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|Title:||Velocity Dependence of Transient Hyperfine Fields Following Coulomb Excitation|
|Authors:||Gibb, William Merson Allan|
|Abstract:||<p>This thesis studies the velocity dependence of the transient magnetic field that is experienced by ions while slowing down in polarized ferromagnetic materials. Thick targets of Fe₈₀Rh₂₀, Fe₇₀Pd₃₀, and Fe₈₅Pt₁₅ alloys were bombarded by 5 to 10 Mev alpha particle, 35 Mev ¹⁶O, and 20 Mev ¹²C beams from the McMaster Tandem van de Graaff accelerator. The precession angles of Coulomb-excited rhodium, palladium and platinum nuclei that recoil and stop in the ferromagnetic target were measured using the technique of perturbed angular distributions following Coulomb excitation. The singles mode, in which gamma ray events are accepted irrespective of projectile scattering angle, was employed. A detailed theoretical analysis was developed to indicate how the double average over projectile scattering angle and energy required in a thick target singles experiment would modify the observed rotation angle. Calculations were carried out using the Coulomb excitation theory of Alder et al and the transient field theory of Lindhard and Winther. The doubly-averaged transient field contribution to the rotation angle was found, in general, to be somewhat smaller than the transient field contribution before averaging, but the difference was not large for the cases of interest.</p> <p>The data analysis permitted the separation of transient and average static rotations. The transient rotation as a function of initial recoil velocity was shown to be adequately described within experimental error by the Lindhard and Winther theory in both low and high velocity regimes. The average static field was seen to vary with the choice of projectile, but was not noticeably affected by changing the target coolant from water to liquid nitrogen.</p> <p>Indirect feeding of a nuclear state, by Coulomb excitation of a higher-energy state and subsequent decay to the state of interest, was found to modify the observed precession angle of the state. The theory of this effect was developed for both singles and backscatter coincidence experiments; indirect feeding corrections were applied to the 295 kev state in ¹⁰³Rh and the 211 kev state in ¹⁹⁵Pt. The g-factor of the 211 kev state in ¹⁹⁵Pt was measured to be .164(66).</p> <p>The g factors of the first 2+ states in ¹⁰⁴Pd, ¹⁰⁸Pd, and ¹¹⁰Pd were measured from the average of 6, 7 and 8 Mev alpha particle bombardments of a Fe₇₀Pd₃₀ target. The analysis assumed that (1) the transient field rotation was negligible at these bombarding energies and (2) the 9 factors of the 2+ states were not very different from the g factor of the first 2+ state in 106pd, which had been measured using a radioactive source. The results were (¹⁰⁴Pd)g₂₊ = .479(91), (¹⁰⁸Pd)g₂₊ = .396(46), (¹¹⁰Pd)g₂₊ = .389(36).</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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