g factor measurements of high spin isomeric states in 187,189,191 Au

Abstract

The g factors of three high spin isomers in 187,189,191 Au have been measured, using the time differential perturbed angular distributions. The reactions used and the results obtained for the g factors and the lifetimes are: 172 Yb( 19 F, 4nγ) 187 Au, g (31/2 − or 35/2 − ) = 0.25 (3), T 1/2 = 102 (5) ns; 181 Ta( 12 C, 4nγ) 189 Au, g (31/2 + ) = 0.42 (2), T 1/2 = 242 (10) ns; and 176 Yb( 19 F, 4nγ) 191 Au, g (31/2 + ) = 0.42 (3) T 1/2 = 402 (20) ns. These results show that the structure of these isomers is consistent with a 1 proton, 2 neutrons structure. The experimental set-up was cheked by measuring the g factor of the Coulomb excited 197 keV, T

Observation of an isomeric state inAu197

“…This and the E3 systematics for the lighter odd-A isotopes are shown in Table II. In addition to 197 Au, previously reported isomers in the odd-A gold isotopes from A = 195 to 189 [1,2,11,12] were all observed in the current work. For 191 Au a 1304-keV, (E3) transition was newly identified here with a branching ratio of approximately 10%.…”

“…The odd-A gold isotopes are characterized by decoupled rotational bands based on proton-hole states at low spins and three-hole configurations at medium spins, many of which are isomeric [1,2]. However, while the data for A 193 are relatively complete, for heavier masses few medium-or highspin levels have been reported.…”

“…Comparison with lighter odd-A gold nuclei suggests the possibility of an unidentified low-energy transition directly depopulating the isomeric state. Low-energy transitions are known to directly depopulate the I π = 31 2 + isomers in 191 Au (67 keV) and 189 Au (39 keV) [1]. In the current work the limits for such a decay to be unobserved are E γ < 85 keV (E2), <69 keV (M1), and <45 keV (E1) [10] and would lead to an isomer with a spin of ≈ 31 2 h. In the absence of such a low-energy transition the 436-keV decay would directly depopulate the isomer.…”

Three-quasiparticle isomers and possible deformation in the transitional nuclide,195Au

“…As indicated earlier, one focus in the odd-proton cases has been the relationship between the three-quasiparticle states, such as a 31/2 + isomer, and the two-particle (proton and neutron) structures systematically observed in the even-even Pt and Hg cores (see, for example, Refs. [9,10,[22][23][24][25]). The results of g-factor measurements led to the conclusion that the isomers observed are generally formed by two-neutron, one-proton configurations [24] and, specifically, that the g factor for the 31/2 + isomer in 191 Au is consistent with that expected for an h 11/2 proton coupled to a 10 − neutron core.…”

“…[9,10,[22][23][24][25]). The results of g-factor measurements led to the conclusion that the isomers observed are generally formed by two-neutron, one-proton configurations [24] and, specifically, that the g factor for the 31/2 + isomer in 191 Au is consistent with that expected for an h 11/2 proton coupled to a 10 − neutron core. At lower spin, the 21/2 + isomer in 195 Au was suggested to arise from a coupling of the 11/2 − proton to the 5 − two-neutron-hole state known in the even-even neighbors.…”