Alpha-decay half-life of Hafnium isotopes reinvestigated by a semi-empirical approach

New estimates of partial a-decay half-life, T-1/2, for Hf-156-162,Hf-174,Hf-176 isotopes by a semi-empirical, one-parameter model are given. The used model is based on the quantum mechanical tunneling mechanism through a potential barrier, where the Coulomb, centrifugal and overlapping components to the barrier have been considered within the spherical nucleus approximation. This approach enables to reproduce, within a factor 2, the measured T-1/2 of ground-state to ground-state (gs-gs) alpha-transitions for the artificially produced Hf156-162 isotopes. Half-life predictions for alpha-transitions from the ground-state of Hf-159(,1)61 isotopes to the first gamma-excited level of Yb-155,Yb-157 isotopes are reported for the first time. The model also provides T-1/ 2-values of (2.43 +/- 0.28) x 10(16) a and (1.47 +/- 0.19) x 10(20) a for the naturally occurring Hf-174 and (126) Hf isotopes, respectively, in quite good agreement with a number of estimates by other authors. In addition, the present methodology indicates that Hf-1(74,176) isotopes exhibit alpha-transition to the first gamma-excited level of their daughter Ytterbium isotopes which halflives are found (0.9 +/- 0.1) x 10(18) a and (0.72 +/- 0.08) x 10(22) a, respectively, with a chance of being measured by improved a-detection and alpha-spectrometry methods available nowadays.