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The ³H(α,γ)⁷Li reactions at low energies


Brune, Carl Richard (1994) The ³H(α,γ)⁷Li reactions at low energies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RWJ4-CP08.


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
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Kavanagh, Ralph William
Thesis Committee:
  • Unknown, Unknown
Defense Date:17 May 1994
Funding AgencyGrant Number
National Science FoundationPHY88-17297
National Science FoundationPHY91-15574
Record Number:CaltechTHESIS:11082010-092253508
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6174
Deposited By: Benjamin Perez
Deposited On:08 Nov 2010 18:14
Last Modified:21 Dec 2019 01:26

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