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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Single particle structure of high spin states in promethium-144 and promethium-145

Unknown Date (has links)
The level structures of $\sbsp{61}{144}$Pm$\sb{83}$ and $\sbsp{61}{145}$Pm$\sb{84}$ were investigated using heavy-ion reactions and the techniques of $\gamma$-ray and electron spectroscopy as well as transfer reactions. Decay schemes were constructed from prompt $\gamma$-$\gamma$-coincidence, delayed $\gamma$-$\gamma$-coincidence, excitation function, angular distribution and conversion electron measurements of the $\sp{19}$F + $\sp{130}$Te fusion-evaporation reaction at beam energies between 70 and 85 MeV. / A total of 53 new transitions and 31 new levels were placed in $\sp{144}$Pm. The level scheme extends to spin $J=20\hbar$ and an excitation energy of 5.8 MeV. Transitions feeding the 841 keV ($J\sp\pi=9\sp+$) isomeric state were observed for the first time. The reduced $B(E3)$ transition strength for the 669 keV ($9\sp+\to 6\sp-$) transition deexciting this state was determined to be 3.2(7) Weisskopf units, supporting the interpretation of the 9$\sp+$ level as a ($\pi 1h\sb{11/2}\otimes\nu 2f\sb{7/2}$) non-collective state. / Nineteen new levels connected by 32 new transitions extended the decay scheme of $\sp{145}$Pm up to a tentative spin of (${33\over 2})\hbar$ and an excitation energy of 4.7 MeV. The ${11\over 2}\sp-$ isomeric state at 795 keV was identified as a single $h\sb{11/2}$ proton state in the $\sp{144}$Nd($\sp7$Li,$\sp6$He) stripping reaction at a beam energy of 34 MeV. A measurement of the $B(E3)$ reduced transition strength (7.8(18) Weisskopf units) of the 795 keV (${11\over 2}\sp-\to{5\over 2}\sbsp{\rm g.s.}{+}$) transition deexciting this state supports this interpretation. A weak coupling model can explain the structure of the deduced decay scheme up to an excitation energy of 2.5 MeV. / The spectroscopy of $\sp{144}$Pm and $\sp{145}$Pm is discussed in terms of couplings of single-particle states to a $\sp{146}$Gd core using empirical shell-model calculations. Good agreement with the experimental results is obtained. / Source: Dissertation Abstracts International, Volume: 53-10, Section: B, page: 5262. / Major Professor: Paul D. Cottle. / Thesis (Ph.D.)--The Florida State University, 1992.
12

INVESTIGATION OF HIGH-LYING STATES IN CARBON-14 AND NITROGEN-14 USING MULTI-NUCLEON TRANSFER REACTIONS

Unknown Date (has links)
States in ('14)C and ('14)N have been populated using the lithium induced reactions: ('10)B(('6)Li,d)('14)N, ('11)B(('6)Li,t)('14)N, ('11)B(('6)Li,('3)He)('14)C, ('11)B(('7)Li,(alpha))('14)C, ('12)C(('6)Li,(alpha))('14)N, ('13)C(('7)Li,('6)He)('14)N, and ('13)C(('7)Li,('6)Li)('14)C at bombarding energies between 20 and 34 MeV. States in the residual nuclei were populated selectively in these reactions, as a result of both the states' configurations and their spins. Experimental angular distributions for the ('11)B(('7)Li,(alpha))('14)C, ('11)B(('6)Li,('3)He)('14)C, and ('11)B(('6)Li,t)('14)N reactions were taken at ('7)Li and ('6)Li bombarding energies of 34 MeV. / Comparison of the results for the one, two, three, and four particle transfer reactions to excited states in ('14)N performed here allowed structure information to be obtained for levels in ('14)N. Similarly, the one and three particle transfer reactions to states in ('14)C were compared with states populated by two nucleon transfer. When these results were compared with medium energy inelastic scattering data, these reactions were shown to provide complementary information on high-lying states in the A = 14 mass region. / The usefulness of a DWBA description of the multi-nucleon transfer process was demonstrated through the ability of DWBA to fit the angular distributions and provide information on the parities and spins of the final states. Some limits on the spins of the final states could also be deduced from compound nucleus calculations and their comparisons with the experimental cross sections. / Experimental criteria were developed based on the population of states by the ('11)B(('6)Li,('3)He)('14)C and ('11)B(('6)Li,t)('14)N reactions to known analog states in order to assign high-lying isobaric analog (T = 1) states in ('14)N and ('14)C. The criteria were: the comparisons of differential cross sections, angular distributions, analog energies, and population by other reactions. From these criteria, T = 1 states in ('14)N were identified to 18 MeV excitation. / Source: Dissertation Abstracts International, Volume: 45-01, Section: B, page: 0241. / Thesis (Ph.D.)--The Florida State University, 1984.
13

A STUDY OF THE INELASTIC SCATTERING AND EXCITATION OF LITHIUM-6

Unknown Date (has links)
The results of two studies of the elastic and inelastic scattering of ('6)Li are reported. The analysis of the data in both studies was designed to determine if a moderately parameter-free description of ('6)Li scattering on several targets was possible. The philosophy here was to derive the real nucleus-nucleus interaction potential starting from a microscopic nucleon-nucleon interaction and summing over the contributions from both target and projectile nucleons. A Woods-Saxon imaginary potential was used for the absorptive part of the interaction potential. The inelastic transition strengths were obtained from electron scattering rather than treating them as free parameters. It was found that for the present inelastic ('6)Li scattering, the nuclear and Coulomb transition strengths are equal and are consistent with electron scattering. / In the first study, elastic and inelastic scattering data extending to (theta)(,c.m.)(DBLTURN)175(DEGREES) are reported for ('6)Li + ('28)Si at 27 and 34 MeV. Optical model analyses of the elastic data were made using a variety of real potential forms. The large-angle data cannot be fitted with a Woods-Saxon real potential, but are well described by Woods-Saxon squared, double-folded or Fourier-Bessel potentials. The real potential is the same at both energies, but the imaginary potential is weaker at 27 MeV. The inelastic data were analyzed using the DWBA and coupled-channels techniques with folded real form factors and deformed Woods-Saxon imaginary potentials. The deformation lengths were taken from electron scattering. The 2('+) state was fitted well at both energies with the DWBA, while the prediction decreased too rapidly at large angles for the 4('+) state. The large-angle 4('+) data were better described when two-step excitations were included in the coupled-channels calculations. The forward-angle 2('+) data are sensitive to the interference between Coulomb and nuclear scattering and show that the nuclear and Coulomb deformation parameter (beta)(,2) are equal for this transition. / In the second study, differential cross sections for elastic and inelastic ('6)Li scattering from ('12)C at 24 and 30 MeV, and from ('16)O at 25.7 MeV were measured out to (theta)(,c.m.)(DBLTURN)170(DEGREES). Also by scattering ('12)C and ('16)O from ('6)Li, the inelastic cross sections for the excitation of the 3('+)(2.18 MeV) and the 2('+)(4.31 MeV) states of ('6)Li and an estimate of the continuum inelastic cross sections of ('6)Li were measured. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI / Source: Dissertation Abstracts International, Volume: 45-03, Section: B, page: 0913. / Thesis (Ph.D.)--The Florida State University, 1984.
14

An optically pumped polarized lithium ion source and an investigation of carbon-12 (polarized lithium-6, alpha particle) nitrogen-14

Unknown Date (has links)
A source of vector and tensor polarized $\sp{6,7}$Li ions has been constructed and tested. The ion source uses laser optical pumping of an atomic beam of lithium, followed by adiabatic radiofrequency transitions, selectively populating a single magnetic substate of the neutral atom. The atomic beam is formed by vaporizing lithium metal in an oven and extracting the beam through a heated nozzle/collimator assembly. The atomic beam is irradiated transversely in a weak holding magnetic field by electro-optically modulated, circularly polarized light of wavelength 670.8 nm, obtained from a ring dye laser pumped by an Ar$\sp+$ laser. Optical pumping produces a nearly pure $m\sb{F}$ = F population distribution. Adiabatic rf transitions can then be used to transfer the population to any of the other desired magnetic substates. The polarized atomic beam is ionized positively on an electrically heated tungsten strip and charge exchanged to Li$\sp-$ in a cesium vapor. A Wien filter is used to produce the desired spin axis orientation, and then the beam is injected into a tandem Van de Graaff-superconducting linac for acceleration up to 9 MeV/nucleon. A helium gas polarimeter has been calibrated for use in rapid on-line monitoring of the polarization on target. / Cross section angular distributions and a complete set of analyzing powers $T\sb{kq}(\theta$) for the $\sp{12}$C($\sp6\vec{\rm Li}$, $\alpha$)$\sp{14}$N reaction have been measured at 33 MeV. Full finite range DWBA calculations have been performed to analyze the data for states up to $E\sb{x}$ = 9.70 MeV in $\sp{14}$N. Nilsson model wavefunctions for the $\sp{14}$N states were used to calculate deuteron cluster transfer spectroscopic amplitudes. Although the calculations did not produce a satisfactory description of the entire data set, they showed clear evidence of L-mixing effects and a sensitivity to the $\sp6$Li D state. The deduced D state-S state ratio in $\sp6$Li is in agreement with earlier work, and the uncertainty as to the relative sign of the $\sp6$Li = $\alpha$ + d spectroscopic factors was resolved. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6269. / Major Professor: Kirby W. Kemper. / Thesis (Ph.D.)--The Florida State University, 1993.
15

GAMMA RAY STUDIES OF SELECTIVELY POPULATED HIGHLY EXCITED STATES IN ALUMINUM-26 AND ALUMINUM-27

Unknown Date (has links)
Selective population of highly excited states in ('26)Al and ('27)Al has been observed in the ('16)O(('12)C,d) and ('16)O(('12)C,p) reactions at 17.3 MeV center of mass energy. Particle-gamma angular correlation measurements have been performed simultaneously for both reactions. The outgoing particles were detected at 0(DEGREES) with respect to the beam direction in coincidence with gamma rays detected by three Ge(Li) detectors located at five angles. In addition, proton-gamma coincidence measurements have been performed at 32.0 MeV laboratory energy where the population of the 12.0 MeV state of ('27)Al is significantly enhanced. The selectively populated states in ('26)Al and ('27)Al are expected to have high spin values based on simple grazing angular momentum arguments. The lifetimes and decay modes of these highly excited states in the ('26)Al and ('27)Al nuclei were studied. / Lifetimes were extracted from as many transitions as possible using the Doppler Shift Attenuation technique for the gamma-emitting states of ('26)Al. The coincidence data were analyzed for transitions from states up to 7.0 MeV. Branching ratios and mixing ratios were obtained for four highly excited states in ('26)Al. Spin and parity assignments were also made for these highly excited states. The results have been combined to produce the transition strengths and the reduced transition probabilities. Reduced transition probabilities and energy levels obtained were compared to shell model predictions. A new member of the K('(pi)) = 0('+) rotational band in ('26)Al is suggested here. / Lifetimes were also extracted from transitions evolving from the observed highly excited states of ('27)Al lying between 7.0 MeV and approximately 12.0 MeV. Branching ratios were determined for these states. The lifetimes and branching ratios allow spin limits to be placed on four highly excited states of ('27)Al. The fourth member of the K('(pi)) = 9/2('+) rotational band in ('27)Al is suggested. / Source: Dissertation Abstracts International, Volume: 44-07, Section: B, page: 2187. / Thesis (Ph.D.)--The Florida State University, 1983.
16

PROJECTILE FRAGMENTATION IN THE ALUMINUM-27 (OXYGEN-16, ALPHA+CARBON-12) REACTION

Unknown Date (has links)
Angular correlation measurements, in the ('27)Al(('16)O,(alpha) ('12)C) reaction at 65, 77 and 87 MeV, were used to study the projectile fragmentation process. Three reaction models, incomplete fusion, inelastic breakup and elastic breakup were used to identify the reaction mechanisms responsible for the (alpha)+('12)C production. Comparisons of the predicted angular correlations, from each of the three models, were made with the measured angular correlations at 65, 77 and 87 MeV. The comparisons revealed, that inelastic breakup was the dominant reaction mechanism at all three energies. It was further determined that a small fraction (10-20%) of the (alpha)+('12)C production resulted from the incomplete fusion process at 77 and 87 MeV. At 65 MeV it was found that incomplete fusion could be producing as much as 50% of the (alpha)+('12)C pairs. / The systematics of the measured angular correlations and the measured relative kinetic energy spectra, between the (alpha)+('12)C ejectiles, further supports the conclusion that the inelastic breakup process is predominantly responsible for the (alpha)+('12)C production in the 65 to 87 MeV energy range. / Source: Dissertation Abstracts International, Volume: 47-01, Section: B, page: 0261. / Thesis (Ph.D.)--The Florida State University, 1985.
17

RESONANCES AND COMPOUND FLUCTUATIONS IN OXYGEN-16(OXYGEN-16,ALPHA) SILICON*-28 AND OXYGEN-16(OXYGEN-16,BERYLLIUM-8) MAGNESIUM*-24 REACTION CROSS SECTIONS (STATISTICAL, MODEL, HEAVY, IONS)

Unknown Date (has links)
The reactions ('16)O(('16)O,(alpha)(,0,1))('28)Si* and ('16)O(('16)O,('8)Be(,0,1))('24)Mg* are studied in the energy region from E(,c.m.) (DBLTURN) 12 to 20 MeV. Excitation functions for these reactions leading to the residual 0('+) ground states and 2('+) first excited states are measured in ('(TURN))50 keV steps at (')(THETA)(,c.m.) (DBLTURN) 6.1(DEGREES) for the (alpha)-particle exit channels and at (')(THETA)(,c.m.) (DBLTURN) 1.5(DEGREES) and (DBLTURN)5.7(DEGREES) for the ('8)Be channels. Angular distributions are measured at selected energies and include differential cross sections at 28 angles in the range (THETA)(,c.m.) (DBLTURN) 6(DEGREES) to 91(DEGREES) for the (alpha)(,0,1) exit channels and at 13 angles from (THETA)(,c.m. )(DBLTURN) 12(DEGREES) to 61(DEGREES) for the ('8)Be(,0,1) channels. / A high density of narrow, resonancelike structures ((rho) ('(TURN))3/MeV, (GAMMA) < 100 to ('(TURN))200keV) is observed in the small-angle data. No system- atic variations of the structure width and density with either energy or exit channel are apparent. Distribution-of-maxima statistical tests, applied to the small-angle data, give no evidence for nonstatistical structure in the four exit channels examined. / Energy correlations in angle-summed cross sections reveal several structures which satisfy conventional resonance criteria. Resonant J('(pi)) values are assigned whenever possible based on the energy dependences of coefficients in either linear Legendre expan- sions or interfering angular momentum pair parameterizations of angular distributions of the spin-zero (alpha)(,0) and ('8)Be exit channels. / Statistical-model calculations are used to predict the magnitudes and angular momentum dependences of the compound-nucleus components in the (alpha)(,0,1) and ('8)Be(,0,1) channels. Synthetic excitation functions and angular distributions are generated to determine whether fluctuations resulting from the population and decay of overlapping compound-nucleus levels can produce resonancelike structure similar to that observed in the data. The results of this investigation suggest a fluctuation origin for the intermediate width structure observed in the data including those structures which are found to satisfy conventional resonance criteria. / Source: Dissertation Abstracts International, Volume: 47-06, Section: B, page: 2488. / Thesis (Ph.D.)--The Florida State University, 1986.
18

SPECTROSCOPY OF NEUTRON-UNBOUND HIGH SPIN STATES IN MAGNESIUM-25

Unknown Date (has links)
The gamma-ray decay of new high spin states in ('25)Mg has been studied using the ('12)C(('14)N,p(gamma))('25)Mg reaction at E(lab) = 23.5 MeV. Proton-gamma coincidences were measured between an E (Si(Li))-(DELTA)E (Si) telescope arrangement at 0(DEGREES) to the beam and either of two Ge(Li) detectors at 90(DEGREES) or four gamma-ray detectors at 90(DEGREES), 81(DEGREES), 60(DEGREES) and 22(DEGREES) in an angular correlation experiment. Also, gamma-gamma coincidences were measured at 90(DEGREES). Experiments were performed at the Florida State University Super FN Tandem Van de Graaff accelerator, and one gamma-gamma coincidence measurement was performed at Triangle University Nuclear Laboratory. Twenty new neutron-unbound levels have been identified, with the range of possible spins narrowed to one or two possibilities for nine levels. / This research was performed to try and confirm the existence of "rotational coexistence" or equivalently "rotational isomerism" predicted to occur at J('(pi)) = 13/2('+) and 17/2('+) in ('25)Mg using the cranked Nilsson-Strutinsky formalism developed by Ingemar Ragnarsson, Tord Bengtsson and Sven Aberg at the Lund Institute of Technology. The same phenomenon has previously been identified with the yrast 8('+) state in ('24)Mg, where the eight units of angular momentum result from alignment of the spins of four s-d shell (valence) nucleons along the axis of rotation. The noncollective behavior of this state yields a prolate shape rotating parallel to the nuclear symmetry axis, and it is energetically favored relative to the prolate 8('+) ground state band member rotating perpendicular (collectively) to the symmetry axis. / Shell model calculations performed by Hobson Wildenthal at Drexel University, using an untruncated s-d shell basis space, have also been compared extensively with experiment. Based on the angular correlation results and correspondence with shell model and cranked Nilsson model predictions, tentative spin assignments have been made for the yrast 15/2('+), 17/2('+) and possibly 9/2('-) states, and the 13/2('+) and 15/2('+) ground state band members. The yrast 17/2('+) and previously observed 13/2('+) states are interpreted to be rotationally aligned, prolate shaped configurations. / Source: Dissertation Abstracts International, Volume: 48-02, Section: B, page: 0478. / Thesis (Ph.D.)--The Florida State University, 1987.
19

Distortion and knock-out exchange effects in nucleon-nucleus scattering

Unknown Date (has links)
Mixed density expansion techniques previously used to study the spectroscopic content of the non-local knockout exchange amplitudes for nucleon-nucleus scattering in the plane wave approximation (PWA) are extended to the more realistic distorted wave approximation (DWA). This approach provides a clear basis for assessing specific spectroscopic consequences of the knock-out amplitudes and the means for developing suitable approximations to simplify the treatment of these amplitudes. Since the final reaction amplitudes are computed in momentum space, distortion effects are displayed in a form that allows for the most direct comparison between the strong nucleon-nucleus scattering reaction and the well understood electron-nucleus scattering reaction. As a specific application of the formalism, results are presented for polarization transfer observables for stretched excitations in light nuclei. Polarization transfer is a topic of current interest in nucleon-nucleus scattering. / Source: Dissertation Abstracts International, Volume: 55-03, Section: B, page: 0970. / Major Professor: Fred Petrovich. / Thesis (Ph.D.)--The Florida State University, 1993.
20

THE ELASTIC SCATTERING OF ALPHA-PARTICLES BY ARGON-36 - 12.83 TO 17.83 MEV

Unknown Date (has links)
Source: Dissertation Abstracts International, Volume: 31-09, Section: B, page: 5552. / Thesis (Ph.D.)--The Florida State University, 1970.

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