Research Activities 1991–2016

RIKEN Accel. Prog. Rep. 50 (2017)

Superheavy element research at RIKEN Nishina Center
K. Morimoto ∗1 and K. Morita ∗2,∗3
The study of the heaviest nuclei (elements) by using
heavy-ion beams is one of the most important researchsubjects. When the RIKEN Ring Cyclotron (RRC) was
being constructed in 1985, Dr. Kosuke Morita designed
and constructed the Gas-ﬁlled-type Recoil Ion Separator (GARIS) as the ﬁrst large-scale experimental equipment in the experimental hall E1. New isotopes, 195 At,196
Rn, 197 Rn, 199 Fr, and 200 Fr, were discovered using
RRC and GARIS.
In 2000, the RIBF project was started, and GARIS
was relocated from the E1 room to the energy-upgraded
RIKEN Linear Accelerator (RILAC) facility by adding
CSM accelerators in order to start a full-scale experiment to search for new elements. With the technicaldevelopments of both the accelerator/ion source and theexperimental setups, the experimental system had thehighest possibility in the world of providing the heaviest elements. First, follow-up experiments conductedby the preceding research group, Gesellschaft fur Schwerionenforschung (GSI), were performed. In these experiments, elements 108, 110, 111, and 112 were produced with the highest production rate to date. The
experiment aimed at discovering the 113th element wasstarted in 2003 by using the 209 Bi(70 Zn, n)278 113 reaction. Three decay chains originating from 278 113 weresuccessfully observed in 2004,1) 2005,2) and 2012.3) Furthermore, a connection to the known isotopes 266 Bh and262
Db was established using the 248 Cm(23 Na, 5n)266 Bhreaction in 2009. The prolonged experimental eﬀort for278
113 was concluded in Oct. 2012. The three decaychains of 278 113 are presented in Fig. 1.
IUPAC ﬁnally decided to give our research group theFig. 1. Decay chains related to 278 113. The ﬁrst two decay chains consist of four alpha decays and end with thespontaneous ﬁssion of 262 Db. The third decay chain consists of six alpha decays and is connected to 254 Md.
∗1
∗2

∗3

RIKEN Nishina Center
Director of Research Group for Superheavy Element, RIKEN
Nishina Center (2013–present); Associate Chief Scientist ofSuperheavy Element Laboratory (2006–2013)
Department of Physics, Kyusyu University

S-67right to name and determine the symbol for the element 113 in Dec. 2015. We proposed the name Nihonium with the symbol Nh. The name and symbol
were ﬁnally accepted by IUPAC in Nov. 2016. Figure 2 shows the group members who participated in thenaming meeting.

Fig. 2. Research group members after the conclusion of thenaming meeting of the element 113.

Aiming to discover further new elements, a new Gasﬁlled Recoil Ion Separator (GARIS-II) for asymmetric reaction such as hot fusion reaction was developed.
GARIS-II has a large angular acceptance (18.5 msr)
and short path length. The transmission of GARISII is 1.7 times higher than that of the present GARIS.
New element search using the hot fusion reaction will
be started in the near future at RIKEN Nishina Center.

Fig. 3. Photograph of the GARIS-II separator. The separator has a Q-D-Q-Q-D conﬁguration.

References
1) K. Morita et al., J. Phys. Soc. Jpn. 73,73,2593
2593(2004).
(2004).
2) K. Morita et al., J. Phys.
76, 045001
045001 (2007).
(2007).
Phys. Soc.
Soc. Jpn.
Jpn. 76,3) K. Morita et al., J. Phys.
81, 103201
103201 (2012).
(2012).
Phys. Soc.
Soc. Jpn.
Jpn. 81,