Reorientation-effect measurement of the < 2(1)(+)parallel to(E)over-cap2 parallel to 2(1)(+)> matrix element in Ar-36

The spectroscopic quadrupole moment of the first excited 2(1)(+) state, Q(s)(2(1)(+)), at 1.970 MeV in Ar-36 was determined at energies well below the Coulomb barrier-where nuclear interference effects are negligible- using the Pt-194(Ar-36, Ar-36(+)) Pt-194(+) Coulomb-excitation reaction at 134.2 MeV. Particle-gamma coincidence data were collected using the AFRODITE array-composed of eight high-purity germanium clover detectors-and an upstream double-sided silicon detector at iThemba LABS. A large diagonal matrix element of < 2(1)(+)parallel to(E) over cap2 parallel to 2(1)(+)) = 0.163(42) eb was determined, which yields a more accurate value of Q(s)(2(1)(+)) = +0.12(3) eb as compared with previous work, Q(s)(2(1)(+)) = +0.11(6) eb, in agreement with modern beyond mean-field and large-scale shell-model calculations. This value is consistent with the ratio of electric quadrupole moments found for other A = 4n self-conjugate nuclei extracted from the reorientation effect and the rotor model, which are surprisingly equivalent to those observed in good rotors in the mass A approximate to 160-180 region.