The criteria to be satisfied by a successful theory of the origin of the solar system are discussed before highlighting the difficulties of early two-body interaction theories. It is shown that these do not apply to Woolfson's capture theory which proposes that a light' diffuse protostar was tidally disrupted during a close encounter with the Sun and that the captured material might condense to form massive protoplanets. The smoothed particle hydrodynamic technique of Gingold & Monaghan is improved to provide a model for the computer simulation of stellar encounters. The protostar is replaced by a number of randomly distributed fluid elements, from which a density distribution may be recovered by a statistical technique. This distribution leads to a gravitational field and with a suitable thermodynamic model the pressure is determined at any point, enabling the dynamical evolution of the protostar to be simulated. The model is tested on a number of hydrostatic and hydrodynamic problems. A collapsing protostar is seen to be tidally disrupted during a close stellar encounter and the captured material moves quickly away from the Sun. This provides the optimal conditions for protoplanetary condensation. The effect of an initial protostellar rotation is also considered. It is shown that the quantity of material captured is critically dependent on the alignment of the protostellar spin axis to the orbital plane and, in an extreme case, might prevent the disruption of the protoster. The behaviour of a contracting protoplanet in the solar tidal field is investigated. It is shown that, despite severe distortion, it may well survive a perihelion passage without disruption and after further contraction may regain its spheroidal shape. Finally, a number of extensions to the capture theory are suggested.

The neutron, although electrically neutral, is composed of elementary charged particles and as a result, possesses a charge distribution within. The charge distribution can be studied by measuring a quantity called the neutron electric form factor, GnE. Experiment E02-013 at Jefferson Lab’s Hall A measured GnE at high four-momentum transfer values of Q2 = 1.2, 1.7, 2.5 and 3.4 (GeV/c)2 in double polarized semi-exclusive 3He(e, e'n) scattering in quasi-elestic kinematics by measuring the transverse asymmetry AT of the cross section. The neutron electric form factor is essential to know for a variety of reasons. Results from the recent Jefferson Lab experiment on the proton revealed interesting features at these momentum transfers, whereas no accurate data for the neutron is available. Also the recent development in Generalized Parton Distributions (GPDs) necessitates the need for precise values for GnE in Q2 range between 1 and 10 (GeV/c)2; they appear as limiting conditions for certain GPD functions, for example, to constrain spin-flip GPDs. The experiment used the polarized 3He target and the polarized CEBAF electron beam at energies of about 1.52, 2.08, 2.64 and 3.29 GeV. The electrons were detected in the BigBite spectrometer and the neutrons in a large array of scintillators in coincidence with the electrons. In this dissertation, we report a preliminary result, GnE = 0.03457 ± 0.007239 at Q2 = 1.7 (GeV/c)2.

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