Mössbauer studies and nuclear quadrupole moments of^{186, 188, 189, 190} Os

Abstract

Mössbauer transmission experiments with the 137, 155, 69 and 187 keV gamma rays of^{186, 188, 189, 190}Os, respectively, yielded the electric quadrupole splitting of these gamma resonance lines in OsO₂ and OsP₂. From the results the following ratios of quadrupole moments were derived:Q ₂ ⁺(¹⁸⁶Os, 137 keV):Q ₂ ⁺(¹⁸⁸Os, 155keV):Q ₂ ⁺(¹⁹⁰Os, 187 keV):Q _3/2 ⁻(¹⁸⁹Os, g.s.)=(+1.100±0.020): 1.0:(+0.863±0.051): (−0.586±0.011) andQ _5/2 ⁻(¹⁸⁹Os, 69 keV)/Q _3/2 ⁻(¹⁸⁹Os, g.s.)=−0.735 ±0.012. The ratios for^{180, 188, 190}Os are, within their limits of error, in agreement with the expectation of the rotational model, indicating that the pairing-plusquadrupole model calculations of Kumar and Baranger predict too rapid a transition form rotational to vibrational nuclei. Applying this argument to¹⁸⁶Os in particular and using the measured ratios, one obtains a set of values for the quadrupole moments themselves, namelyQ ₂ ⁺ (¹⁸⁶Os)=−(1.50 ± 0.10)b,Q ₂ ⁺(¹⁸⁸Os)=−(1.36± 0.09) b,Q ₂ ⁺ (¹⁹⁰Os)=−(1.18 ± 0.08) b,Q _3/2 ⁻(¹⁸⁹Os)=+ (0.80 ± 0.06) b, andQ _5/2 ⁻ (¹⁸⁹Os)=− (0.59 ± 0.05) b. For the electric field gradient at Os nuclei in Re metal a value ofV _zz=−(3.3 ± 0.6) · 10¹⁷ V/cm² was found. A measurement with a magnetically split source yielded δ=+ 0.685 ± 0.025 for theE2/M1 mixing parameter of the 69 keV transition of¹⁸⁹Os,g _5/2 ⁻/g _3/2 ⁻=0.895 ± 0.006 for the ratio of theg-factors of the 69 keV state and the groundstate, andH _i=−(1135 ± 20) kOe for the hyperfine field at Os nuclei in an iron matrix.