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Total Yield Measurements for the ²⁴Mg(α,γ)²⁸Si and ²⁷Al(ρ,γ)²⁸Si Reactions


Lyons, Peter Bruce (1969) Total Yield Measurements for the ²⁴Mg(α,γ)²⁸Si and ²⁷Al(ρ,γ)²⁸Si Reactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7ESS-6977.


The 27 Al (ρ,γ)28Si and 24Mg(α,γ)28 Si reactions have been investigated to provide the data needed for calculation of the 28Si photodisintegration rate in astrophysical situations, particularly in the silicon-burning stage of stellar nucleosynthesis. A large solid angle NaI gamma ray spectrometer was employed which provided high detection efficiencies. The 27Al(ρ,γ)28Si reaction was investigated over the proton energy range O.3 – 2.6 MeV; total gamma ray strengths were determined for 85 resonances. From 1.4 – 2.6 MeV, the gamma ray yield curve was measured and an upper limit for the nonresonant cross section was determined. Where possible, total resonance widths were deduced from the data. The gamma-ray detection efficiencies and target purity were investigated experimentally. Comparison was made with resonance strengths, measured by other methods, in the reactions 30Si(ρ,γ) 31P and 26Mg(ρ,γ)27Al. The reaction 24Mg(α,γ)28Si was investigated for alpha particle energies up to 2.8 MeV; total gamma ray strengths were determined for 16 resonances, including a previously unreported resonance at 1.358 ± O.007 MeV. Stellar interaction and photodisintegration rates were calculated from the measured resonance strengths, and semi-empirical fits to these rates were determined for use in astrophysical calculations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Fowler, William A. (advisor)
  • Barnes, Charles A. (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:7 May 1969
Funding AgencyGrant Number
National Phi Kappa Phi FoundationUNSPECIFIED
U.S. Office of Naval ResearchNonr-220(47)
Record Number:CaltechTHESIS:06252018-100112879
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11091
Deposited On:25 Jun 2018 21:23
Last Modified:21 Dec 2019 03:54

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