A study of the ion behaviour in the HBTX1A/B Reversed Field Pinches (RFP's) is presented. A comparison of measured and calculated energy spectra of the neutral deuterium atoms emitted from the plasma enabled the deuterium ion temperature to be measured and its radial profile estimated. The measured ion temperatures of 80.0eV to 600.OeV cannot be explained by collisional heating of the ions by the electrons even indirectly through typical (2.0% CV, 2.0% OVI, 0.1% FeXII) or extreme (9.0% FeXII) concentrations of impurity ions. Measurements of the Doppler broadening of carbon ion line emission, CV(2271.oA), enabled estimates to be made of the CV ion temperature of 150.OeV to 450.OeV and fluid velocity of 3.0x103ms1 to 1.4x10 ms1 toroidally. The measured ion temperatures are shown to be consistent with the heating power per particle being proportional to the particle mass. An ion power balance model is described in which it is assumed thatthe excess power input into the plasma above the Ohmic heating power into the electrons, typically 6.OMWnf3 on average, heats the ions locally through the damping of fluctuations. The resistivity estimated from a helicity balance model can be made to agree with the Spitzer value only if the excess toroidal loop voltage due to helicity loss at the plasma boundary is included. Ion energy losses are calculated from the relative neutral deuterium density profile assuming equal ion and electron energy and particle diffusion coefficients of typically 50.0m s on axis. Using this model the calculated ion temperature profile and ratio of ion to electron temperature, Ti/Te, are consistent with those measured over a wide range of conditions. Ti/Te is predicted to increase with increased helicity loss at the plasma edge. This was demonstrated by insertion of a tile into the plasma edge which increased Ti/Te from 1.0 with limiters to 2.0 and by removal of the limiters which decreased Ti/Te to 0.5 to 0.3 as predicted. A review of ion heating mechanisms indicated that ion heating by viscous damping of fluctuations is the most likely candidate. Estimates of the order of the viscous heating powerusing measured fluctuation levels are of the required magnitude. It isconcluded that the ion temperatures observed can be explained if the power input to the fluctuations associated with the RFP 'dynamo' heats the ions through the viscous damping of these fluctuations.

A brief introduction on the scope of gamma ray spectroscopy is given in Chapter I, Chapter II deals with, the codification of the detecting system is of the prolate spheroidal field b-ray spectrometer (large spectrometer) and the medium size magnetic lens spectrometer (small spectrometer). The "Venetian blind" E.M.I photomultipliers previously used in both the spectrometers have been replaced by 36 a'VP photomultipliers and fast electronics using avalanche discriminator circuits. The NE 102 phosphors were replaced by the fast NE 104 scintillators. further improvement in the large spectrometer was made by replacing the conical phosphor and a straight light guide by an equiangular spiral light guide. Chapter IV describes the preparation of p-sources. An improved technique using the electrospraying method has been applied in the preparation of Th B and Ce sources. The coincidence measurements of 144Ce using the two spectrometers have been described in Chapter VI. But the most important and original contribution of this thesis is the e y coincidence measurements of 144Ce using the large spectrometer and a Go(Li) K-ray detector in con-junction. The e-y coincidence measurements have been described in Chapter VI. Very possibly a magnetic spectrometer and a Ge(Li) x-ray detector have been used for the first time time in these e - y coincidence measurements on 144Ce. The single y-ray spectra of 144Ce neasured with the 5 cc Ge(Li) detector and with X-ray detector are also described in this chapter. The use of a G-e(Li) X-ray detector in the e - y coincidence neasurenents of Ce has nade it possible to solve the ambiguities in the literature concerning sone low energy transitions and in the placing of the upper excited level in 144Pr The results can be talcen as the nost reliable ones obtained so far. Our results agree best with Geiger et al (1960,61). Chapter VII describes some (Tl)/Ge(Li) y - y coincidence measurenents of 207Bi and it is possible that these are the first measurenents on 207Bi with this type of equipment.

Studies on (d,d);(3He,3He); (d,3He);(3He,d) and (d,n) reactions are reported in this work. The (d,d) angular distributions were measured at an incident energy of 12.0 MeV on 45Sc, 40Ca and at 13.0 MeV on 37Cl, 35Cl, 27A1 and 23Na. The (3He,3He) angular distributions were measured at an incident energy of 14.0 MeV on 29Si and 25Mg. The results of elastic scattering studies were analysed to extract optical potential parameters for the analysis of the transfer reaction experiments. The (d,3He) angular distributions were measured on targets 45Sc, 40Ca at an incident energy of 12.0 MeV and on 37Ck, 35Cl, 27Al and 23Na at 13.0 MeV. The (3He,d) angular distributions were measured on targets of 29Si and 25Mg at an incident energy of 14.0 MeV. The reaction 29Si(d,n)30P was studied at 3.0 MeV. The results of transfer reaction studies were analysed using DWBA and Hauser-Feshbach theories and discussed in the light of the structure of the nuclear states involved. It has been possible in some cases to assign spins and parities to nuclear levels from these studies. Implications of reaction mechanism in some cases have also been considered. The problem of absolute normalization of DWBA calculations has been investigated using the results from some (d, 3He) studies.

In chapter I of this thesis the Born series solution of the Schrodinger equation for the scattering of a structure less particle by a static potential is derived and known results about its radius and rate of convergence given. The derivation is generalised to electron-atom scattering in chapter II. It is proved that the second Born scattering amplitude satisfies relationships analagous to the optical theorem and the dispersion relation conjectured by Gerjuoy and Krall. Various approximate methods of evaluating the second born correction to the scattering amplitude are discussed. In chapter III the method used to reduce the second born correction to the scattering amplitude to a sum of known integrals is given and chapter IV contains the method of evaluating these known integrals. The results obtained from applying various forms of the simplified second born approximation to elastic and inelastic collisions of electrons with Helium and Hydrogen atoms are presented in Chapter V. At incident electron energies of up to twenty times threshold a correction of between 5% and 10% to the first Born total cross sections is obtained for the following collisions:- [diagram] For transitions between the ground state and excited d states of both Hydrogen and Helium atoms induced by electrons with impact energy of twenty times threshold the correction to the first Born total cross section is less than 3%, apart from the excitation of the 31D state of Helium when it is 15%. Differential and total cross sections are given for the excitation of model doubly excited states of Helium.

In the first part of this thesis an optical potential approach is applied to the problem of elastic electron-helium scattering at low energies. First the deficiencies in the second order calculation of Pu and Chang arc removed and then third order corrections to the phase shifts are considered. In Chapter I a short review of Brueckner-GoIdstone perturbation theory is presented and explicit expressions for the second order phase shifts are derived. The methods of computing these expressions are considered in Chapter II. Various other theoretical models are discussed in Chapter III where also our second order results for the s, p and d-wave phase shifts are given. Chapter IV comprises our calculation of the polarisability of helium, using a Brueckner-Goldstone approach. In Chapter V a method of determining all the distinct Feynmann diagrams of any order is given, and third order corrections to the d-wave phase shift are discussed. The aim of the work described in Part II of this thesis has been to test for electron-neon scattering the dispersion relation conjectured by Gerjuoy and Krall. An introduction to the dispersion relation and the technique of phase shift analysis is given in Chapter VI and previous work on electron-helium scattering is reviewed. In Chapter VII the various quantities which have to be calculated in order to test the validity of the dispersion relation for electron-neon scattering are discussed. In particular, the analysis involved is the calculation of the Born exchange scattering amplitude,S_B(O, k²) is given. A more accurate evaluation of this amplitude for zero energy, using a configuration interaction ground state wave function, is described in Chapters VIII and IX. Preliminary results for g_B(O, 0) are given in Chapter X.

The dispersion relations are expressions which relate the real and the imaginary parts of the scattering amplitude. The importance of the dispersion relations in collision theory lies in that they can be used to derive rigorous formulae for quantities directly related to the measured values; and can therefore serve as a criterion for the analysis of experimental data. This is done by connecting an integral over the total cross section with the scattering length, the consistency and accuracy of total cross section measurements can be assessed. The most extensive application so far, of the dispersion relations has been to the electron scattering by hydrogen (Gerjuoy and Krall, 1960) and helium (Lawson et al. 1966, Bransden and McDowell 1969, 1970). Part of the problem addressed in the following account is that of accurately calculating the Born exchange contribution at zero energy for electron scattering by helium and lithium in the forward direction using various wavefunctions. The corresponding dispersion relations have also been discussed.

The classical Hamiltonian describing the hydrogen atom in the presence of a static magnetic field of arbitrary strength for arbitrary angular momentum is derived. For this Hamiltonian the transition from the regular to the chaotic motion is observed by means of the Poincare mappings. Two different classes of non-planar periodic orbits are traced in both regular and irregular regions. The bifurcations and variation of the periodic motion with the change of the total energy parameter throughout the regular regime and into the chaotic regime are given together with the relevant frequencies. For both classes the stability/instability of the periodic orbits is studied by calculating the linearization matrix in the neighbourhood of the corresponding fixed points of the Poincare mappings. In one class, the class of orbits that approach very close to the nucleus, we have surprisingly found that a set of periodic orbits bifurcate from the same periodic orbit along the field at various values of the energy. These values are determined numerically. A repeated pattern of stability and instability of these orbits exists over decreasing intervals of energy until the escape energy is approached. All these periodic orbits are unstable beyond the ionization limit. On the other hand we have found that the bifurcation of the second class of orbits is, generally, generic. Three sets of the energy separation lines due to three types of periodic motions are given when B = 60 kG with m - 0. Other sets of lines are given for B = 42 kG with m = 0, m = -1 and m = -2. Many of these lines coincide with the spectral lines obtained experimentally by A. Holle et al (1986).The energy spacing 0.64 near the ionisation limit, which has been found recently in the experiments of Holle et al (1986) is due to one of the non-planar orbits. Other new predicted spacings arising from other orbits have been seen in high resolution experiments on atoms in external fields (Main et al 1986).

The present work has been carried out to investigate the dynamic properties of 3 He film adsorbed on an exfoliated graphite substrate, using pulsed NMR techniques. It has been found that the dipolar interaction is the dominant mechanism for the spin relaxation, although the effect of the grafoil local fields can not be ignored. The spin-lattice relaxation time T1 and the spin-spin relaxation time T2 which characterize the spin system were determined. The study has been concentrated on two phases. The registered phase and the solid phase. Some data were taken at the mixed phase which lies between them. Both relaxation times were determined as functions of monolayer capacity, frequency, temperature and spin orientations. For temperatures less than 2 K, the spins exhibit quantum motion behaviour. The frequency of this motion was determined and was found to be inversely proportional to the spin density. At the registered phase, the activation temperature was determined, where it was a maximum corresponding to perfect registry. Special attention was given to the T1 data at the minima in the solid phase since there the frequency of the motion is comparable to the Larmor frequency.

The interaction of HeII with a solid oscillating (20,34 and 48 MHz) boundary has been studied between 0.03K and T[lambda] by an experimental technique based on the measurements of the change in resonant frequency and Q factor of a shear-mode quartz crystal immersed in the liquid. The results show three separate aspects of this interaction. (i) Below 0.6K the measurements indicate a non-viscous mechanism which is attributed to the formation of a solid layer of 4He atoms on the crystal surface. Estimates of the total adsorbed areal density reveal it to be a monolayer, characterised by a thermal mobilisation energy of 0.15K. (ii) Measurements in the middle temperature region (0.6 T T[lambda]) are used to determine the (complex) transverse acoustic impedance and hence the effective viscosity of Hell. The data is at sufficiently high frequencies to observe the breakdown in hydrodynamics which occurs when the viscous wave penetration depth [delta] becomes comparable to the phonon and roton mean free paths. (iii) Very precise measurements of the change in Q factor near T[lambda] show that the viscous wave samples an enhanced normal fluid density next to the crystal surface when [delta] becomes smaller than [xi], the superfluid healing length. A simple model is developed for the viscous losses in this region which enables an estimate to be made of the amplitude and temperature dependence of [xi]. The results are found to be well described by a power law [xi] = [xi] = [xi]0 (1 - T/T[lambda])-2/3 where [xi]0 = 0.08 nm. The transverse acoustic impedance of a weakly interacting Fermi-liquid is derived from an exact solution of the Landau kinetic equation. Explicit computations for a Fermi-gas are presented.

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