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 19C, while three
peaks with energies of 2.20(3), 3.05(3), and 6.13(9) MeV have been observed in
17C. Deduced cross sections are compared with microscopic DWBA calculations
based on p-sd shell model wave functions and modern nucleon-nucleus optical
potentials. Jpi assignments are made for the four observed states as well as
the ground states of both nuclei.Comment: 20 page
The electric quadrupole transition from the first 2 + state to the ground 0 + state in 18 C was studied through a lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive 18 C nuclei. The measured mean lifetime is 18.9 ± 0.9(stat) ± 4.4(syst) ps, corresponding to a B(E2; 2 + 1 → 0 + g.s. ) value of 4.3 ± 0.2 ± 1.0 e 2 fm 4 , or about 1.5 Weisskopf units. The mean lifetime of the first 2 + state in 16 C was remeasured to be 18.3 ± 1.4 ± 4.8 ps, about four times shorter than the value reported previously. The discrepancy between the two results was explained by incorporating the γ -ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in 16 C persists in 18 C.
The structure of neutron-rich isotopes 60Cr and 62Cr was studied via proton inelastic scattering in inverse kinematics. The deformation lengths (delta) for 60Cr and 62Cr were extracted as 1.12(16) and 1.36(14) fm, respectively, providing evidence for enhanced collectivity in these nuclei. An excited state at 1180(10) keV in 62Cr was identified for the first time. We adopted 4;{+} as its spin and parity, leading to the rapid increase of the Ex(4;{+})/E_{x}(2;{+}) ratio, which indicates the development of large deformation in 62Cr near N=40. Importance of the admixture of the gd-shell component above N=40 is also discussed by comparing with a modern shell model calculation.
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