The N=52Ga83β decay was studied at ALTO. The radioactive 83Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ-ray emission following ...β decay. While β-delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ-ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β-decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei.
Lifetime of the ( 15 2 1 − ) state in 135Te Simpson, G; Regis, J M; Bettermann, L ...
Journal of physics. G, Nuclear and particle physics,
05/2019, Letnik:
46, Številka:
6
Journal Article
Recenzirano
The lifetime of the ( 15 2 1 − ) state of 135Te has been measured to be τ = 809(22) ps, corresponding to a reduced transition rate of B ( E 2 ; 15 2 1 − → 11 2 1 − ) =6.6(2) W.u. The experiment was ...performed at the focal point of the Lohengrin spectrometer and s-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 B ( E 2 ; 15 2 1 − → 11 2 1 − ) value is typical of a vibrational transition, despite 135Te possessing only one valence neutron and two valence protons. Shell model calculations performed with the jj 56 pnb 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) f7/2 couplings are coherent.
The shape of exotic even-mass (182-190)Pb isotopes was probed by measurement of optical isotope shifts providing mean square charge radii (delta(r(2))). The experiment was carried out at the isolde ...(cern) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of delta(r(2)) to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic Z=82 lead isotopes near neutron midshell (N=104).
Systematic off-line fluorination studies on all the stable lanthanide isotopes have been performed. The results are presented as a function of various parameters such as the target temperature, the ...type of ion source used (hot plasma or surface ionization) and the quantity of CF4 introduced. The first on-line measurements allowed us to determine the optimal experimental conditions for producing radioactive lanthanide isotopes.
The SPIRAL1 (Système de Production d’Ions Radioactifs Accélérés en Ligne) facility at GANIL (Grand Accélérateur National d’Ions Lourds) is developing new techniques to access nuclei in the ...neutron-deficient isotope region far from the stability-valley, with Z ranging from 30 to 60. The availability of different primary beams, ranging from carbon to uranium with energies up to 95 MeV/A, gives an opportunity to produce a large variety of radioactive ion beams. The production of neutron-deficient short-lived alkalis by fusion-evaporation reactions is the focus of this work. A simple and compact target ion source system (TISS) is designed to produce isotopes of 74Rb (τ1/2 = 64.8 ms) and 114Cs (τ1/2 = 570 ms). The efficiencies of the different processes involved in the production are evaluated. Radioactive recoils are produced through the interaction of heavy-ion beams, respectively 20Ne beam and 58Ni beam at an intensity of 1013 and 1012 pps, with a thin 58Ni target. High atom-to-ion transformation (ATI) efficiency should be obtained above 70% and 90% for 74Rb and 114Cs nuclei respectively. The expected intensities of the RIBs are estimated to be around 104 pps at the exit of the TISS.
The ALTO facility (Accélérateur Linéaire auprès du Tandem d’Orsay) has been built and is now under commissioning. The facility is intended for the production of low energy neutron-rich ion-beams by ...ISOL technique. This will open new perspectives in the study of nuclei very far from the valley of stability. Neutron-rich nuclei are produced by photofission in a thick uranium carbide target (UCx) using a 10μA, 50MeV electron beam. The target is the same as that already had been used on the previous deuteron based fission ISOL setup (PARRNE F. Clapier et al., Phys. Rev. ST-AB (1998) 013501.). The intended nominal fission rate is about 1011fissions/s. We have studied the adequacy of a thick carbide uranium target to produce neutron-rich nuclei by photofission by means of Monte-Carlo simulations. We present the production rates in the target and after extraction and mass separation steps. The results from Monte-Carlo simulations are compared to experimental data either with the ALTO facility (in the first step of commissioning, i.e. 100nA of the electron beam current intensity), or with fast-neutron-induced fission generated from a 26MeV deuteron beam. The results obtained support the suitability of FLUKA simulation code used to describe all the photofission process with an electron beam energy of 50MeV.
A new β-decay station, COnversion electrons Chasing at Orsay (COeCO), has been developed at ALTO to perform conversion electron spectroscopy studies of neutron-rich nuclei produced by photo-fission ...of a uranium carbide target. It is based on the collection of a low-energy ISOL beam on a mylar tape, and the transportation of the electrons emitted by the produced radioactive source through a magnetic field induced by two copper coils, towards a cooled Si(Li) detector. In this article, a detailed description of the new decay station and its components is given. The magnetic field induced by the coils was measured and compared to simulations performed with the COMSOL® software. The efficiency of the detection setup was estimated using a 207Bi and a 152Eu source as an off-line commissioning. Finally, the results obtained with a 96Rb radioactive beam for the on-line commissioning are presented.
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