Hindered proton collectivity in 16(28)S12: possible magic number at Z=16.

The reduced transition probability B(E2; 0(gs)(+) -> 2(1)(+)) for S-28 was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e(2)fm(4) is smaller than the expectation based on empirical B(E2) systematics. The double ratio vertical bar M-n/M-p vertical bar/(N/Z) of the 0(gs)(+) -> 2(1)(+) transition in S-28 was determined to be 1.9(2) by evaluating the M-n value from the known B(E2) value of the mirror nucleus Mg-28, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z = 16 in the vertical bar T-z vertical bar = 2 nucleus S-28.