RIKEN Accel. Prog. Rep. 50 (2017)

Research Activities 1991–2016

Spin Isospin Laboratory
Tomohiro Uesaka∗1ment Group, we have constructed a heavy-ion storage
ring, the Rare RI Ring, for precise mass measurementsof short-lived radioactive nuclei. Masses of the radioactive nuclei play a decisive role in the establishment of
our understanding of nucleosynthesis, such as the rapid
neutron capture process (r-process) and the rapid proton capture process (rp-process), in the Universe.
During 2014–2016, we accomplished two important
technical achievements. One is the world’s ﬁrst realization of individual injection to a storage ring.4) This
technique has paved the way in the ﬁeld of storage-ringscience and has opened up applications in cyclotron
facilities. The other is the construction of a Schottky pickup detector with the world’s highest sensitivity. We have tested the newly constructed Schottky
pickup detector with a 78 Kr beam at 168 MeV/nucleon
and have conﬁrmed that the sensitivity is twice thosein other facilities. Mass measurements of radioactive
nuclei will start soon.
The last pillar consists of interdisciplinary studies
based on a nuclear polarization technique. We havedeveloped a method to produce nuclear polarization
using photo-excited triplet states of pentacene (TripletDNP ). A distinguished feature of the Triplet-DNP
technique is that it works under a low magnetic ﬁeldof 0.1–0.7 T and at a high temperature of 77–300 K, in
striking contrast to standard dynamic nuclear polarization (DNP) techniques working in extreme conditionsof magnetic ﬁelds of several Tesla and sub-Kelvin temperatures. We have applied the technique to constructa polarized proton target system for use in RI-beam experiments and performed several experiments at RIPS
and SAMURAI.
The nuclear polarization technique is now being applied to a broad ﬁeld of science: a research program
to apply the Triplet-DNP technique for sensitivity enhancement in the NMR spectroscopy of biomolecules
started in 2016 in close collaboration with QBiC
(RIKEN), Yokohama City University, the University ofTokyo, and Kansei Gakuin University. In the program,protein-protein interaction in a relatively short timescale will be investigated via two-dimensional NMR
spectroscopy with sensitivity enhanced by the TripletDNP method. The ﬁrst results will be obtained in afew years.

The Spin Isospin Laboratory was started on 1stApril, 2011 and, as of July 2017, consists of ﬁve staﬀ researchers (one is concurrently appointed), nine postdoc
researchers, two JRA, three IPA, four resident trainees,secretaries, and several tens of visiting researchers.
The Spin Isospin Laboratory pursues research activities with a primary focus on the interplay of spin andisospin in exotic nuclei. Understanding nucleosynthesis in the universe, especially in r- and rp-processes, isanother signiﬁcant goal of our laboratory.
The three big pillars of our research activities are
as follows: 1) direct reaction studies of nuclear matter and structure, 2) storage ring experiments for nuclear physics and nuclear astrophysics, and 3) interdisciplinary studies based on a nuclear polarization technique.
Direct reaction studies of nuclear matter and structure are being conducted mainly with the SAMURAIand SHARAQ spectrometers. We investigate spinisospin responses in nuclei with newly developed experimental methods. Highlights from the activities are
an observation of β + -type isovector spin monopole resonances (IVSMR) in 208 Pb and 90 Zr via the (t, 3 He)
reaction at 300 MeV/nucleon 1) and the discovery of
a candidate of tetraneutron resonant state via the4He(8 He, 8 Be) reaction.2) Another double-charge exchange reaction, (12 C, 12 Be(0+2 )), is planned to be used
to search for yet-to-be-discovered double Gamow-Teller
resonances.
To investigate spin-isospin properties, the neutronskin thickness, and the incompressibility for a single
symbolic nucleus, in this case the doubly magic 132 Sn,
we performed three experiments during 2014–2016: the(p, n) experiment to probe spin-isospin responses conducted in 2014 with the WINDS neutron detector andSAMURAI, the proton elastic scattering experiments
to determine the neutron-skin thickness with the ESPRI setup, and the (d, d ) experiment to extract theincompressibility performed with the CNS active target. Results from the three experiments will provide
us a better understanding of isospin dependencies ofnuclear-matter properties.
The laboratory hosted the MINOS setup from CEA
Saclay and the NeuLAND neutron detector from GSI,and performed the SEASTAR campaigns 3) in collaboration with the RI Physics laboratory and the SAMURAI experiments to explore multi-neutron correlations
in near- and beyond-dripline nuclei such as tetraneutron, 7 H, 11 Li, 17 B, and 28 O.
The second pillar consists of storage ring experiments for nuclear physics and nuclear astrophysics. In
close collaboration with the Instrumentation Develop∗1References
1) K. Miki et al., RIKEN Accel. Prog. Rep. 44, iii (2011)
and Phys. Rev. Lett. 108, 262503 (2012).
2) K. Kisamori et al., RIKEN Accel. Prog. Rep. 49, 3(2016) and Phys. Rev. Lett. 116 052501 (2016).
3) C. Santamaria et al., RIKEN Accel. Prog. Rep. 49, 1(2016) and Phys. Rev. Lett. 115 192501 (2016).
4) Y. Yamaguchi et al., RIKEN Accel. Prog. Rep. 49, 18(2016).

Chief Scientist of Spin Isospin Laboratory (2011–present)

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