Development of a Monte Carlo code for the data analysis of the ~(18)F(p,α)~(15)O reaction at astrophysical energies

摘要

Novae are astrophysical events (violent explosion) occurring in close binary systems consisting of a white dwarf and a main-sequence star or a star in a more advanced stage of evolution. They are called :narrow systems"because the two components interact with each other: there is a process of mass exchange with resulting in the transfer of matter from the companion star to the white dwarf, leading to the formation of this last of the so-called accretion disk, rich mainly of hydrogen. Over time, more and more material accumulates until the pressure and the temperature reached are sufficient to trigger nuclear fusion reactions, rapidly converting a large part of the hydrogen into heavier elements. The products of "hot hydrogen burning"are then placed in the interstellar medium as a result of violent explosions. Studies on the element abundances observed in these events can provide important information about the stages of evolution stellar. During the outbursts of novae some radioactive isotopes are synthesized: in particular, the decay of short-lived nuclei such as ~(13)N and ~(18)F with subsequent emission of gamma radiation energy below 511 keV. The gamma rays from products electronpositron annihilation of positrons emitted in the decay of ~(18)F are the most abundant and the first observable as soon as the atmosphere of the nova starts to become transparent to gamma radiation. Hence the importance of the study of nuclear reactions that lead both to the formation and to the destruction of ~(18)F. Among these, the ~(18)F(p,α)~(15)O reaction is one of the main channels of destruction. This reaction was then studied at energies of astrophysical interest. The experiment done at Riken, Japan, has as its objective the study of the ~(18)F(p,α)~(15)O reaction , using a beam of ~(18)F produced at CRIB, to derive important information about the phenomenon of novae. In tis paper we present the experimental technique and the Monte Carlo code developed to be used in the data analysis process.