[en] Thanks to advances in production of radioactive nuclear beams in the last two decades, we are able to study nuclear systems that are very far from stability. The region of the nuclear landscape in the vicinity of ⁷⁸Ni remains still unexplored. This region, with very neutron-rich ⁷⁸Ni hypothetically considered as a doubly magic core, is interesting in terms of nuclear structures. The experimental information is equally important to guide the emerging shell-model effective interactions in this region. We have studied β-decay of a neutron rich ⁸⁴Ga isotope at the ALTO facility in IPN Orsay (France). The fission fragments were produced with photo-fission reaction induced by 50 MeV electron beam in a thick uranium carbide (UC_x) target. For the first time the maximum electron driver beam intensity at ALTO - 10 μA - was used. The gallium atoms were selectively ionized with a newly developed laser ion source. With this ion source the ionization of the gallium was more than ten times higher compared to the surface ion source previously used by our group. The ions were separated with the PARRNe mass separator and implanted on a movable mylar tape. Two germanium detectors in close geometry were used for the detection of γ-rays and γ-γ coincidence measurement, and a plastic 4πβ for beta tagging. We present the results of our experiment: the improved level schemes of the neutron-rich ^83;84Ge and ⁸⁴As isotopes. We discuss their structure and compare the experimental results with the shell model calculations made with the new effective interaction ni78-jj4b with ⁷⁸Ni core, constructed in the framework of this thesis. Particularly this study has allowed us to find new transitions and to improve the level schemes of ⁸³Ge, ⁸⁴Ge and ⁸⁴As

No abstract available

[en] Beta-decay properties are among the easiest and, therefore, the first ones to be measured to study new neutron-rich isotopes. Eventually, a very small number of nuclei could be sufficient to estimate their lifetime and neutron emission probability. With the new radioactive beam facilities which have been commissioned recently (or will be constructed shortly) new areas of neutron-rich isotopes will become reachable. To study beta-decay properties of such nuclei at IPN (Orsay) in the framework of collaboration with JINR (Dubna), a new experimental setup including the neutron detector of high efficiency TETRA was developed and commissioned

[en] For many fission products, the $\gamma$ rays emitted following $\beta$ decay provide an easily-detectable signature that can be used to identify their quantities and distributions in a sample. As a result, $\gamma$-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the $\gamma$-ray intensity is available. However, in many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. To address this need, we have developed a new experimental method that is well suited to precisely measure absolute $\gamma$-ray intensities in the $\beta$ decay of long-lived fission products. The approach involves the production of a radiopure sample by implantation of a mass-separated ion beam from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility on a thin carbon foil. The emitted $\beta$-decay radiation is detected with a 4$\pi$ gas proportional counter and a meticulously efficiency-calibrated high-purity germanium (HPGe) detector. As a first measurement to demonstrate the approach, we studied the absolute $\gamma$-ray intensities of the strongest transitions following the $\beta$ decay of ${}^{95}$Zr and its decay-daughter ${}^{95}$Nb, and determined them to fractional precisions of better than 1–2%. In addition, with a larger sample of activity produced through neutron irradiation of an isotopically-enriched Zr foil, we performed a high-precision measurement of the relative $\gamma$-ray intensities following the decay of ${}^{95}$Zr with just the HPGe detector. The sample-production method at CARIBU and the coincidence detection approach demonstrated here can be applied to study fission products with half-lives longer than a day, which includes isotopes important not only for nuclear-energy and national-security applications, but also for medical-isotope research and environmental monitoring.

[en] Angular and energy distributions of neutrons produced by the interaction of deuterons of 40 MeV in carbon, light- and heavy-water targets, in which they are stopped, have been measured by the activation method. A discrepancy with a time-of-flight measurement for d+C has been found. The results are compared with a Monte-Carlo calculation and are discussed in the frame of building a deuteron-to-neutron converter for the SPIRAL2 radioactive ion-beam facility.

[en] In the context of radioactive ion beams, fission targets, often based on uranium compounds, have been used for more than 50 years at isotope separator on line facilities. The development of several projects of second generation facilities aiming at intensities two or three orders of magnitude higher than today puts an emphasis on the properties of the uranium fission targets. A study, driven by Institut de Physique Nucléaire d’Orsay (IPNO), has been started within the SPIRAL2 project to try and fully understand the behavior of these targets. In this paper, we have focused on five uranium carbide based targets. We present an off-line method to characterize their fission product release and the results are examined in conjunction with physical characteristics of each material such as the microstructure, the porosity and the chemical composition.

[en] The goal of this project was to develop a new approach to measuring (n,2n) reactions for isotopes of interest. We set out to measure the ²³⁹Pu(n,2n) and ²⁴¹Pu(n,2n) cross sections by directly detecting the 2n neutrons that are emitted. With the goal of improving the ²³⁹Pu(n,2n) cross section and to measure the ²⁴¹Pu(n,2n) cross section for the first time. To that end, we have constructed a new neutron-charged-particle detector array called NeutronSTARS. It has been described extensively in Casperson et al. [1] and in Akindele et al. [2]. We have used this new neutron-charged-particle array to measure the ²⁴¹Pu and ²³⁹Pu fission neutron multiplicity as a function of equivalent incident-neutron energy from 100 keV to 20 MeV. We have made a preliminary determination of the ²³⁹Pu(n,2n) and ²⁴¹Pu(n,2n) cross sections from the surrogate ²⁴⁰Pu(α,α’2n) and ²⁴²Pu(α,α’2n) reactions respectively. The experimental approach, detector array, data analysis, and results to date are summarized in the following sections.

[en] The N = 28 isotone "6"0Ge, T_z = -2, was produced and selected among the products of the fragmentation reaction of a "7"8Kr beam at 150 MeV/nucleon and a Be target by means of the A1900 fragment separator at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Its decay was studied for the first time using the optical time projection chamber. The β-decay of "6"0Ge was found to be dominated by β-delayed proton emission, with a branching of ∼ 100 % and half-life T_1_/_2 = 20_-_5"+"7 ms. (orig.)

[en] A new cosmic-ray experiment is under construction in the Pyhaesalmi mine, Finland. It aims to study the (mass) composition of cosmic rays at and above the knee region. The array, called EMMA (Experiment with MultiMuon Array), will cover approximately 130 m² of detector area at a depth of 75 metres (∼210 mwe). It is able to locate shower cores in an area of approximately 400 m² with an accuracy better than 6 metres. The array detects underground muons and the muon multiplicity, their lateral distribution and the arrival direction of the air shower can be determined. First scientific measurements can be started during the spring 2009 with a partial-size array. The full-size array is expected to be ready by autumn 2010. The full-size array consist of two type of detectors: drift chambers and plastic scintillation detectors. Besides the composition study, it is also expected that the array contributes on the study of high-multiplicity muon bundles that were observed at the cosmic-ray experiments at the LEP detectors.

[en] We report on the result of several multi-step Coulomb excitation measurement on refractory fission fragments from the CARIBU facility at ANL, USA. The experiments were performed with the GRETINA γ-ray and CHICO2 particle detector arrays. A highlight is made on the results of ¹¹⁰Ru where we obtained reduced transition probabilities for several levels near the ground state as well as the quadrupole moment of the first excited 2⁺ state. These data provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations. This document is made up of an abstract and the slides of the presentation. (authors)