RECENT PROGRESS IN THE GROSS THEORY OF β-DECAY
Science and Engineering Research Laboratory, Waseda University
3-4-1 Okubo, Shinjuku-ku, Tokyo 160, Japan
The gross theory of β-decay has recently been improved. First, the effect of partial occupation of single-particle states in the pairing theory has been taken into account. Second, the function to represent the effect of the Pauli exclusion principle has been modified in order to observe the sum rule for the Fermi transition more accurately. Third, the single-particle strength function for the Gamow-Teller transition has been modified from consideration of the experimental data on Gamow-Teller giant resonances in (p,n) reactions; about 40% of the strength has been moved from the giant resonance region to the far tail part. Some single-particle strength functions for the first forbidden transitions have also been modified correspondingly. Results of calculations for β strength functions, β-decay half-lives, and average β-ray and γ-ray energies are discussed, and it is shown that the above modification really improve the agreement between theory and experiment on the average. Also discussed are methods for predicting deviations of the properties of individual nuclides from the average. In particular, a simple method is proposed for estimating the β-decay half-life of a nuclide from seven quantities, i.e., experimental half-lives of three neighboring nuclides and calculated half-lives of these four nuclides.
KEYWORDS: β-decay, half-life, β strength function, average β-ray energy, average γ-ray energy, nuclear systematics