检索结果-内蒙古大学图书馆

The puzzling two-proton decay of 67Kr

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Wang, S.M. Nazarewicz, W. FRIB/NSCL Laboratory Michigan State University East LansingMI48824 United States Department of Physics and Astronomy FRIB Laboratory Michigan State University East LansingMI48824 United States

Two-proton (2p) radioactivity is a rare decay mode found in a few proton-unbound nuclei. The 2pdecay lifetime and properties of emitted protons carry invaluable information on nuclear structure in the presence of low-lying proton continuum. The recently measured 2p decay of 67Kr [1] turned out to be unexpectedly fast. Since 67Kr is expected to be a deformed system, we investigate the impact of deformation effects on the 2p radioactivity. We apply the recently developed Gamow coupledchannel framework, which allows for a precise description of three-body systems in the presence of rotational and vibrational couplings. This is the first application of a three-body approach to a two-nucleon decay from a deformed nucleus. We show that deformation couplings significantly increase the 2p decay width of 67Kr;this finding explains the puzzling experimental data. The calculated angular proton-proton correlations reflect a competition between 1p and 2p decay modes in this nucleus. Copyright © 2018, The Authors. All rights reserved.

关键词： Couplings

Quenching of nuclear matrix elements for 0νββ decay by chiral two-body currents

学校读者我要写书评

暂无评论

Physical Review C 2018年第3期98卷 031301(R)-031301(R)页

作者： Long-Jun Wang Jonathan Engel Jiang Ming Yao Department of Physics and Astronomy University of North Carolina Chapel Hill North Carolina 27599-3255 USA FRIB/NSCL Laboratory Michigan State University East Lansing Michigan 48824 USA

We examine the leading effects of two-body weak currents from chiral effective field theory on the matrix elements governing neutrinoless double-β decay. In the closure approximation these effects are generated by the product of a one-body current with a two-body current, yielding both two- and three-body operators. When the three-body operators are considered without approximation, they quench matrix elements by about 10%, less than suggested by prior work, which neglected portions of the operators. The two-body operators, when treated in the standard way, can produce somewhat larger quenching. In a consistent effective field theory, however, these two-body effects become divergent and must be renormalized by a contact operator, the coefficient of which we cannot determine at present.

关键词： Electroweak interactions in nuclear physics Nuclear many-body theory Nuclear structure & decays Nuclear tests of fundamental interactions 59 ≤ A ≤ 89

Resonant spectra of multipole-bound anions

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Mao, X. Fossez, K. Nazarewicz, W. Department of Physics and Astronomy and Frib Laboratory Michigan State University East Lansing Michigan48824 United States Nscl Laboratory Michigan State University East Lansing Michigan48824 United States

In multipole-bound anions, the excess electron is attached by a short-range multipole potential of a neutral molecule. Such anions are prototypical marginally-bound open quantum systems. In particular, around the critical multipole moment required to attach the valence electron, multipolebound anions exhibit critical behavior associated with a transition from bound states dominated by low- partial waves to the electron continuum. In this work, multipole-bound anions are described using a nonadiabatic electron-plus-rotor model. The electron-molecule pseudo-potential is represented by a short-range multipole field with a Gaussian form-factor. The resulting coupled-channel Schroodinger equation is solved by means of the Berggren expansion method, in which the electron's wave function is decomposed into bound states, narrow resonances, and the non-resonant scattering continuum. We show that the Gaussian model predicts the critical transition at the detachment threshold. Resonant states, including bound states, decaying resonances, subthreshold resonances, and antibound states are studied, and exceptional points where two resonant states coalesce are predicted. We discuss the transition of rotational band structures around the threshold and study the effects of channel coupling on the decay width of resonant poles. Copyright © 2018, The Authors. All rights reserved.

关键词： Electrons

Electron and Nucleon Localization Functions of Oganesson: Approaching the Thomas-Fermi Limit

学校读者我要写书评

暂无评论

Physical Review Letters 2018年第5期120卷 053001-053001页

作者： Paul Jerabek Bastian Schuetrumpf Peter Schwerdtfeger Witold Nazarewicz Centre for Theoretical Chemistry and Physics The New Zealand Institute for Advanced Study Massey University Auckland 0632 Auckland New Zealand NSCL/FRIB Laboratory Michigan State University East Lansing Michigan 48824 USA Centre for Advanced Study (CAS) at the Norwegian Academy of Science and Letters Drammensveien 78 NO-0271 Oslo Norway Department of Physics and Astronomy and FRIB Laboratory Michigan State University East Lansing Michigan 48824 USA

Fermion localization functions are used to discuss electronic and nucleonic shell structure effects in the superheavy element oganesson, the heaviest element discovered to date. Spin-orbit splitting in the 7p electronic shell becomes so large (∼10 eV) that Og is expected to show uniform-gas-like behavior in the valence region with a rather large dipole polarizability compared to the lighter rare gas elements. The nucleon localization in Og is also predicted to undergo a transition to the Thomas-Fermi gas behavior in the valence region. This effect, particularly strong for neutrons, is due to the high density of single-particle orbitals.

关键词： Electron correlation calculations for atoms & ions Relativistic & quantum electrodynamic effects in atoms, molecules,& ions Shell model

Neutron Energy Dependence of Delayed Neutron Yields and its Assessments

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Minato, Futoshi Nuclear Data Center Japan Atomic Energy Agency Tokai319-1195 Japan NSCL/FRIB Laboratory Michigan State University East LansingMI48824 United States

Incident neutron energy dependence of delayed neutron yields of uranium and plutonium isotopes is investigated. A summation calculation of decay and fission yield data is employed, and the energy dependence of the latter part is considered in a phenomenological way. Our calculation systematically reproduces the energy dependence of delayed neutron yields by introducing an energy dependence of the most probable charge and the odd-even effect. The calculated fission yields are assessed by comparison with JENDL/FPY-2011, delayed neutron activities, and decay heats. Although the fission yields in this work are optimized to delayed neutron yields, the calculated decay heats are in good agreement with the experimental data. Comparison of the fission yields calculated in this work and JENDL/FPY-2011 gave an important insight for the evaluation of the next JENDL nuclear data. Copyright © 2018, The Authors. All rights reserved.

关键词： Neutrons

Bayesian approach to model-based extrapolation of nuclear observables

学校读者我要写书评

暂无评论

Physical Review C 2018年第3期98卷 034318-034318页

作者： Léo Neufcourt Yuchen Cao (曹宇晨) Witold Nazarewicz Frederi Viens Department of Statistics and Probability Michigan State University East Lansing Michigan 48824 USA FRIB Laboratory Michigan State University East Lansing Michigan 48824 USA Department of Physics and Astronomy and NSCL Laboratory Michigan State University East Lansing Michigan 48824 USA Department of Physics and Astronomy and FRIB Laboratory Michigan State University East Lansing Michigan 48824 USA

Background: The mass, or binding energy, is the basis property of the atomic nucleus. It determines its stability and reaction and decay rates. Quantifying the nuclear binding is important for understanding the origin of elements in the universe. The astrophysical processes responsible for the nucleosynthesis in stars often take place far from the valley of stability, where experimental masses are not known. In such cases, missing nuclear information must be provided by theoretical predictions using extreme extrapolations. To take full advantage of the information contained in mass model residuals, i.e., deviations between experimental and calculated masses, one can utilize Bayesian machine-learning techniques to improve predictions.

关键词： Learning Nuclear many-body theory Nuclear structure & decays Nuclear binding Metropolis algorithm Monte Carlo methods Nuclear density functional theory

Quenching of nuclear matrix elements for 0vββ decay by chiral two-body currents

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Wang, Long-Jun Enge, Jonathan Yao, Jiang Ming Department of Physics and Astronomy University of North Carolina Chapel HillNC27599-3255 United States FRIB/NSCL Laboratory Michigan State University East LansingMI48824 United States

We examine the leading effects of two-body weak currents from chiral effective field theory on the matrix elements governing neutrinoless double-beta decay. In the closure approximation these effects are generated by the product of a one-body current with a two-body current, yielding both two- and three-body operators. When the three-body operators are considered without approximation, they quench matrix elements by about 10%, less than suggested by prior work, which neglected portions of the operators. The two-body operators, when treated in the standard way, can produce much larger quenching. In a consistent effective field theory, however, these large effects become divergent and must be renormalized by a contact operator, the coefficient of which we cannot determine at present. Copyright © 2018, The Authors. All rights reserved.

关键词： Quenching

Half-lives of La132 and La135

学校读者我要写书评

暂无评论

Physical Review C 2018年第3期97卷 034312-034312页

作者： E. P. Abel H. K. Clause J. Fonslet R. J. Nickles G. W. Severin Department of Chemistry and NSCL/FRIB Laboratory Michigan State University East Lansing Michigan 48824 USA Hevesy Laboratory Center for Nuclear Technologies Technical University of Denmark 4000 Roskilde Denmark Department of Medical Physics University of Wisconsin-Madison Madison Wisconsin 53706 USA

The half-lives of La135 and La132 were determined via serial gamma spectroscopy, and the half-life of La135 was further determined by a high-precision ionization-chamber measurement. The results are 18.91(2) hr for La135 and 4.59(4) hr for La132 compared with the previously compiled values of 19.5(2) hr and 4.8(2) hr, respectively. These lanthanum isotopes comprise a medically interesting system with positron emitter La132 and Auger-electron emitter La135 forming a theranostic pair for internal diagnostics and therapeutics. The precise half-lives are necessary for proper evaluation of their value in medicine and for a more representative tabulation of nuclear data.

关键词： Lifetimes & widths Nuclear structure & decays 90 ≤ A ≤ 149 Nuclear data analysis & compilation

Bayesian approach to model-based extrapolation of nuclear observables

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Neufcourt, Leo Cao, Yuchen Nazarewicz, Witold Viens, Frederi Department of Statistics and Probability Michigan State University East LansingMI48824 United States Frib Laboratory Michigan State University East LansingMI48824 United States Department of Physics and Astronomy and Nscl Laboratory Michigan State University East LansingMI48824 United States Department of Physics and Astronomy and Frib Laboratory Michigan State University East LansingMI48824 United States

Background: The mass, or binding energy, is the basis property of the atomic nucleus. It determines its stability, and reaction and decay rates. Quantifying the nuclear binding is important for understanding the origin of elements in the universe. The astrophysical processes responsible for the nucleosynthesis in stars often take place far from the valley of stability, where experimental masses are not known. In such cases, missing nuclear information must be provided by theoretical predictions using extreme extrapolations. In order to take full advantage of the information contained in mass model residuals, i.e., deviations between experimental and calculated masses, one can utilize Bayesian machine learning techniques to improve predictions. Purpose: In order to improve the quality of model-based predictions of nuclear properties of rare isotopes far from stability, we consider the information contained in the residuals in the regions where the experimental information exist. As a case in point, we discuss two-neutron separation energies S2n of even-even nuclei. Through this observable, we assess the predictive power of global mass models towards more unstable neutron-rich nuclei and provide uncertainty quantification of predictions. Methods: We consider 10 global models based on nuclear Density Functional Theory with realistic energy density functionals as well as two more phenomenological mass models. The emulators of S2n residuals and credibility intervals (Bayesian confidence intervals) defining theoretical error bars are constructed using Bayesian Gaussian processes and Bayesian neural networks. We consider a large training dataset pertaining to nuclei whose masses were measured before 2003. For the testing datasets, we considered those exotic nuclei whose masses have been determined after 2003. By establishing statistical methodology and parameters, we carried out extrapolations towards the 2n dripline. Results: While both Gaussian processes and Bayesian neu

关键词： Extrapolation