Foram medidas distribuições angulares dos canais quase-elásticos e do decaimento em fragmentos binários fortemente amortecidos dos sistemas ANTPOT. 18 O+ANTPOT. 10,11 B E ANTPOT. 28 Si + ANTPOT. 16 O em energias de E IND. LAB(ANTPOT. 18 0) = 52,5 MeV e E IND. LAB(ANTPOT. 28 0) = 107,5 e 139 MeV. Em todos os sistemas, as distribuições angulares quase-elásticas apresentam oscilações com uma subida da seção de choque em ângulos traseiros. As distribuições integradas em valor de Q, apresentam o comportamento 1/sen IND. CM em todos os sistemas indicando uma vida-média longa. Medidas de distribuição de massa de fragmentos emitidos e razão (ANTPOT. 16 O/ANTPOT. 12 C) sugerem que o mecanismo de reação no caso do sistema ANTPOT. 28 Si + ANTPOT. 16 O é de orbiting, não passando pela formação do núcleo composto. Cálculos de canais acoplados, incluindo grande número de canais populados nas reações, permitem reproduzir as distribuições angulares oscilantes e com forte subida em ângulos traseiros dos estados individuais, bem como as distribuições angulares integradas em Q, lisas, com comportamento 1/sen IND. CM para os sistemas ANTPOT. 18 O+ANTPOT. 10,11 B E ANTPOT. 28 Si + ANTPOT. 16 O. / The binary decay into strongly damped fragments and the quasielastic reactions of the systems 18O + 10,11B and 28Si + 16O were measured at ELAB(18O)=52.5 MeV, ELAB(28O)=107.5 e 139 MeV in the angular range of 30ºCM160º. In bolh systems the quasielastic angular distributions present oscillations and strong increase in the backward region. The angular distributions of the Q-value integrated cross-section follow the tendency 1/sinCM in both systems indicating a long life-time. Mass distribution measurement and the (16O/12C) ration suggest that the reaction mechanism in the case of the 28Si+16O system is orbiting/deep-inelastic. Coupled channels calculations, including a great number of the channels populated in the reactions yield angular distributions which agree well with experimental data for both systems.

Foram medidas distribuições angulares dos canais quase-elásticos e do decaimento em fragmentos binários fortemente amortecidos dos sistemas ANTPOT. 18 O+ANTPOT. 10,11 B E ANTPOT. 28 Si + ANTPOT. 16 O em energias de E IND. LAB(ANTPOT. 18 0) = 52,5 MeV e E IND. LAB(ANTPOT. 28 0) = 107,5 e 139 MeV. Em todos os sistemas, as distribuições angulares quase-elásticas apresentam oscilações com uma subida da seção de choque em ângulos traseiros. As distribuições integradas em valor de Q, apresentam o comportamento 1/sen IND. CM em todos os sistemas indicando uma vida-média longa. Medidas de distribuição de massa de fragmentos emitidos e razão (ANTPOT. 16 O/ANTPOT. 12 C) sugerem que o mecanismo de reação no caso do sistema ANTPOT. 28 Si + ANTPOT. 16 O é de orbiting, não passando pela formação do núcleo composto. Cálculos de canais acoplados, incluindo grande número de canais populados nas reações, permitem reproduzir as distribuições angulares oscilantes e com forte subida em ângulos traseiros dos estados individuais, bem como as distribuições angulares integradas em Q, lisas, com comportamento 1/sen IND. CM para os sistemas ANTPOT. 18 O+ANTPOT. 10,11 B E ANTPOT. 28 Si + ANTPOT. 16 O. / The binary decay into strongly damped fragments and the quasielastic reactions of the systems 18O + 10,11B and 28Si + 16O were measured at ELAB(18O)=52.5 MeV, ELAB(28O)=107.5 e 139 MeV in the angular range of 30ºCM160º. In bolh systems the quasielastic angular distributions present oscillations and strong increase in the backward region. The angular distributions of the Q-value integrated cross-section follow the tendency 1/sinCM in both systems indicating a long life-time. Mass distribution measurement and the (16O/12C) ration suggest that the reaction mechanism in the case of the 28Si+16O system is orbiting/deep-inelastic. Coupled channels calculations, including a great number of the channels populated in the reactions yield angular distributions which agree well with experimental data for both systems.

Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 135-143).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1957. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 99-100).

Population pulsations are fluctuations in the population difference (of a two level system) due to the presence of two or more coherent waves interfering in the medium. In this work, we show that population pulsations generated by three waves, a central wave and two mode-locked sidebands, are responsible for both the multiwavelength and the single-wavelength instabilities of single-mode lasers containing homogeneously-broadened media. The role of the population pulsations in establishing these instabilities, however, diminish as the central mode is detuned away from the atomic resonance frequency. For homogeneously-broadened lasers, we find two regions of single-wavelength instability. The first is at line center, for which population pulsations are solely responsible, and the second is off line center where the unsaturated medium provides the required gain and anomalous dispersion. For the case of inhomogeneously-broadened lasers, we show that population pulsations significantly increase the instability range over that predicted by Casperson for single-mode bad-cavity lasers. Both the unidirectional ring and the standing-wave cavities are treated. The Fourier expansion technique, used in this work, for treating three-frequency operation in saturation spectroscopy is shown to be equivalent (in appropriate limits) to the linear stability analysis in laser theory and optical bistability. We also show, in single-sideband saturation spectroscopy, that for long interaction lengths propagation effects can significantly influence the absorption and dispersion coefficients of the medium. Finally, we show that under certain conditions the pronounced splittind effects of the population pulsations develop into regions of intense absorption.

No description available.

Thesis (PhD (Physics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this dissertation we present, for the first time, a relativistic distorted wave impulse approximation formalism to describe quasielastic proton-nucleus scattering. We start from a full many-body description of the transition matrix element and show systematically how to derive the equivalent two-body form. This procedure allows for a clear and unambiguous method to introduce relativistic distorted waves. It is shown that the polarized double differential cross section may be written as the contraction of two tensors namely, the hadronic tensor (describing the projectile and ejectile), and the polarization tensor describing the target nucleus. The basic nucleon-nucleon (NN) interaction is described by the SPVAT or IA1 representation of the NN scattering matrix. Analytical expressions are derived for the polarization tensor using a Fermi gas model for the target nucleus. The nuclear distortion effects on the projectile and ejectile are described using the relativistic eikonal formalism. The expression for the double differential cross section is a nine dimensional oscillatory integral and an efficient procedure is developed to calculate this quantity. Comparison of Gaussian, Monte Carlo and quasi-Monte Carlo numerical integration schemes reveal that for this work, Gaussian quadrature is best suited for this problem. Traditional Gaussian quadrature is used to generate single variable functions whereby these functions are used in combination with modern software such as MATLAB to complete the computation of the full multidimensional integral in a reasonable amount of time. Even though the calculation of the cross section for a single value of the energy transfer is still time consuming, the computational time can be decreased by spreading the calculational burden across a number of nodes in a cluster computing system. A test calculation is performed whereby a proton with incident laboratory energy of 400 MeV is scattered off a 40Ca target nucleus at θcm = 40◦. For this reaction we calculate the unpolarized double differential cross section, as well as a complete set of spin observables namely Ay, Dℓ′,ℓ, Ds′s, Dnn,Ds′ℓ and Dℓ′s. We find that the distortions lead to a reduction of the unpolarized double differential cross section. On the other hand the spin observables are complex entities which show no uniformity in behaviour. However, the differences between the distorted wave spin observables and that of the plane wave observables are minor and we conclude that distortions have little effect on spin observables. / AFRIKAANSE OPSOMMING: Hierdie proefskrif bevat, vir die eerste keer, ’n relatiwistiese vervormdegolf impuls benadering formalisme vir die beskrywing van kwasielastiese proton-kern verstrooiing. Daar word aangetoon hoe om stapsgewys te gaan vanaf ’n veel-deeltjie beskrywing van die oorgangsmatriks element na die ekwivalente twee-deeltjie vorm. Hierdie metode laat toe dat die vervormde golwe op ’n duidelike en ondubbelsinnige manier ingevoer kan word. Daar word aangetoon dat die gepolariseerde dubbele differensiële kansvlak geskryf kan word as die kontraksie van twee tensore naamlik, die hadroniese tensor (wat die projektiel en uitgaande nukleon beskryf), sowel as die polarisasie tensor wat die kern beskryf. Die basiese kern-kern (NN) wisselwerking word beskryf deur gebruik te maak van die SPVAT of IA1 daarstelling van die NN verstrooiingsmatriks. Analitiese uitdrukkings word ook afgelei vir die polarisasie tensor binne die Fermi gas model. Die vervormdegolf beskrywing van die projektiel en uitgaande deeltjie word gedoen deur gebruik te maak van die eikonal vervormdegolf benadering. Die uitdrukking vir die ongepolariseerde dubbele differsieële kansvlak bevat ’n nege dimensioneële ossilatoriese integraal en ’n prakties-effektiewe prosedure is ontwikkel om hierdie waarneembare te bereken. Vegelyking van Gauss, Monte Carlo en kwasi-Monte Carlo numeriese integrasie tegnieke het uitgewys dat die Gauss integrasie tegniek die beste geskik is om die probleem op te los. Die gebruik van Gauss integrasie om funksies te bereken wat afhanklik is van net een veranderlike en dit te kombineer met moderne sagteware programme soos MATLAB laat ons toe om die gepolariseerde dubbele differensieële kansvlak te bekeren in ’n redelike tyd. Alhoewel die berekening van die kansvlak vir een waarde van die energie-oordrag nogsteeds tydrowend is, word dit bespoedig deur die berekeningslas te versprei oor ’n aantal nodusse in ’n rekenaarbondel sisteem. ’n Toets berekening word gedoen waarby ’n proton met inkomende laboratoriese energie van 400 MeV vanaf ’n 40Ca kern verstrooi word teen ’n hoek van θcm = 400. Vir hierdie reaksie word die ongepolariseerde dubbele differensieële kansvlak bereken sowel as ’n volledige stel spin waarneembares naamlik Ay, Dℓ′,ℓ, Ds′s, Dnn, Ds′ℓ en Dℓ′s. Daar word gevind dat die versteurings lei tot ’n afname in die differensieële kansvlak. Die spin waarneembares egter, is komplekse hoeveelhede wat geen univorme gedrag toon nie. Die verskil tussen die vervormde golf spin waarneembares en die van vlak golf waarneembares is minimaal en ons lei daarvan af dat spin waarneembares onsensitief is teen oor versteurings.

Thesis (M.S.)--Miami University, Dept. of Physics, 2009. / Title from first page of PDF document. Includes bibliographical references (p. Xx-Xx).

Thesis (PhD (Physics))--University of Stelllenbosch, 2010. / ENGLISH ABSTRACT: In this dissertation a fully relativistic model for polarized inclusive quasielastic proton-nucleus scattering is developed. Using a standard relativistic impulse approximation (RIA) treatment of quasielastic scattering and a two-body SPVAT form of the current operator, it is shown how the behaviour of projectile and target can be decoupled. Subsequently, different models for projectile and target can be adopted and combined to examine a variety of relativistic effects. The most simplistic model of the target is provided by a mean-field nuclear matter approximation to the relativistic meson-nucleon model, quantum hadrodynamics (QHD). Here relativistic effects manifest as an effective mass, which is lower than the free mass, of the constituent nucleons. This model is improved upon by including many-body correlations through medium-modification of meson propagators in the relativistic random-phase approximation (RPA). Since it is generally accepted that the strong nuclear force and the extended range of the nuclear potential lead to distortion effects on the projectile and ejectile (seen as a modulation of the wave functions), our formalism is geared towards the use of relativistic distorted waves (RDWIA). The distorted waves are written as partial wave expansions and are solutions to the Dirac equation with potentials. The inclusion of distortions, however, greatly increases the computational burden and we show how a number of analytical and numerical techniques can be used to facilitate the process of calculation. It is also shown how the standard relativistic plane wave treatment (RPWIA) can, instead, be easily employed to obtain a baseline for determining the impact of distortions. A calculation is performed for the reaction 40Ca(!p, !p !) at a beam energy of 500 MeV. Here it is found that the effect of correlations on the RPWIA calculation can be seen as a quenching of the cross section that is expected to become more pronounced at lower energies or for higher density targets. A RDWIA calculation shows additional reduction and if target correlations are included this effect is enhanced. To our knowledge this is the first calculation that attempts to include both these effects (RPA and RDWIA) in the context of quasielastic proton-nucleus scattering. / AFRIKAANSE OPSOMMING: In hierdie proefskrif word ’n ten volle relatiwistiese model vir die berekening van inklusiewe kwasielastiese proton-kern verstrooiing daargestel. Deur gebruik te maak van ’n standaard relatiwistiese impulsbenadering (RIA) vir kwasi-elastiese verstrooiing asook ’n twee-deeltjie-SPVAT-vorm vir die stroom-operator, word daar gewys hoedat die gedrag van die projektiel en teiken ontkoppel kan word. Verskillende modelle kan dus vir die projektiel en teiken gebruik word om ’n verskeidenheid relatiwistiese effekte te bestudeer. Die mees simplistiese model vir die teiken word verskaf deur ’n gemiddelde-veld kernmateriaalbenadering tot die relatiwistiese meson-nukleon-model, kwantum-hadrodinamika (QHD). In hierdie model manifesteer relatiwistiese effekte as ’n effektiewe massa, wat kleiner is as die vrye massa, van nukleone in die kern. Hierdie model word verbeter deur die inagneming van veeldeeltjie korrelasies deur medium-gewysigde meson-propagators in die relatiwistiese ewekansige-fase-benadering (RPA). Aangesien dit algemeen aanvaar word dat die sterk-wisselwerking en die reikwydte van die kernpotensiaal aanleiding gee tot vervormingseffekte op die projektiel en ejektiel (gesien as die modulasie van golffunksies), is ons model optimaal geformuleer om gebruik te maak van relatiwistiese vervormde golwe (RDWIA). Die vervormde golwe word geskryf as parsi¨elegolf uitbreidings en dien as oplossings vir die Dirac-vergelyking met potensiale. Insluiting van vervormings vermeerder egter die berekeningslas geweldig en ons toon hoedat ’n aantal analitiese en numeriese tegnieke gebruik kan word om die proses te vergemaklik. Daar word ook aangetoon hoe die standaard- relatiwistiese-vlakgolf-benadering (RPWIA), in plaas van vevormde golwe, maklik gebruik kan word om ’n verwysingspunt vir die meting van die effek van vervormings te bepaal. ’n Berekening vir die reaksie 40Ca(!p, !p !) teen ’n projektiel-energie van 500 MeV word getoon. Hier word dit gevind dat die effek van korrelasies op die RPWIA-berekening gesien kan word as ’n verlaging van die kansvlak. Daar word verwag dat hierdie effek duideliker sal word by laer energie¨e en ho¨er kerndigthede. ’n RDWIA-berekening word getoon wat daarop dui dat addisionele verlaging in die kansvlak voorkom en indien korrelasies hier ingesluit word, word hierdie effek vergroot. Sover ons kennis strek, is hierdie die eerste berekening wat poog om beide hierdie effekte (RPA en RDWIA) in die konteks van kwasi-elastiese proton-kern verstrooiing in te sluit.

No description available.