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Electromagnetic decay of the second excited state of C^(12)

Citation

Seeger, Philip A. (1963) Electromagnetic decay of the second excited state of C^(12). Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:04272012-155927120

Abstract

It was desired to determine what fraction of C^(12) nuclei in the second excited state decay electromagnetically to the ground state instead of by alpha emission. The state was formed with the reaction N^(14)(d,α)C^(12)* by bombarding a thin vanadium nitride target on carbon foil with 1.8-MeV deuterons. Recoil C^(12)nuclei were observed in coincidence with the alpha particles from the reaction. The alphas were detected with a surface-barrier counter set at the appropriate unique angle, and the recoiling nuclei at 90° were analyzed in momentum with a magnetic spectrometer, in energy by a surface-barrier counter at the spectrometer focus, and in velocity by the time delay between the alpha and the C^(12) counts. Pulses of 40-nsec width were recorded photographically from a Tektronix type 555 dual-beam oscilloscope, providing a time resolution of 5 nsec, and also allowing pulse height analysis on the fast pulses. Of the C^(12) nuclei formed in the second excited state, 99.9+ per cent decay by alpha emission to Be^8 and are not detected; only those which decay to the C^(12) ground state by gamma or pair emission will be seen. Thus the experiment provides a direct measurement of Г_(rad)/Г. The value of Г_(rad) = (Г_γ + Г_e±) has astrophysical significance determining the rate of C^(12) formation in the He-burning process in red giant stars. Analysis of 170 observed events gives Г_(rad)/Г = (2.8±0.3) x 10^(-4) . Averaged with a value of (3.3 ± 0.9) X 10^(-4) obtained by Alburger, and combined with a value of Г =(8 ± 5) eV, the result is Г_(rad) = (0.0024 ± 0.0015) eV, which is two-and-one-half times the value used in previous 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):
  • Kavanagh, Ralph William
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1963
Record Number:CaltechTHESIS:04272012-155927120
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:04272012-155927120
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6988
Collection:CaltechTHESIS
Deposited By: John Wade
Deposited On:30 Apr 2012 15:12
Last Modified:26 Dec 2012 04:42

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