Reorientation-effect measurement of the (21+ ? Ê 2? 21+) matrix element in Ar 36 REORIENTATION-EFFECT MEASUREMENT OF THE ... J. N. ORCE et al.

The spectroscopic quadrupole moment of the first excited 21+ state, QS(21+), at 1.970 MeV in Ar36 was determined at energies well below the Coulomb barrier - where nuclear interference effects are negligible - using the Pt194(Ar36,Ar36)Pt194 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 (21+E221+)=0.163(42) eb was determined, which yields a more accurate value of QS(21+)=+0.12(3) eb as compared with previous work, QS(21+)=+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 A160-180 region.