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  • 1.
    Zhang, Yu
    et al.
    Liaoning Normal Univ, Dept Phys, Dalian 116029, Peoples R China..
    He, Ying-Wen
    Liaoning Normal Univ, Dept Phys, Dalian 116029, Peoples R China..
    Karlsson, Daniel
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Pan, Feng
    Liaoning Normal Univ, Dept Phys, Dalian 116029, Peoples R China.;Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA..
    Draayer, J. P.
    Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA..
    A theoretical interpretation of the anomalous reduced E2 transition probabilities along the yrast line of neutron-deficient nuclei2022In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 834, article id 137443Article in journal (Refereed)
    Abstract [en]

    The anomalous low-energy E2-related behavior of a triaxially deformed nuclei is examined within the framework of the interacting boson model. The results show striking features that include a B(E2; 4(1)(+) -> 2(1)(+))/B(E2; 2(1)(+) -> 0(1)(+)) < 1.0 transition rate and a E(4(1)(+))/E(2(1)(+)) > 2.0 excitation energy ratio that can be tracked back to a finite-Neffect, which in a large-Nlimit of the theory yields normal results for a stable gamma-deformation. This description is shown to explain experimentally observed results in Pt-172 and Os-168, and in doing so yields a deeper understanding of the physical features of a soft triaxially-deformed nucleus.

  • 2.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Andreyev, A. N.
    Huyse, M.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Van Duppen, P.
    Wyss, Ramon A.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Abrupt changes in alpha-decay systematics as a manifestation of collective nuclear modes2010In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 81, no 6, p. 064319-Article in journal (Refereed)
    Abstract [en]

    An abrupt change in alpha-decay systematics around the N = 126 neutron shell closure is discussed. It is explained as a sudden hindrance of the clustering of the nucleons that eventually form the a particle. This is because the clustering induced by the pairing mode acting upon the four nucleons is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.

  • 3.
    Zheng, S.
    et al.
    Peking University.
    Xu, F.
    Yuan, C.
    Qi, Chong
    Peking University.
    Alignments in the nobelium isotopes2009In: Chinese Physics C, ISSN 1674-1137, E-ISSN 2058-6132, Vol. 33, no 2, p. 107-109Article in journal (Refereed)
  • 4.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Alpha decay as a probe for the structure of neutron-deficient nuclei2016In: Reviews in Physics, ISSN 2405-4283, Vol. 1, p. 77-89Article in journal (Refereed)
    Abstract [en]

    The advent of radioactive ion beam facilities and new detector technologies have opened up new possibilities to investigate the radioactive decays of highly unstable nuclei, in particular the proton emission, α decay and heavy cluster decays from neutron-deficient (or proton-rich) nuclei around the proton drip line. It turns out that these decay measurements can serve as a unique probe for studying the structure of the nuclei involved. On the theoretical side, the development in nuclear many-body theories and supercomputing facilities have also made it possible to simulate the nuclear clusterization and decays from a microscopic and consistent perspective. In this article we would like to review the current status of these structure and decay studies in heavy nuclei, regarding both experimental and theoretical opportunities. We then discuss in detail the recent progress in our understanding of the nuclear α formation probabilities in heavy nuclei and their indication on the underlying nuclear structure.

  • 5.
    Cai, Boshuai
    et al.
    Sun Yat Sen Univ, Sino French Inst Nucl Engn & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Chen, Guangshang
    Sun Yat Sen Univ, Sino French Inst Nucl Engn & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Xu, Jiongyu
    Sun Yat Sen Univ, Sino French Inst Nucl Engn & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Yuan, Cenxi
    Sun Yat Sen Univ, Sino French Inst Nucl Engn & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Yao, Yuan
    Beijing Normal Univ, Coll Nucl Sci & Technol, Beijing 100875, Peoples R China..
    alpha decay half-life estimation and uncertainty analysis2020In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 101, no 5, article id 054304Article in journal (Refereed)
    Abstract [en]

    Background: alpha decay is one of the most important decay modes of atomic nuclei. The half-life of alpha decay provides valuable information for nuclear structure study. Many theoretical models and empirical formulas have been suggested to describe the half-life of alpha decay as a function of decay energy (Q(alpha)), atomic number (Z), nucleon number (A), and other related variables. However, the analysis of theoretical uncertainty is rarely done for those alpha decay models. Purpose: We aim to perform a systematic and detailed study on the theoretical uncertainty of existing alpha decay formulas based on statistical methods. Methods: The nonparametric bootstrap method is used to evaluate the uncertainties of two alpha decay formulas, the universal decay law (UDL) and the new Geiger-Nuttall law (NGNL). Such a method can simultaneously obtain the uncertainty of each parameter, the correlation between each pair of parameters, and the total, statistical, and systematic uncertainties of each formula. Both even-even (ee) nuclei and odd-A (oA) nuclei are used in the analysis. The collected data are separated into three parts: ee nuclei, oA nuclei without spin or parity change (oA_nc), and oA nuclei with spin and/or parity change (oA_c). Based on the residues between observed data and corresponding calculations, the statistical and systematic uncertainties are decomposed from the total uncertainty, from which one can clarify the effects from the shell structure, pairing, and angular momentum change on describing alpha decay half-life. Results: If N > 126 and N <= 126 nuclei are considered together, the systematic uncertainty of residues between observed and predicted half-lives are larger than if those groups are considered separately. Without a shell correction term, a much larger systematic uncertainty is found if parameters obtained for N <= 126 nuclei are used to describe the half-lives of N > 126 nuclei. Based on the Bohr-Sommerfeld quantization condition and simple assumptions, a detailed shell correction term is obtained for N > 126 nuclei, for which the value is similar to that in NGNL. A global hindrance on the alpha decay process is found in oA_nc (oA_c) nuclei compared with ee (oA_nc) nuclei. If parameters obtained from ee (oA_nc) nuclei are used, the half-lives of oA_nc (oA_c) nuclei are generally underestimated with large systematic uncertainties, which can be related to the contribution of pairing effect and angular momentum. The parameter of angular momentum term in NGNL is obtained with large uncertainty and very sensitive to the selections of the dataset. The recently observed superallowed decay from Te-104 to Sn-100 is also discussed based on uncertainty analysis. Conclusions: The theoretical uncertainty of existing alpha decay formulas is successfully evaluated by the nonparametric bootstrap method, which simultaneously indicates the important effect in alpha decay, such as the shell effect and the pairing effect. In addition, statistical results show strong correlations between the parameters of the second and third terms in both UDL and NGNL, which demands further investigations.

  • 6.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon Alexander
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Alpha decay measured in single-particle units as a manifestation of nuclear collectivity2021In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 818, article id 136373Article in journal (Refereed)
    Abstract [en]

    A salient feature of quantum mechanics is the inherent property of collective quantum motion, when apparent independent quasiparticles move in highly correlated trajectories, resulting in strongly enhanced transition probabilities. To assess the extend of a collective quantity requires an appropriate definition of the uncorrelated average motion, often expressed by single particle units. A well known example in nuclear physics is the Weisskopf unit for electromagnetic transitions which reveals different aspects of collective motion. In this paper we define the corresponding single particle unit for alpha decay as induced by four uncorrelated/non-interacting protons and neutrons. Our definition facilitates an unified description of all alpha decay processes along the nuclear chart, revealing a simple mass dependence. The comparison of the uncorrelated decay rates with the experimentally observed ones, shows a significant enhancement of the decay rates pointing towards collective alpha like correlations in the nuclear ground state. As a limiting case, the formalism presented here is applied to proton decay revealing its single particle nature.

  • 7.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    alpha FORMATION PROBABILITIES IN NUCLEI AND PAIRING COLLECTIVITY2010In: NUCLEAR STRUCTURE IN CHINA 2010 / [ed] Bai, HB Meng, J Zhao, EG Zhou, SG, WORLD SCIENTIFIC PUBL CO PTE LTD , 2010, p. 169-174Conference paper (Refereed)
    Abstract [en]

    alpha formation amplitudes extracted from experimental data are presented and an abrupt change around the N = 126 shell closure is noted. It is explained as a sudden hindrance of the clustering of nucleons. The clustering induced by the pairing mode acting upon the four nucleons is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.

  • 8.
    Wang, S.
    et al.
    Peking University.
    Xu, C.
    Peking University.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, F.
    Peking University.
    Jiang, D.
    Peking University.
    Alpha-particle decays from excited states in Mg-242011In: Science China Physics, Mechanics & Astronomy, ISSN 1674-7348, E-ISSN 1869-1927, Vol. 54, no 1, p. S130-S135Article in journal (Refereed)
    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.

  • 9.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wang, X. B.
    Xu, Zhen Xiang
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, F. R.
    Alternate proof of the Rowe-Rosensteel proposition and seniority conservation2010In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 82, no 1, p. 014304-Article in journal (Refereed)
    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.

  • 10.
    Guan, Xin
    et al.
    Liaoning Normal Univ, Dept Phys, Dalian 116029, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    An iterative approach for the exact solution of the pairing Hamiltonian2022In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 275, article id 108310Article in journal (Refereed)
    Abstract [en]

    A new iterative algorithm is established for the exact solution of the standard pairing problem, based on the Richardson-Gaudin method using the polynomial approach. It provides efficient and robust solutions for both spherical and deformed systems at a large scale. The key to its success is that the initial guess for the solutions of such a large set of the non-linear equations is provided in a physically meaningful and controllable manner. Moreover, one reduces the large-dimensional problem to a one-dimensional Monte Carlo sampling procedure, which improves the algorithm's efficiency and avoids the non-solutions and numerical instabilities that persist in most existing approaches. We calculated the ground state and low-lying excited states of equally spaced systems at different pairing strengths G. We then applied the model to study the quantum phase transitional Sm isotopes and the actinide nuclei Pu isotopes, where an excellent agreement with experimental data is obtained. Program summary Program Title: IterV1.m CPC Library link to program files: https://doi.org/10.17632/rjnbhgk2p6.1 Licensing provisions: GPLv3 Programming language: Mathematica Nature of problem: The program calculates exact pairing energies based on a new iterative algorithm. The key is the procedure of determining the initial guesses for the large-set non-linear equations involved in a controllable and physically motivated manner. It provides an efficient and robust solver for both spherical and deformed systems in super large model spaces. Solution method: The new iterative algorithm approach starts with simple systems with knucleon pairs and n = klevels, which can be solved iteratively by including one pair and one level at each step using the Newton-Raphson algorithm with a Monte Carlo sampling procedure. Then it takes the solutions of those systems as initial values and obtain the converged results for the full space by gradually adding the remaining levels. In this way, one reduces the k-dimensional Monte Carlo sampling procedure to a one-dimensional sampling, which improves the efficiency of the algorithm and avoids the non-solutions and numerical instabilities.

  • 11.
    Xu, Zhenxiang
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto J.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Roger, T.
    GANIL, France.
    Roussel-Chomaz, P.
    GANIL, France.
    Savajols, H.
    GANIL, France.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Analysis of the unbound spectrum of 12Li.2011In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 850, p. 53-68Article in journal (Refereed)
    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.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, Zhen Xiang
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto J.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Analytic proof of partial conservation of seniority in j=9/2 shells2012In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 884, p. 21-35Article in journal (Refereed)
    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.

  • 13. Procter, M. G.
    et al.
    Cullen, D. M.
    Scholey, C.
    Ruotsalainen, P.
    Angus, L.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Dewald, A.
    Fransen, C.
    Grahn, T.
    Greenlees, P. T.
    Hackstein, M.
    Jakobsson, U.
    Jones, P. M.
    Julin, R.
    Juutinen, S.
    Ketelhut, S.
    Leino, M.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Lumley, N. M.
    Mason, P. J. R.
    Nieminen, P.
    Nyman, M.
    Pakarinen, J.
    Pissulla, T.
    Peura, P.
    Rahkila, P.
    Revill, J.
    Rigby, S. V.
    Rother, W.
    Sandzelius, M.
    Saren, J.
    Sorri, J.
    Taylor, M. J.
    Uusitalo, J.
    Wady, P.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, F. R.
    Anomalous transition strength in the proton-unbound nucleus (109)(53)I562011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 704, no 3, p. 118-122Article in journal (Refereed)
    Abstract [en]

    A lifetime measurement has been made for the first excited 11/2(+) state in the proton-unbound nucleus (109)(53)I56 using the recoil-distance Doppler-shift method in conjunction with recoil-proton tagging. The experimental reduced transition probability is considerably smaller than the prediction of theoretical shell-model calculations using the CD-Bonn nucleon-nucleon potential. The discrepancy between the theoretical and experimental reduced transition strengths in this work most likely arises from the inability of the current shell-model calculations to accurately account for the behavior of the unbound nuclear states.

  • 14. Li, K. A.
    et al.
    Lam, Y. H.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Tang, X. D.
    Zhang, N. T.
    beta-decay rate of Fe-59 in shell burning environment and its influence on the production of Fe-60 in a massive star2016In: Physical Review C - Nuclear Physics, ISSN 2469-9985, Vol. 94, no 6, article id 065807Article in journal (Refereed)
    Abstract [en]

    We deduced the stellar beta-decay rate of Fe-59 at typical carbon-shell burning temperature by taking the experimental Gamow-Teller transition strengths of the Fe-59 excited states. The result is also compared with those derived from large-scale shell model calculations. The new rate is up to a factor of 2.5 lower than the theoretical rate of Fuller, Fowler, and Newman (FFN) and up to a factor of 5 higher than decay rate of Langanke and Martinez-Pinedo (LMP) in the temperature region 0.5 <= T <= 2 GK. We estimated the impact of the newly determined rate on the synthesis of cosmic gamma emitter Fe-60 in C-shell burning and explosive C/Ne burning using a one-zone model calculation. Our results show that Fe-59 stellar beta decay plays an important role in Fe-60 nucleosynthesis, even though the uncertainty of the decay rate is rather large due to the error of B(GT) strengths.

  • 15.
    Das, Biswarup
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering. GSI Helmholtzzentrum für Schwerionenforschung GmbH - Darmstadt, 64291 Germany.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering.
    Vasiljevic, Jana
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Science and Engineering.
    Zhao, J.
    GSI Helmholtzzentrum für Schwerionenforschung GmbH - Darmstadt, 64291 Germany.
    et al.,
    Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh 952024In: Physical Review Research, E-ISSN 2643-1564, Vol. 6, no 2, article id L022038Article in journal (Refereed)
    Abstract [en]

    Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.

  • 16.
    Ghazi Moradi, Farnaz
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ataç, Ayşe
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Doncel, Maria
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Johnson, Arne
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aktas, Özge
    et al.,
    Character of particle-hole excitations in Ru-94 deduced from gamma-ray angular correlation and linear polarization measurements2014In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 89, no 1, p. 0143011-0143019Article in journal (Refereed)
    Abstract [en]

    Linear polarization and angular correlations of γ-rays depopulating excited states in the neutron-deficient nucleus 9444Ru50 have been measured, enabling firm spin-parity assignments for several excited states in this nucleus. The deduced multipolarities of strong transitions in the yrast structure were found to be mostly of stretched M1, E1, and E2 types and, in most cases, in agreement with previous tentative assignments. The deduced multipolarity of the 1869 keV and the connecting 257 and 1641 keV transitions indicates that the state at 6358 keV excitation energy has spin parity 12−1 rather than 12+3 as proposed in previous works. The presence of a 12−1 state is interpreted within the framework of large-scale shell-model calculations as a pure proton-hole state dominated by the π(p−11/2⊗g−59/2) and π(p−13/2⊗g−59/2) configurations. A new positive-parity state is observed at 6103 keV and is tentatively assigned as 12+2. The 14−1 state proposed earlier is reassigned as 13−4 and is interpreted as being dominated by neutron particle-hole core excitations. The strengths of several E1 transitions have been measured and are found to provide a signature of core-excited configurations.

  • 17.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Blomqvist, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Johnson, Arne
    KTH, School of Engineering Sciences (SCI), Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Coherence features of the spin-aligned neutron-proton pair coupling scheme2012In: Physica scripta. T, ISSN 0281-1847, Vol. T150, p. 014031-Article in journal (Refereed)
    Abstract [en]

    The seniority scheme has been shown to be extremely useful for the classification of nuclear states in semi-magic nuclei. The neutron-proton (np) correlation breaks the seniority symmetry in a major way. As a result, the corresponding wave function is a mixture of many components with different seniority quantum numbers. In this paper, we show that the np interaction may favor a new kind of coupling in N = Z nuclei, i.e. the so-called isoscalar spin-aligned np pair mode. Shell model calculations reveal that the ground and low-lying yrast states of the N = Z nuclei Pd-92 and Cd-96 may be mainly built upon such spin-aligned np pairs, each carrying the maximum angular momentum J = 9 allowed by the shell 0 g(9/2) which is dominant in this nuclear region.

  • 18.
    Li, Hongjie J.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xiao, Z. G.
    Zhu, S. J.
    Patial, Monika
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics.
    Zhang, Z.
    Wang, R. S.
    Yi, H.
    Yan, W. H.
    Cheng, W. J.
    Huang, Y.
    Lyu, L. M.
    Zhang, Y.
    Wu, X. G.
    He, C. Y.
    Zheng, Y.
    Li, G. S.
    Li, C. B.
    Li, H. W.
    Liu, J. J.
    Luo, P. W.
    Hu, S. P.
    Wang, J. L.
    Wu, Y. H.
    Collective band structures in the Tc-99 nucleus2015In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 91, no 5, article id 054314Article in journal (Refereed)
    Abstract [en]

    Excited states in Tc-99 with energies up to 6 MeV have been populated using the Zr-96(Li-7, 4n)Tc-99 reaction with a laboratory beam energy of 35 MeV. Coincident gamma rays from excited nuclei produced in the reactions were detected using an array of coaxial, planar, and clover-type high-purity germanium detectors. A total of 60 new gamma-ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the pi g(9/2)[422]5/2(+) and pi p(1/2)[301]1/2(-) Nilsson configurations have been extended with spins up to 35/2 and 33/2 h, respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in Tc-99 may be caused by a triaxial deformation, which agrees well with the electromagnetic properties, theoretical calculations based on total Routhian surface, and triaxial particle-rotor model calculations.

  • 19.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Competition of different coupling schemes in atomic nuclei2012In: Advanced Many-Body And Statistical Methods In Mesoscopic Systems, Institute of Physics Publishing (IOPP), 2012, Vol. 338, no 012027, p. 012027-Conference paper (Refereed)
    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.

  • 20. Yuan, C. X.
    et al.
    Xu, F. R.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Configuration mixing effects in neutron-rich carbon isotopes2013In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 420, no 1Article in journal (Refereed)
    Abstract [en]

    Shell model calculations are done to study the structure of neutron-rich carbon isotopes. For both even-A and odd-A neutron-rich carbon isotopes, the energy levels are strongly affected by the configuration mixing of valence neutrons. The calculated energy levels in the nucleus 17C are significantly improved compared with experimental values when the model space of the three valence neutrons is enlarged from pure v(0d5/2) 3 configuration to full sd space. We also investigate the configuration mixing effect on the B(E2) values in even-even nuclei 16-20C.

  • 21.
    Zeng, Q. B.
    et al.
    Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Guo, S.
    Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Liu, Z.
    Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhou, X. H.
    Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Configurations of the low-lying states in Eu-1462022In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 106, no 3, article id 034307Article in journal (Refereed)
    Abstract [en]

    The low-lying states of Eu-146 populated in the decay of the 9(+) isomer were studied. The gamma-ray intensities were reanalyzed employing germanium detectors, and the lifetimes of the 6(1)(-) and 6(2)(-) states were measured using the mirror symmetric centroid difference (MSCD) method with fast-timing LaBr3(Ce) scintillator detectors. The B(M1) values of the 6(1)(-) -> 5(1)(-) and 6(2)(-) -> 5(1)(-) transitions were deduced, and all observed states were interpreted as members of the pi d(5/2)(-1)nu f(7/2) and pi g(7/2)(-1)nu f(7/2) multiplets. In particular, the 5(1)(-) level is shown to be dominated by the pi d(5/2)(-1)nu f(7/2) configuration, solving the discrepancy in its configuration assignment proposed in previous works. These experimental results were compared with the shell model calculations using several different effective interactions. The systematics of low-lying structure in the N = 83 isotones Pr-142, Pm-144, and Eu-146 was established.

  • 22.
    Olofsson, Klara
    KTH, School of Engineering Sciences (SCI).
    Constraining the Neutron Star Equation of State2022Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Neutron stars are stellar objects of extreme properties. The dense core enables usto study nuclear matter beyond saturation density. The exact composition of matterat such densities is not yet established, but the thermodynamic states of the matteris theoreticized by the Equation of State (EOS). The EOS cannot be derived analyt-ically and is dependent on constraints from neutron stars and nuclear experiments inlaboratories on earth. Recent advances in astrophysical experiments have probed newconstraints on the EOS by studying properties such as mass, radius and tidal deformabil-ity of neutron stars. Especially the possibility to detect gravitational waves from mergingbinary systems by the LIGO/VIRGO collaboration and the mass-radius measurementsby NICER have contributed a great deal. Constraints from terrestrial experiments havebeen derived by studying matter at supra saturation density in Heavy Ion Collisions andby determining the neutron skin thickness. In this work, an overview of neutron stars,dense matter and the EOS is presented. Further, results of studies aiming to determineand constrain the EOS are reviewed. Even though there is consensus about some neutronstar properties among different research groups, there are still major uncertainties as allresult depend on a relatively small set of observational data. Therefore, the EOS can stillbe considered to be far from precise and the knowledge of the true neutron star matterremains undisclosed.

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  • 23. Jiao, L. F.
    et al.
    Sun, Z. H.
    Xu, Z. X.
    Xu, F. R.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Correlated-basis method for shell-model calculations2014In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 90, no 2, p. 024306-Article in journal (Refereed)
    Abstract [en]

    We present a basis selection method for truncated shell-model calculations. In this method, the correlated basis is constructed with the eigenvectors of the Hamiltonian that is diagonalized in each partition of the shell model. A truncation scheme is established by naturally taking the low-lying correlated-basis vectors in different partitions, which is equivalent to the jj-coupling scheme of the shell model when all the correlated-basis vectors are considered. The results are compared with standard shell-model calculations. The convergence properties of the correlated-basis method are discussed.

  • 24. Zhang, W.
    et al.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ertoprak, Aysegul
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Valiente-Dobon, J. J.
    Ist Nazl Fis Nucl, Lab Nazl Legnaro, I-35020 Legnaro, Italy..
    Decay spectroscopy of 171,172Os and 171,172,174Ir2023In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 107, no 1, article id 014308Article in journal (Refereed)
    Abstract [en]

    We report on a study of the alpha-decay fine structure and the associated E alpha-E gamma correlations in the decays of 171,172Os and 171,172,174Ir. In total, 13 new alpha-decay energy lines have been resolved, and three new gamma-ray transitions have been observed following the new decay branches to 168Re and 167W. The weak alpha-decay branch from the bandhead of the nu i13/2 band in 171Os observed in this work highlights an unusual competition between alpha, beta, and electromagnetic decays from this isomeric state. The nucleus 171Os is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in 92Mo(83Kr, xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyvaskyla, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt gamma-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that alpha-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.

  • 25.
    Changizi, Sara A.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics.
    Density dependence of the pairing interaction and pairing correlation in unstable nuclei2015In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 91, no 2, article id 024305Article in journal (Refereed)
    Abstract [en]

    This work aims at a global assessment of the effect of the density dependence of the zero-range pairing interaction. Systematic Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface, and mixed pairing forces are carried out to study the pairing gaps in even-even nuclei over the whole nuclear chart. Calculations are also done in coordinate representation for unstable semimagic even-even nuclei. The calculated pairing gaps are compared with empirical values from four different odd-even staggering formulas. Calculations with the three pairing interactions are comparable for most nuclei close to the beta-stability line. However, the surface interaction calculations predict neutron pairing gaps in neutron-rich nuclei that are significantly stronger than those given by themixed and volume pairing. On the other hand, calculations with volume andmixed pairing forces show noticeable reduction of neutron pairing gaps in nuclei far from stability.

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  • 26.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Differential evolution algorithm for global optimizations in nuclear physics2017In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 44, no 4, article id 045107Article in journal (Refereed)
    Abstract [en]

    We explore the applicability of the differential evolution algorithm in finding the global minima of three typical nuclear structure physics problems: the global deformation minimum in the nuclear potential energy surface, the optimization of mass model parameters and the lowest eigenvalue of a nuclear Hamiltonian. The algorithm works very effectively and efficiently in identifying the minima in all problems we have tested. We also show that the algorithm can be parallelized in a straightforward way.

  • 27.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Double binding energy differences: Mean-field or pairing effect?2012In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 717, no 4-5, p. 436-440Article in journal (Refereed)
    Abstract [en]

    In this Letter we present a systematic analysis on the average interaction between the last protons and neutrons in atomic nuclei, which can be extracted from the double differences of nuclear binding energies. The empirical average proton-neutron interaction V-pn thus derived from experimental data can be described in a very simple form as the interplay of the nuclear mean field and the pairing interaction. It is found that the smooth behavior as well as the local fluctuations of the V-pn in even-even nuclei with N not equal Z are dominated by the contribution from the proton-neutron monopole interactions. A strong additional contribution from the isoscalar monopole interaction and isovector proton-neutron pairing interaction is seen in the V-pn for even-even N = Z nuclei and for the adjacent odd-A nuclei with one neutron or proton being subtracted.

  • 28.
    Cheragwandi, Twana
    KTH, School of Engineering Sciences (SCI), Physics.
    Dynamics of Nuclear Clusters in Neutron Stars2024Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The inner crust of a neutron star is explored, using nuclear models andimplementing them in an open quantum system formalism. The purposeof the investigation is to extract valuable dynamics of the predictednuclear clusters that may exist in this region. We begin by setting up thenuclear models to extract the total energy per particle per system in orderto see if the results are corroborated with the works of others. Thereafter,the single-particle energies of the nuclear clusters are extracted. Theseenergies are then used in the Lindblad formalism to work out the timedependenceof the density matrix, which will allow us to extract thetime-dependence of the average energy of the system in interaction withan environment.

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  • 29.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Delion, Doru S.
    Liotta, Roberto J.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Effects of formation properties in one-proton radioactivity2012In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 85, no 1, p. 011303-Article in journal (Refereed)
    Abstract [en]

    It is shown that the proton formation probability, extracted from experimental data corresponding to one-proton radioactivity, is divided into two regions when plotted as a function of an universal parameter. This parameter is derived from a microscopic description of the decay process. In this way we explain the systematics of proton emission half-lives. At the same time the formation probability is shown to be a useful quantity to determine the deformation property of the mother nucleus.

  • 30.
    Wang, X.
    et al.
    Peking University.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, F.
    Peking University.
    Eigen-Property of Single-j System and Seniority Conservation Condition2012In: Plasma Science and Technology, ISSN 1009-0630, Vol. 14, no 5, p. 383-385Article in journal (Refereed)
    Abstract [en]

    In this paper we study the system with three nucleons within a single-j shell, which can be described as the angular momentum coupling of a nucleon pair and the odd nucleon. The overlaps between these non-orthonormal states form a special matrix coincidental with the one obtained by Rowe and Rosensteel. They proposed a proposition related to the eigenvalue problems of that matrix and dimensions of the associated subspaces. We prove their proposition with the help of the symmetric properties of the six-j symbols. We also derive algebraic expressions for eigen energies as well as conditions for conservation of seniority through the decomposition of the angular momentum.

  • 31.
    Changizi, Sara A.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei2015In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 940, p. 210-226Article in journal (Refereed)
    Abstract [en]

    The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-j shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula δC(3)(N)=12[B(N,Z)+B(N-2,Z)-2B(N-1,Z)] can provide a good measure of the neutron pairing gap in even-N nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around N=Z. We also show that the strength of δC(3)(N) can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of δC(3)(N) in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.

  • 32.
    Wu, Zheying
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Changizi, Sara
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Empirical residual neutron-proton interaction in odd-odd nuclei2016In: PHYSICAL REVIEW C, ISSN 2469-9985, Vol. 93, no 3, article id 034334Article in journal (Refereed)
    Abstract [en]

    Two types of average neutron-proton interaction formulas are compared: In the first type, neutron-proton interactions for even-even and odd-A nuclei extracted from experimental binding energies show a smooth behavior as a function of mass number A and are dominated by the contribution from the symmetry energy. Whereas in the second type large systematic staggering is seen between even-A and odd-A nuclei. This deviation is understood in terms of the additional neutron-proton interaction in odd-odd nuclei relative to the neighboring even-even and odd-A systems. We explore three possible ways to extract this additional interaction from the binding energy difference of neighboring nuclei. The extracted interactions are positive in nearly all cases and show weak dependence on the mass number. The empirical interactions are also compared with theoretical values extracted from recent nuclear mass models where large unexpected fluctuations are seen in certain nuclei. The reproduction of the residual neutron-proton interaction and the correction of those irregular fluctuations can be a good criterion for the refinement of those mass models.

  • 33.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Energy expressions for n=3 and 4 systems in a single-j shell2010In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 81, no 3, p. 034318-Article in journal (Refereed)
    Abstract [en]

    For systems with three and four fermions within a single-j shell, analytical expressions for the state energies are presented from a decomposition of the angular momentum. In some important cases the expressions acquire a very simple form. The expression may help us in understanding the structure of isomeric states. The decomposition also makes it possible to construct the algebraic condition for conservation of seniority.

  • 34.
    Cederwall, Bo
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ghazi Moradi, Farnaz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Johnson, Arne
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Blomqvist, Jan-Erik
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Clément, E.
    Grand Accélérateur National d´lons Lourds, Cean Cedex, France.
    de France, G.
    Grand Accélérateur National d´lons Lourds, Cean Cedex, France.
    Wadsworth, R.
    Department of Physics, University of York, UK.
    Andgren, Karin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Lagergren, Karin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Dijon, A.
    Grand Accélérateur National d´lons Lourds, Cean Cedex, France.
    Jaworski, G.
    Heavy Ion Laboratory, Univeristy of Warsaw, Warsaw, Poland.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Nyakó, B. M.
    Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary.
    Nyberg, J.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Palacz, M.
    Heavy Ion Laboratory, Univeristy of Warsaw, Warsaw, Poland.
    Al-Azri, H.
    Department of Physics, University of York, UK.
    Algora, A.
    IFIC, CSIC University of Valencia, Valencia, Spain.
    de Angelis, G.
    Instituto Nazionael di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro, Italy.
    Atac Nyberg, Ayse
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bhattacharyya, S.
    Grand Accélérateur National d´lons Lourds, Cean Cedex, France.
    Brock, T.
    Department of Physics, University of York, York, UK.
    Brown, J. R.
    Department of Physics, University of York, York, UK.
    Davies, P.
    Department of Physics, University of York, York, UK.
    Di Nitto, A.
    Dipartimento di Scienze Fisiche, Universitá di Napoli and Instituto Nazionale di Fisica Nucleare, Napoli, Italy.
    Dombrádi, Zs.
    Institute of Nuclear Research of the Hungarian Academy of Science, Debrecen, Hungary.
    Gadea, A.
    IFIC, CSIC, University of Valencia, Valencia, Spain.
    Gál, J.
    Institute of Nuclear Research of the Hungarian Academy of Science, Debrecen, Hungary.
    Hadinia, Baharak
    KTH, School of Engineering Sciences (SCI), Physics.
    Johnston-Theasby, F.
    Department of Physics, University of York, York, UK.
    Joshi, P.
    Department of Physics, University of York, York, UK.
    Juhász, K.
    Department of Information Technology, Universty of Debrecen, Debrecen, Hungary.
    Julin, R.
    Department of Physics, University of Jyväskylä, Jyväskylä, Finland.
    Jungclaus, A.
    Instituto de Estructura de la Materia, Madrid, Spain .
    Kalinka, G.
    Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary.
    Kara, S. O.
    Department of Physics, Ankara University, Tandogan Ankarar, Turkey.
    Khaplanov, Anton
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Kownacki, J.
    Heavy Ion Laboratory, Universty of Warsaw, Warsaw, Poland.
    La Rana, G.
    Dipartimento di Scienze Fisiche, Universitá di Napoli and Instituto Nazionale di Fisica Nucleare, Napoli, Italy.
    Lenzi, S. M.
    Dipartimento di Fisica dell'Universitá di Padova and Instituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova, Italy.
    Molnár, J.
    Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary.
    Moro, R.
    Dipartimento di Scienze Fisiche, Universitá di Napoli and Instituto Nazionale di Fisica Nucleare, Napoli, Italy.
    Napoli, D. R.
    Instituto Nazionale di Fisica Nucleare, Laboratori Natzionali di Legnaro, Legnaro, Italy.
    Nara Singh, B. S.
    Department of Physics, University of York, York, UK.
    Persson, Andreas
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Recchia, F.
    Dipartimento di Fisica dell'Universitá di Padova and Instituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova, Italy.
    Sandzelius, Mikael
    KTH, School of Engineering Sciences (SCI), Physics.
    Scheurer, J. -N
    Université Bordeaux, Centre d'Etudes Nucléaires de Bordeaux Gradignan, Gradignan, France.
    Sletten, G.
    The Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
    Sohler, D.
    Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary.
    Söderström, P. -A
    Department of Physics and Astromony, Uppsala University, Uppsala, Sweden.
    Taylor, M. J.
    Department of Physics, University of York, York, UK.
    Timár, J.
    Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary.
    Valiente-Dobón, J. J.
    instituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro, Italy.
    Vardaci, E.
    Dipartimento di Scienze Fisiche, Universitá di Napoli and Instituto Nazionale di Fisica Nucleare, Napoli, Italy.
    Williams, S.
    TRIUMF, Vancouver, British Columbia, Canada.
    Evidence for a spin-aligned neutron-proton paired phase from the level structure of 92Pd2011In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 469, no 7328, p. 68-71Article in journal (Refereed)
    Abstract [en]

    Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work(1) that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing(2-6), in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus Pd-92. Gamma rays emitted following the Ni-58(Ar-36,2n)Pd-92 fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution c-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction(2-6). We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling(7,8)) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.

  • 35. Liu, X.
    et al.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics.
    Wyss, Ramon Alexander
    KTH, School of Engineering Sciences (SCI), Physics.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ertoprak, Aysegul
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhang, Wei
    KTH, School of Engineering Sciences (SCI), Physics.
    Nyberg, Ayse
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. Royal Inst Technol, Dept Phys, S-10405 Stockholm, Sweden..
    Back, Tove
    KTH, School of Engineering Sciences (SCI), Physics.
    Zielinska, M.
    Univ Paris Saclay, CEA, Itfu, F-91191 Gif Sur Yvette, France..
    Evidence for enhanced neutron-proton correlations from the level structure of the N = Z+1 nucleus Tc-87(43)442021In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 104, no 2, article id L021302Article in journal (Refereed)
    Abstract [en]

    The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.

  • 36.
    Liu, Xiaoyu
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon Alexander
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ertoprak, Aysegul
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhang, Wei
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Clement, E.
    de France, G.
    Ralet, D.
    Gadea, A.
    Goasduff, A.
    Jaworski, G.
    Kuti, I.
    Nyako, B. M.
    Nyberg, J.
    Palacz, M.
    Wadsworth, R.
    Valiente-Dobon, J. J.
    Al-Azri, H.
    Nyberg, Ayse
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    de Angelis, G.
    Doncel, M.
    Dudouet, J.
    Gottardo, A.
    Jurado, M.
    Ljungvall, J.
    Mengoni, D.
    Napoli, D. R.
    Petrache, C. M.
    Sohler, D.
    Timar, J.
    Barrientos, D.
    Bednarczyk, P.
    Benzoni, G.
    Birkenbach, B.
    Boston, A. J.
    Boston, H. C.
    Burrows, I.
    Charles, L.
    Ciemala, M.
    Crespi, F. C. L.
    Cullen, D. M.
    Desesquelles, P.
    Domingo-Pardo, C.
    Eberth, J.
    Erduran, N.
    Erturk, S.
    Gonzalez, V.
    Goupil, J.
    Hess, H.
    Huyuk, T.
    Jungclaus, A.
    Korten, W.
    Lemasson, A.
    Leoni, S.
    Maj, A.
    Menegazzo, R.
    Million, B.
    Perez-Vidal, R. M.
    Podolyak, Zs.
    Pullia, A.
    Recchia, F.
    Reiter, P.
    Saillant, F.
    Salsac, M. D.
    Sanchis, E.
    Simpson, J.
    Stezowski, O.
    Theisen, C.
    Zieliska, M.
    Evidence for enhanced neutron-proton correlations from the level structure of theN = Z + 1 nucleus 87TcIn: PHYSICAL REVIEW CArticle in journal (Other academic)
    Abstract [en]

    The low-lying excited states in the neutron-deficient N = Z + 1 nucleus 8743 Tc 44 have been studiedvia the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at the Grand Accélérateur National d’IonsLourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliaryNEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ-rays, neutrons, and charged particles emitted in the reaction. A level scheme of 87 Tc from the (9/2 +g.s. ) state to the (33/2 +)statewasestablishedbasedon6mutuallycoincidentγ-ray transitions. The con-1structed level structure exhibits a rotational behavior with a sharp back bending at ~ω ≈ 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.

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    fulltext
  • 37.
    Ertoprak, Aysegul
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. Department of Physics, Faculty of Science, Istanbul University, Vezneciler/Fatih, 34134, Istanbul, Turkey.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Doncel, Maria
    KTH, School of Engineering Sciences (SCI), Physics.
    Hadinia, Baharak
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Sandzelius, M.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Scholey, C.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Andgren, Karin
    KTH, School of Engineering Sciences (SCI), Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Badran, H.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Braunroth, T.
    Institut fur Kernfhysik, Universität zu Köln, 50937 Cologne, Germany.
    Calverley, T.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland., Department of Physics, Oliver Lodge Laboratory, Univeristy of Liverpool, Liverpool L69 7ZE, United Kingdom .
    Cox, D. M.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Cullen, D. M.
    Schuster Building, School of Physics and Astronomy, the University of Manchester, Manchester M13 9PL, United Kingdom.
    Fang, Y. D.
    Research Center for Nuclear Physics, Osaka University, Osaka 567-0047, Japan .
    Ganioglu, E.
    Department of Physics, Faculty of Science, Istanbul University, Vezneciler Fatih, 34134 Istanbul, Turkey.
    Giles, M.
    Schuster Building, School of Physics and Astronomy, the University of Manchester, Manchester M13 9PL, United Kingdom.
    Gomez-Hornillos, M.B.
    STFC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, United Kingdom.
    Grahn, T.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Greenlees, P. T.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Hilton, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland., Department of Physics, Oliver Lodge Laboratory, Univeristy of Liverpool, Liverpool L69 7ZE, United Kingdom .
    Hodge, D.
    Schuster Building, School of Physics and Astronomy, the University of Manchester, Manchester M13 9PL, United Kingdom.
    Ideguchi, E.
    Research Center for Nuclear Physics, Osaka University, Osaka 567-0047, Japan .
    Jakobsson, U.
    Department of Chemistry, University of Helsinki, P.O. Box 3, 00014, Helsinki, Finland.
    Johnson, Arne
    KTH, School of Engineering Sciences (SCI), Physics.
    Jones, P.M.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Julin, R.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Juutinen, S.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Ketelhut, S.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Khaplanov, Anton
    KTH, School of Engineering Sciences (SCI), Physics.
    Kumar Raju, M.
    Research Center for Nuclear Physics, Osaka University, Osaka 567-0047, Japan .
    Leino, M.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Li, H.
    KTH, School of Engineering Sciences (SCI), Physics.
    Liu, H.
    KTH, School of Engineering Sciences (SCI), Physics.
    Matta, Sanya
    KTH, School of Engineering Sciences (SCI), Physics.
    Modamio, V.
    Department of Physics, University of Oslo, 0316 Oslo Norway.
    Nara Singh, B. S.
    Schuster Building, School of Physics and Astronomy, the University of Manchester, Manchester M13 9PL, United Kingdom.
    Niikura, M.
    CNS, University of Tokyo, Wako 351-0198, Japan.
    Nyman, M.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Özgur, I.
    Department of Physics, Faculty of Science, Istanbul University, Vezneciler Fatih, 34134 Istanbul, Turkey.
    Page, R. D.
    Department of Physics, Oliver Lodge Laboratory, Univeristy of Liverpool, Liverpool L69 7ZE, United Kingdom.
    Pakarinen, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Papadakis, P.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland., STFC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, United Kingdom.
    Partanen, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Paul, E. S.
    Department of Physics, Oliver Lodge Laboratory, Univeristy of Liverpool, Liverpool L69 7ZE, United Kingdom.
    Petrache, C. M.
    Univ Paris Saclay, CNRS IN2P3, Ctr Sci Nucl & Sci Mat, F-91405 Orsay, France..
    Peura, P.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Rahkila, P.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Ruotsalainen, P.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Saren, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Sorri, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Stolze, S.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Subramaniam, Pranav
    KTH, School of Engineering Sciences (SCI), Physics.
    Taylor, M. J.
    Division of Cancer Sciences, School of Medical Sciences, the University of Manchester, Manchester, M13 9PL, United Kingdom.
    Uusitalo, J.
    Univ Jyvaskyla, Dept Phys, FI-40014 Jyvaskyla, Finland..
    Valiente-Dobon, J. J.
    Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, 35020 Legnaro, Italy.
    Wyss, Ramon Alexander
    KTH, School of Engineering Sciences (SCI), Physics.
    Evidence for octupole collectivity in 172Pt2020In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 56, no 2, article id 65Article in journal (Refereed)
    Abstract [en]

    Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of  ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing direct evidence for octupole collectivity in 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3- state as a collective octupole-vibrational state.

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    Ertoprak2020_Article_EvidenceForOctupoleCollectivity
  • 38.
    Liu, Xiaoyu
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ertoprak, Aysegul
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhang, Wei
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Clement, E.
    de France, G.
    Ralet, D.
    Gadea, A.
    Goasduff, A.
    Jaworski, G.
    Kuti, I.
    Nyako, B. M.
    Nyberg, J.
    Palacz, M.
    Wadsworth, R.
    Valiente-Doblon, J. J.
    Al-Azri, H.
    Nyberg, Ayse
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    de Angelis, G.
    Doncel, M.
    Dudouet, J.
    Gottardo, A.
    Jurado, M.
    Ljungvall, J.
    Mengoni, D.
    Napoli, D. R.
    Petrache, C. M.
    Sohler, D.
    Timar, J.
    Barrientos, D.
    Bednarczyk, P.
    Benzoni, G.
    Boston, A. J.
    Boston, H. C.
    Burrows, I.
    Charles, L.
    Ciemala, M.
    Crespi, F. C. L.
    Cullen, D. M.
    Desesquelles, P.
    Domingo-Pardo, C.
    Eberth, J.
    Erduran, N.
    Erturk, S.
    Gonzalez, V.
    Goupil, J.
    Hess, H.
    Huyuk, T.
    Jungclaus, A.
    Korten, W.
    Lemasson, A.
    Leoni, S.
    Maj, A.
    Menegazzo, R.
    Million, B.
    Perez-Vidal, R. M.
    Podolyak, Zs.
    Pullia, A.
    Recchia, F.
    Reiter, P.
    Saillant, F.
    Salsac, M. D.
    Sanchis, E.
    Simpson, J.
    Stezowski, O.
    Theisen, C.
    Zielinska, M.
    Evidence for Spherical-Oblate Shape Coexistence in 87TcIn: THE EUROPEAN PHYSICAL JOURNAL AArticle in journal (Other academic)
    Abstract [en]

    Excited states in the neutron-deficient nucleus 87 Tc have been studied via the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at 115 MeV beam energy. The AGATA γ-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of γ rays and light particles. Six transitions from the de-excitation of excited states belonging to a new band in 87 Tc were identified by comparing γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87 Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band

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    fulltext
  • 39.
    Liu, Xiaoyu
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China; University of Chinese Academy of Sciences, Beijing, China.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon Alexander
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aktas, Özge
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Ertoprak, Aysegul
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. Istanbul Univ, Fac Sci, Dept Phys, TR-34134 Istanbul, Turkey..
    Zhang, Wei
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Nyberg, Ayse Ataç
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bäck, Torbjörn
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zielinska, M.
    Univ Paris Saclay, CEA, IRFU, F-91191 Gif Sur Yvette, France..
    et al.,
    Evidence for spherical-oblate shape coexistence in Tc-872022In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 106, no 3, article id 034304Article in journal (Refereed)
    Abstract [en]

    Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.

  • 40.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Chen, T.
    Exact solution of the pairing problem for spherical and deformed systems2015In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 92, no 5Article in journal (Refereed)
    Abstract [en]

    There has been increasing interest in studying the Richardson model from which one can derive the exact solution for certain pairing Hamiltonians. However, it is still a numerical challenge to solve the nonlinear equations involved. In this paper we tackle this problem by employing a simple hybrid polynomial approach. The method is found to be robust and is valid for both deformed and nearly spherical nuclei. It also provides important and convenient initial guesses for spherical systems with large degeneracy. As an example, we apply the method to study the shape coexistence in neutron-rich Ni isotopes.

  • 41.
    Liu, Xiaoyu
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Experimental Studies of the Neutron Deficient Atomic Nuclei 88Ru and 87Tc, and the Diagonalization of the General Pairing Hamiltonian2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This doctoral thesis consists of two parts: the experimental study of the neutron-deficient atomic nuclei 88Ru and 87Tc, and the computational study on the diagonalization of general pairing Hamiltonian. In the first part, which constitutes the main content of the thesis, the low-lying excited states in the N = Z nucleus 88Ru and N = Z + 1 nucleus 87Tc were studied via fusion-evaporation reactions induced by 115 MeV 36 Ar ions bombarding6 mg/cm 2 thick metallic 54 Fe target foils at the Grand Accélérateur Nationald’Ions Lourds (GANIL), Caen, France. The prompt γγ-neutron and charged-particle coincidences from the de-excitation of the reactions were measured by the AGATA γ-ray spectrometer coupled to the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays. The results for 88 Ru confirmed and extended the previous level scheme to a tentative (14+) state. The constructed level structure exhibits a moderately deformed rotational behavior but shows a band crossing at a significantly higher rotational frequency compared with neighboring nuclei with N > Z. Such band crossings are associated with quasiparticle alignment within the standard isovector pairing scheme. The observation of a “delayed” rotation alignment in the deformed N = Znucleus is consistent with theoretical predictions related to the existence of strong isoscalar neutron-proton pair condensate. The yrast band in 87 Tc from the (9/2+) state to the (33/2+) state was established based on six mutually coincident γ-ray transitions. The constructed yrast band exhibits a sharp backbending at ~ω ≈ 0.50 MeV. In the odd-A isotonic chains around N = 44, approaching the N = Z line, the observed decrease in alignment frequency and increase in alignment sharpness were proposed as an effect of the enhanced isoscalar neutron-proton interactions. In addition to the yrast band in 87 Tc, six new mutually coincident γ-ray transitions were identified by comparing the γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level scheme was compared with shell model and TRS calculations. The results indicate that these low-lying states exhibit spherical behavior different from the previously identified oblate yrast band, and the band might be built on a (7/2 +1 ) ground state.

    In the second part, an OpenMP parallel Fortran program, PairDiag, for the diagonalization of the general pairing Hamiltonian in deformed systems was developed. In the program, the ‘01’ inversion algorithm is used to generate the seniority-zero basis vectors; all the non-zero Hamiltonian matrix elements are evaluated “on the fly” by the scattering operators and a search algorithm; the matrix diagonalization is achieved by the Lanczos + QR algorithm. The PairDiag program is packaged in a Fortran module and can be easily used to replace the BCS approximation in other nuclear structure programs.

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    fulltext
  • 42.
    Zhang, Zhaozhan
    et al.
    Sun Yat sen Univ, Sino French Inst Nucl Engineenng & Technol, Zhuhai 519082, Guangdong, Peoples R China.;Univ Tokyo, Grad Sch Sci, Dept Phys, Tokyo 1130033, Japan.;Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Peoples R China..
    Yuan, Cenxi
    Sun Yat sen Univ, Sino French Inst Nucl Engineenng & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cai, Boshuai
    Sun Yat sen Univ, Sino French Inst Nucl Engineenng & Technol, Zhuhai 519082, Guangdong, Peoples R China..
    Xu, Xinxing
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China.;Adv Energy Sci & Technol Guangdong Lab, Huizhou 516003, Peoples R China..
    Extended R-matrix description of two-proton radioactivity2023In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 838, p. 137740-, article id 137740Article in journal (Refereed)
    Abstract [en]

    Two-proton (2p) radioactivity provides fundamental knowledge on the three-body decay mechanism and the residual nuclear interaction. In this work, we propose decay width formulae in the extended R-matrix framework for different decay mechanisms, including sequential 2p decay, diproton decay, tri-body decay, and sequential two-diproton decay. The diproton and tri-body formulae, combined with information on the two-nucleon transfer amplitude and Wigner single-particle reduced width, can reproduce well experimental 2p radioactivity half-lives. For the case of 67Kr, theoretical predictions for direct 2p decay give much larger half-lives than the recent measurement from RIKEN. A combination of direct and sequential 2p emission is analyzed by considering a small negative one-proton separation energy and a possible enhanced contribution from the p-wave component. The present method predicts that 71Sr and 74Zr may be the most promising candidates for future study on 2p radioactivity. Our model gives an upper limit of 55(4) keV for the decay width of 4p emission in recently found four-proton resonant nuclide, 18Mg, which agrees with the observed width of 115(100) keV.

  • 43.
    Soylu, Asim
    et al.
    Nigde Omer Halisdemir Univ, Dept Phys, TR-51240 Nigde, Turkey..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Extended universal decay law formula for the alpha and cluster decays2021In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 1013, article id 122221Article in journal (Refereed)
    Abstract [en]

    The Universal Decay Law (UDL) formula for the alpha and cluster decays is extended to include the effects of the angular momentum and isospin. The parameters for all formulas are obtained by fitting to available experimental data. We also evaluated the uncertainty of the parameters as well as the uncertainties of predictions of the formulas. The rms values are computed and the best rms among them is obtained for the formula including both the angular momentum and isospin terms. The modified UDL formula is applied to get the half-lives of cluster and alpha decays of nuclei. Branching ratios (alpha/cluster) are calculated and compared with experimental ones. The half-lives for heavier cluster decays are obtained by using UDL and new UDL formulas.

  • 44.
    Zhang, M. M.
    et al.
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Peoples R China..
    Wang, Y. S.
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China.;Lanzhou Univ, Sch Nucl Sci & Technol, Lanzhou 730000, Peoples R China..
    Zhang, Z. Y.
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhou, S. G.
    Chinese Acad Sci, Inst Theoret Phys, CAS Key Lab Theoret Phys, Beijing 100190, Peoples R China.;Natl Lab Heavy Ion Accelerator, Ctr Theoret Nucl Phys, Lanzhou 730000, Peoples R China..
    Fine structure in the a decay of the 8(+) isomer in U-216,U-2182022In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 106, no 2, article id 024305Article in journal (Refereed)
    Abstract [en]

    The extremely neutron-deficient even-even uranium isotopes( 216,218)U were produced in the complete-fusion reactions induced by impinging Ar-40 and Ca-40 ions on W-180,W-182,W-184 targets. Fusion evaporation residues were separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure) and subsequently identified using the recoil-alpha-correlation method. The improved ground-state to ground-state alpha-decay properties of( 216,218)U were reported in [Z. Y. Zhang et al., Phys. Rev. Lett. 126, 152502 (2021)]. In this paper, we report on new alpha-decay activities with E-alpha = 10 163(27) keV for 216U and E-alpha = 10 073(16) keV for 218U, which decay from the 8(+) isomeric states of( 216,218)U into the 2(+) states of their daughter nuclei Th-212,Th-214, respectively. The new results extend the systematics of the alpha-decay fine structure for the N = 124 and 126 even-even isotones.

  • 45.
    Sun, M. D.
    et al.
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Gansu, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China.;Lanzhou Univ, Lanzhou 730000, Gansu, Peoples R China..
    Liu, Z.
    Chinese Acad Sci, Inst Modern Phys, CAS Key Lab High Precis Nucl Spect, Lanzhou 730000, Gansu, Peoples R China.;Univ Chinese Acad Sci, Sch Nucl Sci & Technol, Beijing 100049, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Zhang, F. S.
    Beijing Normal Univ, Coll Nucl Sci & Technol, Key Lab Beam Technol & Mat Modificat, Minist Educ, Beijing 100875, Peoples R China.;Beijing Radiat Ctr, Beijing 100875, Peoples R China..
    et al.,
    Fine structure in the alpha decay of U-2232020In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 800, article id 135096Article in journal (Refereed)
    Abstract [en]

    Fine structure in the alpha decay of U-223 was observed in the fusion-evaporation reaction Re-187(Ar-40, p3n) by using fast digital pulse processing technique. Two alpha-decay branches of U-223 feeding the ground state and 244 keV excited state of Th-219 were identified by establishing the decay chain U-223 (alpha(1)) under right arrow Th-219 (alpha(2)) under right arrow Ra-215 (alpha(3)) under right arrow Rn-211. The alpha-particle energy for the ground-state to ground-state transition of U-223 was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62(-10)(+14) mu s. Evolution of nuclear structure for N = 131 even-Z isotones from Po to U was discussed in the frameworks of nuclear mass and reduced alpha-decay width, a weakening octupole deformation in the ground state of U-223 relative to its lighter isotones Ra-219 and Th-221 was suggested.

  • 46.
    Ekelund, Emil
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems.
    Fogelberg Skoglösa, David
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems.
    Geant4 Simulations of Hadron Therapy and Refinement of User Interface2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Radiotherapy is one of the most used methods for treating cancer and the most common way to execute such treatments is to irradiate tumors with high energy photons. This can damage healthy tissue along the irradiation line. By using hadron therapy and instead irradiate the tumor with charged particles (protons or Carbon 12 ions), the energy can be concentrated to a more specific place in the body. However, the method is not well studied and the tools available for simulating hadron therapy can be hard to use.

    When simulating hadron therapy and other nuclear interactions a large amount of calculations need to be executed. Monte Carlo methods is a numerical method to solve equations based on repeated number sampling and is used in the simulation program Geant4. Hadron therapy was simulated with Geant4 and the data was analyzed with the data analysis framework ROOT. New macros and analysis scripts were created with the intention to help new Geant4 users. The aim to make Geant4 easier to use was partially met. The implementation of code for the low energy region of Carbon 12 projectiles was unsuccessful.

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  • 47.
    Qi, Chong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Generalization of the Geiger-Nuttall law and alpha clustering in heavy nuclei2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 381, p. 012131-Article in journal (Refereed)
    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.

  • 48. Jia, L. Y.
    et al.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Generalized-seniority pattern and thermal properties in even Sn isotopes2016In: PHYSICAL REVIEW C, ISSN 2469-9985, Vol. 94, no 4, article id 044312Article in journal (Refereed)
    Abstract [en]

    Even tin isotopes of mass number A = 108-124 are calculated with realistic interactions in the generalized-seniority approximation of the nuclear shell model. For each nucleus, we compute the lowest 10 000 states (5000 of each parity) up to around 8 MeV in excitation energy, by allowing as many as four broken pairs. The lowest 50 eigen energies of each parity are compared with the exact results of the large-scale shell-model calculation. The wave functions of the midshell nuclei show a clear pattern of the stepwise breakup of condensed coherent pairs with increasing excitation energy. We also compute in the canonical ensemble the thermal properties-level density, entropy, and specific heat-in relation to the thermal pairing phase transition.

  • 49.
    Wu, Zhe-Ying
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liu, Hong-Liang
    Global calculations of microscopic energies and nuclear deformations: Isospin dependence of the spin-orbit coupling2015In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 92, no 2, article id 024306Article in journal (Refereed)
    Abstract [en]

    Background: The deviation between different model calculations that may occur when one goes toward regions where the masses are unknown is getting increased attention. This is related to the uncertainties of the different models which may have not been fully understood. Purpose: To explore in detail the effect of the isospin dependence of the spin-orbital force in the Woods-Saxon potential on global binding energy and deformation calculations. Method: The microscopic energies and nuclear deformations of about 1850 even-even nuclei are calculated systematically within the macroscopic-microscopic framework using three Woods-Saxon parametrizations, with different isospin dependencies, which were constructed mainly for nuclear spectroscopy calculations. Calculations are performed in the deformation space (beta(2), gamma, beta(4)). Both the monopole and doubly stretched quadrupole interactions are considered for the pairing channel. Results: The ground-state deformations obtained by the three calculations are quite similar to each other. Large differences are seen mainly in neutron-rich nuclei and in superheavy nuclei. Systematic calculations on the shape-coexisting second minima are also presented. As for the microscopic energies of the ground states, the results are also very close to each other. Only in a few cases the difference is larger than 2 MeV. The total binding energy is estimated by adding the macroscopic energy provided by the usual liquid drop model with its parameters fitted through the least square root and minimax criteria. Calculations are also compared with the results of other macroscopic-microscopic mass models. Conclusions: All the three calculations give similar values for the deformations, microscopic energies, and binding energies of most nuclei. One may expect to have a better understanding of the isospin dependence of the spin-orbital force with more data on proton- and neutron-rich nuclei.

  • 50. Huang, Y.
    et al.
    Xiao, Z. G.
    Zhu, S. J.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Xu, Q.
    Cheng, W. J.
    Li, H. J.
    Lyu, L. M.
    Wang, R. S.
    Yan, W. H.
    Yi, H.
    Zhang, Y.
    Chen, Q. M.
    He, C. Y.
    Hu, S. P.
    Li, C. B.
    Li, H. W.
    Luo, P. W.
    Wu, X. G.
    Wu, Y. H.
    Zheng, Y.
    Zhong, J.
    High-spin structures in the Xe-129 nucleus2016In: Physical Review C, ISSN 2469-9985, Vol. 93, no 6, article id 064315Article in journal (Refereed)
    Abstract [en]

    High-spin states in the Xe-129 nucleus are studied with the reaction Sn-124(Be-9,4n) at a beam energy of 36 MeV. The level scheme is extended significantly. For the positive-parity band, the alpha = +1/2 and the alpha = -1/2 signature components are combined to form a complete band structure based on the 3/2(+) state with spin and parity up to 21/2(+). For the negative-parity band based on the 11/2(-) state, the alpha = +1/2 signature component is newly established and both the alpha = +1/2 and the alpha = -1/2 signature components also form a complete band structure up to the 35/2(-) state. The positive-and negative-parity bands are proposed to originate from nu d(3/2) 3/2(+)[402] and nu h(11/2)11/2(-)[505] Nilsson configurations, respectively. A backbending is observed in the negative-parity band, which originates from the alignments of two h(11/2) protons according to crank shell model calculations. Based on the total Routhian surface and quasiparticle triaxial rotor model calculations, the negative-parity band is interpreted as a triaxially deformed shape with gamma approximate to -30 degrees, while the positive-parity band is associated with. softness, in accordance with previous studies. In the high-spin states, three decoupled bands and one oblate band with gamma approximate to -60 degrees are newly identified. The systematics and other characteristics of these bands are discussed.

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