Uncertainly analysis: towards more accurate predictions for the synthesis of superheavy nuclei
Description
The nuclear reaction theories describing the synthesis of superheavy nuclei are not firmly established. Although, the basic qualitative features of fusion-evaporation have reached a consensus, the quantitative predictions of the available models are still unsatisfactory. The production cross-section is the product of the capture cross-section, the formation probability and survival probability. Previous studies have shown that the dominating part of the remaining discrepancies came from our inability to properly constrain the formation probability. The main goal of this thesis is to theoretically constrain this quantity. This is achieved by examining the uncertainties in the capture cross-section and the survival probability using regression analysis. The fission barrier being the most influential factor in survival probability calculations, it is assumed to be the only source of uncertainties. Since the fission barrier is the difference between the ground-state and saddle-point masses, we started investigating the uncertainties in the liquid drop model. Based on this analysis we have refined a method to constrain the shell correction energies. To determine the uncertainties in the fission barriers, a simplified phenomenological macroscopic-microscopic model was used. The uncertainties in the capture step were determined using a model based on a parametrization of the barrier distribution. From the propagation of the uncertainties in the capture cross-section and fission barrier, the constraints on the formation probability were determined. Separately, the effects of inertia on the formation probability were investigated using perturbation theory and a new mechanism reducing fusion hindrance was described as a shift in the initial condition within the Smoluchowski approximation. Additionally, based on this approach, an explanation for the phenomenological energy dependent parametrization of the injection point was found. (author)
Abstract (French)
Les theories de reaction nucleaire decrivant la synthese des noyaux superlourds ne sont pas fermement etablies. Bien qu'un consensus existe sur les caracteristiques qualitatives de la fusion-evaporation, les predictions quantitatives des modeles disponibles sont encore insatisfaisantes. La section efficace de production est le produit de la section efficace de capture, de la probabilite de formation et de la probabilite de survie. Des etudes anterieures ont etabli que la partie dominante des divergences restantes provenait de notre incapacite a contraindre correctement la probabilite de formation. L'objectif principal de cette these est de contraindre theoriquement cette quantite. Celui-ci a ete atteint en examinant les incertitudes associees a la section efficace de capture ainsi qu'a la probabilite de survie par le biais de l'analyse de regression. La barriere de fission etant le facteur le plus influent dans les calculs de probabilite de survie, on supposera qu'elle est la seule source de ses incertitudes. Et puisque la difference entre les masses du fondamental et du point-selle definit la barriere de fission, nous avons commence par etudier les incertitudes d'un modele de type goutte liquide afin d'obtenir les incertitudes sur les masses. Sur la base de cette analyse, nous avons affine une methode permettant de contraindre les energies de correction de couches. Afin de determiner les incertitudes sur les barrieres de fission, un modele microscopique-macroscopique simplifie a ete utilise. Les incertitudes sur la phase de capture ont ete obtenues a l'aide d'un modele base sur une parametrisation de la distribution de barrieres. Les contraintes portant sur la probabilite de formation ont ete ensuite deduites a partir de la propagation des incertitudes sur la section efficace de capture et sur la barriere de fission. Par ailleurs, les effets de l'inertie sur la probabilite de formation ont ete etudies en utilisant la theorie des perturbations et un nouveau mecanisme reduisant l'entrave a la fusion a ete decrit comme un decalage de la condition initiale dans l'approximation de Smoluchowski. Enfin, sur la base de cette approche, une explication de la dependance en energie du point d'injection phenomenologique a ete obtenue
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Additional details
Additional titles
- Original title (English)
- Analyse d'incertitude: Vers des predictions plus precises pour la synthese des noyaux superlourds
Publishing Information
- Imprint Pagination
- 161 p.
- Report number
- FRCEA-TH--14376
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 53111350
- Subject category
- S73: NUCLEAR PHYSICS AND RADIATION PHYSICS;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- COLLISIONS; DATA COVARIANCES; ENERGY DEPENDENCE; FISSION BARRIER; INTEGRAL CROSS SECTIONS; LIQUID DROP MODEL; NUCLEAR REACTIONS; PERTURBATION THEORY; REGRESSION ANALYSIS; SYNTHESIS; TRANSACTINIDE ELEMENTS
- Descriptors DEC
- CROSS SECTIONS; ELEMENTS; ENERGY; MATHEMATICAL MODELS; MATHEMATICS; NUCLEAR MODELS; NUCLEAR POTENTIAL; POTENTIAL ENERGY; POTENTIALS; STATISTICS; TRANSPLUTONIUM ELEMENTS; TRANSURANIUM ELEMENTS
Optional Information
- Notes
- 102 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses