The lifetime of the state of 135Te has been measured to be τ = 809(22) ps, corresponding to a reduced transition rate of =6.6(2) W.u. The experiment was performed at the focal point of the Lohengrin spectrometer and μs-delayed γ rays from mass-selected A = 135 ions were detected by four LaBr3(Ce) scintillators. This allowed the fast-timing technique to be used to access lifetimes in the 10s-of-ps to ns time region. The value is typical of a vibrational transition, despite 135Te possessing only one valence neutron and two valence protons. Shell model calculations performed with the state-of-the-art effective interaction predict a B(E2) value close to the experimental one and show that contributions from the π(g7/2, d5/2)νf7/2 couplings are coherent.
FIPPS is the new nuclear physics instrument of ILL for the spectroscopy of nuclei produced in neutron-induced reactions. The performance of the first implementation of the setup will be shown, together with an overview of the first experimental campaign (December 2016-March 2017). Future perspectives and physics opportunities will then be discussed.
Radiative capture reactions on rare targets and prompt spectroscopy of neutron-rich nuclei produced in the neutron-capture induced-fission of 235U and 241Pu have been performed at the Institut Laue-Langevin (ILL). The high efficiency germanium (Ge) EXOGAM array has been used, complemented with Ge detectors from GASP and the ILL. LaBr3 detectors from the FATIMA collaboration have also been coupled to EXOGAM to measure lifetimes of lowlying excited states. The measured characteristics indicate very good performances of the overall setup. Some recent results will be discussed.
The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.
A large array of Ge detectors installed at ILL, around a 235U target irradiated with cold neutrons, (EXILL) allowed measurement of prompt gamma-ray cascades occurring in fission fragments with an unambiguous determination of fragments. Here we present preliminary results of a systematic comparison between experimental γ-ray intensities and those obtained from the Monte-Carlo simulation code FIFRELIN, which is dedicated to the de-excitation of fission fragments. Major γ-ray intensities in the 142Ba and 92Kr fission products, extracted from EXILL data, were compared to FIFRELIN, as well as to reported values (when available) obtained with EUROGAM2 in the spontaneous fission of 248Cm. The evolution of γ-ray intensities in 92Kr versus the complementary partner in fission (i.e. versus the total number of evaporated neutrons by the fission pair) was then extracted and compared to FIFRELIN.
A search for new isotopes in the neutron-rich rare-earth region has been carried out using a 345 MeV/nucleon 238U beam at the RIKEN Nishina Center RI Beam Factory. Fragments produced were analyzed and identified using the BigRIPS in-flight separator. We observed a total of 29 new neutron-rich isotopes: 153Ba, 154,155,156La, 156,157,158Ce, 156,157,158,159,160,161Pr, 162,163Nd, 164,165Pm, 166,167Sm, 169Eu, 171Gd, 173,174Tb, 175,176Dy, 177,178Ho, and 179,180Er.
A new isomer with ms half-life was observed in 160Nd at RIBF, RIKEN Nishina Center by using in-flight fission of 238U beam and a cluster-type Ge detector array, EURICA. The experimental results and a PSM calculation indicate that the isomer in 160Nd is a 2 quasi-particle excitation of neutrons with a configuration of n1/2[521]x7/2[633] as the case in other N = 100 isotones. The E(4+)/E(2+) ratio of the ground-state band, 3.29, shows the 160Nd is well deformed and the ground band has a rotational nature. The 4- excitation of 160Nd showed an increase in energy by ~100 keV compared to that of 162Sm as predicted by the PSM calculation. A PSM calculation was performed by changing input beta_4 value and confirmed that the large hexadecupole deformation in Nd was responsible for the increase of the isomer energy.
The mixing ratio of the main 320-keV, M1 + E2 ground-state γ transition in 210Bi has been more precisely quantified, allowing a significant reduction in the uncertainty of measurements of the neutron-capture cross section to the ground state of 210Bi from 25% to 0.9%. Accurate values for neutron-capture cross sections to both the ground and long-lived 9− isomeric state at 271 keV in 210Bi are of particular importance as Pb-Bi finds increased usage in Accelerator Driven Systems.
The EURICA array has currently been in operation at RIKEN Nishina Center for one year.During this time several physics campaigns have been performed.In this paper we report about the
The combination of the intense cold neutron beam available at the PF1b beam position of the Institute Laue-Langevin (ILL) in Grenoble, together with the high detection efficiency of a large array of high purity Ge detectors (HPGe) has offered a unique opportunity for a set of experiments devoted to nuclear spectroscopy on stable isotopes as well as on exotic nuclei produced in the fission process of uranium and plutonium samples. The emitted γ-rays from neutron capture on stable targets as well as from the decay of fission fragments have been acquired in a trigger-less mode to preserve a maximum of information for further off-line treatment. A dedicated fully digital acquisition system using a combination of a 14-bit 100 MS/s digitisers with a PowerPC-based VME single board computer has been developed to ensure data collection and real-time processing capabilities. The present article will describe the experimental setup as well as the specific electronic configuration used during the EXILL campaign of measurements with particular emphasis on the technical achievements as well as on the preliminary results obtained in the various experiments.
We report on a $\ensuremath{\gamma}\ensuremath{\gamma}$ angular-correlation experiment investigating ${}^{200}$Hg after cold-neutron capture. The experiment was performed using eight high-purity germanium detectors mounted on an array installed at the PF1B neutron beam line of the research reactor of the Institut Laue-Langevin in Grenoble, France. The geometry of the array allows $\ensuremath{\gamma}\ensuremath{\gamma}$ angular-correlation analyses that can be used for the determination of level spins and multipole mixing ratios in ${}^{200}$Hg. We present multipole mixing ratios for secondary $\ensuremath{\gamma}$ rays and investigate the nature of the ${}^{200}$Hg neutron-capture state by analyzing the observed primary $\ensuremath{\gamma}$ rays of this nucleus.