Atomic Shell Recovery Times Following 181Hf β−-Decay

Systematic measurements of perturbed angular correlation (PAC) for the 133–482 keV cascade of ¹⁸¹Ta have been performed in the viscous media of glycerol, diethylene glycol and ethylene glycol. The similar PAC spectra observed and the same values of different parameters like quadrupole frequency, relaxation constant and anisotropy parameter found (within errors) confirm atomic “after effects” following β^?-decay of ¹⁸¹Hf in these media. The PAC measurements have also been performed in these media at different viscosities by adding H₂O. For the glycerol-H₂O system, it is found that atomic recovery time do not changes in the viscosity range of greater than 5 mPa?s. In this range of viscosity, the recovery time was measured to be ～50 nsec. In the low viscosity region (≤2 mPa?s), however, the atomic recovery process becomes faster. In case of diethylene glycol-H₂O and ethylene glycol-H₂O systems also, it is found that atomic recovery times becomes smaller in the low viscosity region.