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Study of reaction mechanisms for the synthesis of super-heavy elements

PhD in theoretical nuclear physics

One of the main questions in nuclear physics is why is there a finite number of nuclei? This limited number is related to their stability, as it is well known. Consequently, challenging research programmes are devoted to the study of very exotic nuclei at the limit of stability where new properties may appear. One of these limits is the limit in mass or size.

The so-called super-heavy elements are expected to exist beyond the liquid drop limit of existence defined by a vanishing fission barrier thanks to the shell effects. These nuclei are particularly interesting because they are at the limit between few body and large n-body physics: magic numbers are replaced by a magic zone or island.

Synthesis of these very and super-heavy elements by fusion-evaporation reactions is an experimental challenge due to the extremely low cross-sections. Modelling the complete reaction in order to guide the experiments is also a difficult challenge because models developed for lighter nuclei cannot be simply extrapolated. Fusion reactions are hindered with respect to what is observed with light nuclei because of the very strong Coulomb energy. Consequently, the predictive power of the models is low although the origin of the hindrance phenomenon is qualitatively well understood. But quantitative ambiguities are large enough to observe few orders of magnitude differences in the fusion probabilities calculated by various models. A small change of the cross-section could mean months of experiments.

In such a context, the main purpose of the theoretical researches performed at GANIL on the synthesis of super-heavy elements are aimed to find ways to assess the models in order to improve their predictive power. One way is based on uncertainty analysis that is very new in theoretical nuclear physics. Standardized methods as well as state-of-the-art data analysis methods such as Bayesian analysis are used. Moreover, a special effort will be done on designing specific experiments dedicated to the reaction mechanisms that could help to constrain the so-called fusion hindrance.

This thesis is done in collaboration with laboratories in Japan, China and Poland. Depending on the skill of the student, the thesis will be more oriented towards formal developments in statistical physics or towards the experimental at the new facility Spiral2. Participation to experiments is an option.

Expected skills: English, computer programming


Contact:  David BOILLEY

GANIL, BP 5027, F-14 076 Caen cedex 05


Phone: +33 (0)2 31 45 47 81

Fax: +33 (0)2 31 45 44 21

e-mail : boilley_at_ganil.fr


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