| 1. |
- Kristan, Matej, et al.
(author)
-
The Sixth Visual Object Tracking VOT2018 Challenge Results
- 2019
-
In: Computer Vision – ECCV 2018 Workshops. - Cham : Springer Publishing Company. - 9783030110086 - 9783030110093 ; , s. 3-53
-
Conference paper (peer-reviewed)abstract
- The Visual Object Tracking challenge VOT2018 is the sixth annual tracker benchmarking activity organized by the VOT initiative. Results of over eighty trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis and a “real-time” experiment simulating a situation where a tracker processes images as if provided by a continuously running sensor. A long-term tracking subchallenge has been introduced to the set of standard VOT sub-challenges. The new subchallenge focuses on long-term tracking properties, namely coping with target disappearance and reappearance. A new dataset has been compiled and a performance evaluation methodology that focuses on long-term tracking capabilities has been adopted. The VOT toolkit has been updated to support both standard short-term and the new long-term tracking subchallenges. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website (http://votchallenge.net).
|
|
| 2. |
- Kristanl, Matej, et al.
(author)
-
The Seventh Visual Object Tracking VOT2019 Challenge Results
- 2019
-
In: 2019 IEEE/CVF INTERNATIONAL CONFERENCE ON COMPUTER VISION WORKSHOPS (ICCVW). - : IEEE COMPUTER SOC. - 9781728150239 ; , s. 2206-2241
-
Conference paper (peer-reviewed)abstract
- The Visual Object Tracking challenge VOT2019 is the seventh annual tracker benchmarking activity organized by the VOT initiative. Results of 81 trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis as well as the standard VOT methodology for long-term tracking analysis. The VOT2019 challenge was composed of five challenges focusing on different tracking domains: (i) VOT-ST2019 challenge focused on short-term tracking in RGB, (ii) VOT-RT2019 challenge focused on "real-time" short-term tracking in RGB, (iii) VOT-LT2019 focused on long-term tracking namely coping with target disappearance and reappearance. Two new challenges have been introduced: (iv) VOT-RGBT2019 challenge focused on short-term tracking in RGB and thermal imagery and (v) VOT-RGBD2019 challenge focused on long-term tracking in RGB and depth imagery. The VOT-ST2019, VOT-RT2019 and VOT-LT2019 datasets were refreshed while new datasets were introduced for VOT-RGBT2019 and VOT-RGBD2019. The VOT toolkit has been updated to support both standard short-term, long-term tracking and tracking with multi-channel imagery. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website(1).
|
|
| 3. |
- Le Yang, Gao, et al.
(author)
-
Neutron-proton interaction in odd-odd nuclei from statistical analysis
- 2022
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 106:2
-
Journal article (peer-reviewed)abstract
- The statistical distribution and correlation relationship of the empirical neutron-proton (np) interaction are analyzed, whereby the interaction strengths are extracted from the binding energies using a known four-point formula. By comparing the correlations of the data and those from numerical simulations of the random number method, it is shown that an additional attractive np interaction persists between the last proton and last neutron in odd-odd nuclei. It provides evidence of the residual np interaction from statistical analysis. The adopted new analytical method might be a useful way to clarify the inherent correlation.
|
|
| 4. |
- Xu, Q., et al.
(author)
-
Investigation of high spin states in Cs-133
- 2018
-
In: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 54:5
-
Journal article (peer-reviewed)abstract
- High spin states in Cs-133 nucleus have been studied with the reaction Te-130 (Li-7, 4n) at a beam energy of 38 MeV. The level scheme has been expanded with spin up to 31/2 (h) over bar. Compared with a recent paper, ground state band and other two collective band structures at lower spin states have been confirmed. Another collective band structure at higher spin states as well as some levels and transitions are updated. Compared with the experimental data, large-scale shell model and tilted axis cranking model calculations have been carried out. The results show that the band-head configuration of yrast band based on 7/2(+) ground state and the side band built on the 5/2(+) state are a pair of pseudospin partner states with pi (f) over tilde 7/2,5/2. The negative parity band based on 1071.5 keV level originates from pi h(11/2) orbital. Another band built on 2642.9 keV level at high spin states has been proposed with oblate deformation. Other characteristics for these bands were also discussed.
|
|
| 5. |
- Ahlgren Cederlöf, Ebba, et al.
(author)
-
Lifetime measurement of the yrast 2+ state in 118Te
- 2023
-
In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:12
-
Journal article (peer-reviewed)abstract
- The electromagnetic transition probabilities of the yrast 2+ states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118Te and the missing data for 116Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast 2+ state in 118Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is τ2+ = 7.46(19) ps. In addition, the lifetime of the 4+ state was measured to be τ4+ = 4.25(23) ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations. The trend of the B(E2; 0+ → 2+) values in the midshell area is in good agreement with the calculations and the calculated B4/2 ratio provide evidence for 118Te as a near perfect harmonic vibrator.
|
|
| 6. |
- Ahmed, I., et al.
(author)
-
Shell-model studies relevant for the low-energy Coulomb excitation in Zn isotopes
- 2023
-
In: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 59:12
-
Journal article (peer-reviewed)abstract
- The low-lying nuclear structure of even-even Zn isotopes ranging from 62 Zn to 70 Zn has been comprehensively examined through large scale shell model calculations. These calculations encompassed the f 5 / 2p 3 / 2 , 1 / 2g 9 / 2 (fpg) model space without any truncation, employing 56 Ni as an inert core. Two different effective interactions, JUN45 and jj44b, were utilized in these calculations. Various critical observables, including excitation energies, reduced transition strengths, and electric quadrupole moments, were computed and then evaluated in the context of existing experimental data. The configurations of the resulting wave functions were also thoroughly analyzed. Furthermore, occupation probabilities for distinct single-particle orbitals were determined, with particular attention given to the pivotal role of the g 9 / 2 orbital in elucidating the nuclear structure of heavy Zn isotopes. Additionally, rotational invariants were calculated for the ground state, shedding light on a prolate deformation in 62 Zn and 64 Zn, while suggesting moderate prolate-triaxial excitations in 66 Zn, 68 Zn, and 70 Zn. These findings hold significant relevance for interpreting the intriguing outcomes of sub-barrier Coulomb excitation experiments, offering invaluable insights into the static electromagnetic properties of the nucleus through a model-independent approach.
|
|
| 7. |
- Aktas, Özge, et al.
(author)
-
Single-particle structures in 85,87Ge
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X.
-
Journal article (peer-reviewed)abstract
- Gamma-ray transitions have been identified for the first time in the extremely neutron-rich (N =Z + 25) nucleus 87 Ge following nucleon knockout reactions studied at the RIBF, RIKEN, Japan.New γ-ray transitions from excited states in 85 Ge were also observed and placed in a tentative levelscheme. The exclusive parallel momentum distribution was measured for the 1/2 + state for theneutron knockout reaction leading to 85 Ge which is compared with calculated distorted wave impulseapproximation (DWIA) distributions. The 85,87 Ge results are compared with large-scale shell-modelcalculations and potential energy surface calculations based on the total Routhian surface formalism.
|
|
| 8. |
- Amaro, Mário B., et al.
(author)
-
Multilinear analysis of the systematics of proton radioactivity
- 2023
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 108:5
-
Journal article (peer-reviewed)abstract
- It is shown that the proton formation probabilities, extracted from experimental decay half-lives, can be well reproduced by a simple multilinear formula with only three parameters. The parameters obtained by considering the standard root mean square deviation and the mini-max criteria are very similar to each other. In addition, we applied Bayesian analysis to study the uncertainties of the parameters and the model predictions. In this way we explain the systematics of proton decay half-lives. The multilinearity of the model also provides a way to classify the relative hindrance of different proton decays. All the recent experimental data agree very well with the model prediction. Our Bayesian analysis suggests that those new data do help constrain the uncertainty of the model parameters.
|
|
| 9. |
- Cai, Boshuai, et al.
(author)
-
alpha decay half-life estimation and uncertainty analysis
- 2020
-
In: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 101:5
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 10. |
- Cederwall, Bo, 1964-, et al.
(author)
-
Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru 88
- 2020
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 124:6
-
Journal article (peer-reviewed)abstract
- The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
|
|
| 11. |
- Cederwall, Bo, 1964-, et al.
(author)
-
Lifetime Measurements of Excited States in Pt-172 and the Variation of Quadrupole Transition Strength with Angular Momentum
- 2018
-
In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 121:2
-
Journal article (peer-reviewed)abstract
- Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N approximate to 90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
|
|
| 12. |
- Changizi, Sara A., 1982-
(author)
-
Pairing correlation in atomic nuclei under extreme conditions
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- The pairing correlation has long been recognized as the dominant many-body correlation beyond the nuclear mean field. Pairing plays an essential role in many nuclear phenomena including the occurrence of a systematic odd-even staggering (OES) of the nuclear binding energy. Pairing interaction plays, in particular, a significant role in the stability of weakly bound nuclei. Therefore it has been one of the most critical topics in nuclear physics because of the weakly bound structure of all newly discovered nuclei. Beyond the line of stability, pairing interaction is not a residual interaction anymore. Its strength can be of the same order of magnitude as the mean field. In this thesis we have focused on the pairing interaction in atomic nuclei under extreme conditions to investigate the structure of loosely bound nuclei near the dripline; to probe and globally assess different outcomes of various zero-range pairing interactions and their effect on the loosely bound low angular momentum states. How much can density-dependence in zero-range pairing interaction nuclei affect the line of stability? Calculations predict that pure density-dependent pairing interaction so-called surface interaction enhances the collectivity and gives stronger neutron pairing gap in nuclei far from stability, while, the density dependence pairing interaction does not affect the gap for bound nuclei as much. The odd-even staggering of nuclear binding energies has been investigated to estimate the empirical pairing gap. A 3-point formula Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) is advocated in this thesis, which we believe it is more suitable to measure the magnitude of pairing gap in even-even nuclei. The strength of Δ(3)C can be a good indicator of the two-particle spatial correlation. One-quasiparticle energies and binding energy for those odd nuclei, which can be approximated by spherical symmetry, are calculated to obtain binding energy odd-even staggering (OES) in all known semi-magic even-even nuclei. The pairing strength is fitted globally to all available data on the OES of semi-magic nuclei with Z ≥ 8. The difference between different zero-range density-dependent pairing interactions reduces with this global fitted parameter. The difference between the mean pairing gap and the OES gets larger as we get closer to the dripline. At the end of the thesis, a simple model has been developed which shows that when the mean-field becomes shallower the odd-even staggering of charge radii is reduced.This thesis covers results that are not included in the three published papers and some complementary works on the subject.
|
|
| 13. |
- Das, Biswarup, et al.
(author)
-
Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh 95
- 2024
-
In: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 6:2
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 14. |
- Das, B., et al.
(author)
-
Nature of seniority symmetry breaking in the semimagic nucleus Ru-94
- 2022
-
In: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 105:3
-
Journal article (peer-reviewed)abstract
- Direct lifetime measurements via gamma -gamma coincidences using a fast timing detector array consisting of LaBr3(Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N = 50) nucleus Ru-94. The experiment was carried out as the first in a series of "FAIR-0" experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru-94 were populated primarily via the beta-delayed proton emission of Pd-95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe-124 beam impinging on a 4 g/cm(2) Be-9 target. While the deduced E2 strength for the 2(+) -> 0(+) transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4(+) -> 2(+) transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the f pg proton hole space with respect to doubly magic Sn-100. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority v = 2, I-pi = 4(+) state and that of a close-lying v = 4 state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive 6(+) -> 4(+) transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.
|
|
| 15. |
- Doncel, Maria, et al.
(author)
-
Lifetime measurements of excited states in W-162 and W-164 and the evolution of collectivity in rare-earth nuclei
- 2017
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 95:4
-
Journal article (peer-reviewed)abstract
- Lifetimes of the first excited 2(+) states in the extremely neutron- deficient W-162 and W-164 nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data for the isotopic chains of hafnium, tungsten, and osmium, from the midshell region near the beta-stability line towards the N = 82 closed shell and the most neutron-deficient nuclides, are compared with predictions of nuclear deformations and 2(1)(+) -> 0(g.s)(.+) reduced transition strengths from different classes of state-of-the-art theoretical model calculations. The results reveal striking differences and deficiencies in the predictive power of current nuclear structure models.
|
|
| 16. |
- Dutt, S., et al.
(author)
-
Large-scale shell-model calculations near mass region 100-130
- 2020
-
In: Indian Journal of Pure & Applied Physics. - : NISCAIR. - 0019-5596 .- 0975-1041. ; 58:4, s. 308-313
-
Journal article (peer-reviewed)abstract
- In this work, we have presented a microscopic shell-model description of the structure and collective behavior of intermediate-mass nuclei around doubly magic Sn-100 and Sn-132 nuclei. The Sn-isotopes lie between the two doubly magic nuclei and cover a range from exotic proton-rich N=Z nuclei to exotic neutron-rich nuclei with N/Z > 1.6. The results obtained using BIGSTICK code for the low-level excitation states and transition probabilities for the studied Sn and Ba isotopic chains have been discussed in the radiance of available experimental data. We have used Sn-100 as a core for all the studied isotopes with the same valence space (i.e. 1d(5/2), 2s(1/2), 1d(3/2), 0g(7/2), 0h(11/2) or 'sdgh') for both protons (Z) and neutrons (N) between 50 and 82. These calculations are performed by means of globally optimized monopole effective interaction for the sdgh-shell.
|
|
| 17. |
- Ertoprak, Aysegul, et al.
(author)
-
Evidence for octupole collectivity in 172Pt
- 2020
-
In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 18. |
- Ertoprak, Aysegul, et al.
(author)
-
Lifetime measurements of core-excited states in semi-magic 95Rh
-
Other publication (other academic/artistic)abstract
- Lifetimes of negative-parity states have been determined in the semi-magic (N=50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca, 3p) was used to populate high-spin states in 95Rh at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6~ mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
|
|
| 19. |
- Ertoprak, A., et al.
(author)
-
Lifetimes of core-excited states in semi-magic Rh-95
- 2020
-
In: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 56:11
-
Journal article (peer-reviewed)abstract
- Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus Rh-95. The fusion-evaporation reaction Ni-58(Ca-40, 3p) was used to populate high-spin states in Rh-95 at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6 mg/cm(2) metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations. state-of-the-art theory. Remarkably, the structural features up to moderate angular momentum of nuclei immediately below the N = Z = 50 shell closures can be described with high accuracy in a very simple way by shell-model calculations including only the g(9/2) and p(1/2) subshells. Of special interest is the neutron-proton pair coupling scheme which is expected to appear in the heaviest N=Z nuclei [1,2] and the seniority structure of the N = 50 isotones [3-7]. However, multiple core-excited states have been observed in the semi-magic nuclei of the Sn-100 region [8-10]. The theoretical study of those states is a challenging task, which requires a significantly larger model space for their interpretation. Transition probabilities between nuclear states provide important constraints for theoretical modelling of the structure of the nuclei of interest. Our previous lifetime study of the semimagic (N = 50) nucleus Ru-94 [ 11,12] provided information on the electromagnetic decay properties of neutron-core excited states. We now address lifetime measurements in its closest, more neutron deficient, isotone Rh-95 using the same DSAM technique. The experimental results have been interpreted within the framework of large-scale shell-model (LSSM) calculations.
|
|
| 20. |
- Ertoprak, Aysegul, 1987-, et al.
(author)
-
M1 and E2 transition rates from core-excited states in semi-magic 94Ru
-
Other publication (other academic/artistic)abstract
- Lifetimes of high-spin states have been measured in the semi-magic (N=50) nucleus 94Ru. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru∗ fusion-evaporation reaction at the Grand Accelerateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from γ-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range I = (13 − 20)ħ have been measured, five of which were determined for the first time. The deduced corresponding B(M1) and B(E2)reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
|
|
| 21. |
- Ertoprak, Aysegul, et al.
(author)
-
M1 and E2 transition rates from core-excited states in semi-magic Ru-94
- 2018
-
In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 54:9
-
Journal article (peer-reviewed)abstract
- Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
|
|
| 22. |
- Gao, B., et al.
(author)
-
New Fe-59 Stellar Decay Rate with Implications for the Fe-60 Radioactivity in Massive Stars
- 2021
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 126:15
-
Journal article (peer-reviewed)abstract
- The discrepancy between observations from gamma-ray astronomy of the Fe-60/Al-26 gamma-ray flux ratio and recent calculations is an unresolved puzzle in nuclear astrophysics. The stellar beta-decay rate of Fe-59 is one of the major nuclear uncertainties impeding us from a precise prediction. The important Gamow-Teller strengths from the low-lying states in Fe-59 to the Co-59 ground state are measured for the first time using the exclusive measurement of the Co-59(t, He-3 + gamma) Fe-59 charge-exchange reaction. The new stellar decay rate of Fe-59 is a factor of 3.5 +/- 1.1 larger than the currently adopted rate at T = 1.2 GK. Stellar evolution calculations show that the Fe-60 production yield of an 18 solar mass star is decreased significantly by 40% when using the new rate. Our result eliminates one of the major nuclear uncertainties in the predicted yield of Fe-60 and alleviates the existing discrepancy of the Fe-60/Al-26 ratio.
|
|
| 23. |
- Guan, Xin, et al.
(author)
-
An iterative approach for the exact solution of the pairing Hamiltonian
- 2022
-
In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 275
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 24. |
- Hadinia, B., et al.
(author)
-
IN-BEAM gamma-RAY SPECTROSCOPY ABOVE THE HIGH-SPIN ISOMERIC STATE IN Lu-155
- 2013
-
In: CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS. - : WORLD SCIENTIFIC PUBL CO PTE LTD. ; , s. 139-144
-
Conference paper (peer-reviewed)abstract
- Excited states in Lu-155 have been studied at the Accelerator Laboratory of the University of Jyvaskyla in Finland. The Lu-155 nuclei were populated using the reaction of Ni-58 on (102)pd at a beam energy of 280 MeV. The nuclei of interest were selected using the RITU gas filled recoil separator and the prompt gamma rays belonging to 155Lu were identified using the recoil-decay tagging technique. The gamma-ray transitions de-exciting the excited states above the high-spin isomeric a-decaying state in Lu-155 have been identified. A gamma-ray coincidence analysis shows that the previously reported level scheme for Lu-155 should be revised.
|
|
| 25. |
- Li, K. -A, et al.
(author)
-
The Stellar β-decay Rate of 134Cs and Its Impact on the Barium Nucleosynthesis in the s-process
- 2021
-
In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 919:2, s. L19-
-
Journal article (peer-reviewed)abstract
- We have calculated the stellar β-decay rate of the important s-process branching point 134Cs based on the state-of-the-art shell model calculations. At typical s-process temperatures (T ∼ 0.2-0.3 GK), our new rate is one order of magnitude lower than the widely used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with various masses and metallicities. Our new decay rate leads to an overall decrease in the 134Ba/136Ba ratio, and well explains the measured ratio in meteorites without introducing the i-process. We also derive the elapsed time from the last AGB nucleosynthetic event that polluted the early solar system to be >28 Myr based on the 135Cs/133Cs ratio, which is consistent with the elapsed times derived from 107Pd and 182Hf. The s-process abundance sum of 135Ba and 135Cs is found to increase, resulting in a smaller r-process contribution of 135Ba in the solar system.
|
|
| 26. |
- Liu, J. J., et al.
(author)
-
Observation of a Strongly Isospin-Mixed Doublet in Si-26 via beta-Delayed Two-Proton Decay of P-26
- 2022
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 129:24
-
Journal article (peer-reviewed)abstract
- beta decay of proton-rich nuclei plays an important role in exploring isospin mixing. The beta decay of P-26 at the proton drip line is studied using double-sided silicon strip detectors operating in conjunction with high-purity germanium detectors. The T = 2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in Si-26 are unambiguously identified through beta-delayed two-proton emission (beta 2p). Angular correlations of two protons emitted from Si-26 excited states populated by P-26 beta decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the Si-26 IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in beta-decay experiments.
|
|
| 27. |
- Liu, Xiaoyu, et al.
(author)
-
Evidence for enhanced neutron-proton correlations from the level structure of theN = Z + 1 nucleus 87Tc
-
In: PHYSICAL REVIEW C.
-
Journal article (other academic/artistic)abstract
- 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.
|
|
| 28. |
- Liu, X., et al.
(author)
-
Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44
- 2021
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 29. |
- Liu, Xiaoyu, et al.
(author)
-
Evidence for Spherical-Oblate Shape Coexistence in 87Tc
-
In: THE EUROPEAN PHYSICAL JOURNAL A.
-
Journal article (other academic/artistic)abstract
- 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
|
|
| 30. |
- Liu, Xiaoyu, et al.
(author)
-
Evidence for spherical-oblate shape coexistence in Tc-87
- 2022
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 31. |
- Liu, Xiaoyu
(author)
-
Experimental Studies of the Neutron Deficient Atomic Nuclei 88Ru and 87Tc, and the Diagonalization of the General Pairing Hamiltonian
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- 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.
|
|
| 32. |
- Liu, Xiaoyu, et al.
(author)
-
PairDiag : An exact diagonalization program for solving general pairing Hamiltonians
- 2020
-
In: Computer Physics Communications. - : Elsevier B.V.. - 0010-4655 .- 1879-2944.
-
Journal article (peer-reviewed)abstract
- We present a program for solving exactly the general pairing Hamiltonian based on diagonalization. The program generates the seniority-zero shell-model-like basis vectors via the ‘01’ inversion algorithm. The Hamiltonian matrix is constructed in this seniority-zero space. The program evaluates all non-zero elements of the Hamiltonian matrix “on the fly” using the scattering operator and a search algorithm. The matrix is diagonalized by using the iterative Lanczos algorithm. The OpenMP parallel program thus developed, PairDiag, can efficiently calculate the ground-state eigenvalue and eigenvector of the general pairing Hamiltonian for both the even-mass and the odd-mass system. The program is packaged in a Fortran module, which makes it easy to use the program to replace the BCS approximation in standard self-consistent mean field calculations. For systems with dimension around 108, the calculation can be done within hours on standard desktop computers. Program summary: Program Title: PairDiag. Program Files doi: http://dx.doi.org/10.17632/dzzspfszsh.1 Licensing provisions: CC by NC 3.0. Programming language: Fortran 95. Nature of problem: The numerically exact solution of general pairing Hamiltonian can be solved by diagonalization in configuration spaces of fixed seniority. Solution method: The program constructs the seniority-zero space by the ‘01’ inversion algorithm, and diagonalizes the general pairing Hamiltonian by the Lanczos plus QR algorithm. Restrictions: The total number of orbits involved must be less than 63, and the dimension that can be calculated is restricted by the local RAM condition.
|
|
| 33. |
- Liu, Xiaoyu, et al.
(author)
-
PairDiagSph : Generalization of the exact pairing diagonalization program for spherical systems
- 2021
-
In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 263
-
Journal article (peer-reviewed)abstract
- We present an efficient program for the exact diagonalization solution of the pairing Hamiltonian in spherical systems with rotational invariance based on the SU(2) quasi-spin algebra. The basis vectors with quasi-spin symmetry considered are generated by using an iterative algorithm. Then the Hamiltonian matrix constructed on this basis is diagonalized with the Lanczos algorithm. All non-zero matrix elements of the Hamiltonian matrix are evaluated "on the fly" by the scattering operator and hash search acting on the basis vectors. The OpenMP parallel program thus developed, PairDiagSph, can efficiently calculate the ground-state eigenvalue and eigenvector of general spherical pairing Hamiltonians. Systems with dimension up to 10(8) can be calculated in few hours on standard desktop computers. Program summary Program Title: PairDiagSph. CPC Library link to program files: https://doi.org/10.17632/t5txsg3s5g.1 Code Ocean capsule: https://codeocean.com/capsule/9159628 Licensing provisions: CC by NC 3.0. Programming language: Fortran 95. Nature of problem: The exact diagonalization of spherical pairing Hamiltonian can be achieved in the quasi-spin space. Solution method: The program generates the basis vectors via the adjacency excitation algorithm, and diagonalizes the spherical pairing Hamiltonian by the Lanczos + QR algorithm. Additional comments including restrictions and unusual features: The total number of spherical must be less than 64; The maximal dimension that can be handled is restricted by the local RAM capacity.
|
|
| 34. |
- Ortner, K., et al.
(author)
-
Low-spin states in 118Sn populated by the radiative capture of thermal neutrons
- 2024
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 109:5
-
Journal article (peer-reviewed)abstract
- Background: gamma -ray spectroscopy studies of the Sn isotopes provide important information on nuclear structure and shell evolution across the long isotopic chain between the doubly-magic Sn-100 and Sn-132 nuclei. These studies also offer great value to test and tune nuclear models which can then be applied to other regions of the nuclear chart. Purpose: We aim to expand the level scheme of Sn-118 by populating low-spin states in the range of 3-5 MeV and determine their angular momentum for the possible connection of these states to pygmy quadrupole Resonances, a new phenomenon observed in the neighboring Sn-112,Sn-114,Sn-124 isotopes as a resonance-like structure in the 3-5 MeV range. Method: Excited states in Sn-118 were populated via the Sn-117(n, gamma)Sn-118 reaction at the Institut Laue-Langevin in Grenoble, France. The FIssion Product Prompt gamma-ray Spectrometer (FIPPS), an array of eight n -type high purity Germanium clover detectors augmented with eight additional clover detectors from IFIN "Horia Hulubei" were used to detect gamma rays from excited states in Sn-118. The array provides a superior efficiency for gamma -ray detection and nearly 4 pi coverage for the measurements of angular correlations for spin assignment of excited nuclear levels. Results: Through gamma -gamma coincidences, 112 excited states were identified with 57 being newly placed in the level scheme. From these states, 567 gamma -ray transitions were observed with 501 being newly identified. Many levels were identified in the 3-5 MeV region. Further, an indirect measurement of the E0 transition which decays from the 0(3)(+) state to the 2p -2h, 0(2)(+) state was performed and the q(K)(2)(E0/E 2) and X(E0/E2) for this transition were determined to be 12.7(11) and 6.3(5), respectively. The 10(3) x rho(2)(E0) was determined to be >38 based on a half-life limit of <200 ps of the 2057-keV, 0(3)(+) level. Conclusions: The abundant spectroscopic information on Sn-118 obtained in the present experiment is an important input to the theoretical description of nuclei in the region and highlights the capabilities of the FIPPS array at ILL in conjunction with neutron capture reactions. Many states identified in the 3-5 MeV region could very likely have J = 2(+) and contribute to the pygmy quadrupole resonances.
|
|
| 35. |
- Pan, Feng, et al.
(author)
-
np-Pair Correlations in the Isovector Pairing Model
- 2021
-
In: Symmetry. - : MDPI. - 2073-8994. ; 13:8
-
Journal article (peer-reviewed)abstract
- A diagonalization scheme for the shell model mean-field plus isovector pairing Hamiltonian in the O(5) tensor product basis of the quasi-spin SU Lambda(2) circle times SUI(2) chain is proposed. The advantage of the diagonalization scheme lies in the fact that not only can the isospin-conserved, charge-independent isovector pairing interaction be analyzed, but also the isospin symmetry breaking cases. More importantly, the number operator of the np-pairs can be realized in this neutron and proton quasi-spin basis, with which the np-pair occupation number and its fluctuation at the J = 0(+) ground state of the model can be evaluated. As examples of the application, binding energies and low-lying J = 0(+) excited states of the even-even and odd-odd N similar to Z ds-shell nuclei are fit in the model with the charge-independent approximation, from which the neutron-proton pairing contribution to the binding energy in the ds-shell nuclei is estimated. It is observed that the decrease in the double binding-energy difference for the odd-odd nuclei is mainly due to the symmetry energy and Wigner energy contribution to the binding energy that alter the pairing staggering patten. The np-pair amplitudes in the np-pair stripping or picking-up process of these N = Z nuclei are also calculated.
|
|
| 36. |
- Pan, Feng, et al.
(author)
-
On the importance of np-pairs in the isovector pairing model
- 2020
-
In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 132:3
-
Journal article (peer-reviewed)abstract
- It is shown that the isovector np-pair number operator can be realized in the O(5) quasi-spin basis. The computation of the isovector np-pair number is demonstrated for even-even and odd-odd ds-shell nuclei described by the charge-independent mean field plus isovector pairing model restricted within the O(5) seniority-zero subspace, thereby binding energies and low-lying excited states of these ds-shell nuclei are fit, along with estimates for the isovector neutron-proton pairing contributions. For reasonable neutron-proton pairing strengths the isovector np-pairing energy contribution to the total binding energy in odd-odd N = Z nuclei is systematically larger than that in the even-even nuclei. In sum, the results suggest that the isovector np-pairing mode is favored in odd-odd N = Z nuclei; and additionally, a decrease in the double binding-energy difference for odd-odd nuclei is primarily due to the symmetry and Wigner energy contributions to the binding energy.
|
|
| 37. |
- Qi, Chong, 1983-, et al.
(author)
-
Alpha decay measured in single-particle units as a manifestation of nuclear collectivity
- 2021
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 818
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 38. |
- Qi, Chong, 1983-
(author)
-
alpha FORMATION PROBABILITIES IN NUCLEI AND PAIRING COLLECTIVITY
- 2010
-
In: NUCLEAR STRUCTURE IN CHINA 2010. - : WORLD SCIENTIFIC PUBL CO PTE LTD. ; , s. 169-174
-
Conference paper (peer-reviewed)abstract
- 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.
|
|
| 39. |
- Qi, Chong, 1983-, et al.
(author)
-
Coherence features of the spin-aligned neutron-proton pair coupling scheme
- 2012
-
In: Physica scripta. T. - 0281-1847. ; T150, s. 014031-
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 40. |
- Qi, Chong, 1983-, et al.
(author)
-
Competition of different coupling schemes in atomic nuclei
- 2012
-
In: Advanced Many-Body And Statistical Methods In Mesoscopic Systems. - : Institute of Physics Publishing (IOPP). ; , s. 012027-
-
Conference paper (peer-reviewed)abstract
- 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.
|
|
| 41. |
- Qi, Chong, 1983-
(author)
-
Differential evolution algorithm for global optimizations in nuclear physics
- 2017
-
In: Journal of Physics G. - : IOP PUBLISHING LTD. - 0954-3899 .- 1361-6471. ; 44:4
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 42. |
- Qi, Chong, 1983-, et al.
(author)
-
Generalization of the Geiger-Nuttall law and alpha clustering in heavy nuclei
- 2012
-
In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 381, s. 012131-
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 43. |
|
|
| 44. |
|
|
| 45. |
|
|
| 46. |
- Qi, Chong, 1983-
(author)
-
Partial conservation of seniority and its unexpected influence on E2 transitions in g(9/2) nuclei
- 2017
-
In: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 773, s. 616-619
-
Journal article (peer-reviewed)abstract
- There exist two uniquely defined v = 4 states in systems within a j = 9/2 subshell, which automatically conserve seniority and do not mix with other states. Here I show that the partial conservation of seniority plays an essential role in our understanding of the electric quadrupole transitions of the semimagic nuclei involving j = 9/2 subshells, including the long-lived 8(+) isomer in (94) Ru. The effects of configuration mixing from neighboring subshells on the structure of those unique states are analyzed. It is shown that a sharp transition from pure seniority coupling to a significant mixture between the v = 2 and v = 4 states may be induced by the cross-orbital non-diagonal interaction matrix elements. Such strong mixture is essential to explain the observed E2 transition properties of N = 50 isotones Pd-96 and Ru-94.
|
|
| 47. |
- Qi, Chong, 1983-, et al.
(author)
-
Proton resonance properties in light nuclei with mean-field type potentials
- 2008
-
In: INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS. ; , s. 1955-1964
-
Conference paper (peer-reviewed)abstract
- The properties of proton resonances in the p and sd shells are studied with a single-particle potential generated by self-consistent-mean field calculations. Besides, we also propose to calculate the proton-nucleus interaction by a double-folding procedure with the density of the daughter nucleus represented by the result of the same mean-field model. With out raising any adjustable parameter, these calculations provide reasonable estimates for the widths of observed proton resonances in light nuclei. The mean-field-based calculation is particularly useful for the predications of the properties of resonances in light exotic nuclei and the direct proton capture reactions of astrophysics.
|
|
| 48. |
- Qi, Chong, 1983-, et al.
(author)
-
Recent developments in radioactive charged-particle emissions and related phenomena
- 2019
-
In: Progress in Particle and Nuclear Physics. - : Elsevier. - 0146-6410 .- 1873-2224. ; 105, s. 214-251
-
Research review (peer-reviewed)abstract
- The advent and intensive use of new detector technologies as well as radioactive ion beam facilities have opened up possibilities to investigate alpha, proton and cluster decays of highly unstable nuclei. This article provides a review of the current status of our understanding of clustering and the corresponding radioactive particle decay process in atomic nuclei. We put alpha decay in the context of charged-particle emissions which also include one- and two-proton emissions as well as heavy cluster decay. The experimental as well as the theoretical advances achieved recently in these fields are presented. Emphasis is given to the recent discoveries of charged-particle decays from proton-rich nuclei around the proton drip line. Those decay measurements have shown to provide an important probe for studying the structure of the nuclei involved. Developments on the theoretical side in nuclear many-body theories and supercomputing facilities have also made substantial progress, enabling one to study the nuclear clusterization and decays within a microscopic and consistent framework. We report on properties induced by the nuclear interaction acting in the nuclear medium, like the pairing interaction, which have been uncovered by studying the microscopic structure of clusters. The competition between cluster formations as compared to the corresponding alpha-particle formation are included. In the review we also describe the search for super-heavy nuclei connected by chains of alpha and other radioactive particle decays.
|
|
| 49. |
|
|
| 50. |
- Qi, Chong, 1983-, et al.
(author)
-
Shell-model studies of isomeric states in Fe-51,Fe-52,Fe-53
- 2008
-
In: Chinese Physics C. - 1674-1137 .- 2058-6132. ; 32, s. 112-115
-
Journal article (peer-reviewed)abstract
- The yrast bands of (51,52,53)Fe have been studied with a microscopical effective Hamiltonian derived from the charge-dependent Bonn NN potential. Calculations obtain satisfactory agreements with experimental data, reproducing the observed isomeric states. The possible origins of the isomers are discussed.
|
|
