"Using beta-decay to map the E2 strength in the Cd isotopes and the downfall of vibrational motion"
Paul Garrett, University of Guelph
(id #134)
Seminar: YesPoster: No
Invited talk: No
The nuclear structures of the even-even Cd isotopes near stability, especially 110-116Cd, were long thought to be prime examples of low-lying vibrational motion. Their level schemes display a nearly harmonic spacing of one, two, and three-phonon levels. Due to their importance as paradigms of vibrational motion, their structures were previously investigated by a variety of reactions. While these reactions were essential for establishing the location of levels and their main decay branches, and in most cases their lifetimes, they did not have the sensitivity to probe the weak low-energy branches that are necessary to assess the degree of collectivity that the states possess.
In order to complement the data used to test the collectivity present in the Cd isotopes, we have initiated a programme of extensive beta-decay experiments using the 8pi spectrometer at the TRIUMF-ISAC radioactive-beam facility. The goal of these experiments is to achieve a sufficient sensitivity to weak, low-energy branches amongst the multi-phonon levels so that the collective branches would either be observed, or very stringent upper limits set. Thus far, we have examined the decay of 110In to 110Cd, and 112In/112Ag to 112Cd. These experiments have revealed that the individual low-spin multi-phonon states do not decay in the expected manner. Further, and much more surprising, the missing E2 strength is not due to fragmentation (i.e., mixing) amongst the levels below ~ 3 MeV. This lack of the E2 strength has forced a re-evaluation of the structure, suggesting a more rotational picture rather than vibrational. This also raises the issue that if our long-standing paradigms of vibrations can no longer be considered as vibrational nuclei, are there any spherical vibrational nuclei?
In order to complement the data used to test the collectivity present in the Cd isotopes, we have initiated a programme of extensive beta-decay experiments using the 8pi spectrometer at the TRIUMF-ISAC radioactive-beam facility. The goal of these experiments is to achieve a sufficient sensitivity to weak, low-energy branches amongst the multi-phonon levels so that the collective branches would either be observed, or very stringent upper limits set. Thus far, we have examined the decay of 110In to 110Cd, and 112In/112Ag to 112Cd. These experiments have revealed that the individual low-spin multi-phonon states do not decay in the expected manner. Further, and much more surprising, the missing E2 strength is not due to fragmentation (i.e., mixing) amongst the levels below ~ 3 MeV. This lack of the E2 strength has forced a re-evaluation of the structure, suggesting a more rotational picture rather than vibrational. This also raises the issue that if our long-standing paradigms of vibrations can no longer be considered as vibrational nuclei, are there any spherical vibrational nuclei?
