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Monochromator studies of nuclear resonance fluorescence in carbon, silicon, and magnesium

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Title: Monochromator studies of nuclear resonance fluorescence in carbon, silicon, and magnesium
Author(s): Kuehne, Herbert Wayne
Doctoral Committee Chair(s): Axel, P.
Department / Program: Physics
Discipline: Physics
Degree: Ph.D.
Genre: Dissertation
Subject(s): monochromator nuclear resonance fluorescence carbon silicon magnesium Bremsstrahlung monochromator
Abstract: This thesis describes the first experimental studies of isolated energy levels with the aid of the University of Illinois bremsstrahlung monochromator. The studies had as objectives both the development of techniques needed to make the monochromator a better tool for studying nuclear levels and the investigation of the properties of selected levels. There are three aspects of the monochromator performance which were improved or studied during the course of the experiment. The first consisted of the design of a very fast transistorized scaler to count random electron pulses coming at an average rate of about one per microsecond. The circuit which was developed . scaled reliably to frequencies above 35 Mc/sec. The second monochromator improvement involved the energy stability and energy calibration. A precise power regulator was designed and installed to maintain a constant electron beam energy to O. 1 % or better. The energy calibration used the 15.11 MeV resonance in C12 as a standard. The energies of the other resonances were determined to approximately 0.25% relative to the carbon standard. The third facet of the monochromator performance which was especially important was the energy resolution. Since the resolution enters, essentially linearly,. in extracting level parameters from the observed scattering, it was necessary to know the resolution fairly accurately for each of the resonances studied. Although the resolution of the monochromator is still not understood fully, it is known well enough to obtain better values for level parameters than were obtainable with other techniques. The experimental results related to nuclear structure consisted of information about six different energy levels. The energies of five of these levels were determined precisely as 15.11 MeV in C 12 (standard). 11. 40±0. 02 MeV in Si 28 • 12. 31±0. 03 MeV in Si28, 10. 64±0. 02 MeV in Mg24, and 9. 90±0. 025 MeV in Mg24. The sixth level was found incidentally while studying the 9.90 MeV resonance. Its energy has been estimated . . 26 as 10. 05±0. 05 MeV. The resonance is assumed to be due to Mg The level parameters for all resonances excepttlie 12.·31 MeV resonance were measurements . of the, absolute scattering . and;the self abs'Orption .. Fairly complete descriptions wer~ obtained for the 15.11 MeV, 11.40 MeV,. and 10.64 Me V resonances. These resonances are known from other experimental work to be Ml transitions. The dat,a of the present experiment determined for the 15.11 MeV resonance, +0.25 +0 +4 I = 1. 79--':'0,~.23 MeVmb, r;:/r = 1. 0 -0.18' and 4= 36 -6 eV; for the 11. 40 MeVresonance, , . +0.42 . +0 +6 I = 2.01_0• 28 MeVmb, r;:/r = 1. 0 -0.19' and ~ = 23 -3 eV; and for the 10.64 MeV res on- +0.35 .'. ""/r' +0.2 T'1 +6 V ance, I = 1. 53 -0.26 MeVmb, .1.0 = 0.8 -0.12' and .l.o = 19 -6 e. The multipolarities of the 9.90 MeV and 10.05 MeV transitions .are not definitely established; however, they have also been assumed to be Ml transitions. The parameters of the weak 9. 90 MeV +0.16 +0.33 resonance are I = O. 52_ 0 . 16 MeVmb, I;/r=o.67_0. 33 , and 3.2 eV<r,<15 eV. The 10.05 MeV resonance appeared very weak; thus,. onlyacrude estiniateof its integrated. scattering c'ross ;sectiqn was obtained. Assuining that. theresonance is due to, Mg2~ I~O. 5 MeVmb. Although no absorption measurements were made for the 12.31 MeV resonance, the integrated cross section was estimated from resonant energy data to be I = 0.28 +0.1 Me Vm b. -0.1 The experiment did not clearly distinguish between elastic and inelastic scattering; however, the data for the 15.11 MeV and 11.40 MeV resonances indicate little or no inelastic scattering. The 10.64 MeV and 9.90 MeV data can be interpreted asjndicating level widths to the first excited state which are respectively about 10% and 37% of the ground state widths.
Issue Date: 1964
Genre: Dissertation / Thesis
Type: Text
Language: English
Rights Information: 1964 Herbert Wayne Kuehne
Date Available in IDEALS: 2011-05-18
Identifier in Online Catalog: 6152316

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