C. M. Campbell, N. Aoi, D. Bazin, M. D. Bowen, B. A. Brown, J. M. Cook, D. -C. Dinca, A. Gade, T. Glasmacher, M. Horoi, S. Kanno, T. Motobayashi, W. F. Mueller, H. Sakurai, K. Starosta, H. Suzuki, S. Takeuchi, J. R. Terry, K. Yoneda, H. Zwahlen
Excited states in 40Si have been established by detecting gamma-rays coincident with inelastic scattering and nucleon removal reactions on a liquid hydrogen target. The low excitation energy, 986(5) keV, of the 2+[1] state provides evidence of a weakening in the N=28 shell closure in a neutron-rich nucleus devoid of deformation-driving proton collectivity.
N. Imai, N. Aoi, N. Fukuda, T. Kishida, T. Kubo, T. Minemura, T. Motobayashi, S. Takeuchi, K. Yoneda, H. Watanabe, M. Ishihara, H. J. Ong, H. Sakurai, H. Iwasaki, T. K. Ohnishi, M. K. Suzuki, K. Demichi, H. Kawasaki, H. Baba, T. Gomi, H. Hasegawa, E. Kaneko, S. Kanno, K. Kurita, E. Takeshita, A. Saito, Zs. Dombradi, Z. Elekes, Zs. Fulop, A. Gelberg, K. Ishikawa, Y. Kondo, M. Miura, T. Nakamura, T. Sugimoto, S. Michimasa, M. Notani, S. Shimoura, M. Tamaki
The electric quadrupole transition from the first 2+ state to the ground 0+ state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured lifetime is 75 +- 23 ps, corresponding to a B(E2;2_1+ -> 0^+) value of 0.63 +- 0.19 e2fm4, or 0.26 +- 0.08 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.
P. Doornenbal, H. Scheit, N. Aoi, S. Takeuchi, K. Li, E. Takeshita, H. Wang, H. Baba, S. Deguchi, N. Fukuda, H. Geissel, R. Gernhäuser, J. Gibelin, I. Hachiuma, Y. Hara, C. Hinke, N. Inabe, K. Itahashi, S. Itoh, D. Kameda, S. Kanno, Y. Kawada, N. Kobayashi, Y. Kondo, R. Krücken, T. Kubo, T. Kuboki, K. Kusaka, M. Lantz, S. Michimasa, T. Motobayashi, T. Nakamura, T. Nakao, K. Namihira, S. Nishimura, T. Ohnishi, M. Ohtake, N. A. Orr, H. Otsu, K. Ozeki, Y. Satou, S. Shimoura, T. Sumikama, M. Takechi, H. Takeda, K. N. Tanaka, K. Tanaka, Y. Togano, M. Winkler, Y. Yanagisawa, K. Yoneda, A. Yoshida, K. Yoshida, H. Sakurai
We report on the first spectroscopic study of the N=22 nucleus 32Ne at the newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line with an energy of 722(9) keV was observed in both inelastic scattering of a 226 MeV/u 32Ne beam on a Carbon target and proton removal from 33Na at 245 MeV/u. This transition is assigned to the de-excitation of the first J^pi = 2+ state in 32Ne to the 0+ ground state. Interpreted through comparison with state-of-the-art shell model calculations, the low excitation energy demonstrates that the Island of Inversion extends to at least N=22 for the Ne isotopes.
Y. Togano, Y. Yamada, N. Iwasa, K. Yamada, T. Motobayashi, N. Aoi, H. Baba, S. Bishop, X. Cai, P. Doornenbal, D. Fang, T. Furukawa, K. Ieki, T. Kawabata, S. Kanno, N. Kobayashi, Y. Kondo, T. Kuboki, N. Kume, K. Kurita, M. Kurokawa, Y. G. Ma, Y. Matsuo, H. Murakami, M. Matsushita, T. Nakamura, K. Okada, S. Ota, Y. Satou, S. Shimoura, R. Shioda, K. N. Tanaka, S. Takeuchi, W. Tian, H. Wang, J. Wang, K. Yoneda
The reduced transition probability B(E2;0 ->2+) for 28S was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2) systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S was determined to be 1.9(2) by evaluating the M_n value from the known B(E2) value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T_z|=2 nucleus 28S.
N. Aoi, S. Kanno, S. Takeuchi, H. Suzuki, D. Bazin, M. D. Bowen, C. M. Campbell, J. M. Cook, D. -C. Dinca, A. Gade, T. Glasmacher, H. Iwasaki, T. Kubo, K. Kurita, T. Motobayashi, W. F. Mueller, T. Nakamura, H. Sakurai, M. Takashina, J. R. Terry, K. Yoneda, H. Zwahlen
The neutron-rich nucleus 74Ni was studied with inverse-kinematics inelastic proton scattering using a 74Ni radioactive beam incident on a liquid hydrogen targetat a center-of-mass energy of 80 MeV. From the measured de-excitation gamma-rays, the population of the first 2+ state was quantified. The angle-integrated excitation cross section was determined to be 14(4) mb. A deformation length of delta = 1.04(16) fm was extracted in comparison with distorted wave theory, which suggests that the enhancement of collectivity established for 70Ni continues up to 74Ni. A comparison with results of shell model and quasi-particle random phase approximation calculations indicates that the magic character of Z = 28 or N = 50 is weakened in 74Ni.
S. Ota, S. Shimoura, H. Iwasaki, M. Kurokawa, S. Michimasa, N. Aoi, H. Baba, K. Demichi, Z. Elekes, T. Fukuchi, T. Gomi, S. Kanno, S. Kubono, K. Kurita, H. Hasegawa, E. Ideguchi, N. Iwasa, Y. U. Matsuyama, K. L. Yurkewicz, T. Minemura, T. Motobayashi, T. Murakami, M. Notani, A. Odahara, A. Saito, H. Sakurai, E. Takeshita, S. Takeuchi, M. Tamaki, T. Teranishi, Y. Yanagisawa, K. Yamada, M. Ishihara
The neturon rich nucleus 13B was studied via the proton transfer reaction 4He(12Be,13B γ) at 50AMeV. The known 4.83-MeV excited state was strongly populated and its spin and parity were assigned to 1/2+ by comparing the angular differential cross section data with DWBA calculations. This low-lying 1/2+ state is interpreted as a proton intruder state and indicates a deformation of the nucleus.
D. Q. Fang, Y. G. Ma, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
The proton-proton momentum correlation functions ($C_{pp}(q)$) for kinematically complete decay channels of $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne have been measured at the RIKEN RI Beam Factory. From the very different correlation strength of $C_{pp}(q)$ for $^{23}$Al and $^{22}$Mg, the source size and emission time information were extracted from the $C_{pp}(q)$ data by assuming a Gaussian source profile in the correlation function calculation code (CRAB). The results indicated that the mechanism of two-proton emission from $^{23}$Al was mainly sequential emission, while that of $^{22}$Mg was mainly three-body simultaneous emission. By combining our earlier results of the two-proton relative momentum and the opening angle, it is pointed out that the mechanism of two-proton emission could be distinguished clearly.
Y. G. Ma, D. Q. Fang, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
Two-proton relative momentum ($q_{pp}$) and opening angle ($θ_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim20$ MeV/c as well as a peak in $θ_{pp}$ around 30$^\circ$ are seen in the two-proton break-up channel from a highly-excited $^{22}$Mg. In contrast, such peaks are absent for the $^{23}$Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$Mg is quite different from the $^{23}$Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.