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  • 51.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    NUCLEAR CLUSTERING AND GENERALIZATION OF THE GEIGER-NUTTALL LAW2012Ingår i: Romanian Journal of Physics, ISSN 1221-146XArtikel i tidskrift (Refereegranskat)
  • 52.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Competition of different coupling schemes in atomic nuclei2012Ingår i: Advanced Many-Body And Statistical Methods In Mesoscopic Systems, Institute of Physics Publishing (IOPP), 2012, Vol. 338, nr 012027, s. 012027-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Shell model calculations reveal that the ground and low-lying yrast states of the N = Z nuclei Pd-92(46) and Cd-96 are mainly built upon isoscalar spin - aligned neutron - proton pairs each carrying the maximum angular momentum J = 9 allowed by the shell 0g(9)/(2) which is dominant in this nuclear region. This mode of excitation is unique in nuclei and indicates that the spin - aligned pair has to be considered as an essential building block in nuclear structure calculations. In this contribution we will discuss this neutron - proton pair coupling scheme in detail. In particular, we will explore the competition between the normal monopole pair coupling and the spin - aligned coupling schemes. Such a coupling may be useful in elucidating the structure properties of N = Z and neighboring nuclei.

  • 53.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Generalization of the Geiger-Nuttall law and alpha clustering in heavy nuclei2012Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 381, s. 012131-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A generalization of the Geiger-Nuttall law is deduced, which is valid for the radioactivity of all clusters (including alpha particles), by considering the clusterization and subsequent decay of nucleons within the nucleus. This universal decay law (UDL) is a linear relation between the half-lives of the decaying clusters and the corresponding Q-values. In this universal decay law (UDL) the penetrability is still a dominant quantity. By using three free parameters only, one finds that all known ground state to ground state radioactive decays are explained rather well. This allows us to search for new cluster decay modes and to carry out a simple and model-independent study of the decay properties of nuclei over the whole nuclear chart. It also helps in distinguishing the role played by pairing collectivity in the clustering process in heavy nuclei.

  • 54.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Spin-aligned neutron-proton pair coupling in the era of large scale computing2012Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 381, nr 1, s. 012106-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shell model calculations reveal that the ground and low-lying yrast states of the N = Z nuclei Pd-92(46) and Cd-96(48) are mainly built upon isoscalar spin-aligned neutron-proton pairs each carrying the maximum angular momentum J = 9 allowed by the shell 0g(9/2) which is dominant in this nuclear region. This mode of excitation is unique in nuclei and indicates that the spin-aligned pair has to be considered as an essential building block in nuclear structure calculations. In this contribution we will discuss this neutron-proton pair coupling scheme in detail. It may help in understanding the intrinsic structure of the shell-model wave function. In particular, we will explore the competition between the normal monopole pair coupling and the spin-aligned coupling schemes.

  • 55.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Wyss, Ramon A.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Nuclear clustering and generalization of the Geiger-Nuttall law 100 years after its formulation2011Ingår i: MANY-BODY CORRELATIONS FROM DILUTE TO DENSE NUCLEAR SYSTEMS (MBC 2011), 2011, Vol. 321Konferensbidrag (Refereegranskat)
    Abstract [en]

    The formation of clusters in nuclei is discussed and conditions to assess clusterization are formulated. By using these conditions a generalization of the Geiger-Nuttall law is deduced. This universal decay law (UDL) is a linear relation between the half-lives of the decaying clusters (including alpha particles) and the corresponding Q-values. The agreement between the UDL and available experimental data is excellent. This allows us to distinguish the role played by pairing collectivity in the clustering process.

  • 56.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Recent developments in radioactive charged-particle emissions and related phenomena2019Ingår i: Progress in Particle and Nuclear Physics, ISSN 0146-6410, E-ISSN 1873-2224, Vol. 105, s. 214-251Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The advent and intensive use of new detector technologies as well as radioactive ion beam facilities have opened up possibilities to investigate alpha, proton and cluster decays of highly unstable nuclei. This article provides a review of the current status of our understanding of clustering and the corresponding radioactive particle decay process in atomic nuclei. We put alpha decay in the context of charged-particle emissions which also include one- and two-proton emissions as well as heavy cluster decay. The experimental as well as the theoretical advances achieved recently in these fields are presented. Emphasis is given to the recent discoveries of charged-particle decays from proton-rich nuclei around the proton drip line. Those decay measurements have shown to provide an important probe for studying the structure of the nuclei involved. Developments on the theoretical side in nuclear many-body theories and supercomputing facilities have also made substantial progress, enabling one to study the nuclear clusterization and decays within a microscopic and consistent framework. We report on properties induced by the nuclear interaction acting in the nuclear medium, like the pairing interaction, which have been uncovered by studying the microscopic structure of clusters. The competition between cluster formations as compared to the corresponding alpha-particle formation are included. In the review we also describe the search for super-heavy nuclei connected by chains of alpha and other radioactive particle decays.

  • 57.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wang, X. B.
    Xu, Zhen Xiang
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Xu, F. R.
    Alternate proof of the Rowe-Rosensteel proposition and seniority conservation2010Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 82, nr 1, s. 014304-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For a system with three identical nucleons in a single-j shell, the states can be written as the angular-momentum coupling of a nucleon pair and the odd nucleon. The overlaps between these nonorthonormal states form a matrix that coincides with the one derived by Rowe and Rosensteel [Phys. Rev. Lett. 87, 172501 ( 2001)]. The propositions they state are related to the eigenvalue problems of the matrix and dimensions of the associated subspaces. In this work, the propositions are proven from the symmetric properties of the 6j symbols. Algebraic expressions for the dimension of the states, eigenenergies, as well as conditions for conservation of seniority can be derived from the matrix.

  • 58.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Xu, F. R.
    Liotta, Roberto J.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Zhang, M. Y.
    Asawatangtrakuldee, C.
    Hu, D.
    Microscopic mechanism of charged-particle radioactivity and generalization of the Geiger-Nuttall law2009Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 80, nr 4, s. 044326-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A linear relation for charged-particle emissions is presented starting from the microscopic mechanism of the radioactive decay. It relates the logarithms of the decay half-lives with two variables, called. chi' and. rho', which depend upon the Q values of the outgoing clusters as well as the masses and charges of the nuclei involved in the decay. This relation explains well all known cluster decays. It is found to be a generalization of the Geiger-Nuttall law in a radioactivity, and therefore we call it the universal decay law. Predictions of the most likely emissions of various clusters are presented by applying the law over the whole nuclear chart. It is seen that the decays of heavier clusters with nonequal proton and neutron numbers are mostly located in the trans-lead region. The emissions of clusters with equal protons and neutrons, like C-12 and O-16, are possible in some neutron-deficient nuclei with Z >= 54.

  • 59.
    Qi, Chong
    et al.
    Peking University.
    Xu, Furong
    Peking University.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Universal Decay Law in Charged-Particle Emission and Exotic Cluster Radioactivity2009Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, nr 7, s. 072501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A linear universal decay formula is presented starting from the microscopic mechanism of the charged-particle emission. It relates the half-lives of monopole radioactive decays with the Q values of the outgoing particles as well as the masses and charges of the nuclei involved in the decay. This relation is found to be a generalization of the Geiger-Nuttall law in α radioactivity and explains well all known cluster decays. Predictions on the most likely emissions of various clusters are presented.

  • 60.
    Qi, Chong
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Xu, Zhen Xiang
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto J.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Analytic proof of partial conservation of seniority in j=9/2 shells2012Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 884, s. 21-35Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A partial conservation of the seniority quantum number in j = 9/2 shells has been found recently in a numerical application. In this paper an analytic proof for this problem is derived as an extension of the work [L. Zamick, P. Van Isacker, Phys. Rev. C 78 (2008) 044327]. We analyze the properties of the non-diagonal interaction matrix elements with the help of the one-particle and two-particle coefficients of fractional parentage (cfp's). It is found that all non-diagonal (and the relevant diagonal) matrix elements can be re-expressed in simple ways and are proportional to certain one-particle cfp's. This remarkable occurrence of partial dynamic symmetry is the consequence of the peculiar property of the j = 9/2 shell, where all it = 3 and 5 states are uniquely defined.

  • 61.
    Sandulescu, Neculai
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Van Giai, N
    Liotta, Roberto
    KTH, Tidigare Institutioner, Fysik.
    Superfluid properties of the inner crust of neutron stars2004Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 69, nr 4, s. 045802-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Superfluid properties of the inner crust matter of neutron stars, formed by nuclear clusters immersed in a dilute neutron gas, are analyzed in a self-consistent Hartree-Fock-Bogoliubov approach. The calculations are performed with two pairing forces, fixed so as to obtain in infinite nuclear matter the pairing gaps provided by the Gogny force or by induced interactions. It is shown that the nuclear clusters can either suppress or enhance the pairing correlations inside the inner crust matter, depending on the density of the surrounding neutrons. The profile of the pairing field in the inner crust is rather similar for both pairing forces, but the values of the pairing gaps are drastically reduced for the force which simulates the polarization effects in infinite neutron matter.

  • 62.
    Wang, S.
    et al.
    Peking University.
    Xu, C.
    Peking University.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Qi, Chong
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Xu, F.
    Peking University.
    Jiang, D.
    Peking University.
    Alpha-particle decays from excited states in Mg-242011Ingår i: Science China: Physics, Mechanics and Astronomy, ISSN 1674-7348, Vol. 54, nr 1, s. S130-S135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a cluster model based on the Woods-Saxon potential, alpha-particle decays from excited states in Mg-24 have been systematically investigated. Calculations can in general reproduce experimental data, noticing the fact that the preformation factor P of alpha particle in alpha-decaying nuclei is of order from 10(0) to 10(-2). This can be the evidence for the alpha+Ne-20 structure in Mg-24. Meanwhile, the results also show the existence of other configurations, such as O-16+2 alpha. Since the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster (alpha particle), our results could serve as a guide to experimental spin assignments.

  • 63. Xu, Chen
    et al.
    Qi, Chong
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Wang, S. M.
    Xu, F. R.
    Jiang, D. X.
    Molecular structure of highly excited resonant states in Mg-24 and the corresponding Be-8+O-16 and C-12+C-12 decays2010Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 81, nr 5, s. 054319-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Exotic Be-8 and C-12 decays from high-lying resonances in Mg-24 are analyzed in terms of a cluster model. The calculated quantities agree well with the corresponding experimental data. It is found that the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster. It is shown that this property makes cluster decay a powerful tool to determine the spin as well as the molecular structures of the resonances.

  • 64.
    Xu, Zhen Xiang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Qi, Chong
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Blomqvist, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Multistep shell model description of spin-aligned neutron-proton pair coupling2012Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 877, s. 51-58Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recently proposed spin-aligned neutron-proton pair coupling scheme is studied within a non-orthogonal basis in term of the multistep shell model. This allows us to identify simultaneously the roles played by other configurations such as the normal pairing term. The model is applied to four-, six- and eight-hole N = Z nuclei below the core Sn-100.

  • 65.
    Xu, Zhen Xiang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Qi, Chong
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Multistep shell model in the complex energy plane2012Ingår i: Advanced Many-Body And Statistical Methods In Mesoscopic Systems, Institute of Physics Publishing (IOPP), 2012, s. 012029-Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have adopted the multistep shell model in the complex energy plane to study nuclear excitations occurring in the continuum part of the spectrum. In this method one proceeds by solving the shell model equations in a successive manner. That is, in each step one constructs the building blocks to be used in future steps. We applied this formalism to analyze the unbound nuclei Li-12,Li-13 starting from the one - particle states in Li-10 and two - particle states in Li-11. In the former case the excitations correspond to the motion of three particles partitioned as the product of a one - particle and two - particle systems. The ground state of Li-12 is thus calculated to be an antibound (virtual) state. In the four - particle system Li-13 the states can be constructed as the coupling of two correlated pairs. We found that there is no bound or antibound state in Li-13.

  • 66.
    Xu, Zhenxiang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Liotta, Roberto J.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Qi, Chong
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Roger, T.
    GANIL, France.
    Roussel-Chomaz, P.
    GANIL, France.
    Savajols, H.
    GANIL, France.
    Wyss, Ramon
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Analysis of the unbound spectrum of 12Li.2011Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 850, s. 53-68Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The unbound nucleus 12Li is evaluated by studying three-neutron one-proton excitations within the multistepshell model in the complex energy plane. It is found that the ground state of this system consists of anantibound 2− state. A number of narrow states at low energy are found which ensue from the coupling ofresonances in 11Li to continuum states close to threshold.

12 51 - 66 av 66
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  • en-GB
  • en-US
  • fi-FI
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