Shell-model study of the highly forbidden beta decay Ca-48 -> Sc-48

Ordinary beta(-) decay of the 0(+) ground state of Ca-48 is studied. Partia l half-lives for the highly-forbidden transitions to the three lowest-lying states (6(+), 5(+), 4(+)) of Sc-48 are calculated by using both the harmon ic oscillator and the Woods-Saxon mean-field wave functions. We find the de cay to be dominated, as expected, by the unique fourth-forbidden transition to the excited 5(+) state of Sc-48. Th, theoretical beta-decay half-life o f Ca-48 is found to be 1.1(-0.6)(+0.8) . 10(21) years which is approximatel y 25 times longer than the measured double-beta-decay half-life of T-1/2(2v ) = (4.3(-1.1)(+2.4)[stat] +/- 1.4[syst]) . 10(19) years.