In classical novae, the endpoint of nucleosynthesis occurs near A ~ 40. Currently,
observations of classical novae predict an order of magnitude enhancement of endpoint
elements, such as Ar, K, and Ca, relative to solar abundances; however, simulations
predict abundances closer to that of solar abundances.
A sensitivity study examining the effect of reaction rates on the abundances of these
elements has shown that the reaction 38-K(p,g)39-Ca can change the abundances of endpoint
nuclides by an order of magnitude or more. In temperatures characteristic of
this environment, this reaction rate is dominated by l =0 resonance reactions within
the Gamow window. These correspond to states in 39-Ca with spin-parity of 5/2+ and 7/2+ between Ex = 6.0−6.5 MeV . While a direct measurement was carried out for these states, more precise values for the excitation energies were recommended.
In this work high resolution spectroscopic studies of 39-Ca were carried out to provide
more information on the various resonances that lie in the Gamow window, and
illuminate additional undiscovered states. The first study was conducted at the Maier-
Leibnitz-Laboratory (MLL), employing the 40-Ca(d,t)39-Ca reaction, and the follow up
study was conducted at the Triangle Universities Nuclear Laboratory (TUNL) using the
39-K(3-He,t)39-Ca reaction. The method and apparatus are discussed in this work. Energy
levels in 39-Ca with 10 keV uncertainties had uncertainties reduced to 3-4 keV. In addition,
several new states were found in 39-Ca from the TUNL experiment. Finally, there
is an ~ 10 keV systematic difference between previously evaluated states and the states
measured in this work - a factor that affects the direct measurement carried out previously.
This factor in combination with the results of this work show that the reaction
rate of this may be higher than previously thought, and have a higher impact on the
final abundances of elements synthesized in classical novae. / Thesis / Doctor of Science (PhD) / The goal of this work is to investigate processes that create the chemical elements of the
universe. This occurs through nuclear reactions of elements produced after Big Bang nucleosynthesis.
These nuclear reactions are only possible in the hot, dense environments
found in stars and explosive stellar events. One such stellar event is the classical nova,
which can produce elements as heavy as Calcium. Although a multitude of nuclear reactions
occur during a classical nova, only a handful have a large effect on the abundance
of elements produced. This work studies the properties of a specific nuclear reaction
that can strongly affect the abundances of elements synthesized in classical novae.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26019 |
| Date | January 2020 |
| Creators | Liang, Johnson |
| Contributors | Chen, Alan, Physics and Astronomy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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