Observation of isoscalar and isovector dipole excitations in neutron-rich 20 O

作者：N. Nakatsuka, H. Baba, T. Aumann, R. Avigo, Sanjoy Banerjee, A. Bracco, C. Caesar, F. Camera, S. Ceruti, Shasha Chen, V. Derya, P. Doornenbal, A. Giaz, A. Horvat, K. Ieki, Tsunenori Inakura, N. Imai, T. Kawabata, N. Kobayashi, Y. Kondo, S. Koyama, M. Kurata-Nishimura, S. Masuoka, M. Matsushita, S. Michimasa, B. Million, T. Motobayashi, T. Murakami, T. Nakamura, T. Ohnishi, H. J. Ong, S. Ota, H. Otsu, T. Ozaki, Akira Saito, H. Sakuraï, H. Scheit, F. Schindler, P. Schrock, Yoshinori Shiga, M. Shikata, S. Shimoura, D. Steppenbeck, T. Sumikama, I. Syndikus, H. Takeda, Shoji Takeuchi, A. Tamii, R. Taniuchi, Y. Togano, J. Tscheuschner, J. Tsubota, H. Wang, O. Wieland, K. Wimmer, Y. Yamaguchi, K. Yoneda, J. Zenihiro · 发表于：Physics Letters B · 年份：2017 · DOI：10.1016/j.physletb.2017.03.017 · 被引用次数：29 · 研究领域：Nuclear physics research studies、Advanced NMR Techniques and Applications、Atomic and Molecular Physics

The isospin characters of low-energy dipole excitations in neutron-rich unstable nucleus 20O were investigated, for the first time in unstable nuclei. Two spectra obtained from a dominant isovector probe (O20+Au) and a dominant isoscalar probe (O20+α) were compared and analyzed by the distorted-wave Born approximation to extract independently the isovector and isoscalar dipole strengths. Two known 1− states with large isovector dipole strengths at energies of 5.36(5) MeV (11−) and 6.84(7) MeV (12−) were also excited by the isoscalar probe. These two states were found to have different isoscalar dipole strengths, 2.70(32)% (11−) and 0.67(12)% (12−), respectively, in exhaustion of the isoscalar dipole-energy-weighted sum rule. The difference in isoscalar strength indicated that they have different underlying structures.