原子核理論研究室

A new generation radioactive isotope facility (RIBF) has started providing highest intensity neutron-rich nuclei using in-flight fission of a 345 MeV/nucleon 238U beam. Bringing together with high detection efficiency gamma-ray detectors (Euroball HPGe) and newly developed beta-counting system (WAS3ABi), harvest of decay properties for several hundreds of exotic nuclei has been conducted using the EURICA spectrometer [1-5].

My talk will describes the basis and recent progress made in beta-gamma spectroscopy and related topics of the rapid-neutron capture process (r process), sequence of neutron-capture and beta-decay processes. Future projects related to nuclear structure and nuclear astrophysics will be presented to discuss our perspective at RIBF.

[1] S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006 (2012).

[2] H. Watanabe et al., Phys. Rev. Lett. 111, 152501 (2013).

[3] Z.Y. Xu et al., Phys. Rev. Lett. 113, 032505 (2014).

[4] G.S. Simpson et al., Phys. Rev. Lett. 113, 132502 (2014).

[5] G. Lorusso et al., Phys. Rev. Lett. 114, 192501 (2015).

Lecturer: Prof. Anatoli Afanasjev (Mississippi State University)

Title: Addressing theoretical uncertainties in nuclear DFT

Abstract:

Even with new generation of experimental facilities such as RIKEN, FRIB and SU- PERHEAVY FACTORY, almost half of the Z ≤ 120 nuclei will be beyond of experimental reach. However, the modeling of nuclear astrophysical processes requires precise nuclear information on masses, β-decay rates, fission properties etc. In such a situation it is im- portant to understand theoretical uncertainties on global scale and their sources. This will also allow to improve nuclear structure models and to define better fitting protocols. In my talk these questions will be addressed within the framework of covariant density functional theory.

I will start from the global assessment of the description of ground state observables of even-even nuclei in the CDFT framework. Calculated binding energies, the deformations, radii, neutron skins, two-neutron separation energies and the positions of the proton-drip line will be compared in a systematic way with available experimental data. The estimates of theoretical uncertainties in these observables with increasing isospin and their evolution up to two-neutron drip line will be provided. Then I will focus on two-neutron drip line and superheavy nuclei and the sources of theoretical uncertainties in their description.

It is clear that the current generation of energy density functionals has some important limitations. The possibilities of their extension and thus the improvement of the descrip- tion of experimental data and the decrease of theoretical uncertainties will be discussed.

Date/Time: June 8 (Mon), 13:45 pm-

Place: B214 (Institute of Natural Sciences, Univ. of Tsukuba)

Lecturer:  Panagiota PAPAKONSTANTINOU (Institute for Basic Science, Rare Isotope Science Project)

Title: Beyond the mean-field picture, with realistic nuclear interactions

Abstract:

In the past decades, energy-density functional methods have advanced greatly the field of nuclear structure. They have allowed a microscopic and unified description of many properties in medium-mass and heavy nuclei, from masses and sizes to giant resonances, as well as nuclear matter. Known issues include the poorly constrained time-odd terms and the concept of non-linear density dependencies. Fitting the free parameters on the mean-field level means, moreover, that double counting of unknown effects is inevitable in beyond-mean-field applications. In this talk I will present an effort to describe nuclear properties, starting from microscopic NN(N) Hamiltonians, which allows for systematic and controlled extensions of mean-field theory, and can thus be applied in heavy nuclei. The Hamiltonians are first softened via unitary transformations. They can describe nuclear ground states within perturbation theory. They are then applied in linear response theory, namely the random phase approximation and its extensions, to study giant resonances and other vibrational modes. This line of work bridges strictly ab initio methods, restricted to very low energies and light nuclei, and more phenomenological, traditional approaches. It exploits nsights from both and could help them advance in tandem.

Lecturer: Javier Menendez (Univ. of Tokyo)

Title: From nuclear structure to double-beta decay

Abstract:

First I will cover the main achievements, and point to future work, in nuclear structure shell model calculations of medium-mass nuclei based on nuclear forces predicted by chiral effective field theory. These include very successful description of masses and spectroscopy of oxygen, calcium isotopes as well as ‘sd-shell’ nuclei. Secondly I will discuss neutrinoless double-beta decay, a key process to access neutrino properties given that the nuclear matrix elements of the process are known accurately. I will present state-of-the-art shell-model neutrinoless double-beta decay calculations, and a comparison to other approaches such as based on mean-field, which is essential to improve our understanding of the nuclear matrix elements.

(1)

Title: Ultrafast dynamics in light-harvesting and photovoltaics: a theoretical and experimental investigation

Speaker: Carlo Andrea Rozzi (CNR – Istituto Nanoscienze)

Place: Workshop room, Center for Computational Sciences

Time: May 18, 11:00-12:00

Abstract:

It is known that the primary steps of photoinduced energy and charge transfer occur on extremely fast time scales in many natural and man-made compounds that perform conversion of sunlight into chemical or electrical energy. These processes have traditionally been interpreted in terms of the incoherent kinetics of optical excitations and of charge hopping, but recently signatures of quantum coherence were observed in energy transfer in photosynthetic bacteria and algae [1,2]. We have studied the early steps of photoinduced charge separation in reference systems for artificial photosynthesis and photovoltaics by combining Time-dependent Density Functional Theory simulations of the quantum dynamics and high time resolution femtosecond spectroscopy. Our results show that the coherent coupling between electronic and nuclear degrees of freedom is of key importance for charge delocalization and transfer in both of covalently and non-covalently bonded systems [3,4]. We have exploited the results of our research to design, synthesize and characterize a novel molecular scaffold for photovoltaic applications [5].

[1] Engel, G. S. et al. Nature 446, 782-786 (2007).

[2] Collini, E. et al. Nature 463, 644-647 (2010).

[3] Rozzi, C. A., Falke S. et al., Nat. Comm. 4, 1602 (2013)

[4] Falke S., Rozzi, C. A. et al., Science, 344, 1001 (2014)

[5] Pittalis S., et al., Adv. Func. Mat. (2014)

(2)

Title: A roundtrip journey from spin-entanglement in atoms and molecules

to density functional theory

Speaker: Stefano Pittalis (CNR – Istituto Nanoscienze)

Place: Workshop room, Center for Computational Sciences

Time: 13:30-14:30

Abstract:

I will present an investigation on spin entanglement in many-electron systems within the framework of density functional theory [1]. In particular, I will show that, the entanglement length — which is extracted from the spatial dependence of the local concurrence — is a sensitive indicator of atomic shells, and reveals the character, covalent or metallic, of chemical bonds. These findings shed light on the remarkable success of modern density functionals, which tacitly employ the entanglement length as a variable, and open the way to further research on entanglement-based functionals.

[1] S. Pittalis, F. Troiani, C. A. Rozzi, G. Vignale, Phys. Rev. B 91, 075109 (2015)