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Journal Articles

Stability and synthesis of superheavy elements; Fighting the battle against fission - Example of $$^{254}$$No

Lopez-Martens, A.*; Henning, G.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

EPJ Web of Conferences (Internet), 131, p.03001_1 - 03001_6, 2016/12

 Times Cited Count:1 Percentile:46.38

Fission barrier height and its angular-momentum dependence have been measured for the first time in the nucleus with the atomic number greater than 100. The entry distribution method, which can determine the excitation energy at which fission starts to dominate the decay process, was applied to $$^{254}$$No. The fission barrier of $$^{254}$$No was found to be 6.6 MeV at zero spin, indicating that the $$^{254}$$No is strongly stabilized by the nuclear shell effects.

Journal Articles

Population and decay of a $$K^{pi}$$ = 8$$^{-}$$ two-quasineutron isomer in $$^{244}$$Pu

Hota, S.*; Tandel, S.*; Chowdhury, P.*; Ahmad, I.*; Carpenter, M. P.*; Chiara, C. J.*; Greene, J. P.*; Hoffman, C. R.*; Jackson, E. G.*; Janssens, R. V. F.*; et al.

Physical Review C, 94(2), p.021303_1 - 021303_5, 2016/08

 Times Cited Count:5 Percentile:46.59(Physics, Nuclear)

The decay of a $$K^{pi}$$ = 8$$^{-}$$ isomer in $$^{244}$$Pu and the collective band structure populating the isomer are studied using deep inelastic excitations with $$^{47}$$Ti and $$^{208}$$Pb beams, respectively. Precise measurements of $$M1/E2$$ branching ratios in the band confirm a clean 9/2$$^-$$[734]$$_{nu}$$$$otimes$$7/2$$^+$$[624]$$_{nu}$$ for the isomer, validating the systematics of K$$^{pi}$$ = 8$$^{-}$$ two-quasineutron isomers observed in even-$$Z$$, $$N$$ = 150 isotones. These isomers around the deformed shell gap at $$N$$ = 152 provide critical benchmarks for theoretical predictions of single-particle energies in this gateway region to superheavy nuclei.

Journal Articles

Identification of deformed intruder states in semi-magic $$^{70}$$Ni

Chiara, C. J.*; Weisshaar, D.*; Janssens, R. V. F.*; Tsunoda, Yusuke*; Otsuka, Takaharu*; Harker, J. L.*; Walters, W. B.*; Recchia, F.*; Albers, M.*; Alcorta, M.*; et al.

Physical Review C, 91(4), p.044309_1 - 044309_10, 2015/04

 Times Cited Count:24 Percentile:9.04(Physics, Nuclear)

The neutron-rich isotope $$^{70}$$Ni was produced by multi-nucleon transfer reactions of $$^{70}$$Zn in the Argonne National Laboratory, and an in-beam $$gamma$$-ray experiment were performed using the GRETINA array. The $$2^+_2$$ and $$4^+_2$$ levels of $$^{70}$$Ni were observed for the first time. Those levels are regarded as large deformed states associated with proton excitation from the $$f_{7/2}$$ orbit because they cannot be reproduced by a shell-model calculation assuming a small valence space without $$f_{7/2}$$. A theoretical analysis based on the Monte Carlo shell model published in 2014 indicates that those levels corresponds to a prolate deformed band. The present result demonstrates the occurrence of shape coexistence in neutron-rich Ni isotopes other than a known case of $$^{68}$$Ni, and confirms the predictive power of the Monte Carlo shell-model calculation.

Journal Articles

Fission barrier of superheavy nuclei and persistence of shell effects at high spin; Cases of $$^{254}$$No and $$^{220}$$Th

Henning, G.*; Khoo, T. L.*; Lopez-Martens, A.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

Physical Review Letters, 113(26), p.262505_1 - 262505_6, 2014/12

 Times Cited Count:24 Percentile:16.56(Physics, Multidisciplinary)

Fission barrier heights of a shell-stabilized superheavy nucleus $$^{254}$$No have been determined as a function of spin up to 19$$hbar$$ through the measured distribution of entry points of $$gamma$$ deexcitations in the excitation energy vs. spin plane. The fission barrier height of $$^{254}$$No was determined to be 6.0 MeV at spin 15$$hbar$$, and 6.6 MeV at spin 0$$hbar$$ by extrapolation. This demonstrates that the shell effect actually enlarges the fission barrier in such heavy nuclei and keeps the barrier high even at high spin.

Journal Articles

Exploring the stability of super heavy elements; First measurement of the fission barrier of $$^{254}$$No

Henning, G.*; Lopez-Martens, A.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

EPJ Web of Conferences (Internet), 66, p.02046_1 - 02046_8, 2014/03

 Times Cited Count:3 Percentile:22.25

Fission barrier heights of $$^{254}$$No have been determined through the entry distribution method. The entry distribution is the initial distribution of excitation energy and spin from which the $$gamma$$ deexcitation starts in the fusion-evaporation reaction. The initial distribution is extracted from measured $$gamma$$-ray multiplicity and total $$gamma$$-ray energy. This paper describes the details of the entry distribution method, and reports the first determination of the fission barrier heights of $$^{254}$$No, which is the heaviest nucleus whose fission barrier has been measured.

Journal Articles

Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

Deng, Z.*; Zhao, K.*; Gu, B.; Han, W.*; Zhu, J. L.*; Wang, X. C.*; Li, X.*; Liu, Q. Q.*; Yu, R. C.*; Goko, Tatsuo*; et al.

Physical Review B, 88(8), p.081203_1 - 081203_5, 2013/08

 Times Cited Count:58 Percentile:6.84(Materials Science, Multidisciplinary)

Journal Articles

Energetic ion transport by microturbulence is insignificant in tokamaks

Pace, D. C.*; Austin, M. E.*; Bass, E. M.*; Budny, R.*; Heidbrink, W. W.*; Hillesheim, J. C.*; Holcomb, C. T.*; Gorelenkova, M.*; Grierson, B. A.*; McCune, D. C.*; et al.

Physics of Plasmas, 20(5), p.056108_1 - 056108_18, 2013/05

 Times Cited Count:28 Percentile:12.9(Physics, Fluids & Plasmas)

Energetic ion transport due to microturbulence is investigated in MHD-quiescent plasmas by way of neutral beam injection in the DIII-D tokamak. A range of on-axis and off-axis beam injection scenarios are employed to vary relevant parameters such as the character of the background microturbulence and the value of Eb/Te, where Eb is the energetic ion energy and Te the electron temperature. In all cases it is found that any transport enhancement due to microturbulence is too small to observe experimentally. These transport effects are modeled using numerical and analytic expectations that calculate the energetic ion diffusivity due to microturbulence. It is determined that energetic ion transport due to coherent modes, including possible reductions in neutral beam current drive, is a considerably larger effect and should therefore be considered more important for ITER.

Journal Articles

Multi-intruder structures in $$^{34}$$P

Bender, P. C.*; Tabor, S. L.*; Tripathi, V.*; Hoffman, C. R.*; Hamilton, L.*; Volya, A.*; Clark, R. M.*; Fallon, P.*; Macchiavelli, A. O.*; Paschalis, S.*; et al.

Physical Review C, 85(4), p.044305_1 - 044305_10, 2012/04

 Times Cited Count:12 Percentile:36.39(Physics, Nuclear)

The available experimental information on $$^{34}$$P has been greatly increased through the analysis of $$gamma$$ decays in coincidence with protons from the interaction of an $$^{18}$$O beam at 24 MeV with an $$^{18}$$O target. Light charged particles from the reaction were detected with Microball, and multiple $$gamma$$ ray coincidences with Gammasphere. Many newly observed $$gamma$$ transitions have been identified and placed in the level scheme. Additionally, for most states, spins have been assigned based on measured $$gamma$$ ray angular distributions while parities were inferred from lifetimes determined through Doppler-broadened line-shape analysis. Most of the states observed have been interpreted in terms of shell-model calculations using the WBP-a and SDPF-NR interactions having one particle in the 0$$f$$$$_{7/2}$$ or 1$$p$$$$_{3/2}$$ orbital. The two calculations agree almost equally well with the data resulting in root-mean-square differences of about 200 keV. However, two of a few high-lying states may be associated with stretched $$pi$$$$f$$$$_{7/2}$$ $$otimes$$ $$nu$$$$f$$$$_{7/2}$$ states, but the calculations over-predict their energies by 2-3 MeV. Furthermore, a newly observed long-lived 7919-keV state is established for which no explanation is available at present.

Journal Articles

ITER test blanket module error field simulation experiments at DIII-D

Schaffer, M. J.*; Snipes, J. A.*; Gohil, P.*; de Vries, P.*; Evans, T. E.*; Fenstermacher, M. E.*; Gao, X.*; Garofalo, A. M.*; Gates, D. A.*; Greenfield, C. M.*; et al.

Nuclear Fusion, 51(10), p.103028_1 - 103028_11, 2011/10

 Times Cited Count:32 Percentile:15.04(Physics, Fluids & Plasmas)

Experiments at DIII-D investigated the effects of ferromagnetic error fields similar to those expected from proposed ITER Test Blanket Modules (TBMs). Studied were effects on: plasma rotation and locking; confinement; L-H transition; edge localized mode (ELM) suppression by resonant magnetic perturbations; ELMs and the H-mode pedestal; energetic particle losses; and more. The experiments used a 3-coil mock-up of 2 magnetized ITER TBMs in one ITER equatorial port. The experiments did not reveal any effect likely to preclude ITER operations with a TBM-like error field. The largest effect was slowed plasma toroidal rotation v across the entire radial profile by as much as $$Delta v/v_{0} sim 50%$$ via non-resonant braking. Changes to global $$Delta n/n_{0}$$, $$Delta v/v_{0}$$ and $$Delta H_{98}/H_{98,0}$$ were $$sim$$3 times smaller. These effects are stronger at higher $$beta$$ and lower $$v_{0}$$. Other effects were smaller.

Journal Articles

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; Goko, Tatsuo*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 Times Cited Count:118 Percentile:6.04(Multidisciplinary Sciences)

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)As in bulk materials. We reported that ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess compounds, which have p-type carriers.

Journal Articles

Search for a 2-quasiparticle high-$$K$$ isomer in $$^{256}$$Rf

Robinson, A. P.*; Khoo, T. L.*; Seweryniak, D.*; Ahmad, I.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; Davids, C. N.*; Greene, J.*; et al.

Physical Review C, 83(6), p.064311_1 - 064311_7, 2011/06

 Times Cited Count:24 Percentile:16.78(Physics, Nuclear)

We have identified an isomer with a half-life of 17 $$mu$$s in $$^{256}$$Rf through a calorimetric conversion electron measurement tagged with implanted $$^{256}$$Rf nuclei using the fragment mass analyzer at Argonne National Laboratory. The low population yield for this isomer suggests that this isomer should not be a 2-quasiparticle high-$$K$$ isomer which is typically observed in the N = 152 isotones, but should be a 4-quasiparticle one. Possible reasons of the non-observation of a 2-quasiparticle isomer are this isomer decays by fission with a half-life similar to that of the ground state of $$^{256}$$Rf. Another possibility, that there is no 2-quasiparticle isomer at all, would imply an abrupt termination of axially symmetric deformed shape at Z=104.

Journal Articles

Cross-shell excitations near the "island of inversion"; Structure of $$^{30}$$Mg

Daecon, A. N.*; Smith, J. F.*; Freeman, S. J.*; Janssens, R. V. F.*; Carpenter, M. P.*; Hadinia, B.*; Hoffman, C. R.*; Kay, B. P.*; Lauritsen, T.*; Lister, C. J.*; et al.

Physical Review C, 82(3), p.034305_1 - 034305_7, 2010/09

 Times Cited Count:15 Percentile:28.52(Physics, Nuclear)

no abstracts in English

Journal Articles

Bridging the nuclear structure gap between stable and super heavy nuclei

Seweryniak, D.*; Khoo, T. L.*; Ahmad, I.*; Kondev, F. G.*; Robinson, A.*; Tandel, S. K.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; et al.

Nuclear Physics A, 834(1-4), p.357c - 361c, 2010/03

 Times Cited Count:7 Percentile:47.93(Physics, Nuclear)

Experimental data on single-particle energies in nuclei around Z=100 and N=152 play an important role to test validity of theoretical predictions for shell structure of superheavy nuclei. We found high-K two-quasiparticle isomers in $$^{252}$$No and $$^{254}$$No, and evaluated energies of proton single-particle orbitals around Z=100. We also found a new high-K three quasiparticle isomer in $$^{257}$$Rf. Energies of neutron single-particle orbitals were also evaluated from experimental data of the $$alpha$$ decay of $$^{257}$$Rf. Comparisons between the present experimental data and various theoretical calculations for the proton single-particle orbitals indicate that the calculation by using the Woods-Saxon potential gives the best agreement with the data.

Journal Articles

Spectroscopy of $$^{257}$$Rf

Qian, J.*; Heinz, A.*; Khoo, T. L.*; Janssens, R. V. F.*; Peterson, D.*; Seweryniak, D.*; Ahmad, I.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; et al.

Physical Review C, 79(6), p.064319_1 - 064319_13, 2009/06

 Times Cited Count:27 Percentile:15.33(Physics, Nuclear)

$$alpha$$-, $$gamma$$-, and conversion electron spectroscopy experiments for $$^{257}$$Rf have been performed using Fragment Mass Analyzer at Argonne National Laboratory. A new isomer with a half-life of 160 $$mu$$s has been discovered in $$^{257}$$Rf, and it is interpreted as a three-quasiparticle high-$$K$$ isomer. Neutron configurations of one-quasiparticle states in $$^{253}$$No, the $$alpha$$-decay daughter of $$^{257}$$Rf, have been assigned on the basis of $$alpha$$-decay hindrance factors. Excitation energies of the 1/2$$^{+}$$[620] states in $$N$$=151 isotones indicate that the deformed shell gap at $$N$$=152 increases with the atomic number.

Journal Articles

$$K^{pi}=8^{-}$$ isomers and $$K^{pi}=2^{-}$$ octupole vibrations in $$N=150$$ shell-stabilized isotones

Robinson, A. P.*; Khoo, T. L.*; Ahmad, I.*; Tandel, S. K.*; Kondev, F. G.*; Nakatsukasa, Takashi*; Seweryniak, D.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; et al.

Physical Review C, 78(3), p.034308_1 - 034308_6, 2008/09

 Times Cited Count:42 Percentile:9.25(Physics, Nuclear)

Isomers have been identified in $$^{246}$$Cm and $$^{252}$$No with quantum number $$K^{pi}=8^{-}$$, which decay through $$K^{pi}=2^{-}$$ rotational bands built on octupole vibrational states. For $$N=150$$ isotones with atomic number $$Z=94$$$$sim$$102, the $$K^{pi}=8^{-}$$ and 2$$^{-}$$ states have remarkably stable energies, indicating neutron excitations. An exception is a singular minimum in the 2$$^{-}$$ energy at $$^{246}$$Cm, due to the additional role of proton configurations.

Journal Articles

Influence of self-irradiation on the magnitude of the superfluid density in PuCoGa$$_5$$ probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Ito, Takashi; Higemoto, Wataru; Morris, G. D.*; Bauer, E. D.*; Graf, M. J.*; Zhu, J.-X.*; Morales, L. A.*; Sarrao, J. L.*; et al.

Physica B; Condensed Matter, 403(5-9), p.1013 - 1014, 2008/04

 Times Cited Count:0 Percentile:100(Physics, Condensed Matter)

PuCoGa$$_5$$ has attracted much interest because it is the first Pu-based superconductor, having an order of magnitude higher transition temperature $$T_{rm c}=18.5$$K than the isostructural heavy fermion superconductor CeCoIn$$_5$$ ($$T_{rm c}=2.3$$K). The mechanism of the superconductivity in PuCoGa$$_5$$ is still under investigation, though recent experiments and theory suggest a magnetic origin. A unique aspect of this compound is the self-irradiation damage because Pu ($$^{239}$$Pu, $$T^{1/2}$$ = 24,000 years) creates lattice defects which scatter electrons and, hence, break superconducting pairs. In order to elucidate the magnitude and temperature dependence of the magnetic penetration depth $$lambda$$, we have performed $$mu$$SR measurements in the same PuCoGa$$_5$$ single crystals after 25 and 400 days of aging. We found that $$T_{rm c}$$ decreased from 18.5K to 15K for the aged sample, yet a quasi-linear temperature dependence was found for the low-temperature $$lambda(T)$$ in both the fresh and aged sample, consistent with $$d$$-wave pairing symmetry. The magnitude of the muon spin relaxation rate $$sigma$$ in the aged sample, $$sigmapropto 1/lambda^2proptorho_s/m^*$$, where $$rho_s$$ and $$m^*$$ are the superfluid density and the effective mass, respectively, is reduced by about 70% compared to fresh sample. This indicates that the scattering from self-irradiation induced defects is not in the limit of the conventional Abrikosov-Gor'kov pair-breaking theory, but rather in the limit of short coherence length (about 2nm in PuCoGa$$_5$$) superconductivity.

Journal Articles

Muon spin rotation measurements of the superfluid density in fresh and aged superconducting PuCoGa$$_5$$

Oishi, Kazuki; Heffner, R. H.; Morris, G. D.*; Bauer, E. D.*; Graf, M. J.*; Zhu, J.-X.*; Morales, L. A.*; Sarrao, J. L.*; Fluss, M. J.*; MacLaughlin, D. E.*; et al.

Physical Review B, 76(6), p.064504_1 - 064504_10, 2007/08

 Times Cited Count:13 Percentile:44.81(Materials Science, Multidisciplinary)

17 (Records 1-17 displayed on this page)
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