Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 83-94). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 241-264). Also available via World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references and index.

No description available.

No description available.

The Bogoliubov theory of excitations in superfluid helium is used to study collective modes at zero temperature. A repulsive delta function shell potential is used in the quasiparticle excitation energy spectrum to fit the observed elementary excitation spectrum, except in the plateau region. The linearized equation of motion method is used to obtain the secular equation for a collective mode consisting of a linear combination of one and two free quasiparticles of zero total momentum. It is shown that in this case for high-lying collective modes, vertices involving three quasiparticles cancel, and only vertices involving four quasiparticles are important. A decomposition into various angular momentum states is then made. Bound roton pairs in the angular momentum D-state observed in light-scattering experiments exist only for an attractive coupling between helium atoms in this oversimplified model. Thus, the interaction between particles can be reinterpreted as a phenomenological attractive coupling between quasiparticles, in order to explain the Raman scattering from bound roton pairs in superfluid helium.

by Chan Kwan Leung. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 168-169). / by Chan Kwan Leung. / Acknowledgement --- p.i / Abstract --- p.ii / Chapter 1. --- Introduction / Chapter 1.1 --- Objective of our variational method --- p.2 / Chapter 1.2 --- Outline of the content --- p.5 / Chapter 2. --- Formulation of the new variational method / Chapter 2.1 --- Formulation --- p.14 / Chapter 2.2 --- Motivation --- p.15 / Chapter 3. --- The variational method applied to the anharmonic oscillator problem / Chapter 3.1 --- Formalism --- p.18 / Chapter 3.2 --- Relationship with usual variational method --- p.32 / Chapter 3.3 --- Relationship with W.K.B. approximation --- p.37 / Chapter 3.4 --- Perturbative corrections --- p.45 / Chapter 3.5 --- Diagonalization of non-orthogonal basis --- p.57 / Chapter 3.6 --- Perturbative corrections using the non-orthogonal basis --- p.72 / Chapter 3.7 --- Some previous works on the anharmonic oscillator problem --- p.85 / Chapter 4. --- The variational method applied to the helium-like atomic problem / Chapter 4.1 --- Previous work on the problem --- p.90 / Chapter 4.2 --- Formulation of the variational method on the problem --- p.95 / Chapter 4.3 --- Zeroth order results for atomic helium --- p.103 / Chapter 4.4 --- Diagonalization using the non-orthogonal basis --- p.109 / Chapter 4.5 --- Results for some helium-like ions --- p.136 / Chapter 4.6 --- Possibility of generalization to systems with more electrons --- p.140 / Chapter 5 --- Concluding remarks / Chapter 5.1 --- Range of applicability of our variational method --- p.164 / Chapter 5.2 --- Ground state problem --- p.165 / Chapter 5.3 --- Completeness of our 'basis' --- p.166 / References --- p.168

L'utilisation des lasers de puissance permet l'étude des propriétés de la matière dans des conditions extrêmes de température et de densité. En effet, l'interaction d'un laser de puissance sur une cible créée un plasma dont la température est suffisamment grande pour atteindre des degrés d'ionisation élevés. Ces conditions peuvent permettre, via divers processus, d'exciter le noyau dans un état nucléaire et notamment dans un état isomère. Un noyau d'intérêt pour étudier ces phénomènes est le 201 Hg. Ce travail de thèse s'inscrit dans le cadre du dimensionnement d'une expérience visant la mise en évidence de l'excitation du 201 Hg dans un plasma laser.La première partie de ce manuscrit présente la détermination des taux d'excitation nucléaire dans les plasmas. Depuis une dizaine d'années les taux d'excitation sont déterminés en utilisant le modèle de l'atome moyen. Afin de valider ce modèle, un code, appelé ADAM (Au-Delà de l'Atome Moyen), a été développé afin de calculer le taux d'excitation nucléaire en DCA (Detailed Conguration Accounting). Il nous permettra d'en déduire un domaine thermodynamique en température et densité où les taux d'excitation déterminés avec le modèle de l'atome moyen sont pertinents.La deuxième partie présente le couplage des taux d'excitation nucléaire avec un code hydrodynamique afin d'en déduire, pour différentes intensités laser, le nombre de noyaux qu'il serait possible d'exciter par tir laser. Enfin, dans une dernière partie,les premières approches expérimentales qui serviront au dimensionnement d'une expérience sur une installation laser sont présentées. Ces approches sont basées sur la détection et la détermination de la quantité d'ions multichargés obtenue loin de la cible (~80 cm). Pour cela, un déviateur électrostatique a été utilisé. / The use of high power lasers allows the study of the properties of matter in extremeconditions of temperature and density. Indeed, the interaction of a power laser and atarget creates a plasma in which the temperature is high enough to reach important degrees of ionization. These conditions can allow the excitation of the nucleus. Anucleus of interest to study the processes of nuclear excitation is the 201 Hg. Thiswork aims to design an experiment where the 201 Hg excitation will be observed in aplasma produced by a high power laser. The first part of this manuscript presents the calculation of the expected nuclear excitation rates in the plasma. For about ten years, nuclear excitation rates have been calculated using the average atom model. To validate this model a code named ADAM (french acronym for Beyond The Average Atom Model) was developed to calculate the nuclear excitation rates under the DCA (Detailed Configuration Accounting) hypothesis. ADAM allows us to deduce the thermo dynamical domain where the nuclear excitation rates determined with the average atom model are relevant. The second part of this manuscript presents the coupling of the excitation rate calculation with a hydrodynamic code to calculate the number of excited nuclei produced in one laser shot for different laser intensity. Finally, in the last part, first experimental approaches which will be used to design an experiment on a laser installation are presented. These approaches are based on the detection and determination of the amount of multicharged ions obtained far from the target (~80 cm). For this purpose, an electrostatic analyzer was used.

A delayed-coincidence spectrometer system was developed to measure nuclear lifetimes in the picosecond region by the centroid-shift method. liming signals were derived from two plastic scintillators. A specially constructed NaI(Tl) detector was used to detect the gamma-rays which were Corrpton-scattered from one of the plastic scintillators. Energy identification was achieved by sumning the signals from the plastic detector and the NaI(Tl) detector to give the full energy photopeaks. In order to test the effectiveness of the system, the mean lives of the first excited states of Ni60 and Ba134 were measured. The 1.0-psec mean life in Ni60 could not be measured with the present system. The gamma-gamma and beta-gamma coincidence experiments gave the mean life of the first excited state of Ba134 as 6.1 ±0.8 psec and 4.8 ±0.6 psec, respectively. It is concluded that the shortest mean life that can reliably be measured by the present system is about 5 psec.Ball State UniversityMuncie, IN 47306

Not available