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Nd’ordre 202-2009
LYCEN - .....
These
presentee
devant l’Universite Claude Bernard Lyon-1
pour l’obtention du
DIPLOME de DOCTORAT
(arr^ete du 07 aout^ 2006)
Specialite : Physique Nucleaire
par
DOAN Quang Tuyen
Recherche de la symetrie tetraedrique dans le
156noyau Gd par spectroscopie
soutenue le 26 Novembre 2009
devant la Commission d’Examen
Jury : M. D. CURIEN
M. D. DAVESNE
M. D. GUINET
Mme. A. KORICHI Rapporteur
M. C. PETRACHE Rapp et President du Jury
M. O. STEZOWSKI Directeur de these
Institut de Physique Nucleaire de Lyon
43, Bd du 11 Novembre 1918
69622 Villeurbanne Cedex, France
tel-00561660, version 1 - 1 Feb 2011tel-00561660, version 1 - 1 Feb 2011TetraNUC AGATA
Bernard ILLE
IPNLyon
Olivier STEZOWSKI
CNRS
Daniel GUINET
Daniel
Costel PETRACHE
Amel KORICHI, CSNSM
CNRS
Dany DAVESNE
Dominique CURIEN IPHC
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tel-00561660, version 1 - 1 Feb 2011TetraNUC
Jerzy DUDEK
Jacques MEYER
Michelle MEYER
l’IPNLyon
?l??a?n?a?l?y?s?e?d?e???d?o?n?n???e??.?d?e??c?eM?e?r?c?i??l?o?r???p?o?u?r???l?e???e???s?u?g?g?e?s?t?i?o?n??,?n??l?e???e?t?r?e?J?en?q?u?i??s?e?i?g?n?e?m?e?n?t???t?r?????q?u?'?i?l?c?e???m?'?a?!?d?o?n?n????????p?o?u?r?d?a?m?e?m?e?n?e?r??d????????m?o?n??b?i?e?n??e?n?f?i?n??c?e?t?t?e??a?n?a?l?y?s?e.?nC?e???d?r?e?e?t?m?e?r?c?i?e?m?e?n?t???d?o?n?n??????'?a?d?r?e?s?s?e?n?tt?r?o?i?????g?a?l?e?m?e?n?tB?o?n?n?e???!?l?a??r?e?m?e?r?c?i?e?m?e?n?t?c?o?l?l?a?b?o?r?a?t?i?o?n??m?e???s?u?r??e?t?t?r?a?v?a?i?l?l?e?r??m?'?a?v?o?i?r??p?o?u?r??m?'?a?v?o?i?r?,?e?e?n??j?o?u?r???p?a?r?-?e?n??t?i?c?u?l?i?e?r??M?o?n??l?e??s?i?e?u?r??d?e??S?t?r?a?s?b?o?u?r?g?d?e????f?a?i?t,?s?o?r?t?eP?s?e?r?o?f?e?s?s?e?u?r??d???c?o?n?d?i?t?i?o?n??.??l?l?U?e?n?c?o?u?r?a?g?e?m?e?n?t???n?i?v??p?e?n?d?a?n?te?r?s?i?t???S?t?r?a?s?b?o?u?r?g?a?n?n???e??1?t?h???s?e.,?c?o?n?t?i?n?u?a?t?i?o?n??p?o?u?r?!?l?e??U?c?o?u?r???g?r?a?n?d??s???j?o?u?r????'?a?d?r?e?s?s?e,M?o?n?s?i?e?u?r??r?o?f?e?s?s?e?u?r???q?u?e?l?U,e?r?s?i?t??M?a??y?o?n1,?a?c?c?u?e?i?l?l?i??l?e?u?r??s?u?r??l?a?P?s?y?m???t?r?i?e????t???t?r?a???d?r?i?q?u?e?n?i?v??e?tL?p?o?u?r??p?o?u?r??a?v?o?i?r??a?i?d?e?l?u??p?o?u?r??e?t?e?n?c?o?u?r?a?g???c?o?r?r?i?g???l?l?e??c?p?r?e?m?i?e?r???h?a??d?ep?i?t?r?e?s???j?o?u?r??t?h???o?r?i?q?u?eF?r?a?n?c?e.?d?e?s?o?u?h?a?i?t?e?r?a?i??c?e?r?e?m?e?r?c?i?e?r??t??t?o?u??t?e?m?e?m?b?r?e?t?h???s?e.?J?e?d?i?f?f???r?e?n?t??v?o?u?d?r?a?i???s?e?r?v?i?c?e???p?o?u?r????g?a?l?e?m?e?n?t?r?e?m?e?o?n?t?r?c?i?e?r??e?l??e?n?s?e?m?b?l?e??d?u??q?u?e?g?r?o?u?p?e?t?r?a?v?a?i?lM?a?t?i???r?e?d???r?o?u?l?eN?u?c?l???a?i?r?e?a?n???p?o?u?r??e?l?e???b?o?n?n?e???a?i?d?e??
tel-00561660, version 1 - 1 Feb 2011Resume
Des calculs theoriques utilisant la methode de champ moyen ont suggere l’existence
des formes du noyau avec la symetrie tetraedrique et/ou octraedrique dans la region
156 160des terres rares au voisinage des noyaux Gd et Yb. Dans les noyaux avec une
symetrie tetraedrique pure, des transitions intra-bande E2 a bas spin dans des bandes
de parite negative disparaissent ou sont tres faibles. Ce travail est dedie a une re-
156cherche experimentale de la symetrie tetraedrique dans le noyau Gd. Une experience
a ete faite a Jyv askyl a avec le multi-detecteur JUROGAM, sur la reaction de fusion -
154 156evaporation Sm(, 2n) Gd. L’analyse des donnees, a etabli les rapports d’embran-
chement de deux bandes de parite negative et a permis, par distribution angulaire, de
conna^ tre la nature d’une nouvelle transition. Les rapports d’embranchement obtenus
sont comparables avec ceux des experiences precedentes et quelques limites superieures
ont ete determinees. L’absence de transitions a bas spin (I < 9 ) dans la bande de
parite negative a spin impair a ete con rmee. Ces resultats ont renforce l’hypothese
156d’une symetrie tetraedrique dans le noyau Gd.
La spectroscopie est l’outil majeure utilise dans ce travail. Les principes ainsi
qu’une etude de simulation realiste sont detailles dans ce manuscrit. La simulation
avec des evenements realistes a ete faite pour comparer la fonction de reponse de
deux types de multidetecteurs EUROBALL et AGATA. Les resultats montrent que
sous certain conditions la phase demonstrateur d’AGATA peut ^etre utilisee pour la
recherche d’evenements rares.
tel-00561660, version 1 - 1 Feb 2011tel-00561660, version 1 - 1 Feb 2011Abstract
Theoretical calculations using realistic mean- eld method suggest the existence of
nuclear shapes with tetrahedral and/or octahedral symmetries in some rare earth nuclei
156 160around Gd and Yb. In nuclei with exact tetrahedral symmetry, the E2 intra-band
transitions are predicted to vanish completely or to be very weak. This work is devoted
156to an experimental research of the tetrahedral symmetry in the nucleus Gd. An
experiment has been carried out with the JUROGAM - rays detector at Jyv askyl a by
154 156using the fusion - evaporation reaction Sm(, 2n) Gd. In analysis, the branching
ratios of two parity negative bands were determined, the angular distribution has been
analyzed to determine the nature of one inter-band transition between these two bands.
The transitions strength ratios determined are of the same order of magnitude as
previous experiments, and some upper limits have been established for the lowest spin.
The missing of the E2 transitions below the I = 9 states in the odd spin parity
negative band were con rmed. The results of this work reinforced the hypothesis of the
156tetrahedral symmetry in the nucleus Gd.
-ray spectroscopy is the major tool used for this work. Detection principles and-
ray simulations are detailed in the document. The simulation, based on realistic events,
has been realised to compare the response function of two multidetectors EUROBALL
and AGATA. The results show that under certain conditions the rst phase of AGATA
(demonstrator) is also a tool to search for rare events.
tel-00561660, version 1 - 1 Feb 2011tel-00561660, version 1 - 1 Feb 2011Table des matieres
Introduction 9
I Elements theoriques et symetrie tetraedrique 13
I.1 Les modeles du noyau 14
I-1.1 Modele de la goutte liquide . . . . . . . . . . . . . . . . . . . . . . 14
I-1.2 Parametrisation de la surface nucleaire . . . . . . . . . . . . . . . 15
I-1.3 Model