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Excitation Energies and Decay Properties of T= J/2 States in 170, 17F and 21Na


McDonald, Arthur Bruce (1970) Excitation Energies and Decay Properties of T= J/2 States in 170, 17F and 21Na. Dissertation (Ph.D.), California Institute of Technology.


The two lowest T = 3/2 levels in 21Na have been studied in the 19F(3He, n), 20Ne (p,p) and 20Ne (p,p’) reactions, and their excitation energies, spins, parities and widths have been determined. In a separate investigation, branching ratios were measured for the isospin-nonconserving particle decays of the lowest T = 3/2 levels in 17O and 17F to the ground state and first two excited states of 16O, by studying the 15N(3He,n) 17F*(p) 16O and 18O(3He, α)17O*(n) 16O reactions.

The 19F(3He,n) 21Na reaction was studied at incident energies between 4.2 and 5.9 MeV using a pulsed-beam neutron-time-of-flight spectrometer. Two T = 3/2 levels were identified at excitation energies of 8.99 ± 0.05 MeV (J > ½) and 9.22 ± 0.015 MeV (J π = ½+, Γ ˂ 40 keV). The spins and parities were determined by a comparison of the measured angular distributions with the results of DWBA calculations.

These two levels were also obsesrved as isospin-forbidden resonances in the 20Ne(p,p) and 20Ne(p,p’) reactions. Excitation energies were measured and spins, parities, and widths were determined from a single level dispersion theory analysis. The following results were obtained:

Ex = 8.973 ± 0.007 MeV, J π = 5/2 + or 3/2+, Γ ≤ 1.2 keV,
Γpo = 0.1 ± 0.05 keV; Ex = 9.217 ± 0.007 MeV, Jπ = ½ +,
Γ = 2.3 ± 0.5 keV, Γpo = 1.1 ± 0.3 keV.

Isospin assignments were made on the basis of excitation energies, spins, parities, and widths.

Branching ratios for the isospin-nonconserving proton decays of the 11.20 MeV, T = 3/2 level in 17F were measured by the 15N(3He,n) 17 F*(p) 16O reaction to be 0.088 ± 0.016 to the ground state of 16O and 0.22 ± 0.04 to the unresolved 6.05 and 6.13 MeV levels of 16O. Branching ratios for the neutron decays of the analogous T = 3/2 level, at 11.08 MeV in 17O, were measured by the 16O(3He, α)17O*(n)16O reaction to be 0.91 ± 0.15 to the ground state of 16O and 0.05 ± 0.02 to the unresolved 6.05 and 6.13 MeV states. By comparing the ratios of reduced widths for the mirror decays, the form of the isospin impurity in the T = 3/2 levels is shown to depend on Tz.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Awards:The Nobel Prize in Physics, 2015. Caltech Distinguished Alumni Award, 2018
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Barnes, Charles A.
Thesis Committee:
  • Unknown, Unknown
Defense Date:14 July 1969
Funding AgencyGrant Number
National Research Council of CanadaUNSPECIFIED
Record Number:CaltechTHESIS:08112015-113730783
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9095
Deposited By: Leslie Granillo
Deposited On:13 Aug 2015 22:25
Last Modified:05 Mar 2018 21:33

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