Determination of the Nuclear Matrix Elements for the Beta-Decay of ¹⁴⁹Pm

Abstract

The results of the β-γ directional correlation measurement of the first-forbidden β-transition of ¹⁴⁹Pm showed a slight energy dependence in the reduced β-coefficient ratio, R(E_i)⁄R(E_k), impling a deviation from the ξ-approximation. The analysis is based on the theoretical expressions given by Morita and Morita and performed by the minimization of χ² for the directional correlation coefficient ratio, A₂(E_i)⁄A₂(E_k). Two sets of the nuclear matrix parameters and corresponding values of the γ-coefficient, A_2γ, and E2 mixing of the 286 keV transition were found: set I, x=−0.119±0.140, u=−1.545±0.160, y′=−15.46±1.57, A_2γ=0.09±0.12, 0.2%<E2<3.1%; set II, x=0.795±0.136, u=−1.363±0.126, y′=23.41±1.42, A_2γ=−0.61±0.11, 19.4%<E2<37.8%. Set I is tentatively preferred. The deviation from the ξ-approximation is interpreted in terms of the effect of cancellation among the parameters.