states in oxygen targets, using the microscopic optical potential and inelastic form factor calculated in the folding model. A complex density- and isospin-dependent version of the CDM3Y6 interaction was constructed, based on the Brueckner-Hartree-Fock calculation of nuclear matter, for the folding model input. Given an accurate isovector density dependence of the CDM3Y6 interaction, the isoscalar ({delta}{sub 0}) and isovector ({delta}{sub 1}) deformation lengths of the 2{sub 1}{sup +} states in {sup 18,20,22}O have been extracted from the folding model analysis of the (p,p{sup '}) data. A specific N dependence of {delta}{sub 0} and {delta}{sub 1} has been established which can be linked to the neutron shell closure occurring at N approaching 16. The strongest isovector deformation was found for the 2{sub 1}{sup +} state in {sup 20}O, with {delta}{sub 1} about 2.5 times larger than {delta}{sub 0}, which indicates a strong core polarization by the valence neutrons in {sup 20}O. The ratios of the neutron/proton transition matrix elements (M{sub n}/M{sub p}) determined for the 2{sub 1}{sup +} states in {sup 18,20}O have been compared with those deduced from the mirror symmetry, using the measured B(E2) values of the 2{sub 1}{sup +} states in the proton-rich {sup 18}Ne and {sup 20}Mg nuclei, to discuss the isospin impurity in the 2{sub 1}{sup +} excitation of the A=18, T=1 and A=20, T=2 isobars.

  3. Half-lives and branchings for {beta}-delayed neutron emission for neutron-rich Co-Cu isotopes in the r-process

    SciTech Connect

    Hosmer, P.; Estrade, A.; Montes, F.; Ouellette, M.; Pellegrini, E.; Schatz, H.; Aprahamian, A.; Arndt, O.; Pfeiffer, B.; Clement, R. R. C.; Mueller, W. F.; Morton, A. C.; Pereira, J.; Santi, P.; Steiner, M.; Stolz, A.; Farouqi, K.; Kratz, K.-L.; Liddick, S. N.; Mantica, P. F.

    2010-08-15

    The {beta} decays of very neutron-rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL {beta}-counting station in conjunction with the neutron detector NERO. We measured the branchings for {beta}-delayed neutron emission (P{sub n} values) for {sup 74}Co (18{+-}15%) and {sup 75-77}Ni (10{+-}2.8%, 14{+-}3.6%, and 30{+-}24%, respectively) for the first time, and remeasured the P{sub n} values of {sup 77-79}Cu, {sup 79,81}Zn, and {sup 82}Ga. For {sup 77-79}Cu and for {sup 81}Zn we obtain significantly larger P{sub n} values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of {sup 75}Co (30{+-}11 ms) and {sup 80}Cu (170{sub -50}{sup +110} ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is better able to reproduce the A=78-80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino-driven high-entropy winds in core collapse supernovae.

  4. SiC-based neutron detector in quasi-realistic working conditions: efficiency and stability at room and high temperature under fast neutron irradiations

    SciTech Connect

    Ferone, Raffaello; Issa, Fatima; Ottaviani, Laurent; Biondo, Stephane; Vervisch, Vanessa; Szalkai, Dora; Klix, Axel; Vermeeren, Ludo; Saenger, Richard; Lyoussi, Abadallah

    2015-07-01

    In the framework of the European I SMART project, we have designed and made new SiC-based nuclear radiation detectors able to operate in harsh environments and to detect both fast and thermal neutrons. In this paper, we report experimental results of fast neutron irradiation campaign at high temperature (106 deg. C) in quasi-realistic working conditions. Our device does not suffer from high temperature, and spectra do show strong stability, preserving features. These experiments, as well as others in progress, show the I SMART SiC-based device skills to operate in harsh environments, whereas other materials would strongly suffer from degradation. Work is still demanded to test our device at higher temperatures and to enhance efficiency in order to make our device fully exploitable from an industrial point of view. (authors)

  5. Neutron scattering study of the field-induced tricritical point in MnSi

    NASA Astrophysics Data System (ADS)

    Kindervater, J.; Bauer, A.; Garst, M.; Janoschek, M.; Martin, N.; Mühlbauer, S.; Häussler, W.; Böni, P.; Pfleiderer, C.

    The intermetallic compound MnSi attracts great scientific interest due to two unusual phase transitions, namely the transition from the conical phase to a skyrmion lattice in small fields and the transition from the helical to the paramagnetic phase without external magnetic field that was recently identified to be a fluctuation induced first-order transition, i.e. a so called Brazovskii-transition. Recent measurements of the specific heat provide striking evidence for a tricritical point (TCP), were the first order transition alters to second order. We report neutron spin echo measurements using the MIEZE technique. The recorded quasi elastic linewidth shows a change of the characteristic spin fluctuations at the TCP. The combination with additional SANS measurements and a generalized Brazovskii theory establishes a consistent picture of the statics and dynamics of the transition. Financial support by ERC-AdG (291079 TOPFIT) and through DFG TRR80 is greatfully acknowledged.

  6. Primary photoluminescence in as-neutron (electron) -irradiated n-type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Zhong, Z. Q.; Wu, D. X.; Gong, M.; Wang, O.; Shi, S. L.; Xu, S. J.; Chen, X. D.; Ling, C. C.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.

    2006-05-01

    Low-temperature photoluminescence spectroscopy has revealed a series of features labeled S1, S2, S3 in n-type 6H-SiC after neutron and electron irradiation. Thermal annealing studies showed that the defects S1, S2, S3 disappeared at 500 °C. However, the well-known D1 center was only detected for annealing temperatures over 700 °C. This experimental observation not only indicated that the defects S1, S2, S3 were a set of primary defects and the D1 center was a kind of secondary defect, but also showed that the D1 center and the E1, E2 observed using deep level transient spectroscopy might not be the same type of defects arising from the same physical origin.

  7. Theoretical study on production of heavy neutron-rich isotopes around the N = 126 shell closure in radioactive beam induced transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Long; Su, Jun; Xie, Wen-Jie; Zhang, Feng-Shou

    2017-04-01

    In order to produce more unknown neutron-rich nuclei around N = 126, the transfer reactions 136Xe + 198Pt, 136-144Xe + 208Pb, and 132Sn + 208Pb are investigated within the framework of the dinuclear system (DNS) model. The influence of neutron excess of projectile on production cross sections of target-like products is studied through the reactions 136,144Xe + 208Pb. We find that the radioactive projectile 144Xe with much larger neutron excess is favorable to produce neutron-rich nuclei with charge number less than the target rather than produce transtarget nuclei. The incident energy dependence of yield distributions of fragments in the reaction 132Sn + 208Pb are also studied. The production cross sections of neutron-rich nuclei with Z = 72- 77 are predicted in the reactions 136-144Xe + 208Pb and 132Sn + 208Pb. It is noticed that the production cross sections of unknown neutron-rich nuclei in the reaction 144Xe + 208Pb are at least two orders of magnitude larger than those in the reaction 136Xe + 208Pb. The radioactive beam induced transfer reactions 139,144Xe + 208Pb, considering beam intensities proposed in SPIRAL2 (Production System of Radioactive Ion and Acceleration On-Line) project as well, for production of neutron-rich nuclei around the N = 126 shell closure are investigated for the first time. It is found that, in comparison to the stable beam 136Xe, the radioactive beam 144Xe shows great advantages for producing neutron-rich nuclei with N = 126 and the advantages get more obvious for producing nuclei with less charge number.

  8. ZIRCONIUM—HAFNIUM ISOTOPE EVIDENCE FROM METEORITES FOR THE DECOUPLED SYNTHESIS OF LIGHT AND HEAVY NEUTRON-RICH NUCLEI

    SciTech Connect

    Akram, W.; Schönbächler, M.; Sprung, P.; Vogel, N.

    2013-11-10

    Recent work based on analyses of meteorite and terrestrial whole-rock samples showed that the r- and s- process isotopes of Hf were homogeneously distributed throughout the inner solar system. We report new Hf isotope data for Calcium-Aluminum-rich inclusions (CAIs) of the CV3 carbonaceous chondrite Allende, and novel high-precision Zr isotope data for these CAIs and three carbonaceous chondrites (CM, CO, CK). Our Zr data reveal enrichments in the neutron-rich isotope {sup 96}Zr (≤1ε in {sup 96}Zr/{sup 90}Zr) for bulk chondrites and CAIs (∼2ε). Potential isotope effects due to incomplete sample dissolution, galactic and cosmic ray spallation, and the nuclear field shift are assessed and excluded, leading to the conclusion that the {sup 96}Zr isotope variations are of nucleosynthetic origin. The {sup 96}Zr enrichments are coupled with {sup 50}Ti excesses suggesting that both nuclides were produced in the same astrophysical environment. The same CAIs also exhibit deficits in r-process Hf isotopes, which provides strong evidence for a decoupling between the nucleosynthetic processes that produce the light (A ≤ 130) and heavy (A > 130) neutron-rich isotopes. We propose that the light neutron-capture isotopes largely formed in Type II supernovae (SNeII) with higher mass progenitors than the supernovae that produced the heavy r-process isotopes. In the context of our model, the light isotopes (e.g. {sup 96}Zr) are predominantly synthesized via charged-particle reactions in a high entropy wind environment, in which Hf isotopes are not produced. Collectively, our data indicates that CAIs sampled an excess of materials produced in a normal mass (12-25 M{sub ☉}) SNII.

  9. Decay of the neutron-rich isotope sup 171 Ho and the identification of sup 169 Dy

    SciTech Connect

    Chasteler, R.M.; Nitschke, J.M.; Firestone, R.B.; Vierinen, K.S.; Wilmarth, P.A. )

    1990-10-01

    Neutron-rich rare-earth isotopes were produced in multinucleon transfer reactions between {sup 170}Er ions and {sup nat}W targets. On-line mass separation was used together with {beta}- and {gamma}-ray spectroscopy in these studies. At mass {ital A}=169, the heaviest known dysprosium isotope, 39(8) s,{sup 169}Dy, was identified. It was observed to {beta}{sup {minus}} decay to the ground state of {sup 169}Ho or through a level at 1578 keV. In the {ital A}=171 mass chain, a partial decay scheme for 55(3)-s {sup 171}Ho was determined.

  10. In-Beam {gamma}-Ray Spectroscopy of the N=50 Isotones on the Neutron-Rich Side

    SciTech Connect

    Prevost, A.; Astier, A.; Deloncle, I.; Porquet, M.-G.; Lucas, R.

    2005-11-21

    High-spin states of 84Se, produced as a fission fragment in the fusion-fission reaction 18O+208Pb and studied with the EUROBALL IV array, have been identified for the first time. Their interpretation gives new insights about the evolution of the N=50 shell gap at the vicinity of 78Ni. To characterize this evolution, it would be worth using a new device devoted to the high-spin studies of neutron-rich nuclei produced by asymmetric fission modes. Such dedicated studies are reported in a second part.

  11. IDENTIFICATION OF HIGH-SPIN STATES IN NEUTRON-RICH 88,90,92Kr AND 86Se

    SciTech Connect

    J. D. Cole

    2011-08-01

    Level schemes of even-even neutron-rich {sup 88-92}Kr and {sup 86}Se have been investigated by measuring triple-{gamma} coincidence data from the spontaneous fission of {sup 252}Cf with the Gammasphere detector array. The level scheme of {sup 88}Kr has been extended up to 7169 keV state. Several new excited states with new transitions have been identified in {sup 90,92}Kr and {sup 86}Se. Spins and parities have been assigned to levels in these nuclei by following regional systematics and angular correlation measurements. The level structures of the N = 52, 54, Se, Kr, and Sr isotones are discussed.

  12. New Levels in 118Pd Observed in the β Decay of Very Neutron-Rich 118Rh Isotope

    NASA Astrophysics Data System (ADS)

    Wang, You-Bao; Dendooven, P.; Huikari, J.; Jokinen, A.; Kolhinen S., V.; Lhersonneau, G.; Nieminen, A.; Nummela, S.; Penttilä, H.; Peräjärvi, K.; Rinta-Antila, S.; Szerypo, J.; Wang C., J.; Äystö, J.

    2006-04-01

    We investigate the β decay of very neutron-rich 118Rh isotope using on-line mass-separated sources which are produced by applying 25 MeV proton induced symmetric fission of natural uranium at the IGISOL facility. The β-γ and γ-γ coincidence spectroscopy is employed to establish the level scheme of daughter nucleus 118Pd. Five low-lying new levels are identified for the first time with tentative spin and parity assignments based on the even-mass Pd systematics.

  13. Octupole Deformation Bands of πh11/2 in Neutron-Rich 145,147La Nuclei

    NASA Astrophysics Data System (ADS)

    Zhu, Sheng-jiang; S, Zhu J.; Wang, Mu-ge; J, Hamilton H.; A, Ramayya V.; B, Babu R. S.; W, Ma C.; Long, Gui-lu; Zhu, Ling-yan; Li, Ming; A, Sakhaee; Gan, Cui-yun; Yang, Li-ming; J, Komicki; J, Cole D.; R, Aryaeinejad; M, Drigert W.; J, Rasmussen O.; M, Stoyer A.; S, Chu Y.; K, Gregorich E.; M, Mohar F.; S, Prussin G.; I, Lee Y.; Yu, Oganessian Ts; G, Ter-Akopian M.; A, Daniel V.

    1999-03-01

    Octupole deformation bands built on πh11/2 orbital in neutron-rich odd-Z 145,147La nuclei have been investigated by measuring the prompt γ-rays emitted from the 252Cf source. The alternating parity band structures and strong E1 transitions observed between negative- and positive-parity bands in both nuclei indicate the octupole deformation enhanced by the h11/2 single proton coupling. According to observed energy displacements the octupole deformation becomes stable at the intermediate spin states.

  14. Spectroscopy of neutron-rich Fe isotopes populated in the {sup 64}Ni+{sup 238}U reaction

    SciTech Connect

    Lunardi, S.; Lenzi, S. M.; Farnea, E.; Bazzacco, D.; Beghini, S.; Mason, P.; Mengoni, D.; Montagnoli, G.; Recchia, F.; Scarlassara, F.; Ur, C. A.; Vedova, F. Della; Gadea, A.; Corradi, L.; Angelis, G. de; Fioretto, E.; Napoli, D. R.; Orlandi, R.; Stefanini, A. M.; Valiente-Dobon, J. J.

    2007-09-15

    The neutron-rich Fe isotopes from A=61 to 66 were studied through multinucleon transfer reactions by bombarding a {sup 238}U target with a 400 MeV {sup 64}Ni beam. Unambiguous identification of prompt {gamma} rays belonging to each nucleus was achieved using coincidence relationships with the ions detected in a high-acceptance magnetic spectrometer. The new data extend our knowledge of the level structure of Fe isotopes, which is discussed in terms of the systematics of the region and compared with large-scale shell-model calculations.

  15. Considering Critical Factors of Li-rich Cathode and Si Anode Materials for Practical Li-ion Cell Applications.

    PubMed

    Ko, Minseong; Oh, Pilgun; Chae, Sujong; Cho, Woongrae; Cho, Jaephil

    2015-09-02

    In order to keep pace with increasing energy demands for advanced electronic devices and to achieve commercialization of electric vehicles and energy-storage systems, improvements in high-energy battery technologies are required. Among the various types of batteries, lithium ion batteries (LIBs) are among the most well-developed and commercialized of energy-storage systems. LIBs with Si anodes and Li-rich cathodes are one of the most promising alternative electrode materials for next-generation, high-energy batteries. Si and Li-rich materials exhibit high reversible capacities of <2000 mAh g(-1) and >240 mAh g(-1) , respectively. However, both materials have intrinsic drawbacks and practical limitations that prevent them from being utilized directly as active materials in high-energy LIBs. Examples for Li-rich materials include phase distortion during cycling and side reactions caused by the electrolyte at the surface, and for Si, large volume changes during cycling and low conductivity are observed. Recent progress and important approaches adopted for overcoming and alleviating these drawbacks are described in this article. A perspective on these matters is suggested and the requirements for each material are delineated, in addition to introducing a full-cell prototype utilizing a Li-rich cathode and Si anode. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Neutron irradiation and frequency effects on the electrical conductivity of nanocrystalline silicon carbide (3C-SiC)

    NASA Astrophysics Data System (ADS)

    Huseynov, Elchin

    2016-09-01

    In this present work nanocrystalline silicon carbide (3C-SiC) has been irradiated with neutron flux (∼ 2 ×1013 ncm-2s-1) up to 20 hours at different periods. Electrical conductivity of nanocrystalline 3C-SiC particles (∼18 nm) is comparatively analyzed before and after neutron irradiation. The frequency dependencies of electrical conductivity of 3C-SiC nanoparticles is reviewed at 100 K-400 K temperature range before and after irradiation. The measurements were carried out at 0.1 Hz-2.5 MHz frequency ranges and at different temperatures. Radiation-induced conductivity (RIC) was observed in the nanocrystalline 3C-SiC particles after neutron irradiation and this conductivity study as a function of frequency are presented. The type of conductivity has been defined based on the interdependence between real and imaginary parts of electrical conductivity function. Based on the obtained results the mechanism behind the electrical conductivity of nanocrystalline 3C-SiC particles is explained in detail.

  17. Evaluation of the dark signal performance of different SiPM-technologies under irradiation with cold neutrons

    NASA Astrophysics Data System (ADS)

    Durini, Daniel; Degenhardt, Carsten; Rongen, Heinz; Feoktystov, Artem; Schlösser, Mario; Palomino-Razo, Alejandro; Frielinghaus, Henrich; van Waasen, Stefan

    2016-11-01

    In this paper we report the results of the assessment of changes in the dark signal delivered by three silicon photomultiplier (SiPM) detector arrays, fabricated by three different manufacturers, when irradiated with cold neutrons (wavelength λn=5 Å or neutron energy of En=3.27 meV) up to a neutron dose of 6×1012 n/cm2. The dark signals as well as the breakdown voltages (Vbr) of the SiPM detectors were monitored during the irradiation. The system was characterized at room temperature. The analog SiPM detectors, with and without a 1 mm thick Cerium doped 6Li-glass scintillator material located in front of them, were operated using a bias voltage recommended by the respective manufacturer for a proper detector performance. Iout-Vbias measurements, used to determine the breakdown voltage of the devices, were repeated every 30 s during the first hour and every 300 s during the rest of the irradiation time. The digital SiPM detectors were held at the advised bias voltage between the respective breakdown voltage and dark count mappings repeated every 4 min. The measurements were performed on the KWS-1 instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. The two analog and one digital SiPM detector modules under investigation were respectively fabricated by SensL (Ireland), Hamamatsu Photonics (Japan), and Philips Digital Photon Counting (Germany).

  18. Experimental and simulation studies of neutron-induced single-event burnout in SiC power diodes

    NASA Astrophysics Data System (ADS)

    Shoji, Tomoyuki; Nishida, Shuichi; Hamada, Kimimori; Tadano, Hiroshi

    2014-01-01

    Neutron-induced single-event burnouts (SEBs) of silicon carbide (SiC) power diodes have been investigated by white neutron irradiation experiments and transient device simulations. It was confirmed that a rapid increase in lattice temperature leads to formation of crown-shaped aluminum and cracks inside the device owing to expansion stress when the maximum lattice temperature reaches the sublimation temperature. SEB device simulation indicated that the peak lattice temperature is located in the vicinity of the n-/n+ interface and anode contact, and that the positions correspond to a hammock-like electric field distribution caused by the space charge effect. Moreover, the locations of the simulated peak lattice temperature agree closely with the positions of the observed destruction traces. Furthermore, it was theoretically demonstrated that the period of temperature increase of a SiC power device is two orders of magnitude less than that of a Si power device, using a thermal diffusion equation.

  19. Inelastic neutron scattering study of phonon density of states in nanostructured Si1 xGex thermoelectrics

    SciTech Connect

    Dhital, Chetan; Abernathy, Douglas L; Zhu, Gaohua; Ren, Zhifeng; Broido, D.; Wilson, Stephen D

    2012-01-01

    Inelastic neutron scattering measurements are utilized to explore relative changes in the generalized phonon density of states of nanocrystalline Si1 xGex thermoelectric materials prepared via ball-milling and hot-pressing techniques. Dynamic signatures of Ge clustering can be inferred from the data by referencing the resulting spectra to a density functional theoretical model assuming homogeneous alloying via the virtual-crystal approximation. Comparisons are also presented between as-milled Si nanopowder and bulk, polycrystalline Si where a preferential low-energy enhancement and lifetime broadening of the phonon density of states appear in the nanopowder. Negligible differences are however observed between the phonon spectra of bulk Si andhot-pressed, nanostructured Si samples suggesting that changes to the single-phonon dynamics above 4 meV play only a secondary role in the modified heat conduction of this compound.

  20. Magnetostructural transition in Fe{sub 5}SiB{sub 2} observed with neutron diffraction

    SciTech Connect

    Cedervall, Johan; Kontos, Sofia; Hansen, Thomas C.; Balmes, Olivier; Martinez-Casado, Francisco Javier; Matej, Zdenek; Beran, Premysl; Svedlindh, Peter; Gunnarsson, Klas; Sahlberg, Martin

    2016-03-15

    The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropy energy constant has been estimated to 0.3 MJ/m{sup 3} at 300 K. - Highlights: • The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by diffraction. • At 172 K a spin reorientation occurs in the compound. • The magnetic moments are aligned along the c-axis at high T. • The magnetic moments are aligned in the ab-plane at low T. • The magnetocrystalline anisotropy energy constant has been estimated to 0.3 MJ/m{sup 3}.

  1. A polarized neutron study of the magnetization distribution in Co₂FeSi.

    PubMed

    Brown, P J; Kainuma, R; Kanomata, T; Neumann, K-U; Okubo, A; Umetsu, R Y; Ziebeck, K R A

    2013-05-22

    The magnetization distribution in Co2FeSi which has the largest moment per formula unit ∼6 μB of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L12 structure giving μ Fe = 3.10(3) μB and μ Co = 1.43(2) μB, results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with eg symmetry. This was higher, ≃65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co2FeSi is not a perfect half-metallic ferromagnet.

  2. Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy

    NASA Astrophysics Data System (ADS)

    Kohley, Z.; Christian, G.; Baumann, T.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Jones, M.; Smith, J. K.; Snyder, J.; Spyrou, A.; Thoennessen, M.

    2013-10-01

    The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure the free neutrons and heavy charged particles from the radioactive ion beam induced 32Mg+9Be reaction. The fragmentation reaction was simulated with the constrained molecular dynamics model (CoMD), which demonstrated that the of the heavy fragments and free neutron multiplicities were observables sensitive to the density dependence of the symmetry energy at subsaturation densities. Through comparison of these simulations with the experimental data, constraints on the density dependence of the symmetry energy were extracted. The advantage of radioactive ion beams as a probe of the symmetry energy is demonstrated through examination of CoMD calculations for stable and radioactive-beam-induced reactions.

  3. Medium-spin states of the neutron-rich 87,89Br isotopes: configurations and shapes

    NASA Astrophysics Data System (ADS)

    Nyakó, B. M.; Timár, J.; Csatlós, M.; Dombrádi, Zs; Krasznahorkay, A.; Kuti, I.; Sohler, D.; Tornyi, T. G.; Czerwiński, M.; Rząca-Urban, T.; Urban, W.; Bączyk, P.; Atanasova, L.; Balabanski, D. L.; Sieja, K.; Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T.; de France, G.; Simpson, G. S.; Ur, C. A.

    2016-06-01

    Medium-spin excited states of the neutron-rich 87Br and 89Br nuclei were observed and studied for the first time. They were populated in fission of 235U induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of γ radiation following fission has been performed using the EXILL array of Ge detectors. The observed level schemes were compared with results of large valence space shell model calculations. Both medium-spin level schemes consist of band-like structures, which can be understood as bands built on the πf 5/2, πp 3/2 and πg 9/2 configurations. Both nuclei have 5/2- ground state spin-parity contrary to the odd-mass Br isotopes containing fewer neutrons, which have 3/2- ground state spin-parity. On the basis of the properties of the πg 9/2 decoupled bands the deformations of the 87Br and 89Br fit to the systematics of nuclei in the region. 87Br is close to the vibrational limit, while 89Br is more rotational.

  4. High flux, beamed neutron sources employing deuteron-rich ion beams from D2O-ice layered targets

    NASA Astrophysics Data System (ADS)

    Alejo, A.; Krygier, A. G.; Ahmed, H.; Morrison, J. T.; Clarke, R. J.; Fuchs, J.; Green, A.; Green, J. S.; Jung, D.; Kleinschmidt, A.; Najmudin, Z.; Nakamura, H.; Norreys, P.; Notley, M.; Oliver, M.; Roth, M.; Vassura, L.; Zepf, M.; Borghesi, M.; Freeman, R. R.; Kar, S.

    2017-06-01

    A forwardly-peaked bright neutron source was produced using a laser-driven, deuteron-rich ion beam in a pitcher-catcher scenario. A proton-free ion source was produced via target normal sheath acceleration from Au foils having a thin layer of D2O ice at the rear side, irradiated by sub-petawatt laser pulses (∼200 J, ∼750 fs) at peak intensity ∼ 2× {10}20 {{W}} {{cm}}-2. The neutrons were preferentially produced in a beam of ∼70° FWHM cone along the ion beam forward direction, with maximum energy up to ∼40 MeV and a peak flux along the axis ∼ 2× {10}9 {{n}} {{sr}}-1 for neutron energy above 2.5 MeV. The experimental data is in good agreement with the simulations carried out for the d(d,n)3He reaction using the deuteron beam produced by the ice-layered target.

  5. Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

    PubMed

    Chang, Geng-Rong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2011-12-01

    Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon.

  6. Detection of fast neutrons from D-T nuclear reaction using a 4H-SiC radiation detector

    NASA Astrophysics Data System (ADS)

    Zatko, Bohumir; Sagatova, Andrea; Sedlackova, Katarina; Necas, Vladimir; Dubecky, Frantisek; Solar, Michael; Granja, Carlos

    2016-09-01

    The particle detector based on a high purity epitaxial layer of 4H-SiC exhibits promising properties in detection of various types of ionizing radiation. Due to the wide band gap of 4H-SiC semiconductor material, the detector can reliably operate at room and also elevated temperatures. In this work we focused on detection of fast neutrons generated the by D-T (deuterium-tritium) nuclear reaction. The epitaxial layer with a thickness of 105 μm was used as a detection part. A circular Schottky contact of a Au/Ni double layer was evaporated on both sides of the detector material. The detector structure was characterized by current-voltage and capacitance-voltage measurements, at first. The results show very low current density (<0.1 nA/cm2) at room temperature and good homogeneity of free carrier concentration in the investigated depth. The fabricated detectors were tested for detection of fast neutrons generated by the D-T reaction. The energies of detected fast neutrons varied from 16.0 MeV to 18.3 MeV according to the acceleration potential of deuterons, which increased from 600 kV up to 2 MV. Detection of fast neutrons in the SiC detector is caused by the elastic and inelastic scattering on the silicon or carbide component of the detector material. Another possibility that increases the detection efficiency is the use of a conversion layer. In our measurements, we glued a HDPE (high density polyethylene) conversion layer on the detector Schottky contact to transform fast neutrons to protons. Hydrogen atoms contained in the conversion layer have a high probability of interaction with neutrons through elastic scattering. Secondary generated protons flying to the detector can be easily detected. The detection properties of detectors with and without the HDPE conversion layer were compared.

  7. Near and sub-barrier fusion of neutron-rich oxygen and carbon nuclei using low-intensity beams

    NASA Astrophysics Data System (ADS)

    Steinbach, Tracy K.

    Fusion between neutron-rich light nuclei in the crust of an accreting neutron star has been proposed as a heat source that triggers an X-ray superburst. To explore the probability with which such fusion events occur and examine their decay characteristics, an experimental program using beams of neutron-rich light nuclei has been established. Evaporation residues resulting from the fusion of oxygen and 12C nuclei, are directly measured and distinguished from unreacted beam particles on the basis of their energy and time-of-flight. Using an experimental setup developed for measurements utilizing low-intensity (< 105 ions/s) radioactive beams, the fusion excitation functions for 16O + 12C and 18O + 12C have been measured. The fusion excitation function for 18O + 12C has been measured in the sub-barrier domain down to the 820 mub level, a factor of 30 lower than previous direct measurements. This measured fusion excitation function is compared to the predictions of a density constrained time-dependent Hartree-Fock model. This comparison reveals a shape difference in the fusion excitation functions, indicating a larger tunneling probability for the experimental data as compared to the theoretical calculations. In addition to the measured cross-section, the measured angular distribution of the evaporation residues provides insight into the relative importance of the different de-excitation channels. These evaporation residue angular distributions are compared to the predictions of a statistical model code, evapOR, revealing an under-prediction of the de-excitation channels associated with alpha particle emission.

  8. Effect of neutron irradiation on defect evolution in Ti3SiC2 and Ti2AlC

    DOE PAGES

    Tallman, Darin J.; He, Lingfeng; Garcia-Diaz, Brenda L.; ...

    2015-10-23

    Here, we report on the characterization of defects formed in polycrystalline Ti3SiC2 and Ti2AlC samples exposed to neutron irradiation – up to 0.1 displacements per atom (dpa) at 350 ± 40 °C or 695 ± 25 °C, and up to 0.4 dpa at 350 ± 40 °C. Black spots are observed in both Ti3SiC2 and Ti2AlC after irradiation to both 0.1 and 0.4 dpa at 350 °C. After irradiation to 0.1 dpa at 695 °C, small basal dislocation loops, with a Burgers vector of b = 1/2 [0001] are observed in both materials. At 9 ± 3 and 10 ±more » 5 nm, the loop diameters in the Ti3SiC2 and Ti2AlC samples, respectively, were comparable. At 1 × 1023 loops/m3, the dislocation loop density in Ti2AlC was ≈1.5 orders of magnitude greater than in Ti3SiC2, at 3 x 1021 loops/m3. After irradiation at 350 °C, extensive microcracking was observed in Ti2AlC, but not in Ti3SiC2. The room temperature electrical resistivities increased as a function of neutron dose for all samples tested, and appear to saturate in the case of Ti3SiC2. The MAX phases are unequivocally more neutron radiation tolerant than the impurity phases TiC and Al2O3. Based on these results, Ti3SiC2 appears to be a more promising MAX phase candidate for high temperature nuclear applications than Ti2AlC.« less

  9. Nuclear Shape And Size Properties For Rare-earth Neutron-rich Nuclei

    SciTech Connect

    Benhamouda, N.; Oudih, M. R.; Allal, N. H.; Fellah, M.

    2009-01-28

    Two-neutron separation energies, quadrupole moments and mean square charge radii, are evaluated for even-even Osmium isotopes with 78{<=}N{<=}114. The calculations are performed in the framework of a microscopic model including the pairing correlations rigorously by means of the FSBCS (Fixed-Sharp-BCS) method.

  10. Development of SiPM-based scintillator tile detectors for a multi-layer fast neutron tracker

    NASA Astrophysics Data System (ADS)

    Preston, R.; Jakubek, J.; Prokopovich, D.; Uher, J.

    2012-10-01

    We are developing thin tile scintillator detectors with silicon photomultiplier (SiPM) readout for use in a multi-layer fast-neutron tracker. The tracker is based on interleaved Timepix and plastic scintillator layers. The thin 15 × 15 × 2 mm plastic scintillators require suitable optical readout in order to detect and measure the energy lost by energetic protons that have been recoiled by fast neutrons. Our first prototype used dual SiPMs, coupled to opposite edges of the scintillator tile using light-guides. An alternative readout geometry was designed in an effort to increase the fraction of scintillation light detected by the SiPMs. The new prototype uses a larger SiPM array to cover the entire top face of the tile. This paper details the comparative performance of the two prototype designs. A deuterium-tritium (DT) fast-neutron source was used to compare the relative light collection efficiency of the two designs. A collimated UV light source was scanned across the detector face to map the uniformity. The new prototype was found to have 9.5 times better light collection efficiency over the original design. Both prototypes exhibit spatial non-uniformity in their response. Methods of correcting this non-uniformity are discussed.

  11. Experimental Evaluation of SI Engine Operation Supplemented by Hydrogen Rich Gas from a Compact Plasma Boosted Reformer

    SciTech Connect

    J. B. Green, Jr.; N. Domingo; J. M. E. Storey; R.M. Wagner; J.S. Armfield; L. Bromberg; D. R. Cohn; A. Rabinovich; N. Alexeev

    2000-06-19

    It is well known that hydrogen addition to spark-ignited (SI) engines can reduce exhaust emissions and increase efficiency. Micro plasmatron fuel converters can be used for onboard generation of hydrogen-rich gas by partial oxidation of a wide range of fuels. These plasma-boosted microreformers are compact, rugged, and provide rapid response. With hydrogen supplement to the main fuel, SI engines can run very lean resulting in a large reduction in nitrogen oxides (NO x ) emissions relative to stoichiometric combustion without a catalytic converter. This paper presents experimental results from a microplasmatron fuel converter operating under variable oxygen to carbon ratios. Tests have also been carried out to evaluate the effect of the addition of a microplasmatron fuel converter generated gas in a 1995 2.3-L four-cylinder SI production engine. The tests were performed with and without hydrogen-rich gas produced by the plasma boosted fuel converter with gasoline. A one hundred fold reduction in NO x due to very lean operation was obtained under certain conditions. An advantage of onboard plasma-boosted generation of hydrogen-rich gas is that it is used only when required and can be readily turned on and off. Substantial NO x reduction should also be obtainable by heavy exhaust gas recirculation (EGR) facilitated by use of hydrogen-rich gas with stoichiometric operation.

  12. Effects of nitrogen impurities on the microstructure and electronic properties of P-doped Si nanocrystals emebedded in silicon-rich SiNx films

    NASA Astrophysics Data System (ADS)

    Ma, Deng-Hao; Zhang, Wei-Jia; Luo, Rui-Ying; Jiang, Zhao-Yi; Ma, Qiang; Ma, Xiao-Bo; Fan, Zhi-Qiang; Song, Deng-Yuan; Zhang, Lei

    2016-05-01

    Phosphorus doped Si nanocrystals (SNCs) emebedded in silicon-rich SiNx:H films were prepared using plasma enhanced chemical vapor deposition technique, and the effects of nitrogen incorporation on the microstructure and electronic properties of the thin films have been systematically studied. Transmission electron microscope and Raman observation revealed that nitrogen incorporation prevents the growth of Si nanocrystals, and that their sizes can be adjusted by varying the flow rate of NH3. The reduction of photoluminescence (PL) intensity in the range of 2.1-2.6 eV of photon energy was observed with increasing nitrogen impurity, and a maximal PL intensity in the range 1.6-2.0 eV was obtained when the incorporation flow ratio NH3/(SiH4+H2+PH3) was 0.02. The conductivity of the films is improved by means of proper nitrogen impurity doping, and proper doping causes the interface charge density of the heterojunction (H-J) device to be lower than the nc-Si:H/c-Si H-J device. As a result, the proper incorporation of nitrogen could not only reduce the silicon banding bond density, but also fill some carrier capture centers, and suppress the nonradiative recombination of electrons.

  13. {sup 4}H-SiC neutron sensors based on ion implanted {sup 10}B neutron converter layer

    SciTech Connect

    Issa, F.; Ottaviani, L.; Vervisch, V.; Ferone, R.; Palais, O.; Szalkai, D.; Klix, A.; Vermeeren, L.; Lyoussi, A.; Kuznetsov, A.; Lazar, M.; Hallen, A.

    2015-07-01

    In the framework of the I{sub S}MART project the main aim is to develop an innovative complete radiation detection system based on silicon carbide technology in view to detect neutrons (thermal and fast) and photons for harsh environments. In the present work two geometries have been realized based on ion implantation of boron. In the first geometry, {sup 10}B ions have been implanted into the Al metallic contact to create the neutron converter layer. In the second geometry one single process has been used to realize both the p+-layer and the neutron converter layer. The technological processes followed to fabricate these detectors, with a study of their electrical behavior and their responses under thermal neutron irradiations are addressed in this paper. (authors)

  14. Spectroscopy of Neutron-rich Nuclei of the A{approx_equal}60 region populated through binary heavy-ion collisions

    SciTech Connect

    Lunardi, S.

    2008-11-11

    Neutron-rich nuclei of the mass A = 60 region (from V to Fe) have been studied through multi-nucleon transfer reactions by bombarding a {sup 238}U target with beams of {sup 64}Ni and {sup 70}Zn. Unambiguous identification of prompt {gamma} rays belonging to each nucleus has been achieved by using the efficient gamma-array CLARA coupled to the large-acceptance magnetic spectrometer PRISMA installed at the Legnaro National Laboratories. With the new data, the existence of the N = 32 sub-shell closure has been corroborated through the study of odd V isotopes, whereas a new region of deformation appears for neutron-rich Fe nuclei close to N = 40. The results obtained for all these nuclei are compared with shell model calculations which reproduces quite well the experimental data also for the most neutron-rich nuclei when excitations from the fp shell into the upper g{sub 9/2} orbital are allowed.

  15. Detection of 14 MeV neutrons in high temperature environment up to 500 deg. C using 4H-SiC based diode detector

    SciTech Connect

    Szalkai, D.; Klix, A.; Ferone, R.; Issa, F.; Ottaviani, L.; Vervisch, V.; Gehre, D.; Lyoussi, A.

    2015-07-01

    In reactor technology and industrial applications detection of fast and thermal neutrons plays a crucial role in getting relevant information about the reactor environment and neutron yield. The inevitable elevated temperatures make neutron yield measurements problematic. Out of the currently available semiconductors 4H-SiC seems to be the most suitable neutron detector material under extreme conditions due to its high heat and radiation resistance, large band-gap and lower cost of production than in case of competing diamond detectors. In the framework of the European I-Smart project, optimal {sup 4}H-SiC diode geometries were developed for high temperature neutron detection and have been tested with 14 MeV fast neutrons supplied by a deuterium-tritium neutron generator with an average neutron flux of 10{sup 10}-10{sup 11} n/(s*cm{sup 2}) at Neutron Laboratory of the Technical University of Dresden in Germany from room temperatures up to several hundred degrees Celsius. Based on the results of the diode measurements, detector geometries appear to play a crucial role for high temperature measurements up to 500 deg. C. Experimental set-ups using SiC detectors were constructed to simulate operation in the harsh environmental conditions found in the tritium breeding blanket of the ITER fusion reactor, which is planned to be the location of neutron flux characterization measurements in the near future. (authors)

  16. Examining the interplay between halo effects and deformation in neutron rich neon isotopes

    NASA Astrophysics Data System (ADS)

    Loelius, Charles; Iwasaki, Hironori; Bazin, Daniel; Elder, Robert; Elman, Brandon; Gade, Alexandra; Grinder, Mara; Longfellow, Brenden; Lunderberg, Eric; Heil, Sebastian; Hufnagel, Alexander; Mathy, Michael; Syndikus, Ina; Kobayashi, Nobu; Belarge, Joe; Bender, Peter; Weisshaar, Dirk; Petri, Marina; Whitmore, Kenneth

    2017-01-01

    27 Ne serves as an excellent test case for understanding the interplay between halo effects and deformation. It is known that the neighboring isotopes 26Ne and 28Ne demonstrate substantial deformation, which indicate a potential for deformation in 27Ne. At the same time, the 1/2+ excited state is expected to have a single valence neutron in the s orbital near the neutron separation energy and therefore is expected to exhibit halo effects. Due to the interplay between the halo and deformation effects, the M1 transition strength, which is expected to be large because of the deformation, could be severely reduced, while the E1 transition strength is expected to be large. To examine this effect, precise knowledge of transition rates is required. In this work, the model-independent Recoil Distance Method was employed with fast RI beams to constrain the lifetime of the 1/2+ state down to the lowest achievable limits of precision.

  17. Structural changes in C–S–H gel during dissolution: Small-angle neutron scattering and Si-NMR characterization

    SciTech Connect

    Trapote-Barreira, Ana; Porcar, Lionel; Cama, Jordi; Soler, Josep M.; Allen, Andrew J.

    2015-06-15

    Flow-through experiments were conducted to study the calcium–silicate–hydrate (C–S–H) gel dissolution kinetics. During C–S–H gel dissolution the initial aqueous Ca/Si ratio decreases to reach the stoichiometric value of the Ca/Si ratio of a tobermorite-like phase (Ca/Si = 0.83). As the Ca/Si ratio decreases, the solid C–S–H dissolution rate increases from (4.5 × 10{sup −} {sup 14} to 6.7 × 10{sup −} {sup 12}) mol m{sup −} {sup 2} s{sup −} {sup 1}. The changes in the microstructure of the dissolving C–S–H gel were characterized by small-angle neutron scattering (SANS) and {sup 29}Si magic-angle-spinning nuclear magnetic resonance ({sup 29}Si-MAS NMR). The SANS data were fitted using a fractal model. The SANS specific surface area tends to increase with time and the obtained fit parameters reflect the changes in the nanostructure of the dissolving solid C–S–H within the gel. The {sup 29}Si MAS NMR analyses show that with dissolution the solid C–S–H structure tends to a more ordered tobermorite structure, in agreement with the Ca/Si ratio evolution.

  18. Simulation of radiation-defect formation processes in heterostructures with self-assembled Ge(Si)/Si(001) nanoislands under neutron irradiation

    SciTech Connect

    Skupov, A. V.

    2015-05-15

    TRISQD software is developed for the computer simulation of processes in which radiation defects are formed under the corpuscular irradiation of semiconductor heterostructures with lenticular nanoinclusions of various shapes. The computer program is used to study defect-formation processes in p-i-n diodes with the i region having a built-in 20-period lattice of self-assembled Ge(Si) nanoislands formed under irradiation with high-energy neutrons. It is found that the fraction of Ge(Si) nanoislands in which point radiation defects are formed under the impact of atomic-displacement cascades is ≤3% of their total number in the lattice. More than 94% of the defects are localized in the bulk of the p, n, and i regions of the diode and in silicon layers that separate sheets of Ge(Si) nanoislands.

  19. Influence of pairing correlations on the radius of neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Zhang, Ying; Chen, Ying; Meng, Jie; Ring, Peter

    2017-01-01

    The influence of pairing correlations on the neutron root mean square (rms) radius of nuclei is investigated in the framework of self-consistent Skyrme Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by the Green's function techniques. As an example the nucleus 124Zr is treated for a varying strength of pairing correlations. We find that, as the pairing strength increases, the neutron rms radius first shrinks, reaches a minimum, and beyond this point it expands again. The shrinkage is due to the the so-called pairing antihalo effect, i.e., due to the decrease of the asymptotic density distribution with increasing pairing. However, in some cases, increasing pairing correlations can also lead to an expansion of the nucleus due to a growing occupation of so-called halo orbits, i.e., weakly bound states and resonances in the continuum with low-ℓ values. In this case, the neutron radii are extended just by the influence of pairing correlations, since these halo orbits cannot be occupied without pairing. The term "antihalo effect" is not justified in such cases. For a full understanding of this complicated interplay, self-consistent calculations are necessary.

  20. Structure of molten CaSiO3: neutron diffraction isotope substitution with aerodynamic levitation and molecular dynamics study.

    PubMed

    Skinner, L B; Benmore, C J; Weber, J K R; Tumber, S; Lazareva, L; Neuefeind, J; Santodonato, L; Du, J; Parise, J B

    2012-11-15

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO(3).

  1. The structure of molten CaSiO3: A neutron diffraction isotope substitution and aerodynamic levitation study.

    SciTech Connect

    Skinner, Lawrie; Benmore, Chris J; Weber, Richard; Santodonato, Louis J; Tumber, Sonia; Neuefeind, Joerg C; Lazareva, Lena; Du, Jincheng; Parise, John B

    2012-01-01

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO3, to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a re-distribution of Ca-O bond lengths, especially towards longer distances in the liquid. The first order neutron difference function provides a rigorous test of recent molecular dynamics simulations and supports the model of the presence of short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO3.

  2. Novel triaxial structure in low-lying states of neutron-rich nuclei around A ≈100

    NASA Astrophysics Data System (ADS)

    Xiang, J.; Yao, J. M.; Fu, Y.; Wang, Z. H.; Li, Z. P.; Long, W. H.

    2016-05-01

    Background: In recent years, the study of triaxiality in the low-lying states of atomic nuclei with transition character or shape coexistence has been of great interest. Previous studies indicate that the neutron-rich nuclei in the A ˜100 mass region with Z ˜40 ,N ˜60 serve as good grounds for examining the role of triaxiality in nuclear low-lying states. Purpose: The aim of this work is to provide a microscopic study of low-lying states for nuclei in the A ˜100 mass regions and to examine in detail the role of triaxiality in the shape-coexistence phenomena and the variation of shape with the isospin and spin values at the beyond mean-field level. Method: The starting point of our method is a set of relativistic mean-field plus BCS wave functions generated with a constraint on triaxial deformations (β ,γ ) . The excitation energies and electric multipole transition strengths of low-lying states are calculated by solving a five-dimensional collective Hamiltonian (5DCH) with parameters determined by the mean-field wave functions. Results: The low-lying states of Mo isotopes and of N =60 isotones in the A ˜100 mass region are calculated. The results indicate that triaxiality is essential to reproduce the data of excitation energies and electric quadrupole transition strengths in low-lying states and plays an important role in the shape evolution as a function of nucleon number. However, the decrease of nuclear collectivity with the increase of angular momentum in neutron-rich Mo isotopes has not been reproduced. Conclusions: The evolution of nuclear collectivity in the low-lying states of neutron-rich nuclei in the A ˜100 mass region as a function of nucleon number is governed by the novel triaxial structure. However, the mechanism that governs the variation of nuclear shape with spin in Mo isotopes remains unclear and deserves further investigation by taking into account the effects other than the collective motions.

  3. Production of beams of neutron-rich nuclei between Ca and Ni using the ion-guide technique

    SciTech Connect

    Perajarvi, K.; Cerny, J.; Hager, U.; Hakala, J.; Huikari, J.; Jokinen, A.; Karvonen, P.; Kurpeta, J.; Lee, D.; Moore, I.; Penttila, H.; Popov, A.; Aysto, J.

    2004-09-28

    Since several elements between Z = 20-28 are refractory in their nature, their neutron-rich isotopes are rarely available as low energy Radioactive Ion Beams (RIB) in ordinary Isotope Separator On-Line facilities [1-4]. These low energy RIBs would be especially interesting to have available under conditions which allow high-resolution beta-decay spectroscopy, ion-trapping and laser-spectroscopy. As an example, availability of these beams would open a way for research which could produce interesting and important data on neutron-rich nuclei around the doubly magic {sup 78}Ni. One way to overcome the intrinsic difficulty of producing these beams is to rely on the chemically unselective Ion Guide Isotope Separator On-Line (IGISOL) technique [5]. Quasi- and deep-inelastic reactions, such as {sup 197}Au({sup 65}Cu,X)Y, could be used to produce these nuclei in existing IGISOL facilities, but before they can be successfully incorporated into the IGISOL concept their kinematics must be well understood. Therefore the reaction kinematics part of this study was first performed at the Lawrence Berkeley National Laboratory using its 88'' cyclotron and, based on those results, a specialized target chamber was built[6]. The target chamber shown in Fig. 1 was recently tested on-line at the Jyvaaskylaa IGISOL facility. Yields of mass-separated radioactive projectile-like species such as {sup 62,63}Co are about 0.8 ions/s/pnA, corresponding to about 0.06 % of the total IGISOL efficiency for the products that hit the Ni-degrader. (The current maximum 443 MeV {sup 65}Cu beam intensity at Jyvaaskylaa is about 20 pnA.) This total IGISOL efficiency is a product of two coupled loss factors, namely inadequate thermalization and the intrinsic IGISOL efficiency. In our now tested chamber, about 9 % of the Co recoils are thermalized in the owing He gas (p{sub He}=300 mbar) and about 0.7 % of them are converted into the mass-separated ion beams. In the future, both of these physical

  4. Ground-state configuration of neutron-rich 35Al via Coulomb breakup

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Datta, Ushasi; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Carlson, B. V.; Catford, W. N.; Chartier, M.; Cortina-Gil, D.; De Angelis, G.; Fernandez, P. Diaz; Emling, H.; Ershova, O.; Fraile, L. M.; Geissel, H.; Gonzalez-Diaz, D.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kröll, T.; Krücken, R.; Langer, C.; Le Bleis, T.; Leifels, Y.; Marganiec, J.; Münzenberg, G.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Plag, R.; Rahaman, A.; Reifarth, R.; Ricciardi, M. V.; Rigollet, C.; Rossi, D.; Scheidenberger, C.; Scheit, H.; Simon, H.; Taylor, J. T.; Togano, Y.; Typel, S.; Utsuno, Y.; Wagner, A.; Wamers, F.; Weick, H.; Winfield, J. S.

    2017-09-01

    The ground-state configuration of 35Al has been studied via Coulomb dissociation (CD) using the LAND-FRS setup (GSI, Darmstadt) at a relativistic energy of ˜403 MeV/nucleon. The measured inclusive differential CD cross section for 35Al, integrated up to 5.0 MeV relative energy between the 34Al core and the neutron using a Pb target, is 78(13) mb. The exclusive measured CD cross section that populates various excited states of 34Al is 29(7) mb. The differential CD cross section of 35Al→34Al+n has been interpreted in the light of a direct breakup model, and it suggests that the possible ground-state spin and parity of 35Al could be, tentatively, 1 /2+ or 3 /2+ or 5 /2+ . The valence neutrons, in the ground state of 35Al, may occupy a combination of either l =3 ,0 or l =1 ,2 orbitals coupled with the 34Al core in the ground and isomeric state(s), respectively. This hints of a particle-hole configuration of the neutron across the magic shell gaps at N =20 ,28 which suggests narrowing the magic shell gap. If the 5 /2+ is the ground-state spin-parity of 35Al as suggested in the literature, then the major ground-state configuration of 35Al is a combination of 34Al(g.s.;4-) ⊗νp3/2 and 34Al(isomer;1+) ⊗νd3/2 states. The result from this experiment has been compared with that from a previous knockout measurement and a calculation using the SDPF-M interaction.

  5. Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

    SciTech Connect

    Wen, Guozhi; Zeng, Xiangbin Wen, Xixin; Liao, Wugang

    2014-04-28

    Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

  6. Isomeric states observed in heavy neutron-rich nuclei populated in the fragmentation of a 208Pb beam

    NASA Astrophysics Data System (ADS)

    Steer, S. J.; Podolyák, Zs.; Pietri, S.; Górska, M.; Grawe, H.; Maier, K. H.; Regan, P. H.; Rudolph, D.; Garnsworthy, A. B.; Hoischen, R.; Gerl, J.; Wollersheim, H. J.; Becker, F.; Bednarczyk, P.; Cáceres, L.; Doornenbal, P.; Geissel, H.; Grębosz, J.; Kelic, A.; Kojouharov, I.; Kurz, N.; Montes, F.; Prokopwicz, W.; Saito, T.; Schaffner, H.; Tashenov, S.; Heinz, A.; Pfützner, M.; Kurtukian-Nieto, T.; Benzoni, G.; Jungclaus, A.; Balabanski, D. L.; Bowry, M.; Brandau, C.; Brown, A.; Bruce, A. M.; Catford, W. N.; Cullen, I. J.; Dombrádi, Zs.; Estevez, M. E.; Gelletly, W.; Ilie, G.; Jolie, J.; Jones, G. A.; Kmiecik, M.; Kondev, F. G.; Krücken, R.; Lalkovski, S.; Liu, Z.; Maj, A.; Myalski, S.; Schwertel, S.; Shizuma, T.; Walker, P. M.; Werner-Malento, E.; Wieland, O.

    2011-10-01

    Heavy neutron-rich nuclei were populated via the fragmentation of a E/A=1 GeV 20882Pb beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed γ rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. The newly discovered isomers are in 204,20580Hg, 201,202,204,20579Au, 197,203,20478Pt, 195,199-20377Ir, 193,197-19976Os, 19675Re, 190,19174W, and 18973Ta. Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.

  7. Shell quenching in {sup 78}Ni: A hint from the structure of neutron-rich copper isotopes

    SciTech Connect

    Sieja, K.; Nowacki, F.

    2010-06-15

    Recent progress in experimental techniques allows us to study very exotic systems like neutron-rich nuclei in the vicinity of {sup 78}Ni. The spectroscopy of this region can nowadays be studied theoretically in the large scale shell model calculations. In this work, we perform a shell model study of odd copper nuclei with N=40-50, in a large valence space with the {sup 48}Ca core, using a realistic interaction derived from the CD-Bonn potential. We present the crucial importance of the proton core excitations for the description of spectra and magnetic moments, which are for the first time correctly reproduced in theoretical calculations. Shell evolution from {sup 68}Ni to {sup 78}Ni is discussed in detail. A weakening of the Z=28 gap when approaching the N=50 shell closure, suggested by the experimental evidence, is confirmed in the calculations.

  8. Direct Mass Measurements in the Light Neutron-Rich Region Using a Combined Energy and Time-of-Flight Technique

    NASA Astrophysics Data System (ADS)

    Pillai, C.; Swenson, L. W.; Vieira, D. J.; Butler, G. W.; Wouters, J. M.; Rokni, S. H.; Vaziri, K.; Remsberg, L. P.

    This experiment has demonstrated that direct mass measurements can be performed (albeit of low precision in this first attempt) using the M proportional to ET(2) method. This technique has the advantage that many particle-bound nuclei, produced in fragmentation reactions can be measured simultaneously, independent of their N or Z. The main disadvantage of this approach is that both energy and time-of-flight must be measured precisely on an absolute scale. Although some mass walk with N and Z was observed in this experiment, these uncertainties were largely removed by extrapolating the smooth dependence observed for known nuclei which lie closer to the valley of (BETA)-stability. Mass measurements for several neutron-rich light nuclei ranging from C-17 to NE-26 have been performed. In all cases these measurements agree with the latest mass compilation of Wapstra and Audi. The masses of N-20 N and F-24 have been determined for the first time.

  9. {beta}-decay half-lives of new neutron-rich isotopes of elements from Pm to Tb

    SciTech Connect

    Ichikawa, S.; Asai, M.; Tsukada, K.; Nishinaka, I.; Nagame, Y.; Osa, A.; Sakama, M.; Oura, Y.; Kojima, Y.; Shibata, M.; Kawade, K.

    1999-11-16

    Eight new neutron-rich lanthanide isotopes produced in the proton-induced fission of {sup 238}U have been identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport system. For six of these, each half-life was determined: {sup 159}Pm (2{+-}1 s), {sup 161}Sm (4.8{+-}0.8 s), {sup 165}Gd (10.3{+-}1.6 s), {sup 166}Tb (21{+-}6 s), {sup 167}Tb (19.4{+-}2.7 s) and {sup 168}Tb (8.2{+-}1.3 s). The observed half-lives were compared with theoretical calculations. The recent calculation by the gross theory with the new one-particle strength function shows quite good agreement with the experimental half-lives.

  10. {beta}-Decay Half-Lives of New Neutron-Rich Isotopes of Elements from Pm to Tb

    SciTech Connect

    S. Ichikawa; M. Asai; K. Tsukada; A. Osa; M. Sakama; Y. Kojima; M. Shibata; I. Nishinaka; Y. Nagame; Y. Oura; K. Kawade

    1999-12-31

    Eight new neutron-rich lanthanide isotopes produced in the proton-induced fission of {sup 238}U have been identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport system. For six of these, each half-life was determined: {sup 159}Pm (2 {+-} 1 s), {sup 161}Sm (4.8 {+-} 0.8 s), {sup 165}Gd (10.3 {+-} 1.6 s), {sup 166}Tb (21 {+-} 6 s), {sup 167}Tb (19.4 {+-} 2.7 s) and {sup 168}Tb (8.2 {+-} 1.3 s). The observed half-lives were compared with theoretical calculations. The recent calculation by the gross theory with the new one-particle strength function shows quite good agreement with the experimental half-lives.

  11. Leap to explore the region of neutron-rich heavy element isotopes

    SciTech Connect

    Hoffman, D.C.

    1985-10-01

    The research aims of the Large Einsteinium Activation Program (LEAP) are described. This program is a major initiative to exploit currently existing expertise in heavy element research and the potential for producing very heavy actinide target materials such as 285-day /sup 254/Es at the High Flux Isotope Reactor at Oak Ridge National Laboratory. The stated aims of the program are to produce heavy element isotopes, to conduct chemical studies of these isotopes, to study the nuclear properties of such isotopes, and to produce a superheavy element (183 neutrons) by the using a /sup 254/Es target and /sup 48/Ca projectiles. 13 refs., 2 figs., 2 tabs. (DWL)

  12. Experimental investigations on the nuclear structure of the neutron-rich nuclides 44S and 20O

    NASA Astrophysics Data System (ADS)

    Santiago-Gonzalez, Daniel

    Experimental results of two independent studies on the nuclear structure of the neutron-rich nuclei S4416 and O20 8 O are presented. A short introduction on the context of these studies within nuclear physics is given in chapter 1. Because of the fundamental differences between the experiments and analysis techniques the investigations have been separated in two chapters. The investigation of 44S, extracted via the two-proton knockout reaction from 46Ar with intermediate beam energy, is presented in chapter 2. Four new excited states are identified, of which the first 4+ state presents evidence of deformation, as suggested by line-shape simulations of the detected gamma rays. This is also indicated by a shell-model calculation, where the deformation of the first 4 + state originates in a neutron particle-hole configuration which is fundamentally different from the "intruder"configuration producing the ground state deformation and from the configuration describing the relatively long-lived isomeric 0+ state. Consequently, not three coexisting shapes, rather three coexisting configurations are found in 44S, corresponding to zero, one and two neutron particle-hole excitations. In chapter 3, results from the analysis of the 19O( d,p)20O reaction in inverse kinematics using the active gas target detector array ANASEN are presented. In order to study the location and fragmentation of the d3/2 orbital in 20O, a beam of the short-lived 19O was produced at the RESOLUT radioactive beam facility of the Florida State University. The ejected protons from the (d,p) reaction were measured with large solid angle coverage and for beam energies between 2.2 and 4.3 MeV/A. Data from the 17O(d,p)18O reaction was acquired to verify our experimental methods and analysis techniques.

  13. Beta-Decay Spectroscopy of Neutron-Rich Isotopes Utilizing a Planar Ge Double-Sided Strip Detector

    NASA Astrophysics Data System (ADS)

    Larson, N.; Liddick, S. N.; Prokop, C. J.; Kondev, F. G.; Kumar, S.; Crider, B. P.; Paulauskas, S. V.; Suchyta, S.

    2015-10-01

    In nuclear science, rapid changes in the structure of the atomic nucleus have been inferred with small changes in the neutron and proton numbers. These changes are manifested in variations of the low-energy level schemes of exotic isotopes. One region of the nuclear chart where rapid changes in deformation have been suggested based on the behavior of the first excited 2 + states is in neutron-rich nuclei near A = 110. Beta-decay spectroscopy is a sensitive and selective technique that can be used to investigate the low-energy level schemes exotic nuclei at low production rates. At the National Superconducting Cyclotron Laboratory (NSCL), a recently commissioned planar Ge double-sided strip detector (GeDSSD) is used in a novel application for these studies. Preliminary results from the decay of Tc isotopes in an experiment aimed at nuclei near A = 110 will be presented. This work was supported by the DOE NNSA DE-NA0000979 and the NSF Grant PHY1102511.

  14. β -decay half-lives of neutron-rich nuclei at A ~ 110 on r-process path

    NASA Astrophysics Data System (ADS)

    Nishizuka, Ippei; Sumikama, Toshiyuki; Browne, Frank; Bruce, Alison; Nishimura, Shunji; Doornenbal, Pieter; Lorusso, Giuseppe; Patel, Zena; Rice, Simon; Sinclair, Laura; Soderstom, Par-Ander; Watanabe, Hiroshi; Wu, Jin; Xu, Zhengyu; Yagi, Ayumi; Eurica Collaboration

    2014-09-01

    About half of the elements heavier than iron are thought to be produced by rapid-neutron capture process (r-process). The observed natural abundance in solar system was underestimated by a theoretical model at A ~ 110 , which uses β-decay half-lives. In the present study, we measured new β half-lives of neutron-rich nuclei on r-process path at RIBF in RIKEN. The nuclei of interest were produced by in-flight fission of uranium beam in beryllium target. The WAS3ABi detector which was 5 stacked double-sided silicon strip detectors (60 × 40 × 1 mm3), was used for the implantation of ions and the detection of both the implanted ions and the subsequently-emitted β rays. It is essential to make a position correlation between the mother nucleus and the β rays. In this talk, the analysis of the position correlation will be presented in detail. Preliminary results will be also shown.

  15. First in-beam γ -ray study of the level structure of neutron-rich 39S

    NASA Astrophysics Data System (ADS)

    Chapman, R.; Wang, Z. M.; Bouhelal, M.; Haas, F.; Liang, X.; Azaiez, F.; Behera, B. R.; Burns, M.; Caurier, E.; Corradi, L.; Curien, D.; Deacon, A. N.; Dombrádi, Zs.; Farnea, E.; Fioretto, E.; Gadea, A.; Hodsdon, A.; Ibrahim, F.; Jungclaus, A.; Keyes, K.; Kumar, V.; Lunardi, S.; Mǎrginean, N.; Montagnoli, G.; Napoli, D. R.; Nowacki, F.; Ollier, J.; O'Donnell, D.; Papenberg, A.; Pollarolo, G.; Salsac, M.-D.; Scarlassara, F.; Smith, J. F.; Spohr, K. M.; Stanoiu, M.; Stefanini, A. M.; Szilner, S.; Trotta, M.; Verney, D.

    2016-08-01

    The neutron-rich 39S nucleus has been studied using binary grazing reactions produced by the interaction of a 215-MeV beam of 36S ions with a thin 208Pb target. The magnetic spectrometer, PRISMA, and the γ -ray array, CLARA, were used in the measurements. Gamma-ray transitions of the following energies were observed: 339, 398, 466, 705, 1517, 1656, and 1724 keV. Five of the observed transitions have been tentatively assigned to the decay of excited states with spins up to (11 /2- ). The results of a state-of-the-art shell-model calculation of the level scheme of 39S using the SDPF-U effective interaction are also presented. The systematic behavior of the excitation energy of the first 11 /2- states in the odd-A isotopes of sulfur and argon is discussed in relation to the excitation energy of the first excited 2+ states of the adjacent even-A isotopes. The states of 39S that have the components in their wave functions corresponding to three neutrons in the 1 f7 /2 orbital outside the N =20 core have also been discussed within the context of the 0 ℏ ω shell-model calculations presented here.

  16. Shape of {sup 44}Ar: Onset of deformation in neutron-rich nuclei near {sup 48}Ca

    SciTech Connect

    Zielinska, M.; Goergen, A.; Clement, E.; Korten, W.; Dossat, C.; Ljungvall, J.; Obertelli, A.; Theisen, Ch.; Delaroche, J.-P.; Girod, M.; Buerger, A.; Catford, W.; Iwanicki, J.; Napiorkowski, P. J.; Srebrny, J.; Wrzosek, K.; Libert, J.; Rodriguez-Guzman, R.; Sletten, G.

    2009-07-15

    The development of deformation and shape coexistence in the vicinity of doubly magic {sup 48}Ca, related to the weakening of the N=28 shell closure, was addressed in a low-energy Coulomb excitation experiment using a radioactive {sup 44}Ar beam from the SPIRAL facility at GANIL. The 2{sub 1}{sup +} and 2{sub 2}{sup +} states in {sup 44}Ar were excited on {sup 208}Pb and {sup 109}Ag targets at two different beam energies. B(E2) values between all observed states and the spectroscopic quadrupole moment of the 2{sub 1}{sup +} state were extracted from the differential Coulomb excitation cross sections, indicating a prolate shape of the {sup 44}Ar nucleus and giving evidence of an onset of deformation already two protons and two neutrons away from doubly magic {sup 48}Ca. New Hartree-Fock-Bogoliubov based configuration mixing calculations have been performed with the Gogny D1S interaction for {sup 44}Ar and neighboring nuclei using two different approaches: the angular momentum projected generator coordinate method considering axial quadrupole deformations and a five-dimensional approach including the triaxial degree of freedom. The experimental values and new calculations are furthermore compared to shell-model calculations and to relativistic mean-field calculations. The new results give insight into the weakening of the N=28 shell closure and the development of deformation in this neutron-rich region of the nuclear chart.

  17. Intermediate-range order in permanently densified vitreous SiO sub 2 : A neutron-diffraction and molecular-dynamics study

    SciTech Connect

    Susman, S.; Volin, K.J.; Price, D.L.; Grimsditch, M.; Rino, J.P.; Kalia, R.K.; Vashishta, P. ); Gwanmesia, G.; Wang, Y.; Liebermann, R.C. )

    1991-01-01

    The structure of pressure-densified vitreous SiO{sub 2} has been investigated using neutron-diffraction and molecular-dynamics techniques. After compression to 16 GPa at room temperature, recovered samples have densities 20% higher than normal vitreous SiO{sub 2} and show substantial changes in the first sharp diffraction peak (FSDP): an indication of modification in the intermediate-range order. The changes in the FSDP are due to increased frustration caused by the decrease in the Si-O-Si bond angle and a shift in the Si-Si and O-O correlations in the range of 4--8 A toward lower distances.

  18. Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

    PubMed Central

    2013-01-01

    Silicon-rich Al2O3 films (Six(Al2O3)1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface. PMID:23758885

  19. β-decay study of neutron-rich ^102Rb at TRIUMF-ISAC

    NASA Astrophysics Data System (ADS)

    Wang, Zhimin

    2012-10-01

    Experimental investigations of the β-decay properties of nuclei which lie along the astrophysical r-process are becoming possible with modern facilities and detection systems. In this experiment, a ^102Rb beam was produced by 500 MeV, 10 μA protons impinging on a multilayer UCx target at TRIUMF-ISAC Facility. The beam of ^102Rb ions was implanted on a movable tape at the center of the 8π spectrometer. The 20 HPGe 8π γ-ray detectors were coupled with SCEPTAR, an hemispherical array of scintillators for β-tagging and DANTE, an array of five LaBr3 detectors for fast γ-ray timing. A preliminary analysis has allowed the first identification of the 4^+ to 2^+ transition in the daughter nucleus, ^102Sr. A near identical low-lying band structure of ^102Sr with ^98, 100Sr nuclei has been observed, indicating the rigidly deformed rotational nature continues towards to the N=66 midshell. The current experimental measurements of ^102Rb β-decay half life as well as the β-delayed neutron emission branching ratio compared with reported values, the shorter β-decay half life and the larger β-delayed neutron emission branching ratio will locally reshape astrophysical r-process predictions.

  20. Characterization of isomers in the neutron-rich odd-odd nucleus {sup 156}Pm

    SciTech Connect

    Sood, P. C.; Gowrishankar, R; Sai, K. Vijay; Sainath, M.

    2011-02-15

    Critical examination of the experimental data from {sup 156}Nd and {sup 156}Pm {beta} decays and the observed location of relevant neutron and proton orbitals in the neighboring odd-A isotones and isotopes, taken together with the low-lying two-quasiparticle (2qp) structures expected in {sup 156}Pm from the rotor-particle model, lead to the conclusion that a consistent description of all the available data is achieved with the I{sup {pi}}=4{sup +} spin-parity assignment to the 26.7s {sup 156}Pm ground state (g.s.) and assignment of I{sup {pi}}=1{sup +} to its 150.3-keV isomer with the 2qp configuration 4{sub g.s.}{sup +}{l_brace}p{sub o}:5/2[532{up_arrow}]{+-}n{sub o}:3/2[521{up_arrow}]{r_brace}1{sub 150}{sup +}. In the process, a two-neutron configuration is also suggested for the 1509-keV 4{sup +} level in the daughter nucleus {sup 156}Sm. The present analysis reiterates the important question of whether the {beta}-decay log ft value, by itself, can be employed to deduce the relative parity of the {beta}-connected states.

  1. From laser particle acceleration to the synthesis of extremely neutron rich isotopes via the novel fission-fusion mechanism

    NASA Astrophysics Data System (ADS)

    Thirolf, P. G.

    2015-02-01

    High-power, short pulse lasers have emerged in the last decade as attractive tools for accelerating charged particles (electrons, ions) to high energies over mm-scale acceleration lengths, thus promising to rival conventional acceleration techniques in the years ahead. In the first part of the article, the principles of laser-plasma interaction as well as the techniques and the current status of the acceleration of electron and ion beams will be briefly introduced. In particular with the upcoming next generation of multi-PW class laser systems, such as the one under construction for the ELI-Nuclear Physics project in Bucharest (ELI-NP), very efficient acceleration mechanisms for brilliant ion beams like radiation pressure acceleration (RPA) come into reach. Here, ultra-dense ion beams reaching solid-state density can be accelerated from thin target foils, exceeding the density of conventionally accelerated ion beams by about 14 orders of magnitude. This unique property of laser-accelerated ion beams can be exploited to explore the scenario of a new reaction mechanism called `fission-fusion', which will be introduced in the second part of the article. Accelerating fissile species (e.g. 232Th ) towards a second layer of the same material will lead to fission both of the beam-like and target-like particles. Due to the close to solid-state density of the accelerated ion bunches, fusion may occur between neutron-rich (light) fission products. This may open an access path towards extremely neutron-rich nuclides in the vicinity of the N=126 waiting point of the astrophysical r process. `Waiting points' at closed nucleon shells play a crucial role in controlling the reaction rates. However, since most of the pathway of heavy-element formation via the rapid-neutron capture process (r-process) runs in `terra incognita' of the nuclear landscape, in particular the waiting point at N=126 is yet unexplored and will remain largely inaccessible to conventional nuclear reaction

  2. From laser particle acceleration to the synthesis of extremely neutron rich isotopes via the novel fission-fusion mechanism

    SciTech Connect

    Thirolf, P. G.

    2015-02-24

    High-power, short pulse lasers have emerged in the last decade as attractive tools for accelerating charged particles (electrons, ions) to high energies over mm-scale acceleration lengths, thus promising to rival conventional acceleration techniques in the years ahead. In the first part of the article, the principles of laser-plasma interaction as well as the techniques and the current status of the acceleration of electron and ion beams will be briefly introduced. In particular with the upcoming next generation of multi-PW class laser systems, such as the one under construction for the ELI-Nuclear Physics project in Bucharest (ELI-NP), very efficient acceleration mechanisms for brilliant ion beams like radiation pressure acceleration (RPA) come into reach. Here, ultra-dense ion beams reaching solid-state density can be accelerated from thin target foils, exceeding the density of conventionally accelerated ion beams by about 14 orders of magnitude. This unique property of laser-accelerated ion beams can be exploited to explore the scenario of a new reaction mechanism called ‘fission-fusion’, which will be introduced in the second part of the article. Accelerating fissile species (e.g. {sup 232}Th) towards a second layer of the same material will lead to fission both of the beam-like and target-like particles. Due to the close to solid-state density of the accelerated ion bunches, fusion may occur between neutron-rich (light) fission products. This may open an access path towards extremely neutron-rich nuclides in the vicinity of the N=126 waiting point of the astrophysical r process. ‘Waiting points’ at closed nucleon shells play a crucial role in controlling the reaction rates. However, since most of the pathway of heavy-element formation via the rapid-neutron capture process (r-process) runs in ‘terra incognita’ of the nuclear landscape, in particular the waiting point at N=126 is yet unexplored and will remain largely inaccessible to conventional

  3. Predicted yields of new neutron-rich isotopes of nuclei with Z=64-80 in the multinucleon transfer reaction {sup 48}Ca+{sup 238}U

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Sargsyan, V. V.; Scheid, W.

    2010-05-15

    The production cross sections of new neutron-rich isotopes of nuclei with charge numbers Z=64-80 are estimated for future experiments in the multinucleon transfer reaction {sup 48}Ca+{sup 238}U at bombarding energy E{sub c.m.}=189 MeV close to the Coulomb barrier.

  4. The RNB project in Japanese Hadron Facility and possible use of neutron-rich beam for the study of superheavy nuclei

    SciTech Connect

    Nomura, Toru

    1998-02-15

    We first describe briefly a radioactive nuclear beam (RNB) facility based on the isotope separator on-line and post-accelerator scheme planned in Japanese Hadron Project. In this facility, various radioactive nuclear species produced in 3 GeV proton-induced reactions will be accelerated through heavy-ion linacs in three stages, the maximum output energy in each stage being 0.17, 1.05 and 6.5 meV/nucleon, respectively. Secondly, we discuss the feasibility of the use of neutron-rich RNB for experimental study of more neutron-rich superheavy nuclei than those presently known. It is shown that the increase of the survival probability of neutron-rich compound nuclei can possibly compensate for a difficulty arising from expected weak intensities of the secondary-beams. In addition, cold-fusion-like reactions as well as possible enhancement of near-barrier fusion cross sections that can become more prominent by use of neutron-rich beams are discussed.

  5. Upbend and M1 scissors mode in neutron-rich nuclei - consequences for r-process $$(n,\\gamma )$$ reaction rates

    DOE PAGES

    Larsen, A. C.; Goriely, S.; Bernstein, L. A.; ...

    2015-01-01

    An enhanced probability for low-energy γ-emission (upbend, Eγ < 3 MeV) at high excitation energies has been observed for several light and medium-mass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (Eγ ≈ 2–3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. Furthermore, the experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutron-rich, mid-mass nuclei including the scissors mode are shown.

  6. Upbend and M1 scissors mode in neutron-rich nuclei - consequences for r-process $(n,\\gamma )$ reaction rates

    SciTech Connect

    Larsen, A. C.; Goriely, S.; Bernstein, L. A.; Bleuel, D. L.; Bracco, A.; Brown, B. A.; Camera, F.; Eriksen, T. K.; Frauendorf, S.; Giacoppo, F.; Guttormsen, M.; Gorgen, A.; Harissopulos, S.; Leoni, S.; Liddick, S. N.; Naqvi, F.; Nyhus, H. T.; Rose, S. J.; Renstrom, T.; Schwengner, R.; Siem, S.; Spyrou, A.; Tveten, G. M.; Voinov, A. V.; Wiedeking, M.

    2015-01-01

    An enhanced probability for low-energy γ-emission (upbend, Eγ < 3 MeV) at high excitation energies has been observed for several light and medium-mass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (Eγ ≈ 2–3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. Furthermore, the experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutron-rich, mid-mass nuclei including the scissors mode are shown.

  7. Performance Study of an aSi Flat Panel Detector for Fast Neutron Imaging of Nuclear Waste

    SciTech Connect

    Schumann, M.; Mauerhofer, E.; Engels, R.; Kemmerling, G.; Frank, M.; Havenith, A.; Kettler, J.; Klapdor-Kleingrothaus, T.; Schitthelm, O.

    2015-07-01

    Radioactive waste must be characterized to check its conformance for intermediate storage and final disposal according to national regulations. For the determination of radio-toxic and chemo-toxic contents of radioactive waste packages non-destructive analytical techniques are preferentially used. Fast neutron imaging is a promising technique to assay large and dense items providing, in complementarity to photon imaging, additional information on the presence of structures in radioactive waste packages. Therefore the feasibility of a compact Neutron Imaging System for Radioactive waste Analysis (NISRA) using 14 MeV neutrons is studied in a cooperation framework of Forschungszentrum Juelich GmbH, RWTH Aachen University and Siemens AG. However due to the low neutron emission of neutron generators in comparison to research reactors the challenging task resides in the development of an imaging detector with a high efficiency, a low sensitivity to gamma radiation and a resolution sufficient for the purpose. The setup is composed of a commercial D-T neutron generator (Genie16GT, Sodern) with a surrounding shielding made of polyethylene, which acts as a collimator and an amorphous silicon flat panel detector (aSi, 40 x 40 cm{sup 2}, XRD-1642, Perkin Elmer). Neutron detection is achieved using a general propose plastic scintillator (EJ-260, Eljen Technology) linked to the detector. The thermal noise of the photodiodes is reduced by employing an entrance window made of aluminium. Optimal gain and integration time for data acquisition are set by measuring the response of the detector to the radiation of a 500 MBq {sup 241}Am-source. Detector performance was studied by recording neutron radiography images of materials with various, but well known, chemical compositions, densities and dimensions (Al, C, Fe, Pb, W, concrete, polyethylene, 5 x 8 x 10 cm{sup 3}). To simulate gamma-ray emitting waste radiographs in presence of a gamma-ray sources ({sup 60}Co, {sup 137}Cs, {sup 241

  8. Spectroscopy of the neutron-rich hypernucleus HeΛ7 from electron scattering

    DOE PAGES

    Gogami, T.; Chen, C.; Kawama, D.; ...

    2016-08-12

    Here, the missing mass spectroscopy of themore » $$^{7}_{\\Lambda}$$He hypernucleus was performed, using the $$^{7}$$Li$$(e,e^{\\prime}K^{+})^{7}_{\\Lambda}$$He reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $$\\Lambda$$ binding energy of the ground state (1/2$$^{+}$$) was determined with a smaller error than that of the previous measurement, being $$B_{\\Lambda}$$ = 5.55 $$\\pm$$ 0.10(stat.) $$\\pm$$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $$B_{\\Lambda}$$ = 3.65 $$\\pm$$ 0.20(stat.) $$\\pm$$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2$$^{+}$$ and 5/2$$^{+}$$ states, confirming the "gluelike" behavior of $$\\Lambda$$, which makes an unstable state in $$^{6}$$He stable against neutron emission.« less

  9. Electromagnetic properties of neutron-rich nuclei adjacent to the Z = 50 shell closure

    NASA Astrophysics Data System (ADS)

    Rejmund, M.; Navin, A.; Biswas, S.; Lemasson, A.; Caamaño, M.; Clément, E.; Delaune, O.; Farget, F.; de France, G.; Jacquot, B.; Van Isacker, P.

    2016-02-01

    Low-lying high-spin yrast states in the exotic odd-odd isotopes 124-128Sb (Z = 51) and 118-128In (Z = 49), studied for the first time, show a striking difference in their observed γ-ray decay. With a single valence proton particle/hole occupying the g7/2 /g9/2 spin-orbit partners, dominant electric quadrupole transitions occur in Sb as opposed to magnetic dipole transitions in In. The observed properties are explained on the basis of general principles of symmetry and with large-scale shell-model calculations, and reveal novel aspects of the competition between the neutron-proton interaction and the like-nucleon pairing interaction.

  10. Spectroscopy of the neutron-rich hypernucleus He7Λ from electron scattering

    NASA Astrophysics Data System (ADS)

    Gogami, T.; Chen, C.; Kawama, D.; Achenbach, P.; Ahmidouch, A.; Albayrak, I.; Androic, D.; Asaturyan, A.; Asaturyan, R.; Ates, O.; Baturin, P.; Badui, R.; Boeglin, W.; Bono, J.; Brash, E.; Carter, P.; Chiba, A.; Christy, E.; Danagoulian, S.; De Leo, R.; Doi, D.; Elaasar, M.; Ent, R.; Fujii, Y.; Fujita, M.; Furic, M.; Gabrielyan, M.; Gan, L.; Garibaldi, F.; Gaskell, D.; Gasparian, A.; Han, Y.; Hashimoto, O.; Horn, T.; Hu, B.; Hungerford, Ed. V.; Jones, M.; Kanda, H.; Kaneta, M.; Kato, S.; Kawai, M.; Khanal, H.; Kohl, M.; Liyanage, A.; Luo, W.; Maeda, K.; Margaryan, A.; Markowitz, P.; Maruta, T.; Matsumura, A.; Maxwell, V.; Mkrtchyan, A.; Mkrtchyan, H.; Nagao, S.; Nakamura, S. N.; Narayan, A.; Neville, C.; Niculescu, G.; Niculescu, M. I.; Nunez, A.; Nuruzzaman, Okayasu, Y.; Petkovic, T.; Pochodzalla, J.; Qiu, X.; Reinhold, J.; Rodriguez, V. M.; Samanta, C.; Sawatzky, B.; Seva, T.; Shichijo, A.; Tadevosyan, V.; Tang, L.; Taniya, N.; Tsukada, K.; Veilleux, M.; Vulcan, W.; Wesselmann, F. R.; Wood, S. A.; Yamamoto, T.; Ya, L.; Ye, Z.; Yokota, K.; Yuan, L.; Zhamkochyan, S.; Zhu, L.; HKS JLab E05-115 Collaboration

    2016-08-01

    The missing mass spectroscopy of the He7Λ hypernucleus was performed using the 7Li(e ,e'K+) He7Λ reaction at the Thomas Jefferson National Accelerator Facility Hall C. The Λ -binding energy of the ground-state (1 /2+ ) was determined with a smaller error than that of the previous measurement, being BΛ=5.55 ±0 .10stat .±0 .11sys .MeV . The experiment also provided new insight into charge symmetry breaking in p -shell hypernuclear systems. Finally, a peak at BΛ=3.65 ±0 .20stat .±0 .11sys .MeV was observed and assigned as a mixture of 3 /2+ and 5 /2+ states, confirming the "gluelike" behavior of Λ , which makes an unstable state in 6He stable against neutron emission.

  11. Electromagnetic modeling of waveguide amplifier based on Nd3+ Si-rich SiO2 layers by means of the ADE-FDTD method

    PubMed Central

    2011-01-01

    By means of ADE-FDTD method, this paper investigates the electromagnetic modelling of a rib-loaded waveguide composed of a Nd3+ doped Silicon Rich Silicon Oxide active layer sandwiched between a SiO2 bottom cladding and a SiO2 rib. The Auxilliary Differential Equations are the rate equations which govern the levels populations. The Finite Difference Time Domain (FDTD) scheme is used to solve the space and time dependent Maxwell equations which describe the electromagnetic field in a copropagating scheme of both pumping (λpump = 488 nm) and signal (λsignal = 1064 nm) waves. Such systems are characterized by extremely different specific times such as the period of electromagnetic field ~ 10-15 s and the lifetimes of the electronic levels between ~ 10-10s and ~ 10-4 s. The time scaling method is used in addition to specific initial conditions in order to decrease the computational time. We show maps of the Poynting vector along the propagation direction as a function of the silicon nanograin (Si-ng) concentrations. A threshold value of 1024 Si-ng m-3 is extracted below which the pump wave can propagate so that a signal amplication is possible. PMID:21711829

  12. Electromagnetic modeling of waveguide amplifier based on Nd3+ Si-rich SiO2 layers by means of the ADE-FDTD method.

    PubMed

    Dufour, Christian; Cardin, Julien; Debieu, Olivier; Fafin, Alexandre; Gourbilleau, Fabrice

    2011-04-04

    By means of ADE-FDTD method, this paper investigates the electromagnetic modelling of a rib-loaded waveguide composed of a Nd3+ doped Silicon Rich Silicon Oxide active layer sandwiched between a SiO2 bottom cladding and a SiO2 rib. The Auxilliary Differential Equations are the rate equations which govern the levels populations. The Finite Difference Time Domain (FDTD) scheme is used to solve the space and time dependent Maxwell equations which describe the electromagnetic field in a copropagating scheme of both pumping (λpump = 488 nm) and signal (λsignal = 1064 nm) waves. Such systems are characterized by extremely different specific times such as the period of electromagnetic field ~ 10-15 s and the lifetimes of the electronic levels between ~ 10-10s and ~ 10-4 s. The time scaling method is used in addition to specific initial conditions in order to decrease the computational time. We show maps of the Poynting vector along the propagation direction as a function of the silicon nanograin (Si-ng) concentrations. A threshold value of 1024 Si-ng m-3 is extracted below which the pump wave can propagate so that a signal amplication is possible.

  13. Role of nuclear couplings in the inelastic excitation of weakly-bound neutron-rich nuclei

    SciTech Connect

    Dasso, C.H.; Lenzi, S.M.; Vitturi, A.

    1996-12-31

    Much effort is presently devoted to the study of nuclear systems far from the stability line. Particular emphasis has been placed in light systems such as {sup 11}Li, {sup 8}B and others, where the very small binding energy of the last particles causes their density distribution to extend considerably outside of the remaining nuclear core. Some of the properties associated with this feature are expected to characterize also heavier systems in the vicinity of the proton or neutron drip lines. It is by now well established that low-lying concentrations of multipole strength arise from pure configurations in which a peculiar matching between the wavelength of the continuum wavefunction of the particles and the range of the weakly-bound hole states occurs. To this end the authors consider the break-up of a weakly-bound system in a heavy-ion collision and focus attention in the inelastic excitation of the low-lying part of the continuum. They make use of the fact that previous investigations have shown that the multipole response in this region is not of a collective nature and describe their excited states as pure particle-hole configurations. Since the relevant parameter determining the strength distributions is the binding energy of the last bound orbital they find it most convenient to use single-particle wavefunctions generated by a sperical square-well potential with characteristic nuclear dimensions and whose depth has been adjusted to give rise to a situation in which the last occupied neutron orbital is loosely-bound. Spin-orbit couplings are, for the present purpose, ignored. The results of this investigation clearly indicate that nuclear couplings have the predominant role in causing projectile dissociation in many circumstances, even at bombarding energies remarkably below the Coulomb barrier.

  14. Neutron skins and neutron stars

    SciTech Connect

    Piekarewicz, J.

    2013-11-07

    The neutron-skin thickness of heavy nuclei provides a fundamental link to the equation of state of neutron-rich matter, and hence to the properties of neutron stars. The Lead Radius Experiment ('PREX') at Jefferson Laboratory has recently provided the first model-independence evidence on the existence of a neutron-rich skin in {sup 208}Pb. In this contribution we examine how the increased accuracy in the determination of neutron skins expected from the commissioning of intense polarized electron beams may impact the physics of neutron stars.

  15. Investigation of the agglomeration and amorphous transformation effects of neutron irradiation on the nanocrystalline silicon carbide (3C-SiC) using TEM and SEM methods

    NASA Astrophysics Data System (ADS)

    Huseynov, Elchin M.

    2017-04-01

    Nanocrystalline 3C-SiC particles irradiated by neutron flux during 20 h in TRIGA Mark II light water pool type research reactor. Silicon carbide nanoparticles were analyzed by Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM) devices before and after neutron irradiation. The agglomeration of nanoparticles was studied comparatively before and after neutron irradiation. After neutron irradiation the amorphous layer surrounding the nanoparticles was analyzed in TEM device. Neutron irradiation defects in the 3C-SiC nanoparticles and other effects investigated by TEM device. The effect of irradiation on the crystal structure of the nanomaterial was studied by selected area electron diffraction (SAED) and electron diffraction patterns (EDP) analysis.

  16. J-type Carbon Stars: A Dominant Source of 14N-rich Presolar SiC Grains of Type AB

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Stephan, Thomas; Boehnke, Patrick; Nittler, Larry R.; O'D. Alexander, Conel M.; Wang, Jianhua; Davis, Andrew M.; Trappitsch, Reto; Pellin, Michael J.

    2017-07-01

    We report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB (14N/15N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takes place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show 13C and 14N excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. Because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%-15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.

  17. Solid-State (29)Si NMR and neutron-diffraction studies of Sr(0.7)K(0.3)SiO(2.85) oxide ion conductors.

    PubMed

    Xu, Jungu; Wang, Xiaoming; Fu, Hui; Brown, Craig M; Jing, Xiping; Liao, Fuhui; Lu, Fengqi; Li, Xiaohui; Kuang, Xiaojun; Wu, Mingmei

    2014-07-07

    K/Na-doped SrSiO3-based oxide ion conductors were recently reported as promising candidates for low-temperature solid-oxide fuel cells. Sr0.7K0.3SiO2.85, close to the solid-solution limit of Sr1-xKxSiO3-0.5x, was characterized by solid-state (29)Si NMR spectroscopy and neutron powder diffraction (NPD). Differing with the average structure containing the vacancies stabilized within the isolated Si3O9 tetrahedral rings derived from the NPD study, the (29)Si NMR data provides new insight into the local defect structure in Sr0.7K0.3SiO2.85. The Q(1)-linked tetrahedral Si signal in the (29)Si NMR data suggests that the Si3O9 tetrahedral rings in the K-doped SrSiO3 materials were broken, forming Si3O8 chains. The Si3O8 chains can be stabilized by either bonding with the oxygen atoms of the absorbed lattice water molecules, leading to the Q(1)-linked tetrahedral Si, or sharing oxygen atoms with neighboring Si3O9 units, which is consistent with the Q(3)-linked tetrahedral Si signal detected in the (29)Si NMR spectra.

  18. Annihilation behavior of irradiation defects in Li4SiO4 irradiated with high thermal neutron fluence

    NASA Astrophysics Data System (ADS)

    Ran, Guangming; Xiao, Chengjian; Chen, Xiaojun; Gong, Yu; Zhao, Linjie; Wang, Heyi; Wang, Xiaolin

    2017-08-01

    The annihilation behavior of irradiation defects in Li4SiO4 which were irradiated with thermal neutrons to a high fluence was studied by electron spin resonance (ESR). It was observed that the ratio of O-related centers to E'-centers increased with increasing annealing temperature. The total irradiation defects were annihilated through two processes, namely the fast (120-250 °C, 70%) and the slow ones (250-500 °C, 30%), and their activation energies were determined to be 0.63 ± 0.09 and 0.89 ± 0.14 eV, respectively. The observed annihilation behavior of irradiation defects in Li4SiO4 was found to be very different from that in a previous study, which could be attributed to the difference in concentration and types of irradiation defects generated by different neutron fluences. It was implied that the annihilation behavior of irradiation defects in ternary lithium oxides would become more complicated with increasing neutron fluence.

  19. Small angle neutron scattering modeling of copper-rich precipitates in steel

    SciTech Connect

    Spooner, S.

    1997-11-01

    The magnetic to nuclear scattering intensity ratio observed in the scattering from copper rich precipitates in irradiated pressure vessel steels is much smaller than the value of 11.4 expected for a pure copper precipitate in iron. A model for precipitates in pressure vessel steels which matches the observed scattering typically incorporates manganese, nickel, silicon and other elements and it is assumed that the precipitate is non-magnetic. In the present work consideration is given to the effect of composition gradients and ferromagnetic penetration into the precipitate on the small angle scattering cross section for copper rich clusters as distinguished from conventional precipitates. The calculation is an extension of a scattering model for micelles which consist of shells of varying scattering density. A discrepancy between recent SANS scattering experiments on pressure vessel steels was found to be related to applied magnetic field strength. The assumption of cluster structure and its relation to atom probe FIM findings as well as the effects of insufficient field for magnetic saturation is discussed.

  20. Small angle neutron scattering modeling of copper-rich precipitates in steel

    SciTech Connect

    Spooner, S.

    1997-11-01

    The magnetic-to-nuclear scattering intensity ratio observed in the scattering from copper-rich precipitates in irradiated pressure vessel steels is much smaller than the value of 11.4 expected for a pure copper precipitate in iron. A model for precipitates in pressure vessel steels which matches the observed scattering typically incorporates manganese, nickel, silicon and other elements and it is assumed that the precipitate is non-magnetic. In the present work consideration is given to the effect of composition gradients and ferromagnetic penetration into the precipitate on the small angle scattering cross section for copper-rich clusters as distinguished from conventional precipitates. The calculation is an extension of a scattering model for micelles which consist of shells of varying scattering density. A discrepancy between recent SANS scattering experiments on pressure vessel shells was found to be related to applied magnetic field strength. The assumption of cluster structure and its relation to atom probe FIM findings as well as the effects of insufficient field for magnetic saturation is discussed.

  1. Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides

    NASA Astrophysics Data System (ADS)

    Ramos, D.; Rodríguez-Tajes, C.; Caamaño, M.; Farget, F.; Audouin, L.; Benlliure, J.; Casarejos, E.; Clement, E.; Cortina, D.; Delaune, O.; Derkx, X.; Dijon, A.; Doré, D.; Fernández-Domínguez, B.; de France, G.; Heinz, A.; Jacquot, B.; Navin, A.; Paradela, C.; Rejmund, M.; Roger, T.; Salsac, M. D.; Schmitt, C.

    2016-03-01

    Experimental access to full isotopic fragment distributions is very important to determine the features of the fission process. However, the isotopic identification of fission fragments has been, in the past, partial and scarce. A solution based on the use of inverse kinematics to study transfer-induced fission of exotic actinides was carried out at GANIL, resulting in the first experiment accessing the full identification of a collection of fissioning systems and their corresponding fission fragment distribution. In these experiments, a 238U beam at 6.14 AMeV impinged on a carbon target to produce fissioning systems from U to Am by transfer reactions, and Cf by fusion reactions. Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.

  2. Electric dipole response of neutron-rich calcium isotopes in relativistic quasiparticle time blocking approximation

    NASA Astrophysics Data System (ADS)

    Egorova, Irina A.; Litvinova, Elena

    2016-09-01

    New results for electric dipole strength in the chain of even-even calcium isotopes with the mass numbers A =40 -54 are presented. Starting from the covariant Lagrangian of quantum hadrodynamics, spectra of collective vibrations (phonons) and phonon-nucleon coupling vertices for J ≤6 and natural parity were computed in a self-consistent relativistic quasiparticle random-phase approximation (RQRPA). These vibrations coupled to Bogoliubov two-quasiparticle configurations (2 q ⊗phonon ) formed the model space for the calculations of the dipole response function in the relativistic quasiparticle time blocking approximation. The calculations in the latter approach were performed for the giant dipole resonance (GDR) and compared to those obtained with the RQRPA and to available data. The evolution of the dipole strength with the neutron number is investigated for both high-frequency GDRs and low-lying strengths. The development of a pygmy resonant structure on the low-energy shoulder of the GDR is traced and analyzed in terms of transition densities. A dependence of the pygmy dipole strength on the isospin asymmetry parameter is extracted.

  3. Triaxial shapes in the ground states of even-even neutron-rich Ru isotopes

    SciTech Connect

    Ahmad, I.; Lister, C.J.; Morss, L.R.

    1995-08-01

    Partial level schemes for {sup 108,110,112}Ru, and {sup 114}Ru about which nothing was previously known, were determined from the measurement of prompt, triple-gamma coincidences in {sup 248}Cm fission fragments. A 5-mg {sup 249}Cm source, mixed with 65-mg KCl and pressed in the form of a 7-mm diameter pellet, was used for the experiment. Prompt {gamma} rays emitted from the fission fragments were detected with the Eurogam array at Daresbury, which at that time consisted of 45 Compton suppressed Ge detectors and 5 LEPS spectrometers. Transitions in Ru were identified by gating on {gamma} rays in the complementary Te fragments. Figure I-25 shows the technique used to identify the previously unknown transitions in {sup 114}Ru and its partial level scheme. High spin states up to spin 10 h were observed and the {gamma}-ray branching ratios were determined. The ratios of electric quadrupole transition probabilities deduced from the experimental branching ratios were found to be in good agreement with the predictions of a simple model of rigid triaxial rotor. Our analysis shows that gamma deformation in Ru isotopes is increasing with the neutron number and the gamma value for {sup 112}Ru and {sup 114}Ru is {approximately} 25 degrees. This is one of the highest gamma values encountered in nuclei, suggesting soft triaxial shapes for {sup 112}Ru and {sup 114}Ru. The results of this investigation were published.

  4. Decay properties of neutron-rich 74Co and predictions for 78Co

    NASA Astrophysics Data System (ADS)

    Go, Shintaro; Grzywacz, Robert; Chiara, Mazzocchi; Liddick, Sean; Alshudifat, Mohammad; Batchelder, Jon; Baumann, Thomas; Ginter, Tom; Gross, Carl; Kolos, Karolina; Korgul, Agnieszka; Ciemny, Aleksandra; Paulauskas, Stanley; Prokop, Christpher; Rajabali, Mustafa; Rykaczewski, Krzysztof; Taylor, Steven; Xiao, Yongchi

    2016-09-01

    Experimental studies of doubly magic 78Ni are needed to provide critical data to test the robustness of the nuclear shell structure and model r-process. One of the best ways to investigate the shell structure of 78Ni is the decay of 78Co. While presently it is not possible to produce 78Co with sufficient rates, the decay measurements will be an essential study with new facilities and beam intensity upgrades. We measured the beta-decay properties of 74Co using fragmentation reaction at NSCL. Combining this result and other existing data around 78Ni enabled us to make predictions for the decay properties of 78Co. The half-life and beta-delayed neutron emission probability predicted by shell-model calculations will be presented for the chain of odd-odd cobalt isotopes. This work was funded in part by the U.S. DOE Grant No. DE-FG02-96ER40983 and by the Polish Ministry of Science and Higher Education through Grant No. 0079/DIA/2014/43.

  5. Theoretical study of neutron-rich 107,109,111,113Rh isotopes

    NASA Astrophysics Data System (ADS)

    Kumar, Amit; Singh, Suram; Khosa, S. K.; Bharti, Arun; Bhat, G. H.; Sheikh, J. A.

    2015-10-01

    A theoretical study of the structure of some odd mass Rh nuclei in the A 100 mass region is carried out by using the angular momentum projection technique implemented in the projected shell model (PSM). The influence of the high-j orbitals (h11/2 for neutrons and g9/2 for protons) on the structure of 107-113Rh isotopes is investigated in the present case by assuming an axial symmetry in the deformed basis. For these isotopes, the structure of multi-quasi-particle qp bands is studied along the yrast line in detail. Further, the phenomenon of back-bending is also studied theoretically and is found to be in agreement with the experimental data. The reduced transition probabilities, i.e., B(E2) and B(M1) for the yrast band are also obtained from the PSM wave functions for the first time, thereby providing an opportunity for the experimentalists to work for this data.

  6. Effects of neutron irradiation on the strength of continuous fiber reinforced SiC/SiC composites

    SciTech Connect

    Youngblood, G.E.; Henager, C.H. Jr.; Jones, R.H.

    1997-04-01

    Flexural strength data as a function of irradiation temperature and dose for a SiC{sub f}/SiC composite made with Nicalon-CG fiber suggest three major degradation mechanisms. Based on an analysis of tensile strength and microstructural data for irradiated Nicalon-CG and Hi-Nicalon fibers, it is anticipated that these degradation mechanisms will be alleviated in Hi-Nicalon reinforced composites.

  7. Neutron-rich nuclei in cosmic rays and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

    Prantzos, N.; Arnould, M.; Arcoragi, J. P.; Casse, M.

    1985-01-01

    Wolf-Rayet stars figure prominently in astrophysical research. As a bonus, they seem to offer, in the recent past, an interesting connection between classical astronomy and high energy astrophysics due to their unusual composition and their huge mechanical power. The material flowing from WC stars (carbon-rich WR stars) contains gas which has been processed through core-helium burning, i.e., considerably enriched into 12C,16O, 22Ne, and 25,26Mg. This composition is reminiscent of the cosmic ray source anomalies. Encouraging agreement is obtained with observation in the mass range 12 A 26 assuming acceleration of wind particles at the shock that delineates the WR cavity, and adequate dilution with normal cosmic rays, but silicon poses.

  8. Analysis of silicon nanocrystals in silicon-rich SiO II synthesized by CO II laser annealing

    NASA Astrophysics Data System (ADS)

    Lin, Chun-Jung; Lin, Gong-Ru; Chueh, Yu-Lun; Chou, Li-Jen

    2005-11-01

    The localized synthesis of 4.2-5.6 nm-Si nanocrystals (nc-Si) in Si-rich SiO II (SRSO) by CO 2 laser annealing at laser intensity of below ablation-threshold (6 kW/cm2) is demonstrated. Since the SRSO exhibits a high absorption coefficient of up to 0.102 cm -1 at wavelength of 10.6 μm, a direct-writing CO II laser annealing system with focusing spot size of 0.2 mm2 is used to locally anneal the SRSO and precipitate the nc-Si. A thermophysical model reveals that the surface temperature of SRSO ranging from 130 °C to 3350 °C is achieved by varying the laser power densities from 1.5 to 13.5 kW/cm2. The CO II laser-ablation-threshold power density is about 6 kW/cm2, corresponding to the optimized annealing temperature 1285 °C at the ablation threshold. The CO IIlaser annealing is capable of the precise control on power density and spot size, which benefits from the in-situ and localized annealing temperature control of SRSO film, and also prevents from the eternal damage of the other electronic devices nearby the annealing site. The nc-Si dependent photoluminescence (PL) were observed at 806 nm or longer, whereas the laser-ablation damaged SRSO film exhibits significant blue PL at 410 nm due to the oxygen-related structural defects. The refractive index of the lasertreated SRSO film is increasing from 1.57 to 2.31 as the laser intensity increases from 1.5 to 6.0 kW/cm2 which is mainly attributed to the increasing density of nc-Si embedded in SRSO. High resolution transmission electron microscopy (HRTEM) analysis reveals that the average size of nc-Si embedded in SRSO film is about 5.3 nm, which correlates well with the theoretical prediction of a corresponding PL at 806 nm. The HRTEM estimated square density of the nc-Si in SRSO film under the laser intensity of 6 kW/cm2 is about 10 18 cm -3.

  9. Containerless processing and rapid solidification of Nb-Si alloys in the niobium-rich eutectic range

    NASA Technical Reports Server (NTRS)

    Hofmeister, W. H.; Bayuzick, R. J.; Robinson, M. B.; Bertero, G. A.

    1991-01-01

    Containerless processing and rapid solidification techniques were used to process Nb-Si alloys in the Nb-rich eutectic range. Electromagnetically levitated drops were melted and subsequently splat-quenched from different temperatures. A variety of eutectic morphologies was obtained as a function of the degree of superheating or undercooling of the drops prior to splatting. Metallic glass was observed only in drops quenched from above the melting temperature. Microstructures of splats deeply undercooled prior to quenching were very fine and uniform. These results are discussed in terms of classic nucleation theory concepts and the expected heat evolution at different regions of the splat during the rapid quenching process. The locations of the coupled-zone boundaries for the alpha-Nb + Nb3Si eutectic are also suggested.

  10. Containerless processing and rapid solidification of Nb-Si alloys in the niobium-rich eutectic range

    NASA Technical Reports Server (NTRS)

    Hofmeister, W. H.; Bayuzick, R. J.; Robinson, M. B.; Bertero, G. A.

    1991-01-01

    Containerless processing and rapid solidification techniques were used to process Nb-Si alloys in the Nb-rich eutectic range. Electromagnetically levitated drops were melted and subsequently splat-quenched from different temperatures. A variety of eutectic morphologies was obtained as a function of the degree of superheating or undercooling of the drops prior to splatting. Metallic glass was observed only in drops quenched from above the melting temperature. Microstructures of splats deeply undercooled prior to quenching were very fine and uniform. These results are discussed in terms of classic nucleation theory concepts and the expected heat evolution at different regions of the splat during the rapid quenching process. The locations of the coupled-zone boundaries for the alpha-Nb + Nb3Si eutectic are also suggested.

  11. Lithium dynamics in carbon-rich polymer-derived SiCN ceramics probed by nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Baek, Seung-Ho; Reinold, Lukas Mirko; Graczyk-Zajac, Magdalena; Riedel, Ralf; Hammerath, Franziska; Büchner, Bernd; Grafe, Hans-Joachim

    2014-05-01

    We report 7Li, 29Si, and 13C NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei, we find that only the 13C spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature (T) and Larmor frequency (ωL) dependences of the 7Li linewidth and spin-lattice relaxation rates T1-1 are described by an activated law with the activation energy EA of 0.31 eV and the correlation time τ0 in the high temperature limit of 1.3 ps. The 3 / 2 power law dependence of T1-1 on ωL which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the μs timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T1ρ-1 results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes.

  12. Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers

    NASA Astrophysics Data System (ADS)

    Das, R.; Bera, M. K.; Chakraborty, S.; Saha, S.; Woitok, J. F.; Maiti, C. K.

    2006-11-01

    Rapid thermal oxidation of high-Ge content (Ge-rich) Si 1- xGe x ( x = 0.85) layers in dry O 2 ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (˜6-8 nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO 2 + GeO 2) and pile-up of Ge at the oxide/Si 1- xGe x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance-voltage (C-V) and current-voltage (J-V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.

  13. Magnetic Fe, Si, Al-Rich Impact Spherules from the P-T Boundary Layer at Graphite Peak, Antarctica

    NASA Technical Reports Server (NTRS)

    Petaev, M. I.; Jacobsen, S. B.; Basu, A. R.; Becker, L.

    2004-01-01

    The geological boundary between Triassic and Permian strata coincides with the greatest life extinction in the Earth's history. Although the cause of the extinction is still the subject of intense debates, recent discoveries in the P-T boundary layer of shocked quartz grains, fullerenes with the extraterrestrial noble gases, Fe metal nuggets, and chondritic meteorite fragments all point to a powerful collision of Earth with a celestial body in the late Permian. Here we report the discovery of magnetic Fe, Si, Al-rich impact spherules which accompany the chondritic meteorite fragments in some samples from the P-T boundary layer at Graphite Peak, Antarctica.

  14. Magnetic Fe, Si, Al-Rich Impact Spherules from the P-T Boundary Layer at Graphite Peak, Antarctica

    NASA Technical Reports Server (NTRS)

    Petaev, M. I.; Jacobsen, S. B.; Basu, A. R.; Becker, L.

    2004-01-01

    The geological boundary between Triassic and Permian strata coincides with the greatest life extinction in the Earth's history. Although the cause of the extinction is still the subject of intense debates, recent discoveries in the P-T boundary layer of shocked quartz grains, fullerenes with the extraterrestrial noble gases, Fe metal nuggets, and chondritic meteorite fragments all point to a powerful collision of Earth with a celestial body in the late Permian. Here we report the discovery of magnetic Fe, Si, Al-rich impact spherules which accompany the chondritic meteorite fragments in some samples from the P-T boundary layer at Graphite Peak, Antarctica.

  15. High compositional homogeneity in In-rich InGaAs nanowire arrays on nanoimprinted SiO2/Si (111)

    NASA Astrophysics Data System (ADS)

    Hertenberger, S.; Funk, S.; Vizbaras, K.; Yadav, A.; Rudolph, D.; Becker, J.; Bolte, S.; Döblinger, M.; Bichler, M.; Scarpa, G.; Lugli, P.; Zardo, I.; Finley, J. J.; Amann, M.-C.; Abstreiter, G.; Koblmüller, G.

    2012-07-01

    We report improved homogeneity control of composition-tuned In1-xGaxAs (x < 0.4) nanowire (NW) arrays grown by catalyst-free molecular beam epitaxy (MBE) on nanoimprinted SiO2/Si (111) substrates. Using very high As/(Ga+In) ratios at growth temperatures of 550 °C enabled uniform incorporation of the respective group-III elements (In,Ga) over the investigated composition range, confirmed by high-resolution x-ray diffraction (HRXRD) and energy dispersive x-ray spectroscopy. Low-temperature (20 K) photoluminescence of these In-rich In1-xGaxAs NW ensembles reveal state-of-the-art linewidths of ˜29-33 meV. These are independent of Ga content, suggesting an overall low degree of phase separation. In contrast, self-assembled, non-periodic In1-xGaxAs NW arrays show larger inhomogeneity with increased peakwidths in 2θ-ω HRXRD scans as well as broadened Raman modes. These results demonstrate the excellent potential of site-selective MBE growth of high-periodicity non-tapered In1-xGaxAs NW arrays with low size and composition dispersion for optimized device integration on Si.

  16. Geochemical Effects on Neutron Die-Away: Implications for the Mars Science Laboratory Dynamic Albedo of Neutrons Experiment

    NASA Astrophysics Data System (ADS)

    Hardgrove, C. J.; Moersch, J. E.

    2011-03-01

    We have shown that strong reductions in the total number of thermal neutrons as well as shifts in arrival times may allow DAN, on-board the MSL rover Curiosity, to detect evaporitic Cl-rich deposits, Fe concretions or hydrothermal Si-rich materials.

  17. Strong enhancement of dynamical emission of heavy fragments in the neutron-rich {sup 124}Sn+{sup 64}Ni reaction at 35A MeV

    SciTech Connect

    Russotto, P.; Amorini, F.; Cavallaro, S.; Di Toro, M.; Giustolisi, F.; Porto, F.; Rizzo, F.; De Filippo, E.; Pagano, A.; Cardella, G.; Lanzano, G.; Papa, M.; Pirrone, S.; Piasecki, E.; Auditore, L.; Trifiro, A.; Trimarchi, M.

    2010-06-15

    A quantitative comparison is made between the absolute cross sections associated with statistical and dynamical emission of heavy fragments in the {sup 124}Sn+{sup 64}Ni and {sup 112}Sn+{sup 58}Ni collisions experimentally investigated at 35A MeV beam energy using the multidetector CHIMERA. The result shows that the dynamical process is about twice as probable in the neutron-rich {sup 124}Sn+{sup 64}Ni system as in the {sup 112}Sn+{sup 58}Ni neutron-poor one. This unexpected and significant difference indicates that the reaction mechanism is strongly dependent on the entrance-channel isospin (N/Z) content.

  18. New Isomers in the Full Seniority Scheme of Neutron-Rich Lead Isotopes: The Role of Effective Three-Body Forces

    NASA Astrophysics Data System (ADS)

    Gottardo, A.; Valiente-Dobón, J. J.; Benzoni, G.; Nicolini, R.; Gadea, A.; Lunardi, S.; Boutachkov, P.; Bruce, A. M.; Górska, M.; Grebosz, J.; Pietri, S.; Podolyák, Zs.; Pfützner, M.; Regan, P. H.; Weick, H.; Alcántara Núñez, J.; Algora, A.; Al-Dahan, N.; de Angelis, G.; Ayyad, Y.; Alkhomashi, N.; Allegro, P. R. P.; Bazzacco, D.; Benlliure, J.; Bowry, M.; Bracco, A.; Bunce, M.; Camera, F.; Casarejos, E.; Cortes, M. L.; Crespi, F. C. L.; Corsi, A.; Denis Bacelar, A. M.; Deo, A. Y.; Domingo-Pardo, C.; Doncel, M.; Dombradi, Zs.; Engert, T.; Eppinger, K.; Farrelly, G. F.; Farinon, F.; Farnea, E.; Geissel, H.; Gerl, J.; Goel, N.; Gregor, E.; Habermann, T.; Hoischen, R.; Janik, R.; Klupp, S.; Kojouharov, I.; Kurz, N.; Lenzi, S. M.; Leoni, S.; Mandal, S.; Menegazzo, R.; Mengoni, D.; Million, B.; Morales, A. I.; Napoli, D. R.; Naqvi, F.; Nociforo, C.; Prochazka, A.; Prokopowicz, W.; Recchia, F.; Ribas, R. V.; Reed, M. W.; Rudolph, D.; Sahin, E.; Schaffner, H.; Sharma, A.; Sitar, B.; Siwal, D.; Steiger, K.; Strmen, P.; Swan, T. P. D.; Szarka, I.; Ur, C. A.; Walker, P. M.; Wieland, O.; Wollersheim, H.-J.; Nowacki, F.; Maglione, E.; Zuker, A. P.

    2012-10-01

    The neutron-rich lead isotopes, up to Pb216, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond Pb208.

  19. THE INFLUENCE OF NEUTRON-IRRADIATION AT LOW TEMPERATURES ON THE DIELECTRIC PARAMETERS OF 3C-SiC

    SciTech Connect

    J.A.A. Engelbrecht; G. Deyzel; E. Minnaar; W.E. Goosen; I. J. van Rooyen

    2014-04-01

    3C-SiC wafers were irradiated with neutrons of various fluences and at low (200 - 400 ?C) irradiation temperatures. Fourier Transform infrared (FTIR) reflectance spectra were obtained for the samples, and the spectra used to extract the dielectric parameters for each specimen, using statistical curve-fitting procedures. Analysis of all data revealed trends in reflectance peak heights as well as in the dielectric parameters. The surface roughness of the irradiated samples was measured by atomic force spectroscopy (AFM) and certain trends could be ascribed to surface roughness.

  20. Histidine-rich cationic amphipathic peptides for plasmid DNA and siRNA delivery.

    PubMed

    Kichler, Antoine; Mason, A James; Marquette, Arnaud; Bechinger, Burkhard

    2013-01-01

    Amphipathic, pH-responsive, membrane-active peptides such as LAH4 and derivatives thereof have the ability to effectively deliver genes and small interfering RNA (siRNA) into mammalian cells. Their ability to bind and protect nucleic acids and then disrupt membranes when activated at low pH enables them to harness the endocytic machinery to deliver cargo efficiently and with low associated toxicity. This chapter describes protocols for the chemical synthesis of transfection peptides of the LAH4 family, complex formation with nucleic acids, and their use for the in vitro delivery of either plasmid DNA or siRNA into mammalian cell lines.

  1. Enhancement of fusion at near-barrier energies for neutron-rich light nuclei: 19O +12 C

    NASA Astrophysics Data System (ADS)

    Singh, Varinderjit; Vadas, J.; Steinbach, T. K.; Wiggins, B. B.; Hudan, S.; Desouza, R. T.; Baby, L. T.; Kuvin, S. A.; Tripathi, Vandana; Wiedenhover, I.; Umar, A. S.

    2017-01-01

    Measuring the fusion excitation function for an isotopic chain of projectile nuclei provides a sensitive test of a microscopic description of fusion. To investigate the theoretically predicted fusion enhancement for neutron-rich light nuclei, an experiment was performed to measure the fusion excitation functions for 19 O +12 C and 18 O +12 C . Using the 18O(d,p) reaction and the RESOLUT mass spectrometer at Florida State University, a beam of 19O was produced with an intensity of 2-4 x 103 p/s. This beam bombarded a 100 μg/cm2 carbon target. Using an approach optimized for the measurement of fusion with a low-intensity beam, evaporation residues (ERs) resulting from the de-excitation of the fusion product were measured. The ERs were identified by measuring their energy and time-of-flight. At near-barrier energies, an enhancement of fusion by a factor of three has been observed for 19 O +12 C in comparison to 18 O +12 C . Comparison of the experimental results with the predictions of a density constrained time-dependent Hartree-Fock (DC-TDHF) model provide evidence for the importance of pairing in the fusion process. Supported by the US DOE under Grant No. DEFG02-88ER-40404.

  2. Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 21+ State in Zn80

    NASA Astrophysics Data System (ADS)

    van de Walle, J.; Aksouh, F.; Ames, F.; Behrens, T.; Bildstein, V.; Blazhev, A.; Cederkäll, J.; Clément, E.; Cocolios, T. E.; Davinson, T.; Delahaye, P.; Eberth, J.; Ekström, A.; Fedorov, D. V.; Fedosseev, V. N.; Fraile, L. M.; Franchoo, S.; Gernhauser, R.; Georgiev, G.; Habs, D.; Heyde, K.; Huber, G.; Huyse, M.; Ibrahim, F.; Ivanov, O.; Iwanicki, J.; Jolie, J.; Kester, O.; Köster, U.; Kröll, T.; Krücken, R.; Lauer, M.; Lisetskiy, A. F.; Lutter, R.; Marsh, B. A.; Mayet, P.; Niedermaier, O.; Nilsson, T.; Pantea, M.; Perru, O.; Raabe, R.; Reiter, P.; Sawicka, M.; Scheit, H.; Schrieder, G.; Schwalm, D.; Seliverstov, M. D.; Sieber, T.; Sletten, G.; Smirnova, N.; Stanoiu, M.; Stefanescu, I.; Thomas, J.-C.; Valiente-Dobón, J. J.; van Duppen, P.; Verney, D.; Voulot, D.; Warr, N.; Weisshaar, D.; Wenander, F.; Wolf, B. H.; Zielińska, M.

    2007-10-01

    Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 21+ state in Zn78 could be firmly established and for the first time the 2+→01+ transition in Zn80 was observed at 1492(1) keV. B(E2,21+→01+) values were extracted for Zn74,76,78,80 and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, Zn80 is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni78.

  3. Tetrahedral shapes of neutron-rich Zr isotopes from a multidimensionally constrained relativistic Hartree-Bogoliubov model

    NASA Astrophysics Data System (ADS)

    Zhao, Jie; Lu, Bing-Nan; Zhao, En-Guang; Zhou, Shan-Gui

    2017-01-01

    We develop a multidimensionally constrained relativistic Hartree-Bogoliubov (MDC-RHB) model in which the pairing correlations are taken into account by making the Bogoliubov transformation. In this model, the nuclear shape is assumed to be invariant under the reversion of x and y axes; i.e., the intrinsic symmetry group is V4 and all shape degrees of freedom βλ μ with even μ are included self-consistently. The RHB equation is solved in an axially deformed harmonic oscillator basis. A separable pairing force of finite range is adopted in the MDC-RHB model. The potential energy curves of neutron-rich even-even Zr isotopes are calculated with relativistic functionals DD-PC1 and PC-PK1 and possible tetrahedral shapes in the ground and isomeric states are investigated. The ground state shape of 110Zr is predicted to be tetrahedral with both functionals and so is that of 112Zr with the functional DD-PC1. The tetrahedral ground states are caused by large energy gaps around Z =40 and N =70 when β32 deformation is included. Although the inclusion of the β30 deformation can also reduce the energy around β20=0 and lead to minima with pear-like shapes for nuclei around 110Zr, these minima are unstable due to their shallowness.

  4. Li-rich Li-Si alloy as a lithium-containing negative electrode material towards high energy lithium-ion batteries.

    PubMed

    Iwamura, Shinichiroh; Nishihara, Hirotomo; Ono, Yoshitaka; Morito, Haruhiko; Yamane, Hisanori; Nara, Hiroki; Osaka, Tetsuya; Kyotani, Takashi

    2015-01-28

    Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO2, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li21Si5. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

  5. Li-Rich Li-Si Alloy As A Lithium-Containing Negative Electrode Material Towards High Energy Lithium-Ion Batteries

    PubMed Central

    Iwamura, Shinichiroh; Nishihara, Hirotomo; Ono, Yoshitaka; Morito, Haruhiko; Yamane, Hisanori; Nara, Hiroki; Osaka, Tetsuya; Kyotani, Takashi

    2015-01-01

    Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO2, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li21Si5. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell. PMID:25626879

  6. Shape coexistence in the N = 19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spin-polarized 31Na

    NASA Astrophysics Data System (ADS)

    Nishibata, H.; Shimoda, T.; Odahara, A.; Morimoto, S.; Kanaya, S.; Yagi, A.; Kanaoka, H.; Pearson, M. R.; Levy, C. D. P.; Kimura, M.

    2017-04-01

    The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the "island of inversion" associated with the neutron magic number N = 20, is studied by β-γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ = 1 /2+ and 1 /2- are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.

  7. Indications of a Si-rich bilateral jet of ejecta in the Vela SNR observed with XMM-Newton

    NASA Astrophysics Data System (ADS)

    García, F.; Suárez, A. E.; Miceli, M.; Bocchino, F.; Combi, J. A.; Orlando, S.; Sasaki, M.

    2017-08-01

    Context. The Vela supernova remnant displays several ejecta, which are fragment-like features protruding beyond the front of its primary blast shock wave. They appear to be "shrapnel", bowshock-shaped relics of the supernova explosion. One of these pieces of shrapnel (A), located in the northeastern edge of the remnant, is peculiar because its X-ray spectrum exhibits a high Si abundance, in contrast to the other observed ejecta fragments, which show enhanced O, Ne, and Mg abundances. Aims: In this Letter we present the analysis of another ejecta fragment located opposite to shrapnel A with respect to the center of the shell, in the southwestern boundary of the remnant, named shrapnel G. We aim to fully characterize its X-ray emission to gather new information about the core-collapse supernova explosion mechanism. Methods: We thoroughly analyzed a dedicated XMM-Newton observation of shrapnel G by producing background-subtracted and exposure-corrected maps in different energy ranges, which we complemented with a spatially resolved spectral analysis of the X-ray emission. Results: The fragment presents a bowshock-like shape with its anti-apex pointing to the center of the remnant. Its X-ray spectrum is best fit by a thermal plasma out of equilibrium of ionization with low O and Fe, roughly solar Ne and Mg, and a significantly high Si abundance, which is required to fit a very clear Si line at 1.85 keV. Its chemical composition and spectral properties are compatible with those of shrapnel A, which is located on the opposite side of the remnant. Conclusions: As a consequence of the nucleosynthesis, pieces of Si-rich shrapnel are expected to originate in deeper layers of the progenitor star compared to ejecta with lower-Z elements. A high velocity and density contrast with respect to the surrounding ejecta are necessary to make shrapnel A and G overtake the forward shock. The line connecting shrapnel A and G crosses almost exactly the expansion center of the remnant

  8. Production of new neutron-rich isotopes of heavy elements in fragmentation reactions of {sup 238}U projectiles at 1A GeV

    SciTech Connect

    Alvarez-Pol, H.; Benlliure, J.; Casarejos, E.; Cortina-Gil, D.; Fernandez-Dominguez, B.; Pereira, J.; Audouin, L.; Enqvist, T.; Schmidt, K.-H.; Yordanov, O.; Junghans, A. R.; Jurado, B.; Rejmund, F.

    2010-10-15

    The production of heavy neutron-rich nuclei has been investigated using cold-fragmentation reactions of {sup 238}U projectiles at relativistic energies. The experiment performed at the high-resolving-power magnetic spectrometer Fragment Separator at GSI made it possible to identify 40 new heavy neutron-rich nuclei: {sup 205}Pt, {sup 207-210}Au, {sup 211-216}Hg, {sup 214-217}Tl, {sup 215-220}Pb, {sup 219-224}Bi, {sup 223-227}Po, {sup 225-229}At, {sup 230,231}Rn, and {sup 233}Fr. The production cross sections of these nuclei were also determined and used to benchmark reaction codes that predict the production of nuclei far from stability.

  9. Evidence for a Change in the Nuclear Mass Surface with the Discovery of the Most Neutron-Rich Nuclei with 17{<=}Z{<=}25

    SciTech Connect

    Tarasov, O. B.; Morrissey, D. J.; Amthor, A. M.; Gade, A.; Nettleton, A.; Sherrill, B. M.; Thoennessen, M.; Baumann, T.; Bazin, D.; Ginter, T. N.; Hausmann, M.; Pereira, J.; Portillo, M.; Stolz, A.; Inabe, N.; Kubo, T.

    2009-04-10

    The results of measurements of the production of neutron-rich nuclei by the fragmentation of a {sup 76}Ge beam are presented. The cross sections were measured for a large range of nuclei including 15 new isotopes that are the most neutron-rich nuclides of the elements chlorine to manganese ({sup 50}Cl, {sup 53}Ar, {sup 55,56}K, {sup 57,58}Ca, {sup 59,60,61}Sc, {sup 62,63}Ti, {sup 65,66}V, {sup 68}Cr, {sup 70}Mn). The enhanced cross sections of several new nuclei relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections, indicates that nuclei in the region around {sup 62}Ti might be more stable than predicted by current mass models and could be an indication of a new island of inversion similar to that centered on {sup 31}Na.

  10. The study of neutron-rich nuclei production in the region of the closed shell N=126 in the multi-nucleon transfer reaction 136Xe+208Pb

    NASA Astrophysics Data System (ADS)

    Novikov, K.; Harca, I. M.; Kozulin, E. M.; Dmitriev, S.; Itkis, J.; Knyazheva, G.; Loktev, T.; Corradi, L.; Valiente-Dobon, J.; Fioretto, E.; Montanari, D.; Stefanini, A. M.; Vardaci, E.; Quero, D.; Montagnoli, G.; Scarlassara, F.; Strano, E.; Pollarolo, G.; Piot, J.; Mijatović, T.; Szilner, S.; Ackermann, D.; Chubarian, G.; Trzaska, W. H.

    2016-04-01

    The unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along the neutron closed shell N=126 (probably the last "waiting point" in the r-process of nucleosynthesis) the low-energy multi-nucleon transfer reaction 136Xe+208Pb at Elab=870MeV was explored. Due to the stabilizing effect of the closed neutron shells in both nuclei, N=82 and N=126, and the rather favorable proton transfer from lead to xenon, the light fragments formed in this process are well bound and the Q-value of the reaction is nearly zero. Measurements were performed with the PRISMA spectrometer in coincidence with an additional time-of-flight (ToF) arm on the +20 beam line of the PIAVE-ALPI accelerator in Legnaro, Italy. The PRISMA spectrometer allows identification of the A, Z and velocity of the projectile-like fragments (PLF), while the second arm gives access to the target-like fragments (TLF). Details on the experimental setup and preliminary results are reported.

  11. Neutron-Rich {sup 62,64,64}Fe Show Enhanced Collectivity: The Washout of N = 40 in Terms of Experiment, Valence Proton Symmetry and Shell Model

    SciTech Connect

    Rother, W.; Dewald, A.; Fransen, C.; Hackstein, M.; Jolie, J.; Pissulla, Th.; Zel, K.-O.; Iwasaki, H.; Baugher, T.; Brown, B. A.; Gade, A.; Glasmacher, T.; McDaniel, S.; Ratkiewicz, A.; Voss, P.; Walsh, K. A.; Lenzi, S. M.; Ur, C. A.; Starosta, K.; Bazin, D.

    2011-10-28

    Probing shell structure at a large neutron excess has been of particular interest in recent times. Neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 offer an exotic testing ground for shell evolution. The development of the N = 40gap between neutron fp and lg{sub 9/2} shells gives rise to highly interesting variations of collectivity for nuclei in this region. While {sup 68}Ni shows doubly magic properties in level energies and transition strengths, this was not observed in neighbouring nuclei. Especially neutron-rich Fe isotopes proved particularly resistant to calculational approaches using the canonical valence space (fpg) resulting in important deviations of the predicted collectivity. Only an inclusion of the d{sub 5/2}-orbital could solve the problem [1]. Hitherto no transition strengths for {sup 66}Fe have been reported. We determined B(E2,2{sup +}{sub 1}{yields}0{sup +}{sub 1}) values from lifetimes measured with the recoil distance Doppler-shift method using the Cologne plunger for radioactive beams at National Superconducting Cyclotron Laboratory at Michigan State University. Excited states were populated by projectile Coulomb excitation for {sup 62,64,66}Fe. The data show a rise in collectivity for Fe isotopes towards N = 40. Results [2] are interpreted by means of a modified version of the Valence Proton Symmetry [3] and compared to shell model calculations using a new effective interaction recently developed for the fpgd valence space [4].

  12. Carriers mobility of InAs- and InP- rich InAs-InP solid solutions irradiated by fast neutrons

    SciTech Connect

    Khutsishvili, Elza; Khomasuridze, David; Gabrichidze, Leonti; Kvirkvelia, Bella; Kekelidze, David; Guguchia, Zurab; Aliyev, Vugar; Kekelidze, Nodar

    2013-12-04

    We have studied the low temperature charge carriers mobility in bulk single crystals of InAs- and InP- rich InAs-InP solid solutions irradiated with maximum integral flux 2⋅10{sup 18} n/cm{sup 2} of fast neutrons. Influence of minor component small addition in InAs-InP solid solutions has been revealed. There are also presented data of radiation defects thermal stability.

  13. IRiS—Exploring new frontiers in neutron-rich isotopes of the heaviest elements with a new Inelastic Reaction Isotope Separator

    NASA Astrophysics Data System (ADS)

    Dvorak, J.; Block, M.; Düllmann, Ch. E.; Heinz, S.; Herzberg, R.-D.; Schädel, M.

    2011-10-01

    A dedicated Inelastic Reaction Isotope Separator (IRiS) for multi-nucleon transfer products will be designed and installed at GSI. Research at IRiS will focus on the investigation of new neutron-rich isotopes of the heaviest elements, study of which will advance various research fields, such as nuclear chemistry, nuclear and atomic physics, as well as nuclear astrophysics. The scientific motivation for this project and the alternative design options for the separator and its main components are discussed.

  14. Sensitizing properties of luminescence centers on the emission of Er{sup 3+} in Si-rich SiO{sub 2} film

    SciTech Connect

    Fu, Qianyu; Gao, Yuhan; Li, Dongsheng Yang, Deren

    2016-05-28

    In this paper, we report on the luminescence-center (LC)-mediated excitation of Er{sup 3+} as a function of annealing temperature in Er-doped Si-rich SiO{sub 2} (SRO) films fabricated by electron beam evaporation. It is found that the annealing temperature has significant effects on the emission of Er{sup 3+} and the specific optical-active point-defects called LCs within Er-doped SRO films. Different luminescence centers generated by the evolution of microstructures during annealing process act as efficient sensitizers for Er{sup 3+} in the films when the annealing temperature is below 1100 °C. Moreover, the temperature dependence of the energy coupling between LCs and Er{sup 3+} demonstrates the effective phonon-mediated energy transfer process. In addition, when the annealing temperature reaches 1100 °C, the decreased density of activable erbium ions induced by the aggregation of Er will bring detrimental effects on the emission of Er{sup 3+}. It is demonstrated that an appropriate annealing process can be designed to achieve efficiently enhanced emissions from Er{sup 3+} ions by optimizing the density of LCs and the coupling between Er{sup 3+} and LCs.

  15. Nucleon-nucleon momentum-correlation function as a probe of the density distribution of valence neutrons in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Cao, X. G.; Cai, X. Z.; Ma, Y. G.; Fang, D. Q.; Zhang, G. Q.; Guo, W.; Chen, J. G.; Wang, J. S.

    2012-10-01

    Proton-neutron, neutron-neutron, and proton-proton momentum-correlation functions (Cpn,Cnn, and Cpp) are systematically investigated for 15C and other C-isotope-induced collisions at different entrance channel conditions within the framework of the isospin-dependent quantum-molecular-dynamics model complemented by the correlation after burner (crab) computation code. 15C is a prime exotic nucleus candidate due to the weakly bound valence neutron coupling with closed-neutron-shell nucleus 14C. To study density dependence of the correlation function by removing the isospin effect, the initialized 15C projectiles are sampled from two kinds of density distribution from the relativistic mean-field (RMF) model in which the valence neutron of 15C is populated in both 1d5/2 and 2s1/2 states, respectively. The results show that the density distributions of the valence neutron significantly influence the nucleon-nucleon momentum-correlation function at large impact parameters and high incident energies. The extended density distribution of the valence neutron largely weakens the strength of the correlation function. The size of the emission source is extracted by fitting the correlation function by using the Gaussian source method. The emission source size as well as the size of the final-state phase space are larger for projectile samplings from more extended density distributions of the valence neutron, which corresponds to the 2s1/2 state in the RMF model. Therefore, the nucleon-nucleon momentum-correlation function can be considered as a potentially valuable tool to diagnose exotic nuclear structures, such as the skin and halo.

  16. Neutron removal cross section as a measure of neutron skin

    SciTech Connect

    Fang, D. Q.; Ma, Y. G.; Cai, X. Z.; Tian, W. D.; Wang, H. W.

    2010-04-15

    We study the relation between neutron removal cross section (sigma{sub -N}) and neutron skin thickness for finite neutron-rich nuclei using the statistical abrasion ablation model. Different sizes of neutron skin are obtained by adjusting the diffuseness parameter of neutrons in the Fermi distribution. It is demonstrated that there is a good linear correlation between sigma{sub -N} and the neutron skin thickness for neutron-rich nuclei. Further analysis suggests that the relative increase of neutron removal cross section could be used as a quantitative measure for neutron skin thickness in neutron-rich nuclei.

  17. Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage

    NASA Astrophysics Data System (ADS)

    Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

    2013-12-01

    The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60°C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si

  18. Characteristics of poly- and mono-crystalline BeO and SiO2 as thermal and cold neutron filters

    NASA Astrophysics Data System (ADS)

    Adib, M.; Habib, N.; Bashter, I. I.; Morcos, H. N.; El-Mesiry, M. S.; Mansy, M. S.

    2015-09-01

    A simple model along with a computer code "HEXA-FILTERS" is used to carry out the calculation of the total cross-sections of BeO and SiO2 having poly or mono-crystalline form as a function of neutron wavelength at room (R.T.) and liquid nitrogen (L.N.) temperatures. An overall agreement is indicated between the calculated neutron cross-sections and experimental data. Calculation shows that 25 cm thick of polycrystalline BeO cooled at liquid nitrogen temperature was found to be a good filter for neutron wavelengths longer than 0.46 nm. While, 50 cm of SiO2, with much less transmission, for neutrons with wavelengths longer than 0.85 nm. It was also found that 10 cm of BeO and 15 cm SiO2 thick mono-crystals cut along their (0 0 2) plane, with 0.5° FWHM on mosaic spread and cooled at L.N., are a good thermal neutron filter, with high effect-to-noise ratio.

  19. The evolution of the fraction of Er ions sensitized by Si nanostructures in silicon-rich silicon oxide thin films.

    PubMed

    Noé, P; Okuno, H; Jager, J-B; Delamadeleine, E; Demichel, O; Rouvière, J-L; Calvo, V; Maurizio, C; D'Acapito, F

    2009-09-02

    Photoluminescence (PL) and time-resolved PL experiments as a function of the elaboration process are performed on Er-doped silicon-rich silicon oxide (SRO:Er) thin films grown under NH(3) atmosphere. These PL measurements of the Er(3+) emission at 1.54 microm under non-resonant pumping with the Er f-f transitions are obtained for different Er(3+) concentrations, ranging from 0.05 to 1.4 at.%, and various post-growth annealing temperatures of the layers. High resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) analysis show a high density of Si nanostructures composed of amorphous and crystalline nanoclusters varying from 2.7 x 10(18) to 10(18) cm(-3) as a function of the post-growth annealing temperature. Measurements of PL lifetime and effective Er excitation cross section for all the samples under non-resonant optical excitation with the Er(3+) atomic energy levels show that the number of Er(3+) ions sensitized by the silicon-rich matrix decreases as the annealing temperature is increased from 500 to 1050 degrees C. The origin of this effect is attributed to the reduction of the density of sensitizers for Er ions in the SRO matrix when the annealing temperature increases. Finally, extended x-ray absorption fine-structure spectroscopy (EXAFS) shows a strong correlation between the number of emitters and the mean local order around the erbium ions.

  20. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    SciTech Connect

    Sadoh, Taizoh Chikita, Hironori; Miyao, Masanobu; Matsumura, Ryo

    2015-09-07

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.