Title: Well-developed deformation in 42Si
Abstracts:
Excited states in the 38,40,42Si nuclei have been studied via in-beam
gamma-ray spectroscopy. Intense radioactive ion beams of 40S and 44S
provided at the RIKEN RIBF enabled the systematic studies for excitation
energies towards neutron magic number N=28. For Si isotopes, the
systematic study of the 2+ excitation energy indicate the weakening of
the N = 28 shell closure [1,2]. Recently, several experiments have been
performed to investigate the structures of 42Si [3,4,5] as well as
38,40Si. However until now no experimental data exist for higher excited
states which may relate to the nuclear shape or shell evolution. In
order to study excited states in Si isotopes, we have measured
de-excitation gamma rays from excited states higher than the 2+ state by
the DALI2 array via nucleon removal reactions. Besides a peak
corresponding to the 2+ decay, new gamma lines were observed in 42Si.
Applying a gamma-gamma analysis, a candidate for the 4+ to 2+ transition
was found. The low excitation energy of the 2+ state and an energy ratio
of 2.93(5) between the 4+ and 2+ states indicate a large deformation and
corroborate the suggested disappearance of the N = 28 shell closure in
42Si. Together with the energy ratios of 38Si and 40Si, the results show
a rapid deformation development of Si isotopes from N=24 to N=28.
Refs.
1) R.W.Ibbotson et al., Phys. Rev. Lett. 80 (1998) 2081.
2) C.M.Campbell et al., Phys. Lett. B 652 (2007) 169.
3) S.Grevy et al., Phys. Lett. B 594 (2004) 252.
4) J.Fridmann et al., Phys. Rev. C 74 (2006) 034313.
5) B.Bastin et al., Phys. Rev. Lett. 99 (2007) 022503.
