Transition through triaxial shapes of the light samarium isotopes and the beta decay of136,138,140Eu

Abstract

Levels in ' '' ' Sm were populated by the beta decay of Eu, following (HI, pxn) reactions and on-line mass separation. The beta decay of " Eu with a half-life of 3.9(+0.5j s was observed for the first time. Members of the y band were observed in all three daughter nuclei. Spectroscopic calculations were made using the triaxial rotor model, with all parameters derived microscopically from a Woods-Saxon deformed shell model. Other spectroscopic models were also considered.Comparison with the data supports the characterization of these nuclei in terms of a triaxial intrinsic shape,

Decay of neutron deficient Eu, Sm and Pm isotopes near the proton drip line

“…These summing effects were taken into account before quoting x-ray and r-ray intensities. The smaller 24.3% Ge and planar Ge detectors were less subject to summing and were helpful 6 in identifying the sum peaks caused by cascading r and/or x rays in the 52.3% detector.…”

“…The 4-s tape cycle was too short to confirm the published half-life values 6 ,8,9). The half-life of 22.6±0.5 s measured by Kern et al 6 ) was used in our analysis for the high-sp'in isomer. A higher (3+ /EC=3±1 intensity ratio than in the 134Sm decay was observed which is consistent with the predicted 17 ) larger QEC value for 134Pm ( assuming a similar (3-strength distribution).…”

“…From the proton decay a half-life of 4±1 s was determined and the proton energy range was 2.2 MeV <E p <5. 6 MeV. Twenty-six I rays were assigned to 136Eu {3 decay on the basis of coincidences with Sm K", x-rays or other known "'I rays and by half-life ( fig.…”

Axial and reflection asymmetry of the nuclear ground state

“…In their study of some proton-rich rareearth nuclei, Redon et al [41] find triaxial ground states in the vicinity of N ¼ 76 for Sm, but none for Cd, in qualitative agreement with our results. In a more comprehensive study Kern et al [42] consider the behavior of light rare-earth level spectra and how they evolve in the range 132 6 A 6 140. They find that the level spectra for some of these nuclei are best understood in terms of potential-energy surfaces with well-established triaxial minima.…”

Structure of low-lying states inSm140studied by Coulomb excitation

“…The states of the γ band beyond the 2 + 2 state are unfortunately not known for 140 Sm. The state at 1599 keV excitation energy that was tentatively assigned as the 3 + γ state in an earlier work [12] was shown to have spin-parity I π = 0 (+) in the recent angular correlation measurement [14]. The identification of the 3 + γ and 4 + γ states would shed more light on the character of the axial asymmetry.…”