In this paper,we study low-lying states of odd-even N=79 isotones,including^(129)Sn,^(131)Te,^(133)Xe,^(135)Ba,and^(137)Ce,within the nucleon-pair approximation(NPA)of the shell model.Low-lying energy levels of these ...In this paper,we study low-lying states of odd-even N=79 isotones,including^(129)Sn,^(131)Te,^(133)Xe,^(135)Ba,and^(137)Ce,within the nucleon-pair approximation(NPA)of the shell model.Low-lying energy levels of these nuclei with both positive and negative parities,as well as B(E2)transition rates and g factors of some low-lying states,are calculated.Most of them agree closely with experimental data.The wave functions of yrast 1/2_(1)^(+),5/2_(1)^(+),7/2_(1)^(+),23/2_(1)^(+)states and negative parity 11/2_(1)^(-)~23/2_(1)^(-)and 27/22_(2)^(-)states of these nuclei are discussed in detail.The NPA calculations show that many of these states have a simple structure in the nucleon-pair basis.展开更多
In this paper,we propose an approach to nucleon-pair approximation(NPA)with m-scheme bases,in which the collective nucleon pairs are represented in terms of antisymmetric matrices,and commutations between nucleon pair...In this paper,we propose an approach to nucleon-pair approximation(NPA)with m-scheme bases,in which the collective nucleon pairs are represented in terms of antisymmetric matrices,and commutations between nucleon pairs are given using a matrix multiplication that avoids angular-momentum couplings and recouplings.Therefore the present approach significantly simplifies the NPA computation.Furthermore,it is formulated on the same footing with and without isospin.展开更多
Magnetic excitations for Ba isotopes are discussed within the nucleon-pair shell model truncated in the SD subspace. With the SD pair determined by a surface- interaction, M1 transitions for are well fitted. The M1 a...Magnetic excitations for Ba isotopes are discussed within the nucleon-pair shell model truncated in the SD subspace. With the SD pair determined by a surface- interaction, M1 transitions for are well fitted. The M1 and M3 transitions for and are also predicted. It is shown that the statement, the collective magnetic properties are due to the orbital motion of nucleons, is approximately valid.展开更多
Excited states of ^(206)Rn have been examined via the 197 Au(^(14)N,5n)^(206)Rn fusion reaction at a beam energy of 78 MeV.A number of transitions and levels are identified by the γ-γ coincidence measurement,further...Excited states of ^(206)Rn have been examined via the 197 Au(^(14)N,5n)^(206)Rn fusion reaction at a beam energy of 78 MeV.A number of transitions and levels are identified by the γ-γ coincidence measurement,further enriching the level scheme of ^(206)Rn.The fullconfiguration shell model and nucleon-pair approximation(NPA)were utilized to investigate the single-particle configurations and seniority structures in ^(206)Rn.The results of these two calculations suggest that 2_(1)^(+) and 4_(1)^(+) states exhibit only a 50%component of a seniority-two state associated with a broken neutron pair.The collectivity of these two states primarily arises from configuration mixing due to residual proton-neutron interactions.Furthermore,6_(1)^(+) and 8_(1)^(+) states are predominantly characterized by a seniority-two state marked by a broken proton pair.展开更多
In this study,we investigate the robustness of pair structures for nuclear yrast states,that is,whether the structures of relevant collective pairs as building blocks of different yrast states are the same.We focus on...In this study,we investigate the robustness of pair structures for nuclear yrast states,that is,whether the structures of relevant collective pairs as building blocks of different yrast states are the same.We focus on deformed and transitional nuclei and study the yrast states of^(28)Si,^(50)Cr,and^(132)Xe,whose experimental R_(4/2)values are 2.60,2.40,and 2.16,respectively,using the nucleon-pair approximation(NPA)and shell-model effective interactions.For each yrast state,we consider optimized pair structures to be those providing the energy minimum for this state.To find the minimum,many full NPA calculations are performed with varying pair structures,and the numerical optimization procedure of the conjugate gradient method is implemented.Our results suggest that optimized pair structures remain the same for all states within a rotational band of a deformed nucleus.Our results also suggest that after backbending,that is,changing of the intrinsic state,the structure of the S pair,which is essential to build the monopole pairing correlation,remains approximately unchanged,whereas the structures of the non-S pairs,which are essential to build the quadrupole correlation,change significantly.展开更多
Analysis of various mass formulas related to neutron-proton correlations in atomic nuclei is carried out.Using the example of the N =Z chain it is shown that for self-adjoint nuclei various formulas proposed in litera...Analysis of various mass formulas related to neutron-proton correlations in atomic nuclei is carried out.Using the example of the N =Z chain it is shown that for self-adjoint nuclei various formulas proposed in literature for estimating the np pairing energy lead to similar results. Significant differences between the calculation methods arise when nuclei with N = Z are considered, which allows to reveal the complexity of neutron-proton correlations in different types of atomic nuclei and to make assumptions on the correspondence of the mass relation to the real effect of np pairing. The Shell Model parametrization of the binding energy makes it possible to draw additional conclusions on the structure of mass formulas and their relationship.展开更多
Abstract： Various estimates of the even-odd effect of the mass shell of atomic nuclei are considered. Based on the experimental mass values of the Ca, Sn, and Pb isotopes, the dependence of the energy gap on the neut...Abstract： Various estimates of the even-odd effect of the mass shell of atomic nuclei are considered. Based on the experimental mass values of the Ca, Sn, and Pb isotopes, the dependence of the energy gap on the neutron number is traced and the relationship of this characteristic to the properties of external neutron subshells is shown. In nuclei with closed proton shells, effects directly related to neutron pairing and effects of nucleon shells are discussed.展开更多
基金National Natural Science Foundation of China (11905130)。
文摘In this paper,we study low-lying states of odd-even N=79 isotones,including^(129)Sn,^(131)Te,^(133)Xe,^(135)Ba,and^(137)Ce,within the nucleon-pair approximation(NPA)of the shell model.Low-lying energy levels of these nuclei with both positive and negative parities,as well as B(E2)transition rates and g factors of some low-lying states,are calculated.Most of them agree closely with experimental data.The wave functions of yrast 1/2_(1)^(+),5/2_(1)^(+),7/2_(1)^(+),23/2_(1)^(+)states and negative parity 11/2_(1)^(-)~23/2_(1)^(-)and 27/22_(2)^(-)states of these nuclei are discussed in detail.The NPA calculations show that many of these states have a simple structure in the nucleon-pair basis.
基金the Sichuan Science and Technology Program(2019JDRC0017)Doctoral Program of Southwest University of Science and Technology(18zx7147)+4 种基金National Natural Science Foundation of China(11705100)Youth Innovations and Talents Project of Shandong Provincial Colleges,and Universities(201909118)Higher Educational Youth Innovation Science and Technology Program Shandong Province(2020KJJ004)National Natural Science Foundation of China(11975151,11675101,11961141003)MOE Key Lab for Particle Physics,Astrophysics and Cosmology for financial support。
文摘In this paper,we propose an approach to nucleon-pair approximation(NPA)with m-scheme bases,in which the collective nucleon pairs are represented in terms of antisymmetric matrices,and commutations between nucleon pairs are given using a matrix multiplication that avoids angular-momentum couplings and recouplings.Therefore the present approach significantly simplifies the NPA computation.Furthermore,it is formulated on the same footing with and without isospin.
文摘Magnetic excitations for Ba isotopes are discussed within the nucleon-pair shell model truncated in the SD subspace. With the SD pair determined by a surface- interaction, M1 transitions for are well fitted. The M1 and M3 transitions for and are also predicted. It is shown that the statement, the collective magnetic properties are due to the orbital motion of nucleons, is approximately valid.
基金Supported partially by the National Natural Science Foundation of China (10975191,U1867210,11375023,11475014,11575018,12075169,12322506)the National Key R&D program of China (2016YFA0400504)。
文摘Excited states of ^(206)Rn have been examined via the 197 Au(^(14)N,5n)^(206)Rn fusion reaction at a beam energy of 78 MeV.A number of transitions and levels are identified by the γ-γ coincidence measurement,further enriching the level scheme of ^(206)Rn.The fullconfiguration shell model and nucleon-pair approximation(NPA)were utilized to investigate the single-particle configurations and seniority structures in ^(206)Rn.The results of these two calculations suggest that 2_(1)^(+) and 4_(1)^(+) states exhibit only a 50%component of a seniority-two state associated with a broken neutron pair.The collectivity of these two states primarily arises from configuration mixing due to residual proton-neutron interactions.Furthermore,6_(1)^(+) and 8_(1)^(+) states are predominantly characterized by a seniority-two state marked by a broken proton pair.
基金Supported by the National Natural Science Foundation of China(11875134,11875188,12175071,11975151,11961141003)the Shanghai Key Laboratory of Particle Physics and Cosmology(21DZ2271500-2)。
文摘In this study,we investigate the robustness of pair structures for nuclear yrast states,that is,whether the structures of relevant collective pairs as building blocks of different yrast states are the same.We focus on deformed and transitional nuclei and study the yrast states of^(28)Si,^(50)Cr,and^(132)Xe,whose experimental R_(4/2)values are 2.60,2.40,and 2.16,respectively,using the nucleon-pair approximation(NPA)and shell-model effective interactions.For each yrast state,we consider optimized pair structures to be those providing the energy minimum for this state.To find the minimum,many full NPA calculations are performed with varying pair structures,and the numerical optimization procedure of the conjugate gradient method is implemented.Our results suggest that optimized pair structures remain the same for all states within a rotational band of a deformed nucleus.Our results also suggest that after backbending,that is,changing of the intrinsic state,the structure of the S pair,which is essential to build the monopole pairing correlation,remains approximately unchanged,whereas the structures of the non-S pairs,which are essential to build the quadrupole correlation,change significantly.
基金Supported by Foundation for the Advancement of Theoretical Physics and Mathematics BASIS
文摘Analysis of various mass formulas related to neutron-proton correlations in atomic nuclei is carried out.Using the example of the N =Z chain it is shown that for self-adjoint nuclei various formulas proposed in literature for estimating the np pairing energy lead to similar results. Significant differences between the calculation methods arise when nuclei with N = Z are considered, which allows to reveal the complexity of neutron-proton correlations in different types of atomic nuclei and to make assumptions on the correspondence of the mass relation to the real effect of np pairing. The Shell Model parametrization of the binding energy makes it possible to draw additional conclusions on the structure of mass formulas and their relationship.
文摘Abstract： Various estimates of the even-odd effect of the mass shell of atomic nuclei are considered. Based on the experimental mass values of the Ca, Sn, and Pb isotopes, the dependence of the energy gap on the neutron number is traced and the relationship of this characteristic to the properties of external neutron subshells is shown. In nuclei with closed proton shells, effects directly related to neutron pairing and effects of nucleon shells are discussed.
