Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Single-particle states in fp-shell nuclei through 50 Ca(d, p)51 Ca
transfer reaction
C. Ferrera,∗1 K. Wimmer,∗2,∗3 D. Suzuki,∗3 N. Imai,∗4 M. Armstrong,∗5 T. Chillery,∗4 Y. Cho,∗6M. Dozono,∗3,∗7 F. Endo,∗8,∗3 S. Escrig,∗1 N. Fukuda,∗3 T. Haginouchi,∗3,∗8 S. Hanai,∗4 S. Hayakawa,∗4Y. Hijikata,∗3,∗7 J. W. Hwang,∗6 S. Ishio,∗3,∗8 A. Jungclaus,∗1 A. Kasagi,∗9,∗10 K. Kawata,∗4 N. Kitamura,∗4R. Kojima,∗4 J. Li,∗4 S. Masuoka,∗4 S. Michimasa,∗4 B. Moon,∗6 K. Okawa,∗4 S. Ota,∗4,∗11 T. Saito,∗4H. Sakurai,∗3 Y. Shimizu,∗3 S. Shimoura,∗3,∗4 Y. Son,∗6 T. Sumikama,∗3 H. Suzuki,∗3 H. Takeda,∗3Y. Togano,∗3 J. Vesic,∗12 K. Yako,∗4 R. Yokoyama,∗4 K. Yoshida,∗3 and M. Yoshimoto∗3Neutron-rich Ca isotopes towards neutron number
N = 34 are pivotal for exploring the evolution of thef p-shell orbitals. Beyond the N = 28 shell gap in48
Ca, new magic numbers at N = 32 and 34 were
established through spectroscopy of low-lying statesand mass measurements. Most recently, the spatial
extension of the 1f7/2 and 2p3/2 neutron orbitals wasdetermined via a one-neutron knockout reaction from52Ca.1) However, the single-particle 2p1/2 and 1f5/2 orbitals deﬁning the shell gaps at N = 32, 34 remain tobe established experimentally. The one-neutron transfer reaction is an experimental method well-suited to
study low-spin single-particle orbitals. The cross section of this reaction gives access to the spectroscopicfactors, while the angular distribution of the reaction
products allows for deduction of the angular momentum transfer.
In December 2022, the SHARAQ12 experiment wasperformed at RIKEN, aiming to study the singleparticle structure of 51 Ca via the (d, p) transfer reaction using an energy-degraded secondary 50 Ca beam.
The beam was produced at BigRIPS from a primary70
Zn beam at an energy of 345 MeV/nucleon fragmented on a Be target. For the energy degrading procedure, the 50 Ca beam was conducted to the OEDO2)
beamline, where a combination of an angle-tunablewedge-shaped degrader and an additional aluminum
ﬂat-plate degrader placed at FE9 successfully reduced
the beam energy to approximately 15 MeV/nucleon,
which improves the momentum matching of the reaction compared to the typical beam energies at RIBF.
Particle identiﬁcation based on the ToF-B ρ method
showed excellent isotope separation, is shown in Fig. 1,
where the 50 Ca beam can be clearly identiﬁed. Therefore, the use of the Radio-Frequency Deﬂector (RFD)

Fig. 1. Particle identiﬁcation in OEDO with horizontal position at FE9 and corrected time-of-ﬂight between F3
and FE9.

of OEDO was not required. The secondary target ofCD2 (260 µg/cm2 ) was placed at the SHARAQ spectrometer reaction chamber with the purpose of inducing one-neutron transfer reactions. The recoiling protons were measured with the detector setup TINA2,3)
consisting of a box of four TTT double-sided silicon
strip detectors backed by CsI crystals and a backward
annular YY1-type silicon strip detector array with CsI
crystals behind. The array was placed at laboratory
backward direction covering θlab = 95–165 deg (solidangle 35% of 4π) which is the angular range most sensitive to the angular momentum transfer of the reaction.
The excitation energy of states populated will be determined from the measured missing mass of the reaction.
Heavy 51 Ca ejectiles were measured by the QQD spectrometer equipped with a set of Strip-Readout PPAC
detectors and an ionization chamber, so backgroundcoming from fusion reactions can be suppressed via
charge identiﬁcation. The analysis of excitation energies and angular distributions is ongoing.

∗1

Instituto de Estructura de la Materia, CSICGSI Helmholtzzentrum für Schwerionenforschung GmbH
∗3 RIKEN Nishina Center∗4 Center for Nuclear Study, University of Tokyo∗5 Institute of Nuclear Physics, University of Cologne∗6 CENS Institute for Basic Science∗7 Department of Physics, Kyoto University∗8 Department of Physics, Tohoku University∗9 Department of Physics, Gifu University∗10 RIKEN Cluster for Pioneering Research∗11 Research Center for Nuclear Physics, Osaka University∗12 Department of Low and Medium Energy Physics, Jožef Stefan Institute∗2References
1) M. Enciu et al., Phys. Rev. Lett. 129, 262501 (2022).
2) S. Michimasa et al., Prog. Theor. Exp. Phys. 2019,
043D01 (2019).
3) P. Schrock et al., RIKEN Accel. Prog. Rep. 51, 20(2018).

-8-