Research Activities 1991–2016

RIKEN Accel. Prog. Rep. 50 (2017)

Theoretical Nuclear Physics Laboratory
Takashi Nakatsukasa ∗1,∗2,∗3tivities in these related areas. We studied superﬂuidity in fermionic cold atoms, electronic dynamics insolids, photoresponse in molecules and clusters, etc.,
using techniques identical (similar) to nuclear physics.
Quantum statistics of mesoscopic systems, dissipationin ﬁnite systems, microscopic description of macroscopic properties, etc., these are long-standing problems in the nuclear physics and important issues in
the other ﬁelds of mesoscopic physics as well.
When I started the TNP Laboratory, RIKEN wasin charge of constructing a peta-ﬂops supercomputer,currently known as the “K” computer. I was involved in HPCI Strategic Program Field 5 (URL:
http://www.jicfus.jp/field5/en/) to develop applications in nuclear physics for the K computer. This
became one of major research issues in the TNP Laboratory. We made extensive eﬀort to develop computercodes for large-scale parallel computation, based on
the time-dependent density-functional approaches tocollective dynamics in nuclei. Our project on the K
computer produced a number of novel results in theﬁeld of nuclear physics, including photonuclear reaction, nucleus-nucleus collision, charge-exchange reaction, and neutrinoless double-beta decay.
University of Tokyo and University of Tsukuba established Joint Center for Advanced High Performance
Computing (JCAHPC). JCAHPC has recently introduced a new supercomputer system “Oakforest-PACS”
with 25 PFLOPS peak performance, currently thefastest in Japan. The developments done in the TNPLaboratory have produced several applications, running on the Oakforest-PACS.
I thank all the former members and visiting scientists in the TNP Laboratory. Their contributions andsupport were essential elements to keep the TNP Laboratory lively and active. More details about researches
and history of the TNP Laboratory can be found at
the following site:
http://www.nishina.riken.jp/lab/TNP/.
Cheers and thank you to all!

The Theoretical Nuclear Physics (TNP) Laboratory
started in August 2007 when I was appointed as an
Associate Chief Scientist. This was the ﬁrst researchgroup in RIKEN focusing on studies of theoretical nuclear physics. Main aims of the Laboratory were to develop theories for ﬁnite quantum many-body systems
and to discover/predict new concepts/phenomena inexotic nuclei. To achieve these goals, we have also developed eﬃcient computational methodologies. Dailycontacts with experimental groups provided us withstimulating environments. It was an exciting opportunity as a member of RIKEN Nishina Center, sitting
inside the most powerful RI-beam facility in the world.
Soon after the TNP Laboratory was established,
Dr. Kohama, who was a research staﬀ working on thenuclear theory, moved to the TNP Laboratory fromHeavy-Ion Nuclear Physics (HINP) Laboratory (ChiefSci.: Dr. Motobayashi). Thanks to many brilliant
young postdoctoral fellows, we succeeded to maintaina high level of activities in our group. The numberof group members changed year by year, but steadily
increased up to 2010. Dr. Dinh Dang, who had been aNishina Center Research Scientist in the HINP Laboratory, also joined the TNP Laboratory in 2010 when
the HINP Laboratory was closed at the retirement ofDr. Motobayashi. We had fourteen members and several regular visitors in 2010. In 2013, I myself decided
to leave RIKEN, and moved to University of Tsukuba
in April 2014. Since then, the group was entering aclosing stage, for which I was acting as an invited grouphead for two years. There were three postdocs in 2014,
only one in 2015. And Then There Were None. The
TNP Laboratory was oﬃcially closed in March 2016.
Exploring elementary modes of excitation in nuclei
was one of major research subjects in the TNP Laboratory; collective motion under ultra-fast rotation, thoseassociated with the isospin degrees of freedom, shellstructure dependence, non-adiabatic eﬀect, strong anharmonicity in low-lying collective states, and theirdissipation. The ﬁniteness of nucleus and the nature of
the strong interaction lead to unique properties of collective modes. We were interested in this uniquenessof nuclear-structure physics as a strong-coupling ﬁnitequantum system. Currently in University of Tsukuba,
I am working on somewhat continuous line of thesesubjects, together with graduate students.
Theoretical methodologies developed in nuclear
physics have many things in common in other ﬁeldsof physics. In the TNP Laboratory, there were ac∗1
∗2
∗3

Associate Chief Scientist of Theoretical Nuclear Physics
Laboratory (2007–2016)
Center for Computational Sciences, University of Tsukuba
iTHES Research Group, RIKEN

Fig. 1. Photograph on March 28, 2016, at RIBF Conf.
Room.

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