Brune, Carl Richard (1994) The ³H(α,γ)⁷Li reactions at low energies. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:11082010-092253508
The absolute cross section of the ³H(α,γ)⁷Li reaction has been measured for 50 ≤ E_(c.m.) ≤ 1200 keV. Specially prepared Ti-³H targets were bombarded with an α⁺ beam, and γ rays were detected using an 85% high-purity germanium detector. Total S-factors and the branching ratios for radiative capture to the two final bound states are reported for the entire energy range. Angular distributions of the capture γ rays were measured for nine energies in the range 115 ≤ E_(c.m.) ≤ 1200 keV. Legendre coefficients extracted from fits to the angular distributions are also reported. The preparation and characterization of the radioactive Ti-³H targets are discussed. This experiment is motivated by models of big-bang nucleosynthesis, which require the ³H(α,γ)⁷Li reaction rate for computing the primordial ⁷Li abundance. Our results have considerably smaller uncertainties and reach lower energies than previous experiments. For E ≤ 150 keV, we find the S-factor to be considerably smaller than indicated by previous experiments. The measured branching ratio is found to be approximately energy independent, with a value of 0.45. The energy dependence of the measured S-factors is in agreement with existing theoretical calculations. The new results are used to calculate the thermonuclear reaction rate for temperatures below 10 GK.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||physics, big bang nucleosynthesis, lithium-7, radiative capture, tritium|
|Degree Grantor:||California Institute of Technology|
|Division:||Physics, Mathematics and Astronomy|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||17 May 1994|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||08 Nov 2010 18:14|
|Last Modified:||26 Dec 2012 04:32|
- Final Version
See Usage Policy.
Repository Staff Only: item control page