INVESTIGATIONS IN RADIATIVE CAPTURE REACTIONS

Abstract

Di erent nucleosynthesis processes (e.g., pp-chains, CNO cycles, s-,p-,r - processes) were hypothesized in stellar plasma under di erent physical conditions, leading to the creation of the elements found in today's universe. A majority of these nuclei heavier than iron in the region far away from the stability valley, are produced by the rapid neutron capture or r-process. Although it is understood that r-process happens in explosive conditions of pressure and temperature like neutron star mergers and core collapse supernovae, the speci c astrophysical sites are not clear fully. In this context, the role of low and medium mass exotic nuclei especially their radiative capture, can also become important. This thesis is focused mainly on the application of Coulomb breakup as an indirect method to calculate radiative capture reactions of low neutron rich nuclei away from the line of stability. Chapter 1 provides an introduction to the subject and o ers a short review of the current experimental scenario around the globe. Chapter 2 includes a brief discussion of some of the existing theories used to describe breakup reactions. Chapter 3 comprises of the breakup of the halo nucleus 11Be on a heavy target ( 208Pb). Here we use the antisymmetrized molecular dynamics (AMD) and the phenomenological Woods-Saxon (WS) potential to deduce the n􀀀10Be relative motion wave function, which is further used to calculate the static properties (like charge and matter radii) as well as a host of reaction observables in the breakup of 11Be. Finally, the 10Be(n;)11Be reaction rates and its implications are discussed. In Chapter 4, we calculate the 18C(n; )19C radiative capture cross section and the associated reaction rate per mole as a function of temperature, by studying the Coulomb dissociation of 19C on 208Pb at 67 MeV/u. Eventually, we compare it with the competing 18C( ; n)21O reaction extracted from the Hauser-Feshbach estimates. Chapter 5 presents the results for the 19N(n; )20N radiative capture reaction using Coulomb breakup of 20N on 208Pb at a beam energy of 256 MeV/u. We also try to nd the contribution to the reaction rate from the excited states as well as the ground state and the temperature range of their contribution. We conclude in Chapter 6 with a vision for the future. In the appendix, we present some additional mathematical details about the formalism.