Investigations of the nuclear properties of <super>124</super>Te and <super>154</super>Gd using a dual-parameter energy-time spectrometer

Abstract

Two large volume Ge(Li) detectors and a plastic scintillation counter incorporated in a dual-parameter energy-time spectrometer are used to measure gamma-gamma coincidences following the beta decay of 124Sb and 154Eu. Such an assembly of the detectors also allowed the lifetime of the first excited state of 154Gd to be determined.

A 12 % efficient Ge(Li) detector, an intrinsic Ge detector and a Compton suppression system have been employed in the measurement of gamma-ray energies and relative intensities, allowing the log ft values, multipolarities, spins/ parities and transition probabilities to be deduced for the two medium mass isotopes 124Te and 154Gd. Consequently following the coincidence measurements, the energy level schemes for both nuclei are built up incorporating several new energy levels and transitions; evidence is also found regarding levels which had been tentatively reported earlier, and are now considered as confirmed from the coincidence data.

The apparent vibrational shape of 124Te and the deformation mode of 154Gd are investigated in light of the experimental results concerning their positive parity states. Negative parity states are also considered in terms of Coriolis coupling acting between three octupole bands in the 154Gd nucleus. The calculated electric dipole transition probabilities show good agreement with the experimental values.

Comparisons are made with the predictions of current nuclear models. In particular the application of the group theoretical symmetries of the interacting boson approximation are discussed. The calculations are carried out using the program package PHINT for determining the energy levels, in conduction with FBEM for evaluating the transition rates. In case of 154Gd the consequences of using the hybrid parameters, resulting from proton subshell closure at Z=64 are considered. Earlier nuclear models applied to both nuclei are discussed and compared with the present nuclear predictions.