  The reduced transition probability B(E2;0 ->2+) for 28S was obtained
experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2)
value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2)
systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S
was determined to be 1.9(2) by evaluating the M_n value from the known B(E2)
value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity
relative to that of neutrons. These results indicate the emergence of the magic
number Z=16 in the |T_z|=2 nucleus 28S.
