Neutron-rich Ru Isotopes Research Articles

Investigation of γ softness: Lifetime measurements in Ru104,106

Lifetimes of the ${2}_{1}^{+}, {4}_{1}^{+}, {6}_{1}^{+}, {2}_{\ensuremath{\gamma}}^{+}$, and ${3}_{\ensuremath{\gamma}}^{+}$ states in $^{104,106}\mathrm{Ru}$ were measured by using the recoil-distance Doppler-shift technique and the Cologne Plunger device. Low-lying excited states in both nuclei were populated in a $^{104}\mathrm{Ru}(^{18}\mathrm{O},^{18}\mathrm{O})^{104}\mathrm{Ru}$* inelastic scattering and in a $^{104}\mathrm{Ru}(^{18}\mathrm{O},^{16}\mathrm{O})^{106}\mathrm{Ru}$ two-neutron transfer reaction using the Cologne FN Tandem accelerator. The experimental energy levels and deduced electromagnetic transition probabilities are compared in the context of $\ensuremath{\gamma}$ softness and the mapped interacting boson model with input from the microscopic self-consistent mean-field calculation using a Gogny interaction. The newly obtained results for the $\ensuremath{\gamma}$ band give a more detailed insight about the triaxial behavior of $^{104,106}\mathrm{Ru}$. The results will be discussed in the context of $\ensuremath{\gamma}$ soft and rigid triaxial behavior which is present in the neutron-rich Ru isotopes.

Shape evolutions in the neutron-rich Ru isotopes

Shape evolutions in the neutron-rich Ru isotopes were investigated using the cranked shell model and an excellent agreement was obtained in comparison with the experimental data. These results show that the cranked shell model with nonaxial deformed Woods-Saxon potential can provide a good description of the shape evolution in the neutron-rich Ru isotopes in terms of not only neutron number but also angular momentum.

Level lifetimes in neutron-rich Ru isotopes

The neutron-rich Ru isotopes are situated between the strongly deformed Sr-Zr region with axial deformation of f l _ 0.40 [1] and the spherical Cd-Sn region. Evidence for triaxiality of even-even Ru isotopes has been presented in [2-5], and lifetimes of some of their 2 + states have been measured in fission studies [6-9]. It seems, however, that in these experiments the nearly identical energies of the 2 + ---* 0 + transitions in l~ and 11~ could not be separated. Therefore, high-resolution measurements are required in order to perceive the evolution of deformation with increasing neutron number. So far only few measurements by the delayed-coincidence method [10] have been performed on chemically or massseparated isotopes. Therefore, a systematic study of level lifetimes in neutron-rich Ru nuclei has been undertaken at the Mainz TRIGA reactor. Fission products were obtained from thermal-neutron induced fission of 249Cf. Technetium isotopes were chemically separated within 2 s by the on-line SISAK method [11], allowing the study of levels and lifetimes of their/3decay daughters. Primarily, the short-lived activities of 1~ to 111Tc were measured, whereas long-lived decay products were kept at a low level due to the continuous flow of the liquid phase (containing the technetium activity) passing the detectors. Apart from Tc, also small contaminations of short-lived Ag isotopes were observed in the 7-spectra. The detector setup consisted of a thin plastic scintillator for fi-particles and two Ge-detectors for 7-rays, one being a planar diode with good energy resolution and timing properties (7 ns at 100 keV) and the other a medium-size coaxial detector. Coincidence events from all detector pairs were recorded with the GOOSY mult iparameter system. The delayed coincidences between the fl-scintillator and the planar 7-detector were used for the measurement of the shortest lifetimes. With this setup, a systematical accuracy of the order of 0.05ns could be obtained for the strongest "/-peaks. The 7-7 coincidences were used to check for contaminations in the 7-gates from the planar detector applied for the fl-

The role of triaxiality in the ground states of even-even neutron-rich Ru isotopes

Partial decay schemes for the very neutron-rich nuclei 108,110,112Ru and 114Ru, about which nothing was previously known, have been determined from the study of prompt, triple-γ coincidences in 248Cm fission fragments. Levels with probable spin up to 10ħ have been observed and γ-ray branching ratios obtained. Ratios of reduced electric quadrupole transition probabilities obtained from the branching ratios are in good agreement with predictions of a simple model of a rigid triaxial rotor.

Beta decay of 114Ru and Qβ systematics for n-rich Ru isotopes

New results on a very neutron-rich 114Ru isotope are discussed. A half-life of 0.57(5) s was determined and six γ-rays were observed to belong to this decay, five of which were placed in the decay scheme of 114Ru. Three conversion coefficients were measured experimentally. The beta feeding pattern of 114Ru has been determiined and log ft values are deduced. Q β values of 1.35(6) and 6.1(2) MeV have been measured for the decay of 108Ru and 114Ru. Systematics of decay energies of even neutron-rich Ru isotopes are presented and compared to the various mass predictions. Beta strength of 114Ru is discussed in the framework of the deformed single-particle model.