Well Developed Deformation in 42Si

Excited states in Si-38,Si-40,Si-42 nuclei have been studied via in-beam gamma-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of S-40 and S-44 provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled gamma-gamma coincidence measurements. A prominent gamma line observed with an energy of 742(8) keV in Si-42 confirms the 2(+) state reported in an earlier study. Among the gamma lines observed in coincidence with the 2(+) -> 0(+) transition, the most probable candidate for the transition from the yrast 4(+) state was identified, leading to a 4(1)(+) energy of 2173(14) keV. The energy ratio of 2.93(5) between the 2(1)(+) and 4(1)(+) states indicates well-developed deformation in Si-42 at N = 28 and Z = 14. Also for Si-38,Si-40 energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for Si-42, the results show a rapid deformation development of Si isotopes from N = 24 to N = 28.