Dynamical effects in fusion with exotic nuclei

[Background] Reactions with stable beams have demonstrated a strong interplay between nuclear structure and fusion. Exotic beam facilities open new perspectives to understand the impact of neutron skin, large isospin, and weak binding energies on fusion. Microscopic theories of fusion are required to guide future experiments. [Purpose] To investigate new effects of exotic structures and dynamics in near-barrier fusion with exotic nuclei. [Method] Microscopic approaches based on the Hartree-Fock (HF) mean-field theory are used for studying fusion barriers in $^{40-54}$Ca+$^{116}$Sn reactions for even isotopes. Bare potential barriers are obtained assuming frozen HF ground-state densities. Dynamical effects on the barrier are accounted for in time-dependent Hartree-Fock (TDHF) calculations of the collisions. Vibrational couplings are studied in the coupled-channel framework and near-barrier nucleon transfer is investigated with TDHF calculations. [Results] The development of a neutron skin in exotic calcium isotopes strongly lowers the bare potential barrier. However, this static effect is not apparent when dynamical effects are included. On the contrary, a fusion hindrance is observed in TDHF calculations with the most neutron rich calcium isotopes which cannot be explained by vibrational couplings. Transfer reactions are also important in these systems due to charge equilibration processes. [Conclusions] Despite its impact on the bare potential, the neutron skin is not seen as playing an important role in the fusion dynamics. However, the charge transfer with exotic projectiles could lead to an increase of the Coulomb repulsion between the fragments, suppressing fusion. The effect of transfer and dissipative mechanisms on fusion with exotic nuclei deserve further studies.The authors are grateful to M. Dasgupta, D. J. Hinde, and A. S. Umar for stimulating discussions during this work. This research was undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government. This research was supported under Australian Research Council’s Future Fellowship (Project No. FT120100760), Discovery Projects (Project No. DP140101337), and Laureate Fellowship (Project No. FL110100098) funding schemes

Probing cluster structures through sub-barrier transfer reactions

Multinucleon transfer probabilities and excitation energy distributions have been measured in 16,18O, 19F + 208Pb at energies between 90% - 100% of the Coulomb barrier. A strong 2p2n enhancement is observed for all reactions, though most spectacularly in the 18O induced reaction. Results are interpreted in terms of the Semiclassical model, which seems to suggest α-cluster transfer in all studied systems. The relation to cluster-states in the projectile is discussed, with the experimental results consistent with previous structure studies. Dissipation of energy in the collisions of 18O is compared between different reaction modes, with cluster transfer associated with dissipation over a large number of internal states. Cluster transfer is shown to be a long range dissipation mechanism, which will inform the development of future models to treat these dynamic processes in reactions

Examining the role of transfer coupling in sub-barrier fusion of ⁴⁶,⁵⁰Ti+¹²⁴Sn

Background: The presence of neutron transfer channels with positive Q values can enhance sub-barrier fusion cross sections. Recent measurements of the fusion excitation functions for 58Ni +132,124Sn found that the fusion enhancement due to the influence of neutron transfer is smaller than that in 40Ca +132,124Sn although the Q values for multineutron transfer are comparable. Purpose: To investigate the differences observed between the fusion of Sn + Ni and Sn + Ca. Methods: Fusion excitation functions for 46,50Ti +124Sn have been measured at energies near the Coulomb barrier. Results: A comparison of the barrier distributions for 46Ti +124Sn and 40Ca +124Sn shows that the 40Ca +124Sn system has a barrier strength resulting from the coupling to the very collective octupole state in 40Ca at an energy significantly lower than the uncoupled barrier. Conclusions: The large sub-barrier fusion enhancement in 40Ca induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of 40Ca playing a major role.Research at ANU was supported by the Australian Research Council Grants DP130101569, FT120100760, DP140101337, FL110100098, DE140100784 and by National Collaborative Research Infrastructure Strategy (NCRIS) for the operation of the Heavy Ion Accelerator Facility

Classical dynamical modelling of near-barrier breakup

The complete fusion of light, weakly-bound nuclides is known to be significantly suppressed with respect to comparable well-bound projectiles or with respect to single barrier penetration model calculations. Strong α-clustering in these light systems mean that they very easily disintegrate into clusters, either via direct excitation of their intrinsic cluster continuum, or via transfer reactions which connect to unbound states in neighbouring nuclides. This breakup is thought to reduce the probability for complete fusion. Here we discuss which processes cause breakup, whether or not breakup happens fast enough, and the interpretation of measurements made at the Australian National University of breakup using classical dynamical models. Understanding the intimate details of breakup, and the resonances through which it proceeds, will be crucial in determining its likely influence on fusion

Associations of Underlying Health Conditions With Anxiety and Depression Among Outpatients: Modification Effects of Suspected COVID-19 Symptoms, Health-Related and Preventive Behaviors

Objectives: We explored the association of underlying health conditions (UHC) with depression and anxiety, and examined the modification effects of suspected COVID-19 symptoms (S-COVID-19-S), health-related behaviors (HB), and preventive behaviors (PB).Methods: A cross-sectional study was conducted on 8,291 outpatients aged 18–85 years, in 18 hospitals and health centers across Vietnam from 14th February to May 31, 2020. We collected the data regarding participant's characteristics, UHC, HB, PB, depression, and anxiety.Results: People with UHC had higher odds of depression (OR = 2.11; p < 0.001) and anxiety (OR = 2.86; p < 0.001) than those without UHC. The odds of depression and anxiety were significantly higher for those with UHC and S-COVID-19-S (p < 0.001); and were significantly lower for those had UHC and interacted with “unchanged/more” physical activity (p < 0.001), or “unchanged/more” drinking (p < 0.001 for only anxiety), or “unchanged/healthier” eating (p < 0.001), and high PB score (p < 0.001), as compared to those without UHC and without S-COVID-19-S, “never/stopped/less” physical activity, drinking, “less healthy” eating, and low PB score, respectively.Conclusion: S-COVID-19-S worsen psychological health in patients with UHC. Physical activity, drinking, healthier eating, and high PB score were protective factors

Managing development of resort destinations in Southeast Asia: emerging and peripheral Phu Quoc Island

Southeast Asia located in the tropics offers a variety of sea resort destinations. With the recent economic reforms in Vietnam, Cambodia, and Myanmar for greater integration into the world economy, tourism has been a key sector of attention with many potential sea resorts to be developed in these countries' coastal regions. In this regard, Bali and Phuket among others offer important development lessons within the region for Vietnam's rising and popular resort – Phu Quoc Island. This chapter takes a leaf from Bali's tourism experience as a development strategy that can be learned and considered for Phu Quoc Island's growth. Though these destinations are in different stages of development, such comparative learning provides a new perspective on managing peripheral resorts. Utilizing peripheral areas in tourism development theories as a basis to understand Balinese experience, a framework of key factors such as foreign investments and good environmental practices will be examined. Balinese tourism successes and challenges are analyzed to discern ways in which Phu Quoc Island's development can be managed in the twenty-first century as one of several emerging resort destinations in Southeast Asia

Time-dependent Hartree-Fock Study of Octupole Vibrations in doubly magic nuclei

Octupole vibrations are studied in some doubly magic nuclei using the time-dependent Hartree-Fock (TDHF) theory with a Skyrme energy density functional. Through the use of the linear response theory, the energies and transition amplitudes of the low-lying vibrational modes for each of the nuclei were determined. Energies were found to be close to experimental results. However, transition amplitudes, quantified by the deformation parameter β3, are underestimated by TDHF. A comparison with single-particle excitations on the Hartree-Fock ground-state shows that the collective octupole vibrations have their energy lowered due to attractive RPA residual interaction

Fusion with exotic nuclei using a microscopic approach

Fusion reactions near the barrier energy are studied in this proceedings with the Hartree-Fock (HF) method, on systems involving 40–54Ca+116,132Sn. Both static and time-dependent (TDHF) versions of the method are used to probe what structure effects play a role in the fusion barrier energy. In static HF calculations for fusion, ground state properties of the nuclei influence the barrier energy. When dynamics are added in with TDHF, some effects from static properties (for example, the neutron skin) disappear. To understand the role of vibrations in dynamic reactions, TDHF is used in conjunction with the coupled-channels approach. Discussion on the effects of transfer is also presented

Nuclear structure effects on heavy-ion reactions with microscopic theory

The self-consistent mean-field Hartree–Fock (HF) theory, both static and time-dependent (TDHF) versions, is used to study static and dynamic properties of fusion reactions between even 40–54Ca isotopes and 116Sn. The bare nucleus-nucleus potential, calculated with the frozen HF approach, is affected by the groundstate density of the nuclei. However, once dynamical effects are included, as in TDHF, the static effects on the barrier are essentially washed out. Dynamic properties of the nuclei, including low-lying vibrational modes, are calculated with TDHF and selectively used in coupled-channels calculations to identify which modes have the most effect on the TDHF fusion threshold. Vibrations cannot fully explain the difference between the static HF and TDHF fusion barriers trend so other dynamical effects such as transfer are considered