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An Experimental Investigation of the Parity Purity of the 110-keV Gamma-Decay of ^(19)F


Moline, Robert Alan (1969) An Experimental Investigation of the Parity Purity of the 110-keV Gamma-Decay of ^(19)F. Dissertation (Ph.D.), California Institute of Technology.


If either, or both, of the ground state (Jπ = ½+) and first excited state (110 keV, Jπ = ½- of the 19F nucleus has impure parity, it follows that the de-excitation γ rays would have an angular distribution of the form,

W(θ) = 1 + Pη cos(θ).

In this expression, θ is the angle between the chosen quantization axis and the photon momentum, and P is the polarization of the excited nuclei, with respect to the chosen quantization axis. By assuming the existence of a parity-violating, weak-interaction, nucleon-nucleon force, Maqueda has predicted that the asymmetry parameter, |η| in the above expression, should be 4.3 X 10-4.

The present experiment used the Coulomb excitation of 37.5 MeV 19F projectiles in a gold target to produce 19F*(110 keV) nuclei with a large polarization perpendicular to the scattering plane. After being scattered in the gold foil, the 19F* nuclei recoiled into an iron cylinder. In the geometry used, there was essentially azimuthal symmetry, and therefore no net polarization on any axis perpendicular to the beam direction, until the iron stopper was magnetized. The magnetization produced a net polarization of the 19F* nuclei on a chosen axis perpendicular to the incident beam, by precessing the 19F* nuclei in the hyper fine field in the iron.

From the asymmetry observed in the γ-ray counting rate when the magnetization was reversed, the quantity Pη was determined to be (6.6 ± 5.9) X 10-5.

Since the magnitude (and sign) of P is dependent on the hyperfine magnetic field, investigations were carried out to determine the average hyperfine field of fluorine in iron by using the nuclear reaction 16O(3He,p) 18F* (937 keV).

A p-γ coincidence technique was used, and the average precession angle of the excited nuclei during their mean life of (68 ± 7) ps was observed, when the 18F* recoiled into an iron host lattice. The results indicate an average hyperfine field of (88 ± 19) kG for fluorine in iron, if the g-factor of the 937-keV state is assumed to have the theoretical value 0.61.

There was evidence of serious radiation damage in the iron, produced by the 3He beam and by recoils from the target, during some of the magnetic field measurements. To investigate this effect, a thin iron foil was bombarded with a 100-keV 19F beam. At a radiation dosage of between 2 x 1016 and 7 x 1016 fluorine ions per cm2 the permeability of the iron changed dramatically, in such a way that a several times stronger external field was required to saturate the iron.

If it is assumed that the 110-keV level of 19F has a g-factor of -0.57 and a mean life of 0.88 ns, the most probable value for the net polarization is 0.109 ± 0.023, resulting in an asymmetry coefficient, η, of (6.1 ± 5.6)X 10-4.

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):
  • Barnes, Charles A.
Thesis Committee:
  • Unknown, Unknown
Defense Date:9 September 1968
Funding AgencyGrant Number
Record Number:CaltechTHESIS:03272017-102010777
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10107
Deposited By: Benjamin Perez
Deposited On:27 Mar 2017 20:06
Last Modified:27 Mar 2017 20:06

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