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
This Letter reports on the (1)H((28)Ne, (28)Ne) and (1)H((28)Ne, (27)Ne) reactions studied at intermediate energy using a liquid hydrogen target. From the cross section populating the first 2(+) excited state of (28)Ne, and using the previously determined BE(2) value, the neutron quadrupole transition matrix element has been calculated to be M(n)=13.8 +/- 3.7 fm(2). In the neutron knockout reaction, two low-lying excited states were populated in (27)Ne. Only one of them can be interpreted by the sd shell model while the additional state may intrude from the fp shell. These experimental observations are consistent with the presence of fp shell configurations at low excitation energy in (27,28)Ne nuclei caused by a vanishing N=20 shell gap at Z=10.
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