| 1. |
- Bhagwat, A., et al.
(författare)
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Mic–Mac model based on the Wigner–Kirkwood method
- 2023
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 59:12
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Tidskriftsartikel (refereegranskat)abstract
- About a decade ago we proposed a new Microscopic–Macroscopic (Mic–Mac) model where the semiclassical Wigner–Kirkwood expansion of the energy up to fourth-order in ħ is used to compute the shell corrections in a deformed Woods-Saxon potential instead of the usual Strutinsky averaging scheme [1, 2]. For a set of 551 even-even nuclei computed with this new model, we found a rms deviation of 610 keV from the experimental masses, similar to the value obtained using the well-known Finite Range Droplet Model and the Lublin–Strasbourg Drop Model for the same set of nuclei. In a next step, we compute the ground-state properties of these 551 nuclei with the same method but using the mean-field provided by the Gogny forces within an Extended Thomas-Fermi approximation. We find that this Mic–Mac model using the Gogny D1S (D1M) force gives a fairly good description of the ground-state energies with a rms deviation of 834 keV (819 keV). This implies that Mic–Mac models based on effective two-body forces, for example Gogny D1S and D1M interactions, perform practically as well as the most efficient Mic–Mac models regarding ground-state properties.
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| 2. |
- Ertoprak, Aysegul, et al.
(författare)
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Evidence for octupole collectivity in 172Pt
- 2020
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Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Liu, Xiaoyu, et al.
(författare)
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Evidence for enhanced neutron-proton correlations from the level structure of theN = Z + 1 nucleus 87Tc
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Ingår i: PHYSICAL REVIEW C.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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.
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| 4. |
- Liu, X., et al.
(författare)
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Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44
- 2021
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Liu, Xiaoyu, et al.
(författare)
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Evidence for spherical-oblate shape coexistence in Tc-87
- 2022
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Petrache, C. M., et al.
(författare)
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Diversity of shapes and rotations in the gamma-soft Ba-130 nucleus : First observation of a t-band in the A=130 mass region
- 2019
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 795, s. 241-247
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Tidskriftsartikel (refereegranskat)abstract
- Several new bands have been identified in Ba-130, among which there is one with band-head spin 8(+). Its properties are in agreement with the Fermi-aligned nu h(11/2)(2)[523]circle times 9/2(-)[514] Nilsson configuration. This is the first observation of a two-quasiparticle t-band in the A = 130 mass region. The t-band is fed by a dipole band involving two additional h(11/2) protons. The odd-spin partners of the proton and neutron S-bands and the ground-state band at high spins are also newly identified. The observed bands are discussed using several theoretical models, total Routhians surfaces (TRS), tilted axis cranking (TAC), particle rotor model (PRM) and projected shell model (PSM), which strongly suggest the coexistence of prolate and oblate shapes polarized by rotation aligned two-proton and two-neutron configurations, as well as prolate collective rotations around axes with different orientations. With the new results, 130 Ba presents one of the best and most complete sets of collective excitations that a gamma-soft nucleus can manifest at medium and high spins, revealing a diversity of shapes and rotations for the nuclei in the A = 130 mass region.
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| 7. |
- Qi, Chong, 1983-, et al.
(författare)
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Alpha decay measured in single-particle units as a manifestation of nuclear collectivity
- 2021
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 818
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Reifarth, R., et al.
(författare)
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Nuclear astrophysics with radioactive ions at FAIR
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
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Konferensbidrag (refereegranskat)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 9. |
- Shen, Shuifa, et al.
(författare)
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STABLE TRIAXIALITY IN GERMANIUM AND SELENIUM ISOTOPES
- 2013
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Ingår i: NUCLEAR STRUCTURE IN CHINA 2012. - : WORLD SCIENTIFIC PUBL CO PTE LTD. ; , s. 201-206
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Konferensbidrag (refereegranskat)abstract
- Total-Routhian-surface calculations by means of the pairing-deformation-frequency self-consistent cranked shell model have been carried out for germanium and selenium isotopes, in order to search for possible stable triaxial deformations of nuclear states. The triaxiality of vertical bar gamma vertical bar approximate to 30 degrees for the ground and collective rotational states, that is the limit of the maximum triaxiality, is found in Ge-64,Ge-74. The maximum triaxiality has its origin in a triaxial shell gap at Z = 32.
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| 10. |
- Shreenath, Vinutha Magal, et al.
(författare)
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C-CAMPUS : A Pilot Study On Cross-Cultural And Multi-Disciplinary Learning
- 2014
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Ingår i: EDULEARN14. - : IATED-INT ASSOC TECHNOLOGY EDUCATION A& DEVELOPMENT. ; , s. 1296-1305
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Konferensbidrag (refereegranskat)abstract
- Virtual learning environments are often associated with forms of virtual collaboration. Many studies have reported on the, often mixed, results of student collaborations from within the same population. Fewer studies have been done on cross-cultural collaboration platforms between geographically and culturally separated groups of students for learning more complex tasks. C-Campus is a cross-cultural and multi-disciplinary virtual environment with specifically tailored spaces for students to be able to learn, interact and socialize. In this environment the teachers and course developers can monitor and adjust the optimal learning conditions of the individual students. Students with diverse backgrounds from KTH Royal Institute of Technology in Sweden and Tsinghua University in China collaborated together on C-Campus for a course focusing on Future Highway Design. The structure of the course and the assignments were designed to encourage creative thinking, personal leadership and discussion. Students were split into diverse groups to work on projects with different perspectives on their Future Highway. The discussions among students took place in the space for creative learning on C-Campus. At the end of the course, they were asked to peer review the other members of their group and to assess their own performance during the course. This pilot provided an opportunity to observe individual student behaviour and group dynamics in a cross-cultural and multi-disciplinary setting. Data was gathered on all interactions in the groups, their teacher and mentor evaluations and the peer reviews among members in groups. An exit survey was also conducted on the ease of using the platform, on group activity and on the course itself. In this paper we describe the relation between the data gathered from students' interactions on C-Campus and the perceptions of performance by their peers and teachers. The data shows that interactions on C-Campus were a good indicator for the success of student learning and also to identify different types of behaviour. Having access to this type of data during the course can thus allow teachers to optimise learning for individual students and help nurture their abilities to work in multi-cultural and cross-disciplinary teams. The paper contributes both a unique cross-cultural learning case study, and more insights in the role of specific forms of data collection for monitoring of learning success in such environments.
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| 11. |
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| 12. |
- Wyss, Ramon Alexander, et al.
(författare)
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Fifty Years of Backbending
- 2022
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Ingår i: Nuclear Physics News. - : Informa UK Limited. - 1061-9127 .- 1931-7336. ; 32:2, s. 16-20
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Tidskriftsartikel (refereegranskat)abstract
- While being on a picnic, if you are not sure whether you brought the boiled or the raw eggs in your basket, there is a simple way of telling without smashing them open: Simply spin them. The boiled egg will spin very fast when you rotate it, whereas the raw egg will resist the spinning motion. Nuclear physicists make nuclei spin to study their internal features. Some 50 years ago a most astonishing effect was observed in rapidly rotating nuclei. This surprise discovery, known as backbending, which is a unique phenomenon in the finite, many-body quantum system, triggered a revolution of our studies into the structure of the atomic nucleus that continues to the present day.
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| 13. |
- Wyss, Ramon Alexander, et al.
(författare)
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Mutual innovation capacity building through challenge driven education for sustainable development in an international framework
- 2019
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Ingår i: 12th international conference of education, research and innovation (ICERI 2019). - : IATED Academy. - 9788409147557 ; , s. 5209-5219
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Konferensbidrag (refereegranskat)abstract
- The KTH Royal Institute of Technology and the University of Dar es Salaam (UDSM) have successfully developed a new educational model, 'challenge driven education' (CDE). The Model comprises the following building blocks: Integrating societal challenges into the regular curriculum, close collaboration with external stakeholders 'the challenge owners' through the design thinking methodology, international and cross disciplinary student teams that develop solutions to the formulated challenges, teacher training modules that support the pedagogical learning and interaction with external stakeholders. The formulated challenges as well as the proposed solutions shall contribute to the sustainable development goals (SDGs) as formulated by the UN agenda 2030.The ambition of the program is to develop student and teacher skills that can tackle the challenges of our time, like the sustainable development goals. The program is developed through a strategic partnership of KTH Royal Institute of Technology and the College of ICT of University of Dar es Salaam, UDSM supported by a STINT grant (The Swedish foundation for international cooperation in research and higher education). External stakeholders like the Dar es Salaam water and sewage authority, DAWASA, have defined challenges like clean water supply of Dar es Salaam. Students and teachers develop actionable problem statements in a design thinking process together with DAWASA, the external stakeholder. Student teams of UDSM and KTH develop proposed solutions to the formulated challenges in their final year project. Implementation of the proposed solutions by external stakeholders generates steps towards a sustainable development. In similar fashion, students from UDSM come to Stockholm KTH to participate in challenge based courses developing solutions of the sustainability challenges of the Swedish society. The key contribution to society is students that have become confident of their skills and ability to work for a sustainable future, an academia that interacts directly with external stakeholders, integrating their challenges into the learning curriculum and societal stakeholders learning to interact with the university. The model is transferable and scalable. The presentation reports the successful implementation of the project at UDSM and KTH and report learning outcomes and impact on society. A teacher training book, guide to challenge driven education has been developed [1] prior to the project start, which has been used in the project and which can be downloaded from the KTH web, see also https://www.kth.se/challenge
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