Magic Nature of Neutrons in ^{54}Ca: First Mass Measurements of ^{55-57}Ca

S Michimasa; M Kobayashi; Y Kiyokawa; S Ota; D S Ahn; H Baba; G P A Berg; M Dozono; N Fukuda; T Furuno; E Ideguchi; N Inabe; T Kawabata; S Kawase; K Kisamori; K Kobayashi; T Kubo; Y Kubota; C S Lee; M Matsushita; H Miya; A Mizukami; H Nagakura; D Nishimura; H Oikawa; H Sakai; Y Shimizu; A Stolz; H Suzuki; M Takaki; H Takeda; S Takeuchi; H Tokieda; T Uesaka; K Yako; Y Yamaguchi; Y Yanagisawa; R Yokoyama; K Yoshida; S Shimoura

doi:10.1103/PhysRevLett.121.022506

Magic Nature of Neutrons in ^{54}Ca: First Mass Measurements of ^{55-57}Ca

Phys Rev Lett. 2018 Jul 13;121(2):022506. doi: 10.1103/PhysRevLett.121.022506.

Authors

S Michimasa¹, M Kobayashi¹, Y Kiyokawa¹, S Ota¹, D S Ahn², H Baba², G P A Berg³, M Dozono¹, N Fukuda², T Furuno⁴, E Ideguchi⁵, N Inabe², T Kawabata⁴, S Kawase⁶, K Kisamori¹, K Kobayashi⁷, T Kubo^{8

9}, Y Kubota², C S Lee^{1

2}, M Matsushita¹, H Miya¹, A Mizukami¹⁰, H Nagakura⁷, D Nishimura¹¹, H Oikawa¹⁰, H Sakai², Y Shimizu², A Stolz⁹, H Suzuki², M Takaki¹, H Takeda², S Takeuchi¹², H Tokieda¹, T Uesaka², K Yako¹, Y Yamaguchi¹, Y Yanagisawa², R Yokoyama¹³, K Yoshida², S Shimoura¹

Affiliations

¹ Center for Nuclear Study, The University of Tokyo, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
² RIKEN Nishina Center for Accelerator-Based Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
³ Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
⁴ Department of Physics, Kyoto University, Kitashirakawa-Oiwake, Sakyo, Kyoto 606-8502, Japan.
⁵ Research Center for Nuclear Physics, Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
⁶ Department of Advanced Energy Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
⁷ Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan.
⁸ Facility for Rare Isotope Beams, Michigan State University, 640 South Shaw Lane, East Lansing, Michigan 48824, USA.
⁹ National Superconducting Cyclotron Laboratory, Michigan State University, 640 South Shaw Lane, East Lansing, Michigan 48824, USA.
¹⁰ Department of Physics, Tokyo University of Science, Noda, Chiba 278-8510, Japan.
¹¹ Department of Physics, Tokyo City University, Tamazutsumi 1-28-1, Setagaya-ku, Tokyo 158-8557, Japan.
¹² Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
¹³ Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA.

PMID: 30085708
DOI: 10.1103/PhysRevLett.121.022506

Abstract

We perform the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number 34 at the RIKEN Radioactive Isotope Beam Factory by using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ^{55-57}Ca are determined for the first time to be -18650(160), -13510(250), and -7370(990) keV, respectively. We examine the emergence of neutron magicity at N=34 based on the new atomic masses. The new masses provide experimental evidence for the appearance of a sizable energy gap between the neutron 2p_{1/2} and 1f_{5/2} orbitals in ^{54}Ca, comparable to the gap between the neutron 2p_{3/2} and 2p_{1/2} orbitals in ^{52}Ca. For the ^{56}Ca nucleus, an open-shell property in neutrons is suggested.