Thesis (PhD (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The (p, pα) reaction on 12C was investigated experimentally using polarized incident protons of 100 MeV. Coincident data, which were obtained at ten quasifree angle pairs for proton angles ranging from 25◦ to 110◦, were analyzed in terms of the distorted-wave impulse approximation (DWIA). Calculated energy-sharing cross section and analyzing power distributions reproduce the data reasonably well. The observed agreement allows the extraction of distorted momentum distributions from experimental data. These distributions are very consistent over a wide range of angle pairs at which cross section energy-sharing distributions vary considerably. Since measurements of analyzing powers were made, spin-orbit distortions were included in the DWIA calculations. The effects of spin-orbit distortions were found to be very small near zero recoil momentum and did not destroy the validity of the factorization approximation where the two-body p-α cross section enters as a multiplicative factor in the three-body (p, pα) cross section expression. Spectroscopic factors derived from the data are fairly consistent with the trend of the theoretical predictions. Analyzing power data also follow the trend of free p-4He scattering data, and comparisons with DWIA predictions are in reasonable agreement. The theory reproduces also very well analyzing power angular distributions of the projectile-cluster two-body scattering at large angular momentum of the residual nucleus. This indicates that a quasifree knockout mechanism dominates the reaction. The two-body interaction response between the projectile and the α cluster was found to resemble the scattering of protons from a free α particle to a remarkable degree, the present results strongly imply the existence of preformed α clusters in 12C. / AFRIKAANSE OPSOMMING: Die (p, pα) reaksie op 12C is eksperimenteel ondersoek deur middel van gepolariseerde protone met n invalsenergie van 100 MeV. Ko¨ınsidensie data, wat verkry is by tien kwasievrye hoekpare, met proton hoeke tussen 25◦ en 110◦, is geanaliseer in terme van die vervormde-golf-impuls-benadering (DWIA). Die berekende energie-verdeelde kansvlak en analiseervermo¨e verspreidings reproduseer die data redelik goed. Die waargenome ooreenstemming maak dit moontlik om vervormde momentumverdelings uit die eksperimentele data te verkry. Aangesien analiseervermo¨e metings gedoen is, is spin-baan wisselwerking by die DWIA berekenige ingesluit. Die bydra as gevolg van spin-baan wisselwerking blyk baie klein te wees naby nul terugslag momentum en het nie die geldigheid van die faktoriseringsbenadering, waartydens die twee-deeltjie, p-α kansvlak as ’n vermenigvuldigingsfaktor in die uitdrukking vir die drie-deeltjie (p, pα) kansvlak verskyn, vernietig nie. Spektroskopiese faktore wat uit die data herlei is, is redelik konsistent met die verloop van die teoretiese voorspellings. Analiseervermo¨e data volg ook die verloop van die vrye p-4He verstrooiings-data en vergelyk redelik goed met DWIA voorspellings. Die teorie reproduseer ook die hoekverdelings in die analiseervermo¨e van die twee-deeltjie projektiel-bondel verstrooiing by groot hoekmomentum waardes vir die oorblywende kern baie goed. Dit dui daarop dat ’n kwasie-vrye uitslaanmeganisme die reaksie domineer. Die twee-deeltjie wisselwerkingsgedrag tussen die projektiel en die α-bondel toon sterk ooreenkomste met die verstrooiing van protone vanaf ’n vrye α-deeltjie. Die huidige resultate lewer sterk bewyse vir die bestaan van voorafgevormde α-bondels in 12C.

<p>An experiment measuring the analyzing power A_y(&theta;) for neutron&ndash;helium-3 (<italic>n</italic>-<super>3</super>He) elastic scattering over broad angular distributions for a range of incident neutron energies from 1.60 to 5.54 MeV has been conducted at the Triangle Universities Nuclear Laboratory. These measurements represent an effort to resolve the long-standing discrepancy between experiment and theory in low-energy three-nucleon analyzing powers, through the evaluation of analyzing powers in the four-nucleon systems, which are expected to exhibit sensitivities not accessible with fewer nucleons. The present work is described in terms of the experimental setup and data reduction techniques; a comparison of the results with rigorous calculations using both nucleon-nucleon and, as recently has become available, three-nucleon potential models is presented. While a discrepancy between calculation and measurement was observed, at low energies substantially better agreement was achieved than in related measurements of the proton&ndash;helium-3 (<italic>p</italic>-<super>3</super>He) analyzing power, suggesting a sizeable dependence on isospin in the four-nucleon systems.</p> / Dissertation

Thesis (PhD)--Stellenbosch University, 2012. / Please refer to full text for abstract.

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