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Georgiadou, Anastasia
Universite Paris-Saclay, Ecole doctorale no. 576, particules hadrons energie et noyau - instrumentation, image, cosmos et simulation - Pheniics, Espace Technologique, Immeuble Discovery, Route de l'Orme aux Merisiers RD 128 91190 Saint-Aubin (France); Universite Paris-Sud, Institut de Physique Nucleaire d'Orsay, Nester group (France)2018
Universite Paris-Saclay, Ecole doctorale no. 576, particules hadrons energie et noyau - instrumentation, image, cosmos et simulation - Pheniics, Espace Technologique, Immeuble Discovery, Route de l'Orme aux Merisiers RD 128 91190 Saint-Aubin (France); Universite Paris-Sud, Institut de Physique Nucleaire d'Orsay, Nester group (France)2018
AbstractAbstract
[en] The structure of the unstable doubly magic nucleus 56Ni has been investigated by measuring one- and two-nucleon transfer reactions. Each transfer reaction provides information for two different physical aspects: the robustness of the N=28 shell gap and the strength of the neutron-proton pairing. 56Ni is a self-conjugate doubly magic nucleus with N=28 and Z=28. The magic number 28 is a peculiar shell closure created by spin-orbit splitting effects. The double magic number makes the determination of the single-particle nature of their N±1 neighbors by one-neutron transfer reaction of major interest to test both the robustness of shell closures as well as the evolution of particle and/or valence orbitals. Moreover 56Ni, as a N=Z nucleus with fully closed shells, is a key nucleus to investigate neutron-proton pairing in the largest shell accessible experimentally, the fp shell. Neutron-proton pairing can occur both in the isoscalar (T=0) and in the isovector (T=1) channels. The relative intensity of both channels reveals the collective nature of the states. The radioactive beam of 56Ni was produced at GANIL-Caen, France at 30 MeV/u by fragmentation of 58Ni and purification with the LISE spectrometer. The experimental set-up used, consists of the TIARAMUST2- EXOGAM combination which provides an almost 4π coverage and the ability to perform particle-γ coincidences. To probe the N=28 gap, we studied the spectroscopy of 55Ni through one-nucleon transfer reactions on 56Ni. The excitation energy spectrum is deduced by measuring the light ejectiles only, while particle-γ coincidences are used to improve the resolution of the populated states and select the main ones. Comparison in between the extracted angular distributions and DWBA calculations allow the extraction of the spectroscopic strength of the hole- and particle- states populated by these one neutron pickup reactions. As for neutron-proton pairing, a weakening of the strength is expected in the T=0 channel from previous results. The selectivity in ΔT=0 of the 56Ni(d,α)54Co reaction enables further investigation of the isoscalar channel contribution. (author)
[fr]
La structure du noyau N = Z doublement magique 56Ni (N = 28, Z = 28) a ete etudiee en mesurant les reactions de transfert a un et deux nucleons. Le transfert nous donne des informations sur deux aspects physiques differents: la fermeture de couche N = 28 et l'intensite de l'appariement neutron-proton. Le nombre magique N=28 est particulier, car c'est le premier cree par le spin-orbit. La double magicite permet la determination de la nature de particule independante des voisins N±1 par reaction de transfert d'un nucleon. De plus, en tant que noyau N=Z a couches fermees, le 56Ni est un noyau cle pour l'etude de l'apparement np dans la plus grande couche accessible experimentalement. L'apparement np se manifeste dans le canal isoscalaire (T=0) et isovecteur (T=1). L'intensite relative de chaque canal revele la nature collective des etats. L'experience de ce travail a eu lieu au GANIL-Caen, en France, avec un faisceau radioactif de 56Ni a 30MeV/u produit par fragmentation de 58Ni et purification avec le spectrometre LISE. Les mesures ont ete effectuees en cinematique inverse sur des cibles CH2 et CD2. Les detecteurs MUST2 et TIARA ont ete utilises pour la detection de ejectiles legers et couvraient presque 4π. En outre, quatre detecteurs germanium d'EXOGAM ont ete utilises pour les coincidences de particules-gamma afin d'identifier l'etat peuple du residu de reaction. Pour etudier le gap de N = 28, nous etudions la spectroscopie du 55Ni par les reactions de transfert de nucleons (d, t) et (p, d) sur le 56Ni. Le spectre en energie d'excitation est deduit de la mesure des ejectiles legers seulement. Ensuite, les coincidences particule-gamma sont utilisees pour ameliorer la resolution et identifier les principaux etats peuples. La comparaison des distributions angulaires ainsi obtenues avec des calculs DWBA permet d'extraire les facteurs spectroscopiques pour les etats de particules et de trous ainsi peuples. En ce qui concerne l'appariement np, nous avons analyse la reaction 56Ni(d,α)54Co qui realise un transfert de paires neutron-proton. Un affaiblissement du canal T=0 a cause de l'effet du spin-orbite est attendu. La selectivite en ΔT=0 de la reaction (d, α) permet d'etudier plus en detail le canal isoscalaire T = 0. (auteur)Original Title
Reactions de transfert induites avec 56Ni: l'appariement neutron-proton et la fermeture de couche N=28
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Source
27 Sep 2018; 140 p; 87 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; These de doctorat de l'Universite Paris-Saclay, Specialite: structure et reactions nucleaires
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Miscellaneous
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BARYON-BARYON INTERACTIONS, BETA DECAY RADIOISOTOPES, BETA-PLUS DECAY RADIOISOTOPES, DATA PROCESSING, DAYS LIVING RADIOISOTOPES, DIRECT REACTIONS, ELECTRON CAPTURE RADIOISOTOPES, ENERGY RANGE, EVEN-EVEN NUCLEI, GEV RANGE, HADRON-HADRON INTERACTIONS, INTERACTIONS, INTERMEDIATE MASS NUCLEI, ISOTOPES, MATHEMATICAL MODELS, MEASURING INSTRUMENTS, MULTI-NUCLEON TRANSFER REACTIONS, NICKEL ISOTOPES, NUCLEAR MODELS, NUCLEAR REACTIONS, NUCLEI, PARTICLE INTERACTIONS, PROCESSING, RADIATION DETECTORS, RADIOISOTOPES, TARGETS, TRANSFER REACTIONS
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