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AbstractAbstract
[en] The recent spectroscopy of 78Ni together with indications of shape coexistence just below the N=50 shell closure for 79Zn suggests that deformed intruder configurations could play a crucial role in low-energy structure properties in this region and towards the limits of the nuclear chart. Such configurations are predicted to originate from multiparticle-multi-hole excitations above the N=50 and Z=28 shell gaps pushed down in energy due to neutron-proton correlations which enhance quadrupole collectivity. Because these intruder states involve many-particle excitations more difficult to describe theoretically, their predicted energies vary more drastically between models than for yrast states originating from 'normal' configurations on which they tend to agree. This topic is the main goal of the experiment performed at the RIBF facility (RIKEN, Japan) in November 2020 to identify and characterise for the first time 2p-1h intruder states in 83Ge. Neutron hole states in this N=51 nucleus were populated via neutron knockout reaction from the N=52 nucleus 84Ge that has about two neutrons in the s1/2d5/2 valence space above N=50. This direct reaction allows in some cases to remove one of the neutrons from the quasi-full g9/2 orbital below N=50 to selectively populate the 9/2+ intruder states based on a ν(g9/2)-1(s1/2d5/2)+2 configuration. In order to identify the populated states, gamma-rays from their in-flight decay were measured using the HiCARI Germanium array. We are able to identify a state at 1359 keV as a 2p-1h intruder, in good agreement with phenomenological and shell model calculations. In line with predictions as well, we measure some candidate states at high energy that are still to be fully characterised. A transition at 1240 keV matches with previously identified states and was expected to come from the coupling of a neutron with the excited 82Ge core. However the very high spectroscopic factor measured on this transition does not compare with any prediction and requires more development to be explained. (author)
[fr]
La spectroscopie recente du 78Ni, additionnee aux indications de coexistence de formes juste en dessous de la fermeture de couche N=50 pour le 79Zn, suggere que les configurations intruses deformees pourraient jouer un role crucial dans les proprietes de la structure en couche a basse energie dans la region, et aux abords de la limite du diagramme de Segre. Il est predit que de telles configurations trouvent leurs origines dans les excitations multiparticules-multitrous au dessus des gaps N=50 et Z=28, reduits par les correlations neutrons-protons qui renforcent la collectivite quadrupolaire. Ces etats impliquant de multiples excitations particules-trous difficiles a decrire de maniere theorique, les energies predites varient drastiquement plus selon les modeles que pour les etats yrast provenant de configurations 'normales' pour lesquelles ils tendent a etre en accord. Ce sujet est l'objectif principal de l'experience effectuee en novembre 2020 a l'installation RIBF (RIKEN, Japon) pour identifier et caracteriser pour la premiere fois des etats intrus 2p-1t dans le 83Ge. Les etats trous neutrons dans ce noyau a N=51 ont ete peuples par une reaction d'arrachage de neutron depuis le noyau a N=52 84Ge possedant environ deux neutrons dans l'espace de valence s1/2d5/2 au dessus de N=50. Cette reaction directe permet dans certains cas de retirer un neutron de l'orbitale quasi-pleine g9/2 en dessous de N=50 pour peupler de maniere selective l'etat intrus 9/2+ en se basant sur une configuration ν(g9/2)-1(s1/2d5/2)+2. Afin d'identifier les etats peuples, les rayons gammas emis en vol sont mesures a l'aide du multi-detecteur au Germanium HiCARI. Nous identifions un etat a 1359 keV comme un intrus 2p-1t, en bon accord avec les predictions de phenomenologie et de calculs de modele en couches. Aussi en accords avec les predictions, nous mesurons des etats intrus candidats a haute energie necessitant encore d'etre totalement caracterises. Une transition a 1240 keV correspond avec des etats precedemment identifies et il etait anticipe qu'elle provienne du couplage d'un neutron avec le coeur excite de 82Ge. Cependant le facteur spectroscopique tres eleve mesure pour cette transition est incomparable avec les predictions theoriques et requiert plus de developpement pour etre explique. (auteur)Original Title
Etats intrus et coexistence de forme au dela de N=50 proche du 78Ni etudies par arrachage de neutron a RIBF-RIKEN
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23 Nov 2023; 142 p; 82 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; These de doctorat, Specialite: physique
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Miscellaneous
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BARYONS, BEAMS, BETA DECAY RADIOISOTOPES, BETA-MINUS DECAY RADIOISOTOPES, DIMENSIONLESS NUMBERS, DIRECT REACTIONS, ELECTROMAGNETIC RADIATION, ELEMENTARY PARTICLES, ELEMENTS, ENERGY LEVELS, EVEN-EVEN NUCLEI, EVEN-ODD NUCLEI, FERMIONS, GERMANIUM ISOTOPES, HADRONS, HYDROGEN ISOTOPES, INTERMEDIATE MASS NUCLEI, IONIZING RADIATIONS, ISOTOPES, LIGHT NUCLEI, MATHEMATICAL MODELS, MEASURING INSTRUMENTS, METALS, NICKEL ISOTOPES, NUCLEAR MODELS, NUCLEAR REACTIONS, NUCLEI, NUCLEONS, ODD-EVEN NUCLEI, RADIATION DETECTORS, RADIATIONS, RADIOISOTOPES, SECONDS LIVING RADIOISOTOPES, SEMICONDUCTOR DETECTORS, SPECTROSCOPY, STABLE ISOTOPES, ZINC ISOTOPES
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