Tesi etd-09232016-133004 |
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Tipo di tesi
Tesi di laurea magistrale
Autore
GRASSI, ALESSANDRO
URN
etd-09232016-133004
Titolo
Multipotential analysis of the radiative capture alpha + d -> 6Li + gamma
Dipartimento
FISICA
Corso di studi
FISICA
Relatori
relatore Prof.ssa Marcucci, Laura Elisa
Parole chiave
- alpha d potential
- ANC
- Anders
- astrophysical S-factor
- asymptotic normalization coefficient
- BBN
- Big Bang nucleosynthesis
- deuteron
- deutone
- Dubovichenko
- elio
- fattore astrofisico
- Hammache
- helium
- Lithium
- litio
- metodo variazionale
- Mukhamedzhanov
- nuclear reaction
- nucleosintesi primordiale
- Numerov
- potenziale alpha d
- primordial nucleosynthesis
- reazione nucleare
- second Lithium problem
- secondo problema del litio
- tensor term
- Tursunov
- variational method
Data inizio appello
17/10/2016
Consultabilità
Completa
Riassunto
The thesis deals with the study of the radiative capture
α + d → 6Li + γ, (1)
where α and d indicate the 4He nucleus and the deuteron, respectively, while γ indicates the emitted photon. The reaction is important for the theory of Big Bang Nucleoshyntesis (BBN). During BBN, primordial light nuclei were created, principally 2H, 3He, 4He and 7Li. Some minor quantities of other elements, like 6Li, were also formed. In 2006 Asplund et al. analysed the lithium abundances in old halo stars and found the 6Li/ 7Li ratio about 1000 times the BBN prediction. This discrepancy is known as the second Lithium problem. Many experimental and theoretical studies of reaction (1) have been done since then, but the second Lithium problem is still unsolved. In particular, the available experimental data for the astrophysical S-factor are affected by large errors, since the reaction rate drops exponentially at astrophysical energies. Theoretical studies are also difficult because, in principle, one has to solve a six-body problem, for which the available numerical techniques are quite inaccurate. Instead of solving a six-body problem, in this thesis a two-body framework has been chosen, which considers α and d as point-like particles. A crucial ingredient for the calculation is then the α − d interaction. The ultimate goal of this work is to predict the astrophysical S-factor of the reaction using five different potential models, two of which never appeared in the literature. It has also been demonstrated, using these two unpublished potentials, that the D-state component of the 6Li wave function does not contribute significantly to the astrophysical S-factor, while it is very important to choose a potential which reproduces the asymptotic behaviour of the S-state 6Li wave function correctly. Our results nicely reproduce the available experimental data, and the theoretical uncertainties within this two-body framework is of the order of 3%.
α + d → 6Li + γ, (1)
where α and d indicate the 4He nucleus and the deuteron, respectively, while γ indicates the emitted photon. The reaction is important for the theory of Big Bang Nucleoshyntesis (BBN). During BBN, primordial light nuclei were created, principally 2H, 3He, 4He and 7Li. Some minor quantities of other elements, like 6Li, were also formed. In 2006 Asplund et al. analysed the lithium abundances in old halo stars and found the 6Li/ 7Li ratio about 1000 times the BBN prediction. This discrepancy is known as the second Lithium problem. Many experimental and theoretical studies of reaction (1) have been done since then, but the second Lithium problem is still unsolved. In particular, the available experimental data for the astrophysical S-factor are affected by large errors, since the reaction rate drops exponentially at astrophysical energies. Theoretical studies are also difficult because, in principle, one has to solve a six-body problem, for which the available numerical techniques are quite inaccurate. Instead of solving a six-body problem, in this thesis a two-body framework has been chosen, which considers α and d as point-like particles. A crucial ingredient for the calculation is then the α − d interaction. The ultimate goal of this work is to predict the astrophysical S-factor of the reaction using five different potential models, two of which never appeared in the literature. It has also been demonstrated, using these two unpublished potentials, that the D-state component of the 6Li wave function does not contribute significantly to the astrophysical S-factor, while it is very important to choose a potential which reproduces the asymptotic behaviour of the S-state 6Li wave function correctly. Our results nicely reproduce the available experimental data, and the theoretical uncertainties within this two-body framework is of the order of 3%.
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