Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Measurement of isoscalar giant monopole resonance in 132 Sn using
CNS active target
S. Ota,∗1 H. Tokieda,∗1 C. Iwamoto,∗1 M. Dozono,∗1 U. Garg,∗2 S. Hayakawa,∗1 K. Kawata,∗1 N. Kitamura,∗1M. Kobayashi,∗1 S. Masuoka,∗1 S. Michimasa,∗1 A. Obertelli,∗3,∗4 D. Suzuki,∗4 R. Yokoyama,∗1 J. Zenihiro,∗4H. Baba,∗4 O. Beliuskina,∗1 S. Chebotaryov,∗4 P. Egelhof,∗5 T. Harada,∗6 M.N. Harakeh,∗7 K. Howard∗2N. Imai,∗1 M. Itoh,∗8 Y. Kiyokawa,∗1 C.S. Lee,∗1 Y. Maeda,∗9 Y. Matsuda,∗8 E. Milman,∗4 V. Panin,∗4
H. Sakaguchi,∗10 P. Schrock,∗1 S. Shimoura,∗1 L. Stuhl,∗4 M. Takaki,∗1 K. Taniue,∗9 S. Terashima,∗11T. Uesaka,∗4 Y.N. Watanabe,∗12 K. Wimmer,∗1,∗4,∗12 K. Yako,∗1 Y. Yamaguchi,∗1 Z. Yang,∗4 and K. Yoneda∗4
as 106 particles per second.2)
The experiment was performed at RIBF at RIKEN.
A secondary 132 Sn beam was produced as a ﬁssion fragment of a 238 U beam impinging on the primary beryllium target. The maximum intensity of the primarybeam was 37 pnA. The typical intensities of the secondary beam at F3 and F7 were 8.5×105 and 3.2×105
particles per second, respectively. In order to identify
the particles in such a high-intensity beam on an eventby-event basis, a new method called TOF-Bρ-Bρ3) wasintroduced. The TOF was measured by 200-μm-thickdiamond detectors located at F3 and F7. Bρ was determined using the positions and angles measured by
low-pressure multi-wire drift chambers at F3, F5, andF7. The main components of the secondary beam were132
Sn, 133 Sb, and 134 Te with the purities of 21%, 46%,and 25% at F7, respectively. The data from the beamline detectors at each focus are taken using MOCO4) .
The CAT was placed at F8 with a collimator in frontof it. The CAT was operated with deuterium gas at
0.4 atm and a stack of three THGEMs. The signals
from the CAT were digitized using the V1740 modules(CAEN) and digitized samples were transfered throughoptical links to two computers. The physics trigger forthe data acquisition was made using the trigger out
from V1740 and HIMP, which is the readout systemused for the silicon detectors. The ESPRI system wasplaced at F125) to measure the deuteron elastic scattering oﬀ 132 Sn for large scattering angles to determine
the optical potential parameters.
The excitation-energy resolution for the groundstate, determined from the analysis of recoil particles
stopped in TPC, is 1 MeV in one standard deviation. The energy of ISGMR will be deduced from themultipole-decomposition analysis of double-diﬀerential
cross sections. The analysis is in progress.

The equation of state (EoS) of nuclear matter not
only governs the femto-scale quantum many-body system, namely nuclei, but also plays an important rolein the structure of neutron stars and in supernova phenomena. In particular, the EoS of isospin asymmetricnuclear matter attracts much interest from the view
point of the existence of heavy neutron stars. The
asymmetric term of incompressibility, Kτ , can be abenchmark for various EoSs because it can be directlydeduced from the the energies of the isoscalar giant
monopole resonance (ISGMR) measured along an isotopic chain, such as tin isotopes.1) The present value ofKτ is -550±100 MeV and its error is relatively larger
than those of other parameters of the EoS. In order toimprove the Kτ value, the measurement on the isotopic
chain should be extended to unstable nuclei. A doubly
magic tin isotope, 132 Sn, has been chosen as a ﬂagshipfor the measurements of unstable tin isotopes becauseof its large isospin asymmetry and double magic nature.
The excitation energy and scattering angle inthe center-of-mass frame are extracted by means of
missing-mass spectroscopy, where the low-energy recoil
deuteron has to be measured. In order to measure such
low-energy recoils, a gaseous active target system, CNS
active target (CAT), has been employed. The CAT
consists of a time-projection chamber (TPC) and anarray of silicon detectors on both sides of TPC. A stackof thick gas electron multipliers (THGEM) is used forelectron multiplication in the TPC. The THGEM has
three-fold segmented electrodes. The center electrodeis used for measuring the beam particles and the sideelectrodes are used for measuring the recoil particles.
The multiplication factors at the beam and recoil region can be controlled independently, which enables us
to operate the CAT with a beam of high intensity such
∗1Center for Nuclear Study, the University of Tokyo
Department of Physics, University of Notre Dame
∗3 Le Centre CEA de Saclay∗4 RIKEN Nishina Center∗5 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗6 Department of Physics, Toho University∗7 KVI, Center for Advanced Radiation Technology∗8 Cyclotron and Radio Isotope Center, Tohoku University∗9 Department of Applied Physics, University of Miyazaki∗10 Research Center for Nuclear Physics, Osaka University∗11 Beihang University∗12 Department of Physics, the Univerisity of Tokyo

References∗21) T. Li et al., Phys. Rev. Lett. 99, 162503 (2007).
2) S. Ota et al., J. Radioanal. Nucl. Chem. 305, 907-911(2015).
3) S. Ota et al., RIKEN Accel. Prog. Rep. 49 15 (2017)7).
4) H. Baba et al., in this report.
5) J. Zenihiro et al.: in this report.

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