Abstract
The decay of and has been investigated with the main motive of determining more accurately the first-forbidden branches, in particular the rank-0, transitions. and have been produced by fragmentation of U and Ti targets, respectively, with a 1 GeV proton beam and subsequent on-line mass separation. For -ray spectroscopy, as well as delayed neutron spectroscopy by time of flight, was carried out to obtain a detailed decay scheme to 20 (bound and unbound) levels in The level structure of can be compared to recent calculations which incorporate one-particle–one-hole excitations from the shell. The first-forbidden transition ground state has been evaluated for the first time by a direct measurement of and activities. Its strength is interpreted as an effect of the meson-exchange current (MEC) leading to an enhancement factor of 62(5)% in comparison with the value predicted by shell-model calculations using the impulse approximation. For the decay, chemical selective production was obtained through separation of the molecular ion without contamination by isobars. In these conditions, the measurement of very weak branches, at a level of per 100 decays, could be made and a limit, at the confidence level, has been obtained for the branch to the level at Implications of these results on the general trend of meson-exchange enhancements of first-forbidden transitions within the framework of the spherical shell model are discussed.
- Received 30 March 1998
DOI:https://doi.org/10.1103/PhysRevC.58.1970
©1998 American Physical Society