Mössbauer studies and nuclear quadrupole moments of186, 188, 189, 190 Os

Abstract

Mossbauer transmission experiments with the 137, 155, 69 and 187 keV gamma rays of186, 188, 189, 190Os, 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:Q2+(186Os, 137 keV):Q2+(188Os, 155keV):Q2+(190Os, 187 keV):Q3/2−(189Os, g.s.)=(+1.100±0.020): 1.0:(+0.863±0.051): (−0.586±0.011) andQ5/2−(189Os, 69 keV)/Q3/2−(189Os, g.s.)=−0.735 ±0.012. The ratios for180, 188, 190Os 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, namelyQ2+ (186Os)=−(1.50 ± 0.10)b,Q2+(188Os)=−(1.36± 0.09) b,Q2+ (190Os)=−(1.18 ± 0.08) b,Q3/2−(189Os)=+ (0.80 ± 0.06) b, andQ5/2− (189Os)=− (0.59 ± 0.05) b. For the electric field gradient at Os nuclei in Re metal a value ofVzz=−(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,g5/2−/g3/2−=0.895 ± 0.006 for the ratio of theg-factors of the 69 keV state and the groundstate, andHi=−(1135 ± 20) kOe for the hyperfine field at Os nuclei in an iron matrix.