  Excited states in 38,40,42Si nuclei have been studied via in-beam gamma-ray
spectroscopy with multi-nucleon removal reactions. Intense radioactive beams of
40S and 44S 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 42Si 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 42Si at N=28 and Z=14. Also for 38,40Si energy ratios with
values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for 42Si,
the results show a rapid deformation development of Si isotopes from N=24 to
N=28.
