K-forbidden allowed $\beta$ transitions in heavy nuclei

Abstract

The role of the band quantum number K in influencing the character of allowed $\beta$ transitions in heavy deformed nuclei is examined. The conditions for the occurrence of K -forbidden decays in this region are explored. Specific cases of “allowed” $\beta$ decays proceeding via $\Delta$ K = 2 to $\Delta$ K = 6 channels are presented to illustrate the phenomenon. The listed $\Delta$ K = 2 transitions, which by themselves contribute over 10% of all the presently known allowed transitions for A $\geq$ 228 nuclei, are seen to have an average $\ensuremath\log ft \geq 9.0$ , which is clearly outside the normal range for allowed transitions. It is concluded that, wherever the $\beta$ -connected states can be confidently labelled using the $\ensuremath I^{\pi}K$ quantum numbers, the K -forbiddenness is in general as significant as that involving the other two (spin and parity) quantum numbers.