In-beam study of 144Gd

Abstract

A level scheme of 144Gd has been established using the 144Sm(α, 4nγ) reaction and in-beam spectroscopy methods. Excitation functions, γ-ray angular distributions, γ-γ coincidence spectra, γ-spectra time related to the cyclotron beam bursts and conversion coefficients for the delayed transitions have been measured.

The level scheme comprises 11 levels with spins up to I = 12. Two isomers, a 13 ± 2 ns, 7− state at 2471.4 keV and a 145 ± 30 ns, 10+ state at 3433.0 keV have been observed. The former has similar excitation energy as the 7− isomers in 142Sm, 140Nd and 138Ce and it may arise from the configuration although its lifetime seems to indicate some degree of collectivity. The 10+ state has a similar excitation energy as the 10+ isomer found in 138Ce and it may arise from the dominant configuration. Below the 10+ isomer in 144Gd only two excited states have positive parity; the hitherto known first 2+ and 4+ states. The 11+ and 12+ states must include four-particle configurations or they have to be of collective nature. The latter possibility is supported by the considerable E2/M1 mixture (≈ 20 %) observed for the 11+ to 10+ transition. An analysis of the systematics of ground band levels in the N = 80 isotones shows the same gradual behavior between the two VMI solutions previously found for the Te isotopes.