Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Shell evolution at N = 40 towards 60 Ca: Spectroscopy of 62 Ti
M. L. Cortés,∗1 W. Rodriguez,∗2,∗1 P. Doornenbal,∗1 A. Obertelli,∗3,∗4,∗1 N. Achouri,∗5 H. Baba,∗1 F. Browne,∗1D. Calvet,∗4 F. Château,∗4 S. Chen,∗6,∗1 N. Chiga,∗1 A. Corsi,∗4 A. Delbart,∗4 J-M. Gheller,∗4 A. Giganon,∗4A. Gillibert,∗4 C. Hilaire,∗4 T. Isobe,∗1 T. Kobayashi,∗8 Y. Kubota,∗1,∗7 V. Lapoux,∗4 H. N. Liu,∗4,∗9T. Motobayashi,∗1 I. Murray,∗10,∗1 H. Otsu,∗1 V. Panin,∗1 N. Paul,∗4 H. Sakurai,∗1,∗11 M. Sasano,∗1D. Steppenbeck,∗1 L. Stuhl,∗7 Y. L. Sun,∗4 Y. Togano,∗12,∗1 T. Uesaka,∗1 K. Wimmer,∗11,∗1 K. Yoneda,∗1O. Aktas,∗9 T. Aumann,∗3 L. X. Chung,∗13 F. Flavigny,∗10 S. Franchoo,∗10 I. Gasparic,∗14,∗1 R.-B. Gerst,∗15J. Gibelin,∗5 K. I. Hahn,∗16 D. Kim,∗16,∗1 T. Koiwai,∗11 Y. Kondo,∗17 P. Koseoglou,∗3,∗18 J. Lee,∗19 C. Lehr,∗3B. D. Linh,∗13 T. Lokotko,∗19 M. MacCormick,∗10 K. Moschner,∗15 T. Nakamura,∗17 S. Y. Park,∗16,∗1D. Rossi,∗18 E. Sahin,∗20 D. Sohler,∗21 P-A. Söderström,∗3 S. Takeuchi,∗17 H. Toernqvist,∗18 V. Vaquero,∗22V. Wagner,∗3,∗1 S. Wang,∗23 V. Werner,∗3 X. Xu,∗19 H. Yamada,∗17 D. Yan,∗23 Z. Yang,∗1 M. Yasuda,∗17 andL. Zanetti∗3
state of 62 Ti is necessary.
In the third SEASTAR campaign, 62 Ti was produced by proton knock-out of 63 V at 250 MeV/nucleon
on the MINOS liquid hydrogen target.9) The 63 V
isotopes were produced by fragmentation of a345 MeV/nucleon primary beam of 70 Zn impinging on
a 10-mm Be target and separated using the BigRIPSspectrometer. The average intensity of the Zn beam
was 250 pnA, and the average rate of 63 V was 3 pps.
The MINOS target, of 150 mm length, was placedat the F13 experimental area, in front of the SAMURAI magnet. Reaction products were identified on an
event-by-event basis using the standard SAMURAI detectors.8) NEBULA and NeuLAND neutron detectors
were also used during the experiment. γ-rays emittedby the reaction products were detected using the upgraded DALI2+ array,10) consisting of 226 NaI detectors surrounding MINOS. The ongoing data analysis
has already provided the incoming particle identification as shown in Fig. 1.

Experimental evidence collected in the last years
show the disappearance of the shell closures at N = 8,
20 and 28 in various neutron-rich isotopes, as well as
the appearance of new magic numbers, such as N = 32
and 34 for Ca isotopes.1,2) Given that N = 40, whichcorresponds to the filling of the f p neutron shells, ispredicted to be a sub-shell closure, the study of thestructure of N = 40 isotones can provide insight into
the mechanism governing shell evolution. A low collectivity is observed in 68 Ni, consistent with the magic
character of N = 40.3) However, for the Fe and Cr isotopes, a monotonous decrease of the 2+ energy withincreasing neutron number is observed.4,5) Such a decrease, which extends beyond N = 40, indicates a
rapid increase of collectivity when removing protons
from the f7/2 shell. For the case of the Ti isotopes,measurements of the 2+ energy of 58, 60 Ti 6,7) do notshow an unexpected decrease towards N = 40, although it has been suggested that full consideration ofthe g9/2 orbital is required to understand the structureat N = 40.7) To further understand the shell evolution
in N = 40 isotones towards the supposedly doublymagic 60 Ca, the measurement of the first excited 2+∗1

RIKEN Nishina Center
Departamento de Fı́sica, Universidad Nacional de Colombia∗3 Institut für Kernphysik, Technische Universität Darmstadt∗4 IRFU, CEA, Université Paris-Saclay∗5 LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3∗6 Department of Physics, Peking University∗7 Center for Nuclear Study, University of Tokyo∗8 Department of Physics, Tohoku University∗9 Department of Physics, Royal Institute of Technology∗10 IPN Orsay, CNRS, Univ. Paris Sud, Univ. Paris Saclay∗11 Department of Physics, University of Tokyo∗12 Department of Physics, Rikkyo University∗13 Institute for Nuclear Science & Technology, VINATOM∗14 Rudjer Boskovic Institute∗15 Institut für Kernphysik, Universität zu Köln∗16 Ewha Womans University∗17 Department of Physics, Tokyo Institute of Technology∗18 GSI Helmoltzzentrum für Schwerionenforschung GmbH
∗19 Department of Physics, The University of Hong Kong
∗20 Department of Physics, University of Oslo
∗21 MTA Atomki∗22 Instituto de Estructura de la Materia, CSIC
∗23 Institute of Modern Physics, Chinese Academy of Sciences∗2Fig. 1. Incoming particle ID. 63 V is labeled in red.

References
1) F. Wienholtz et al., Nature (London) 498, 346 (2013).
2) D. Steppenbeck et al., Nature (London) 502, 207(2013).
3) O. Sorlin et al., Phys. Rev. Lett. 88, 092501 (2002).
4) J. Ljungvall et al., Phys. Rev. C 81, 061301 (2010).
5) A. Gade et al., Phys. Rev. C 81, 051304 (2010).
6) H. Suzuki et al., Phys. Rev. C 88, 024326 (2013).
7) A. Gade et al., Phys. Rev. Lett. 112, 112503 (2014).
8) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
9) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).
10) I. Murray et al., in this report.

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