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Elastic and inelastic electron scattering from magnesium isotopes
Başlık:
Elastic and inelastic electron scattering from magnesium isotopes
Yazar:
Curran, C. S., author.
ISBN:
9780438057852
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (253 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: A. Johnston.
Özet:
Two investigations of the nuclear structure of the magnesium isotopes 24Mg, 25Mg and 26Mg were completed by the author with the assistance of members of the group in running the 120 Mev electron linear accelerator, and accumulating the data. The first experiment was designed to obtain information on the ground state nuclear charge distributions of the three magnesium isotopes available as 50mgcm-2 metal foils of better than 99% isotopic purity. The experimental technique took advantage of the careful measurements of Bentz et al. (1) of the 12C elastic electron scattering which provided a reference cross-section. The elastic electron scattering cross-sections for the magnesium targets were therefore measured relative to that of a 12C target machined from reactor graphite. Data was collected for each target at thirteen momentum transfers, in the range 0.20 to 1.15 fm-1. Reduction of the raw data, fitting of the elastic scattering line shapes and extraction of cross-section ratios was performed by the author using computer programs developed by him. The two parameter Fermi function described by Elton (2) and characterized by the half density radius, c, and skin thickness, t, was selected to describe the ground state charge distribution of the magnesium isotopes. Best fit values for c and t were obtained using Powell's minimization routine (3) to match the experimental cross-section ratios to calculated ratios. All the theoretical cross-section ratios were calculated using the elastic electron scattering phase shift code of Rawitscher and Fischer (4). The results of the present analysis are compared to the previous electron scattering results of Helm (5) on natural magnesium, and more recent work on 24Mg and 26Mg due to Khvatsunov et al. (6), and on 24Mg due to Li et al. (7). In previous publications such as those of Litherland et al. (8) and Bishop (9), the Nilsson model has been applied to magnesium isotopes with some success, particularly in the case of 25Mg. The author has calculated ground state wavefunctions for 24Mg, 25Mg and 26Mg using computer programs provided by Dr. T, E. Drake. An axially symmetric Hamiltonian of the Nilsson type was used, the wavefunctions being expanded as linear combinations of harmonic oscillator wavefunctions up to 7hw in energy. Good agreement with the elastic scattering results can be obtained. During this elastic scattering work, inelastic peaks were observed at 1.37 Mev for 24Mg, and also at 0.98 and 1.61 Mev for 25Mg. These 1.37 and 1.61 Mev levels are assumed in the Nilsson model to be members of the respective ground state rotation bands. Form factors for these levels can be obtained from the same wavefunctions used to calculate the elastic electron scattering. Since exhaustive measurements on the 1.37 Mev 24Mg level had been made in the Laboratory meanwhile by A. Johnston (10), it was decided to carry out a second experiment chiefly to obtain form factors for the 1.61 Mev level of 25Mg and the corresponding 1.81 Mev level of 26Mg. The following levels were identified in the inelastic spectra of this second experiment. Spins and parities for the 25Mg levels are taken from Sharpey- Schafer et al. (11). Experimental form factors for these levels were obtained using an inelastic spectrum fitting code developed by the author. Efforts were made to estimate the transverse components in these form factors with longitudinal to transverse separations at 0.70, 0.80 and 1.00 fm-1 using data collected at 120° and 151.7°. All the observed levels were predominantly longitudinal. A copy of the inelastic electron scattering phase shift code of Tuan et al. (12) modified to run on the PDP 10 computer at the Laboratory by S. W. Brain, was used by the author to fit the 1.61 Mev level of 25Mg and the 1.81 Mev level of 26Mg. The best fit transition charge densities so obtained may be used to calculate a form factor in first Born approximation, and in turn this form factor may be compared with Nilsson model predictions. Values for the ground state quadrupole moments of the magnesium isotopes may be deduced in this way, and compared to the previous inelastic electron scattering results of Khvatsunov et al. (6), and the atomic beam measurement on 25Mg by Lurio (13). The author has also been involved in the design and partial construction of a new overlap detection system which will eventually replace the existing detector ladder, and enhance the data collection rate of the Laboratory electron scattering facility. A brief description of the new system is given, together with some preliminary data on its performance.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684644.1) | 684644-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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