M$ouml$ssbauer effect measurements in 176,178,180Hf

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Abstract
The Mössbauer effect has been used to study the 2+ -> 0+ gamma-ray transitions in 176,178,180Hf. Using absorbers of Hf metal, HfO2 and HfB2, the ratios of the quadrupole moments of the first excited 2+ levels of the three isotopes were found to be Q176/Q178 = 1040±0008, Q178/Q180 = 1014±0013 and Q176/Q180 = 1053±0015. The isomer shifts between Hf metal and HfO2 for the three isotopes were found to be ΔE(176Hf) = (021±010) mm s-1, ΔE(178Hf) = (009±003) mm s-1 and ΔE(180Hf) = (010±006) mm s-1. Based on estimates of electronic wave functions, these isomer shifts are shown to correspond to changes in the mean square radius between the first excited and ground states which are a factor of 3-5 lower than predicted by the self-consistent cranking model. Quadrupole splittings were observed at the hafnium sites in Hf(NO3)4, HfOCl2. 8H2O and HfCl4. Evidence was found for an effective magnetic field at the hafnium sites in the intermetallic compounds HfCo2, Co2HfAl and Zr0.5Hf0.5Fe2.