Speaker
Dr
Hooi Jin Ong
(RCNP, Osaka University)
Description
The reduced E2 transition probability from the first excited 2+ (2^+_1) state to the ground state --- B(E2) --- of an even-even nucleus is an important observable that reflects proton collectivity. Recently, an anomalously small B(E2) was reported for the neutron-rich 16C nucleus [1]. The result points to a suppressed proton contribution to the transition strength. This finding raises an intriguing question as to whether or not the neutron contribution is similarly small for the relevant quadrupole excitation. Results from two subsequent experiments [2,3] suggest that the neutron contribution is ``normal''. When combined with the B(E2) value, the results indicate a neutron-dominant quadrupole excitation in 16C.
To shed light on the exotic phenomenon exhibited by 16C and to explore the structural evolution of the carbon isotopes towards the neutron dripline, we have carried out an experiment to determine the B(E2) value for the neighboring 18C nucleus.
To determine the B(E2) value for 18C, we have performed an experiment to measure the mean lifetime of the 2^+_1 in 18C using an upgraded recoil shadow method (RSM) [1]. The experiment was performed at the RIKEN Nishina Center using the RIPS beamline [4]. Besides 18C, we have also remeasured the mean lifetime of the 2^+_1 in 16C. The B(E2) values for 16,18C thus determined were about seven and five times smaller than the empirical values, indicating that the anomalously hindered E2 transition observed in 16C persists in 18C. Details of the experiment will be presented and the results will be discussed.
Reference
[1] N. Imai et al., Phys. Rev. Lett. 92 (2004) 062501.
[2] Z. Elekes et al., Phys. Lett. B586 (2004) 34.
[3] H. J. Ong et al., Phys. Rev. C 73 (2006) 024610.
[4] T. Kubo et al., Nucl. Instrum. Methods B73 (1992) 309.
Primary author
Dr
Hooi Jin Ong
(RCNP, Osaka University)
Co-authors
Mr
Daisuke Suzuki
(Univ. of Tokyo)
Dr
Hidetada Baba
(RIKEN Nishina Center)
Dr
Hironori Iwasaki
(Univ. of Tokyo)
Prof.
Hiroyoshi Sakurai
(RIKEN Nishina Center)
Prof.
Kazuo Kurita
(Rikkyo Univ.)
Dr
Masaru Suzuki
(Univ. of Tokyo)
Prof.
Masayasu Ishihara
(RIKEN Nishina Center)
Dr
Nobuaki Imai
(KEK)
Dr
Nori Aoi
(RIKEN Nishina Center)
Dr
Satoshi Takeuchi
(RIKEN Nishina Center)
Dr
Shawn Bishop
(RIKEN Nishina Center)
Dr
Shunsuke Ota
(CNS, Univ. of Tokyo)
Prof.
Takashi Nakamura
(Titech)
Dr
Takeo Onishi
(Univ. of Tokyo)
Mr
Taro Nakao
(Univ. of Tokyo)
Prof.
Tohru Motobayashi
(RIKEN Nishina Center)
Mr
Toshifumi Okumura
(Titech)
Prof.
Toshiyuki Kubo
(RIKEN Nishina Center)
Dr
Yasuhiro Togano
(Rikkyo Univ.)
Dr
Yoshiyuki Yanagisawa
(RIKEN Nishina Center)
Dr
Yosuke Kondo
(RIKEN Nishina Center)
Dr
Yuichi Ichikawa
(Univ. of Tokyo)
