Nuclear Shell Structure and Beta-Decay. II. EvenANuclei

A systematics of the $\beta$-transitions of even $A$ nuclei is given. An interpretation of the character of the transitions in terms of nuclear shell structure is achieved on the hypothesis that the odd nucleon groups have the same structure as in odd $A$ nuclei, together with a simple coupling rule between the neutron and proton groups in odd-odd nuclei.