Experimental Test of the Kumar-Baranger Pairing-Plus-Quadrupole Force Model in the A=190 Region Through E2-M1 Mixing Amplitudes
The E2M1 multipole mixing ratios δ(γ) of γ transitions in even-even osmium and platinum isotopes have been measured in order to test the predictions of the pairing-plus-quadrupole theory of Kumar and Baranger. The mixing ratios δ(γ) were determined from directional-correlation measurements on γ transitions in 186, 188, 190Os (populated in the decay of 186, 188, 190Ir and in 194, 196Pt (populated in the decay of 194, 196Au). The radioactive iridium isotopes were produced by Re(α,xn) reactions, and the gold isotopes were produced by Pt(d,xn) reactions. The equipment employed for the γ-γ directional-correlation measurements consisted of two coaxial 30-cc Ge(Li) detectors and appropriate electronic equipment for high-resolution pulse-height analysis and timing analysis. The observed directional correlations were analyzed in terms of the appropriate E2M1 mixing ratios, which are defined explicitly. The following results were obtained (predictions of the Kumar-Baranger theory are listed in square brackets): δ(186Os, 630 keV)=-(10+15- 4)[-14.7], δ(186Os, 773 keV)=-(13+9- 6)[-13.5], δ(188Os, 478 keV)=-12.3+/-2.8 [- 9.5], δ(188Os, 635 keV)=-6.9+/-3.2 [- 10.5], δ(190Os, 371 keV)=-8.5+/-1.0 [- 7.6], δ(190Os, 569 keV)=-9.0+/-1.5 [- 9.9], δ(194Pt, 293 keV)=+14.3+/-2.1 [+19.9], δ(196Pt, 333 keV)=-5.7+/-0.3 [- 101.4]. Except for the 333-keV transition in 196Pt the agreement of the experimental mixing ratios with the values and signs predicted by the Kumar-Baranger model is excellent.