M. Tamaki

Anomalously hindered E2 strength B(E2;2+(1)-->0+) in 16C.

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 mean lifetime is 77+/-14(stat)+/-19(syst) ps. The central value of mean lifetime corresponds to a B(E2;2+(1)-->0(+)) value of 0.63e(2) fm(4), or 0.26 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

Unbound excited states in 19,17C

The neutron-rich carbon isotopes 19,17C have been investigated via proton inelastic scattering on a liquid hydrogen target at 70 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum, in which fast neutrons and charged fragments were detected in coincidence using a neutron hodoscope and a dipole magnet system. A peak has been observed with an excitation energy of 1.46(10) MeV in C, while three peaks with energies of 2.20(3), 3.05(3), and 6.13(9) MeV have been observed in C. Deduced cross sections are compared with microscopic DWBA calculations based on p-sd shell model wave functions and modern nucleon-nucleus optical potentials. Jπ assignments are made for the four observed states as well as the ground states of both nuclei.

One-neutron knockout reaction of 17C on a hydrogen target at 70 MeV/nucleon

Abstract First experimental evidence of the population of the first 2 − state in 16 C above the neutron threshold is obtained by neutron knockout from 17 C on a hydrogen target. The invariant mass method combined with in-beam γ -ray detection is used to locate the state at 5.45(1) MeV. Comparison of its populating cross section and parallel momentum distribution with a Glauber model calculation utilizing the shell-model spectroscopic factor confirms the core-neutron removal nature of this state. Additionally, a previously known unbound state at 6.11 MeV and a new state at 6.28(2) MeV are observed. The position of the first 2 − state, which belongs to a member of the lowest-lying p – sd cross shell transition, is reasonably well described by the shell-model calculation using the WBT interaction.

14Be(p,n)14B reaction at 69 MeV in inverse kinematics

Y. Satou, ∗ T. Nakamura, Y. Kondo, N. Matsui, Y. Hashimoto, T. Nakabayashi, T. Okumura, M. Shinohara, N. Fukuda, T. Sugimoto, H. Otsu, Y. Togano, T. Motobayashi, H. Sakurai, Y. Yanagisawa, N. Aoi, S. Takeuchi, T. Gomi, M. Ishihara, S. Kawai, H.J. Ong, T.K. Onishi, S. Shimoura, M. Tamaki, T. Kobayashi, Y. Matsuda, N. Endo, and M. Kitayama Department of Physics and Astronomy, Seoul National University, 599 Gwanak, Seoul 151-742, Republic of Korea Department of Physics, Tokyo Institute of Technology, 2-12-1 Oh-Okayama, Meguro, Tokyo 152-8551, Japan RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan Department of Physics, Rikkyo University, 3 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan Center for Nuclear Study (CNS), University of Tokyo, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan Department of Physics, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan (Dated: January 12, 2013)

Low-lying proton intruder state in 13B

Abstract The neutron-rich nucleus 13 B was studied via the proton transfer reaction 4 He( 12 Be,  13 B γ ) at 50 A MeV . 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.

Low-lying states in {sup 32}Mg studied by proton inelastic scattering

Proton inelastic scattering on the neutron-rich nucleus {sup 32}Mg has been studied at 46.5 MeV/nucleon in inverse kinematics. Populated states were identified by measuring de-excitation {gamma} rays, in which five new states were found by {gamma}-{gamma} coincidence analyses. By analyzing the angular differential cross sections via coupled-channel calculations, their spins and parities were constrained and the amplitudes for each transition were extracted. The spin and parity of the 2321-keV state was assigned as 4{sub 1}{sup +}. The ratio between the energies of the 2{sub 1}{sup +} and 4{sub 1}{sup +} states indicates that {sup 32}Mg is a transitional nucleus rather than an axially deformed rigid rotor. The collectivities in the nucleus {sup 32}Mg with N=20 are discussed based on the results obtained in the present experiment.

Application of Doppler-shift attenuation method to the de-excitation γ rays from the in-flight 12Be beam

The B(E2; ↓) value of the neutron‐rich nucleus 12Be has been determined through the measurement of the lifetime of the first 2+ state using a modified Doppler‐shift attenuation method (DSAM). The first excited state was produced by the inelastic scattering of the intermediate energy 12Be beam off a thick gold target, which played two roles, to excite the beam and to decrease the velocity. The lifetime has been determined to be 2.5±0.7 (stat) ±0.3 (syst) ps, which gives a B(E2) value of 5.0±1.3±0.5 in Weisskopf units. The result shows a large quadrupole strength in the ground state transition. The B(E2) value together with the deformation length measured by proton inelastic scattering yields a neutron quadrupole matrix element two times larger than those for 14C and 16O.

(p, p′) and (p, n) reactions on halo nuclei

We have measured the 1H(19C,18C+n)1H and 1H(14Be,13B+n)n reactions at 70 MeV/nucleon using the invariant mass method in inverse kinematics. A new state was identified at 1.49 MeV in 19C. In the latter (p, n) reaction, a resonance peak corresponding to the 1.28 MeV state in 14B recently reported in a beta-decay study was clearly observed. Forward peaked character in the differential cross section supports the 1+assignment for this state.

Spectroscopy on neutron-rich nuclei near N = 50 via two-step Coulomb excitation at intermediate energies

We have investigated structure of the neutron-rich Ge isotopes at and around N = 50 via intermediate-energy Coulomb excitation. A new method of intermediate-energy twostep Coulomb excitation has been tested to study the second excited states, such as the 2+2 and 4+1states, in neutron-rich even-even nuclei. The first application of the method and its results are presented.

Single-particle States in 23F

The proton single-particle states have been investigated using the in-beam γ-ray spectroscopy technique via the following reactions: 4He(22O,23F); 4He(23F,23F); 4He(24F,23F); and 4He(25Ne,23F). The characters of excited states in 23F were deduced by comparison of the population strengths in these reactions. We found that the 2268- and 4059-keV levels have strong proton single-particle nature of the s1/2 and d3/2 orbitals, respectively. These singleparticle states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which indicates that the centroid energy gaps for πd5/2−πs1/2 and πd5/2−πd3/2 are wider than predicted.