Simple relation for alpha decay half-lives

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

- New estimates of partial α-decay half-life, T_1/2, for ^{156-162,174,176}Hf 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) α-transitions for the artificially produced ^156-162Hf isotopes. Half-life predictions for α-transitions from the ground-state of ^159,161Hf isotopes to the first gamma-excited level of ^155,157Yb isotopes are reported for the first time. The model also provides T_1/2-values of (2.43±0.28)×10¹⁶ a and (1.47±0.19)×10²⁰ a for the naturally occurring ¹⁷⁴Hf and ¹⁷⁶Hf isotopes, respectively, in quite good agreement with a number of estimates by other authors. In addition, the present methodology indicates that ^174,176Hf isotopes exhibit α-transition to the first gamma-excited level of their daughter Ytterbium isotopes which half-lives are found (0.9±0.1)×10¹⁸ a and (0.72±0.08)×10²² a, respectively, with a chance of being measured by improved α-detection and α-spectrometry methods available nowadays.

Signatures of the Z = 82 shell closure in α-decay process

In recent experiments at the velocity filter Separator for Heavy Ion reaction Products (SHIP) (GSI, Darmstadt), an extended and improved set of α-decay data for more than 20 of the most neutron-deficient isotopes in the region from lead to thorium was obtained. The combined analysis of this newly available α-decay data, of which the (186)Po decay is reported here, allowed us for the first time to clearly show that crossing the Z = 82 shell to higher proton numbers strongly accelerates the α decay. From the experimental data, the α-particle formation probabilities are deduced following the Universal Decay Law approach. The formation probabilities are discussed in the framework of the pairing force acting among the protons and the neutrons forming the α particle. A striking resemblance between the phenomenological pairing gap deduced from experimental binding energies and the formation probabilities is noted. These findings support the conjecture that both the N = 126 and Z = 82 shell closures strongly influence the α-formation probability.

Universal decay law in charged-particle emission and exotic cluster radioactivity

A linear universal decay formula is presented starting from the microscopic mechanism of the charged-particle emission. It relates the half-lives of monopole radioactive decays with the Q values of the outgoing particles as well as the masses and charges of the nuclei involved in the decay. This relation is found to be a generalization of the Geiger-Nuttall law in alpha radioactivity and explains well all known cluster decays. Predictions on the most likely emissions of various clusters are presented.