Rapid onset of collectivity in the vicinity of 78Ni

gamma-rays following the B and B-n decay of the very neutron rich 84Ga produced by photo-fission of 238U have been studied at the newly built ISOL facility of IPN Orsay: ALTO. Two activities were observed and assigned to two B-decaying states: 84gGa, I = (0\^-) and 84mGa, I = (3\^-, 4\^-). Excitation energies of the 2+1 and 4+1 excited states of 84Ge were measured at E(2+1) = 624.3 keV and E(4+1) = 1670.1 keV. Comparison with HFB+GCM calculations allows to establish the collective character of this nucleus indicating a substantial N=50 core polarization. The excitation energy of the 1/2+1 state in 83Ga known to carry a large part of the neutron 3s1/2 strength was measured at 247.8keV. Altogether these data allow to confirm the new single particle state ordering which appears immediately after the double Z=28 and N=50 shell closure and to designate 78Ni as a fragile and easily polarized doubly-magic core.Comment: 4 pages, ReVTe

Production de noyaux exotiques par photofission,<br />Le projet ALTO : Premiers Résultats

Titre des travaux : Production de noyaux riches en neutrons par photofissionThis Ph.D thesis has been carried out in the framework of ALTO project (Accélérateur Linéaire Auprès du Tandem d'Orsay), a project exploiting photofission as a production mode of neutron-rich nuclei for ISOL facilities. Our work deals with adaptation modes of the production environment represented by the target-ion source unit. We undertook an exhaustive radioprotection study in order to design and define the kinds of shielding necessary to face intense flux of photons and neutrons generated in the production target. Monte Carlo simulations with FLUKA code allowed us to calculate the simultaneous transport of photons and the neutrons with an entire modelling of the very complicated geometrical structures. For the target-source unit and the critical points of beam loss, we propose an optimised shielding based mainly on the segmented structure. We have studied the adequacy of a thick carbide uranium target to produce neutron-rich nuclei by photofission. In Particular, comparing the results of simulations with the experimental data, we have benchmarked FLUKA code for photofission with a 50 MeV electron beam. Finally, we present our work on the design and development of a FEBIAD-type-ion-source prototype: IRENA ion source, designed for next generation facilities.This work shows how important radioprotection considerations are also involved in the design of the ion source.Ce travail de thèse s'inscrit dans le cadre du projet ALTO (Accélérateur Linéaire Auprès du Tandem d'Orsay), projet exploitant la photofission comme mode de production de noyaux riches en neutrons pour la séparation en ligne. Nos travaux portent sur l'étude des modes d'adaptation de l'environnement de production représenté par son ensemble cible-source d'ions. Nous avons mené une étude exhaustive de radioprotection pour dimensionner et définir la nature des blindages nécessaires pour faire face aux flux intenses de photons et de neutrons générés dans la cible de production. Les simulations Monte Carlo avec le code FLUKA nous ont permis de calculer le transport simultané des photons et des neutrons avec une modélisation intégrale des structures géométriques très complexes. Pour l'ensemble cible-source d'ions et les points critiques de pertes de faisceaux, nous proposons des blindages optimisés basés essentiellement sur la structure segmentée. Nous avons étudié l'adéquation d'une cible épaisse de carbure d'uranium pour la production de noyaux radioactifs riches en neutrons par photofission. En particulier, nous avons montré la validité du code FLUKA pour la photofission avec un faisceau d'électrons de 50 MeV, en comparant les résultats de calculs aux mesures expérimentales réalisées. Enfin, nous présentons nos travaux de conception et de développement d'un prototype de source d'ions de type FEBIAD destinée aux installations de seconde génération : la source IRENA. Ces travaux montrent à quel point les considérations de radioprotection sont également impliquées dans le développement de la source

An optimized plasma ion source for difficult ISOL beams

International audienceThe Ionization by Radial Electron Neat Adaptation (IRENA) ion source has been designed to operate under extreme radiation conditions. Based on the electron beam generated plasma concept, the ion source is specifically adapted for thick target exploitation under intense irradiation. A validation prototype has been already designed and tested offline. The design of a new optimized prototype for online difficult beams production with ISOL facilities will be presented and discussed. In particular, simulation activities for thermionic emission, ions confinement and extraction will be presented and results discussed

An optimized plasma ion source for difficult ISOL beams

International audienceThe Ionization by Radial Electron Neat Adaptation (IRENA) ion source has been designed to operate under extreme radiation conditions. Based on the electron beam generated plasma concept, the ion source is specifically adapted for thick target exploitation under intense irradiation. A validation prototype has been already designed and tested offline. The design of a new optimized prototype for online difficult beams production with ISOL facilities will be presented and discussed. In particular, simulation activities for thermionic emission, ions confinement and extraction will be presented and results discussed

Charting Terra Incognita at Alto and S3

Charting Terra Incognita is a project grant that brings together the IPN Orsay, CSNSM Orsay and Irfu-SPHN laboratories around the common development of knowhow, equipment and techniques for mass spectrometry and nuclear spectroscopy at the low-energy branch of the new S3 spectrometer at Ganil, where likewise the Reglis set-up for intrajet laser spectroscopy is entering its final phase of construction. At the same time its concerted action initiates and sets the pace for the corresponding precursor physics programme at the Alto on-line isotope-separation facility, based on the photofission of uranium. We also collect a review of the Alto laser ion source, which is an essential instrument at any low-energy facility for the production of purified isotopic beams

Charting Terra Incognita at Alto and S3

Charting Terra Incognita is a project grant that brings together the IPN Orsay, CSNSM Orsay and Irfu-SPHN laboratories around the common development of knowhow, equipment and techniques for mass spectrometry and nuclear spectroscopy at the low-energy branch of the new S3 spectrometer at Ganil, where likewise the Reglis set-up for intrajet laser spectroscopy is entering its final phase of construction. At the same time its concerted action initiates and sets the pace for the corresponding precursor physics programme at the Alto on-line isotope-separation facility, based on the photofission of uranium. We also collect a review of the Alto laser ion source, which is an essential instrument at any low-energy facility for the production of purified isotopic beams

rapid onset of collectivity in the vicinity of 78Ni

4 pages, ReVTeXgamma-rays following the β and β-n decay of the very neutron rich 84Ga produced by photo-fission of 238U have been studied at the newly built ISOL facility of IPN Orsay: ALTO. Two activities were observed and assigned to two β-decaying states: 84gGa, I = (0−) and 84mGa, I= (3−,4−). Excitation energies of the 2+1 and 4+1 excited states of 84Ge were measured at E(2+1 ) = 624.3 keV and E(4+1 ) = 1670.1 keV. Comparison with HFB+GCM calculations allows to establish the collective character of this nucleus indicating a substantial N=50 core polarization. The excitation energy of the 1/2+1 state in 83Ga known to carry a large part of the neutron 3s1/2 strength was measured at 247.8keV. Altogether these data allow to confirm the new single particle state ordering which appears immediately after the double Z=28 and N=50 shell closure and to designate 78Ni as a fragile and easily polarized doubly-magic core