Le Département d'Électronique des Détecteurs et d'Informatique pour la Physique

Shape coexistence offers one of the most demanding tests of modern nuclear theories. However, firmly establishing it experimentally requires an exhaustive knowledge of a large number of nuclear properties related to the nuclear deformation. The thesis focuses on the manifestations of the shape-coexistence in atomic nuclei with mass number A ≈ 100, specifically ¹⁰⁶Cd and ¹⁰⁰Zr.

The properties of ¹⁰⁶Cd were studied via “unsafe” Coulomb excitation using the AGATA + VAMOS setup at GANIL, France. The measured excitation cross-sections were analyzed with the help of coupled-channel codes GOSIA and FRESCO. The deduced transition probabilities were compared to results of previous “safe” Coulomb-excitation studies and lifetime measurements, demonstrating that nuclear structure information can be reliably obtained from “unsafe” Coulomb-excitation data. Shape coexistence in ¹⁰⁶Cd is discussed in the context of Beyond-Mean-Field calculations. In addition, information on E3 transition strengths to several negative-parity states in ¹⁰⁶Cd is reported for the first time.

The second half of my PhD work is based on a beta-decay study of ¹⁰⁰Zr performed with the GRIFFIN spectrometer at TRIUMF, Canada. The level scheme of ¹⁰⁰Zr has been extended, and branching and mixing ratios were extracted for multiple transitions. Using gamma-gamma angular correlations, several new low-energy excited 0⁺ states were identified, as well as a candidate for the 2⁺ state built on the newly assigned fourth 0⁺ state. The results are discussed in the framework of recent Monte-Carlo Shell-Model calculations, which predict multiple-shape coexistence.