New results on fission cross sections in actinide nuclei using the surrogate ratio method and on conversion coefficients in triaxial strongly deformed bands in167Lu from ice ball and gammasphere

The surrogate ratio technique is described. New results for neutron induced fission cross sections on actinide nuclei, obtained using this technique are presented. The results benchmark the surrogate ratio technique and indicate that the method is accurate to within 5% over a wide energy range. New results for internal conversion coefficients in triaxial strongly deformed bands in 167Lu are also presented

Lifetime measurements in 162^{162}Dy

International audienceBackground: The nature of oscillations or excitations around the equilibrium deformed nuclear shape remains an open question in nuclear structure. The Dy162 nucleus is one of the most extensively studied nuclei with the (n,γ), (n,e−), (α,2n) reactions and most recently the (p,t) pickup reaction adding 11 0+ states to an excitation energy of 2.8 MeV to an already-well-developed level scheme. However, a major shortfall for a better understanding of the nature of the plethora of bands and levels in this nucleus has been the lack of lifetime measurements. Purpose: To determine the character of the low-lying excited bands in this Dy162 nucleus, we set out to measure the level lifetimes. Method: Lifetimes were measured in the Dy162 nucleus following neutron capture using the Gamma-Ray-Induced Doppler (GRID) broadening technique at the Institut Laue-Langevin in Grenoble, France. Results: In total, we have measured the lifetimes of 12 levels belonging to a number of excited positive- and negative-parity bands in the low-lying spectrum of the Dy162 nucleus. The lifetime of the Kπ=2+ bandhead at 888.16 keV was previously measured. We confirm this value and measure lifetimes of the 3+ and 4+ members of this band yielding B(E2) values that are consistent with a single γ-vibrational phonon of several Weisskopf units. The first excited Kπ=4+ band, with a bandhead at 1535.66 keV, is strongly connected to the Kπ=2+ band with enhanced collective B(E2) values and it is consistent with a double phonon vibrational (γγ) excitation. Lifetime of Kπ=0+ band members have also been measured, including the 4Kπ=02++ state at 1574.29 keV and the 2Kπ=03++ state at 1728.31 keV. This latter state also displays the characteristics of a double phonon excitation built on the Kπ=2+ band. Conclusions: We discuss our findings in terms of the presence or absence of collective quadrupole and octupole vibrational excitations. We find two positive-parity excited bands at 1535.66 keV (Kπ=4+) and the 1728.312-keV 2+ state of a Kπ=0+ band at 1666 keV connected with sizably collective B(E2) values to the (Kπ=2+)γ band at 888 keV

Beta decay of 66^{66}Mn to the N=40N = 40 nucleus 66^{66}Fe

International audienceThe low energy structure of 66Fe was studied by means of γ- and fast-timing spectroscopy at the ISOLDE/CERN facility. The level scheme of 66Fe populated following the ${\beta }^{-}$ decay of 66Mn was established. It confirms and further expands the level scheme from recent publications. The β-delayed neutron emission branch was measured and γ rays in 65Fe were observed following the β–n decay for the first time. The half lives of the ${2}_{1}^{+}$ state and four other states of 66Fe were measured using the advanced time-delayed $\beta \gamma \gamma$(t) method. These results are compared with large-scale shell-model calculations based on the Lenzi–Nowacki–Poves–Sieja interaction. The β-decay of 66Mn to 66Fe has been calculated as well, and log(ft) values derived. Spin and parity assignments are proposed based on the experimental information and the new calculations

Search for shape-coexisting 0+^+ states in 66^{66}Ni from lifetime measurements

International audienceThe lifetime of the 0$_3^+$ state in $^{66}$Ni, two neutrons below the $N=40$ subshell gap, has been measured. The transition $B(E2;0_3^+ \rightarrow 2_1^+)$ is one of the most hindered E2 transitions in the Ni isotopic chain and it implies that, unlike $^{68}$Ni, there is a spherical structure at low excitation energy. We have performed extensive shell-model calculations that correctly predict this result, obtaining a spherical 0$^+$ state at the correct energy and with an extremely low $B(E2;0_3^+ \rightarrow 2_1^+)$ value

Nuclear Structure Studies of 106Pd and 106Cd with the (n,n′γ) Reaction

Excited states in 106Pd and 106Cd have been studied using the (n,n′γ) reaction. The data include level lifetimes, spins, branching ratios, and multipole mixing ratios, and give a comprehensive view of excitations with spin ≤6ħ. The determined E2 strengths show serious discrepancies with the quadrupole phonon structure expected in these nuclei

Nuclear structure of 189Tl states studied via ?+/EC decay and laser spectroscopy of 189m+gPb

The β+/EC decay of 189m, gPb has been studied at the ISOLDE facility using nuclear spectroscopy and in-source laser spectroscopy. A level scheme of 189Tl has been built from gamma - gamma coincidence relationships and information on the feeding of some excited levels of 189Tl provided by the hyperfine spectra obtained from laser ionization. The half-lives of both the 13/2+ and 3/2- 189Pb isomers have been estimated to be T1/2 = 50±3 s and T1/2 = 39±8 s, respectively. Calculations have been performed for different oblate and prolate nuclear deformations using an axial-rotor coupled to one-quasiparticle model, a structure has been suggested for the low-lying levels of the 189Tl nucleus