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Excitation Energies and Decay Properties of T= 3/2 States in ¹⁷O, ¹⁷F and ²¹Na


McDonald, Arthur Bruce (1970) Excitation Energies and Decay Properties of T= 3/2 States in ¹⁷O, ¹⁷F and ²¹Na. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/P0TR-DH36.


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.
Group:Nobel Prize, Caltech Distinguished Alumni Award
Thesis Committee:
  • Unknown, Unknown
Defense Date:14 July 1969
Additional Information:The Nobel Prize in Physics 2015 was awarded jointly to Takaaki Kajita and Arthur B. McDonald "for the discovery of neutrino oscillations, which shows that neutrinos have mass."
Funding AgencyGrant Number
National Research Council of CanadaUNSPECIFIED
Record Number:CaltechTHESIS:08112015-113730783
Persistent URL:
Related URLs:
URLURL TypeDescription Prize announcement (Physics, 2015)
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9095
Deposited On:13 Aug 2015 22:25
Last Modified:16 May 2024 23:56

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