Ⅱ-1. Nuclear Physics
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Study of νp-process nucleosynthesis at OEDO
D. Suzuki,∗1 B. Mauss,∗2 N. Imai,∗3 S. Michimasa,∗3 D. Beaumel,∗4,∗1 K. Y. Chae,∗5 S. Cherubini,∗6T. Chillery,∗3 M. Dozono,∗7,∗1 M. Egeta,∗8,∗1 F. Endo,∗8,∗1 N. Fukuda,∗1 T. Haginouchi,∗8,∗1 S. Hanai,∗3S. Hayakawa,∗3 Y. Hijikata,∗7,∗1 J. W. Hwang,∗9 S. Ishio,∗8,∗1 N. Iwasa,∗8,∗1 S. Kawase,∗10,∗1 K. Kawata,∗3R. Kojima,∗3 S. Kubono,∗1 M. La Cognata,∗6 J. Li,∗3 N. Nishimura,∗1 K. Okawa,∗3 M. Oishi,∗10,∗1H. J. Ong,∗11,∗1,∗12 S. Ota,∗12 S. Palmerini,∗13,∗14 R. Pizzone,∗6 T. Saito,∗3 H. Sakurai,∗1 S. Shimoura,∗3,∗1
Y. Shimizu,∗1 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 H. Tanaka,∗15,∗1 M. Tanaka,∗1 X. Tang,∗12T. Teranishi,∗15,∗1 Y. Togano,∗1 A. Tunimo,∗6 Y. Wang,∗16 K. Yako,∗3 K. Yahiro,∗7,∗1 H. Yamaguchi,∗3R. Yokoyama,∗3 K. Yoshida,∗1 R. Yoshida,∗7,∗1 and M. Yoshimoto∗156Neutron-deﬁcient stable isotopes, referred to as pnuclei, are known to be produced by p process nucleosynthesis. However, certain lighter p-nuclei, e.g. Moand Ru, are signiﬁcantly underproduced in the present
astrophysical scenario. The νp process1) ascribes their
origin to core-collapse supernovae, wherein the availability of neutrons aids the ﬂow to bypass the waiting
point 56 Ni on the synthesis path. The neutron capture
cross section of 56 Ni, howeve, remains experimentally
unknown because both the neutron and 56 Ni are shortlived. To evaluate the cross sections, we applied thesurrogate method2) to the (d, p) reaction by using anenergy-degraded 56 Ni beam at OEDO.
The experiment was performed at the OEDO beamline of RIBF. The secondary beam was produced by
the projectile fragmentation reaction of a 78 Kr beamat 345 MeV/nucleon and puriﬁed by the BigRIPS fragment separator. The total beam intensity at F3 wasmeasured to be about 500 kpps (particles per second)with a purity of about 30% for 56 Ni. The impurities
included 55 Co (50%) and 54 Fe (10%), both isotones of56
Ni with N = 28. The energy of 56 Ni transmitted
from BigRIPS to OEDO was about 113 MeV/nucleon.
The beam energy was degraded at FE9 by an angletunable wedge-shaped degrader (3 mm in central thickness) together with a ﬂat degrader (0.3 mm in thickness),3) both made of aluminum. The angle of theformer was set to 4 mrad to obtain a desired beamenergy. The beam energy of 56 Ni was estimated tobe 15.1(10) MeV/nucleon based on the time of ﬂight
measurement from FE9 to FE12. The RF deﬂector at
FE10 was operated at 100 kV to reduce the spot size ofNi. The phase shift of RF was optimized to increase
the transmission through the target frame aperture of
50 mm in diameter (Fig. 1). The transmission from F3
to FE12 was about 75% with a total rate of 370 kpps
at FE12. CD2 targets of 285 and 644 µg/cm2 , provided by INFN, were set at S0 about 1 m downstreamof FE12. The incident position and angle of the secondary beam were deduced by a pair of SR-PPACs4)
in the vacuum chamber of FE12. The recoiling protons were detected by the silicon and CsI detectors
array TiNA.5) Missing mass spectra are deduced fromthe scattering angle and total kinetic energy measured
by TiNA. The scattered particles were transmitted toa QQD spectrometer at zero degrees for the particle
identiﬁcation, which facillitated the determination ofthe decay channels. The spectrometer was equippedwith a pair of SR-PPACs followed by an ionizationchamber with CF4 gas at 100 Torr. The transmission
through the spectrometer was roughly 50%.

Fig. 1. Horizontal position at S0 vs. TOF from F3 to FE9of the secondary beam with the optimal RF settings.

∗1RIKEN Nishina Center∗2 CEA-DAM∗3 Center for Nuclear Study, University of Tokyo∗4 IJClab, IN2P3, CNRS
∗5 Department of Physics, Sungkyunkwan Unviversity∗6 INFN Laboratori Nazionali del Sud∗7 Department of Physics, Kyoto University∗8 Department of Physics, Tohoku University∗9 CENS, Institute for Basic Science∗10 IGSES, Kyushu University∗11 Institute of Modern Physics, Chinese Academy of Sciences∗12 Research Center for Nuclear Physics, Osaka University∗13 INFN Sezione di Perugia∗14 Department of Physics, University of Perugia∗15 Department of Physics, Kyushu University∗16 Department of Physics, Tsinghua University

The data analysis is underway. The current focus isdirected towards the beam tracking detectors.
References
1) C. Fröhlich et al., Phys. Rev. Lett. 96, 142502 (2006).
2) N. Imai et al., submitted to Phys. Lett. B.
3) J. W. Hwang et al., RIKEN Accel. Prog. Rep. 53, 16(2020).
4) S. Hanai, Master thesis, University of Tokyo (2021).
5) B. Mauss et al., RIKEN Accel. Prog. Rep. 54, 114(2021).

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