Superallowed beta decay

The separation of states of different T implies that one of a set of isobaric nuclei is stable and the others unstable against beta decay. The Wigner theory predicts superallowed decay between the states of a given supermultiplet because no change of spatial wave function is needed. This is found (a) for the positron decay of odd mirror nuclei (b) for transitions between the low states of nuclei with mass number 4 + 2 in which both T= and P = 0 states are found in the (1,0,0) supermultiplet. 

The beta-decay of the ground state between the isobars is superallowed. Application of the isobaric correction to the level system in general shows that the three lowest levels are at a definitely lower excitation than the analogous levels in G . The levels are however unbound, and have larger widths than their counterparts in Ci , particularly in the case of the lowest (s-wave) level. The dispersive level shift (Sect. 9) for this state is thus very marked and with the assumption of a suitable radius of interaction the relative displacement of the... 

The beta decay probabilities calculated using the exact wavefunctions are shown in Fig. 74 as a function of Vf.. The superallowed decay of Ne is not a sharp function of the interaction potential, since there is no change of supermultiplet, but the 0 decays give an estimate of which agrees fairly well with that 0 —obtained from the level spectrum. 

The beta decay between the isobars is superallowed, as expected for mirror nuclei. 

The decay of He to the ground state of Li is superallowed and is the most important evidence for the Gamow-Teller type of coupling in beta-decay. The Fermi allowed decay which would be expected from He to its isobar state at 3.57 MeV in Li is just energetically impossible. No trace of gamma radiation in the He decay has been found, nor has any transition to the 2.189 MeV level (/ = 3 ) been seen. 

The beta decay of is a simple allowed (unfavoured) transition to the 2 excited state of Ne o at I.63 MeV again it is not clear why the equivalent ground state transition does not take place, but the reason probably lies in the particular configurations. Thus if the F o and Ne states were described by a particularly complex set of configurations while the Ne ground state was simply s, the results might be explained. The Na o decay may contain a weak superallowed component to the first T — i level of Ne . 

The beta transitions are both simple that of is of very low energy, so that the excitation of the first T = state in CP is at an energy approximately equal to the isobaric correction. The spin of the radioactive nucleus has been measured and is found to be f, in agreement with the // prediction for d l. The magnetic moment of CP agrees better with the prediction from this same configuration than with the Schmidt value for d /. The S ->CP decay is allowed, but not superallowed since these nuclei are not a true mirror pair. 

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