LITHIUM-8 Burning and Primordial Nucleosynthesis

Details LITHIUM-8 Burning and Primordial Nucleosynthesis LITHIUM-8 Burning and Primordial Nucleosynthesis

Jan 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........76m&link_type=abstract

Thesis (PH.D.)--DREXEL UNIVERSITY, 1992.Source: Dissertation Abstracts International, Volume: 53-05, Section: B, page: 2372.

Astronomy and Astrophysics

Astrophysics

Nucleosynthesis, Big Bang, Lithium-8 Burning

Scientific paper

A QCD phase transition in the early universe may have led to inhomogeneities in the density of baryons. The nucleosynthetic yield from an inhomogeneous big bang might be fundamentally different from that expected within the framework of a standard (homogeneous) big bang; in particular, nuclei more massive than ^7Li could be produced via the ^8Li( alpha,p)11B reaction. Observations of primordial A > 7 nucleosynthesis could therefore provide a clear signature of inhomogeneity. However, the rate of ^8 Li(alpha,n)^ {11}B--a reaction which direct the flow of nucleosynthesis toward heavy elements--is unknown at astrophysical temperatures and hence predictions of nucleosynthesis beyond ^7Li are suspect. In addition, the competing reactions, such as (n,gamma ) and (p,n), have not been studied experimentally at the energies of interest. Direct measurements of these reactions are desirable, but are not currently possible because the short half-life of ^8Li (T_{1/2} = 840.3 ms) requires the development of a low energy ^8Li beam. This thesis pursues indirect measurements and theoretical calculations to help determine the rates for the ^8Li(alpha,n) 11B and ^8Li(n, gamma)^9Li reactions. Astrophysically-interesting states in 12B were studied using the high resolution QDDD spectrometer. Excitation energies, total widths and spins were measured using the ^9 Be(alpha,p)^ {12}B and 11 B(d,p)12B reactions at Ealpha = 35 and 40 MeV, and E_{rm d} = 26 MeV, respectively, using self-supporting ^9Be and ^{11 }B targets. The excitation energies have been determined to within +/-5 keV for most of the states of interest in ^{12 }B. The total widths for these states were extracted, and tentative spin-parity assignments were obtained from DWBA analyses. The ^9Be( alpha,p)12B*(n) 11B*(gamma )11B coincidence reaction was used to measure the decay neutron and neutron -delayed gamma rays, using a 29-MeV DC alpha beam. The relative neutron partial widths for the aforementioned states were obtained. The resonant rate from all the resonant states at astrophysical energies has been obtained experimentally, for the ^8 Li(alpha,n)^ {11}B reaction. Shell model calculations, using both p-shell and spd-shell interactions, were used to predict the spectroscopic properties for the low-lying states in ^9 Li. From this information, we obtained new estimates for the rate of the presumed important leakage reaction, ^8Li(n,gamma) ^9Li. We discussed the astrophysical implications of these new rates for the ^8 Li(n,gamma)^9 Li and ^8Li(alpha ,n)11B reactions.

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