Jensen inequality applied to nuclear fusion probability

Author(s)

Débora Machado Andrade

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2009-09-04

Examining board members

Mahir Saleh Hussein; Luiz Carlos Chamon; Manuel Maximo Bastos Malheiro de Oliveira

• Advisor: Mahir Saleh Hussein

Abstract

We discuss the quantum tunneling problem in physical systems involving many degrees of freedom. We apply the Jensen inequality to the semi-classical analytical probability of fusion between two nuclei, where we considered intrinsic degrees of freedom. We employed different tunneling potential barriers and analytically worked on each of them. We have mathematically proven then the validity of a general inequality which relates the tunneling probability for a sub-system of the many-degrees-of-freedom system when compared to the sub-system alone (with the coupling to the reservoir being averaged). Such inequality is already empirically well-known through numerical calculations for different models, and has a particular relevance in the problem of heavy ion fusion at sub-barrier energies. We have shown that an inequality derived by R. Johnson and C. Goebel, which involves the reflection over a potential barrier and was used to estimate the breakup effect on the elastic scattering of halo nuclei, is but an immediate consequence of the Jensen inequality. A generalization of the ideas contained in the refered work of Johnson and Goebel, which was made possible by using the Jensen inequality, enriches the comprehension towards upper and lower boundaries for tunneling probabilities in systems with many degrees of freedom. (AU)