#tddft

A newly developed theoretical model based on the band theory of solids revealed a qualitatively new phenomenon, called an “anti-entrainment effect,” in the densest solid in the universe, the inner crust of neutron stars. A neutron star is a super-dense, compact star whose mass is as large as Sun, but with radius only about 10 km. Depending on depth from the surface (or density/pressure), it exhibits a variety of phases of nuclear matter, which allows for studying nuclear physics at extreme conditions that are inaccessible in terrestrial laboratories. Amongst many, properties of the so-called inner crust of neutron stars, where crystalline solid of nuclei is immersed in superfluid of dripped neutrons, attract particular interests. It is well known that a proper quantum-mechanical method to describe a system with a periodic potential is the band theory of solids, which is at the heart of material science. However, an application of the band theory for the neutron star crust started only quite recently, and there remain a lot of issues to be addressed. In this paper we have achieved, for the first time, fully-microscopic time-dependent band theory calculations for the slab phase of nuclear matter. Our calculations revealed a qualitatively new phenomenon where part of dripped neutrons is mobilized by the presence of crystalline structure, contrary to a naïve expectation. We call it an “anti-entrainment effect.” The change of conduction neutron density will affect various macroscopic models of neutron stars. The proposed approach will open a new research field, namely, fully-microscopic study of dynamics as well as excitations of the inner crust of neutron stars.

The main article:

K. Sekizawa, S. Kobayashi, and M. Matsuo, Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase, Phys. Rev. C 105, 045807 (2022); preprint: arXiv:2112.14350 [nucl-th].

A newly developed theory explains the production mechanism of a whole set of abundant isotopes in collisions of two atomic nuclei. Production of yet-unknown, unstable nuclei is of paramount importance to answer fundamental questions: Do existing models properly describe physics of extremely unstable nuclei? How were the elements heavier than iron produced in the Universe? What is the heaviest element in nature? However, the production at laboratories is not easy and obvious, and a reliable theoretical prediction is mandatory. In the paper, researchers put a great step forward. They have newly developed a theoretical framework that combines 1) a state-of-the-art quantum many-body theory that incorporates with quantal fluctuations, called Stochastic Mean Field (SMF) theory, with 2) an elaborated statistical model that describes secondary decays (particle evaporation and fission) of produced “hot” fragments. With the hybrid theory it is shown that a complete set of experimental data for collisions of nickel and lead nuclei can be reproduced non-empirically, without adjustable parameters―it makes the theory distinctive and special as compared to many other phenomenological models on the market. The predictive theory will lead us to terra incognita―bright future ahead for nuclear experiments.

Movie: Real-time density evolution in the reaction plane for a collision of Nickel-64 with Lead-208 at Ecm=268 MeV with L=50 hbar.

Figure: Comparison of secondary production cross sections between experimental data (red points) and the new (blue line) and previous (red line) theories.

This article is an outreach summary of our paper: K. Sekizawa and S. Ayik, Quantal diffusion approach for multinucleon transfer processes in the 58,64Ni+208Pb reactions: Toward the production of unknown neutron-rich nuclei, Phys. Rev. C 102, 014620 (2020).

DOI: 10.1103/PhysRevC.102.014620

arXiv:2003.07786 [nucl-th] (https://arxiv.org/abs/2003.07786)

Outreach Summary: Novel Role of Superfluidity in Low-Energy Nuclear Reactions, Phys. Rev. Lett. 119, 042501 (2017)

One more short summary of our recent work:

"Nuclear superfluidity makes fusion more difficult" Simulations of colliding superfluid nuclei revealed that their fusion may be more difficult than previously thought. When nucleons move inside an atomic nucleus they pair up and form “Cooper pairs” behaving like dancers performing a synchronized dance. Let us imagine a situation when two groups, dancing out of phase, are merged. It is easy to visualize the trouble the dancers belonging to different groups may have been trying to synchronize their dance with colleagues from the other group. This resembles the situation encountered in a collision of two superfluid nuclei. Those troubled dancers form a “solitonic excitation,” an abrupt pairing-phase distortion, which stores a large amount of energy. In the Letter we show, based on superfluid DFT framework, that the solitonic excitation gives rise to a variety of changes in reaction dynamics: most intriguingly it can even prevent fusion reaction. Predicted novel role of superfluidity can be detectable with current experimental technology and it is now awaiting for verification.

An example of our simulation:

The main article: P. Magierski, K. Sekizawa, and G. Wlazłowski, Novel Role of Superfluidity in Low-Energy Nuclear Reactions, Phys. Rev. Lett. 119, 042501 (2017)

DOI: https://doi.org/10.1103/PhysRevLett.119.042501

Outreach Summary: Microscopic description of production cross sections including deexcitation effects, Phys. Rev. C 96, 014615 (2017)

Here I supply an outreach short summary of my recent work:

"Toward a complete modeling of low-energy nuclear reactions" A long-awaited important step toward a complete modeling of low-energy nuclear reactions has been put forward. While around 3,200 nuclides have been discovered to date, theory predicts about 7,000 nuclides may exist in nature—more than half of nuclear species are still awaiting for discovery. Experimentalists are thus trying to produce new nuclear species by colliding two nuclei, known as nuclear reactions, at laboratories all over the world. However, it is not at all an easy task, as nuclear reactions are very difficult to understand theoretically. Especially, a theory must describe two completely distinct stages of the reaction, i.e., a very fast creation mechanism (10-22 – 10-20 sec) and a rather slow cooling mechanism (10-18 – 10-16 sec). In the paper, the author has proposed a new reaction model which combines a quantum mechanical many-body theory (for describing the first stage) with a statistical-decay model (for describing the second stage). It has been demonstrated that the model is able to reproduce experimental data fairly well, without any “tuning” of the model parameters. The new theory will guide future experiments to access yet unexplored territories in the chart of nuclides through its non-empirical predictions.

The main article: K. Sekizawa, Microscopic description of production cross sections including deexcitation effects, Phys. Rev. C 96, 014615 (2017)

DOI: https://doi.org/10.1103/PhysRevC.96.014615

Outreach Summary: Enhanced nucleon transfer in tip collisions of 238U+124Sn, Phys. Rev. C 96, 041601(R) (2017)

Here I supply an outreach summary of my work:

"How a giant nucleus splits? ― a new key to produce superheavy nuclei" Numerical simulations suggest a new way to create superheavy nuclei through qualitatively different dynamics than conventionally thought. The search for new superheavy nuclei is one of the most hot topics in nuclear physics community. So far, experimentalists were successful to synthesize them, by colliding, and “merging,” two nuclei, known as nuclear fusion reaction. In this paper, an alternative way other than fusion is pointed out. It is demonstrated that how a giant nucleus―the colliding projectile and target―“splits” depends strongly on orientations of deformed nuclei, quantum mechanical shell effects, as well as collision energies. An interesting observation is that this splitting shortly after collision―known as quasifission―could produce transuranium nuclei in collisions of 238U and 124Sn, indicating a possibility to transfer a number of nucleons from light to heavy nuclei. Further investigations of similar types of reactions may find a pathway to reach yet-unexplored territories of superheavy nuclei.

An example of the simulation:

The main article: K. Sekizawa, Enhanced nucleon transfer in tip collisions of 238U+124Sn, Phys. Rev. C 96, 041601(R) (2017)

DOI: https://doi.org/10.1103/PhysRevC.96.041601