Table of contents

This lecture is a study of some ways in which elementary-particle physics and nuclear-structure physics can complement each other. Each field can aid progress and understanding in the other, and knowledge from one field can be used as a technique for carrying out research in the other.

Theoretical expressions are derived for (³He, p) and (α, n) reactions, on the assumption that the reaction proceeds as a stripping process for both the projectile and the target nucleus. The resulting theoretical formulae are compared with some experimental data. Satisfactory agreement is observed.

The paper is concerned with the solution of the integro-differential equations of atomic scattering theory. In previous work, approximate analytic solutions have been obtained using variational methods and numerical solutions have been obtained by iteration. It is shown that rapid convergence may be obtained in an iteration-variation method in which the trial functions are linear combinations of the iterated functions. For scattering of slow electrons by hydrogen atoms the method gives four-figure accuracy with, at most, two iterations, compared with eight iterations required in previous work.

The formal theory of rearrangement collisions is investigated using correctly symmetrized wave functions. The resulting expression for the scattering amplitude is discussed using a generalized distorted-wave approximation. It is shown that the exchange amplitude known as heavy-particle stripping does not arise from a matrix element of the form discussed recently by Day et al. The possibility of a non-vanishing amplitude for heavy-particle stripping in the case of an infinitely massive target is briefly discussed.

The behaviour of cross sections in the neighbourhood of the 2s excitation threshold is investigated using M matrix theory. Calculations allowing for 1s-2s strong coupling are carried out for zero angular momentum in singlet, triplet and no-exchange cases. Threshold effects in all cases have the form of a cusp. A narrow resonance has been found below the threshold in the singlet case.

The force between a pair of molecules in a liquid arises in part indirectly on account of the interaction of either molecule with neighbouring molecules. The time dependence of this force, determined by the simultaneous movement of numerous molecules, is not readily determined by conventional methods of analytical mechanics. In this paper the thermal movement in a liquid is represented as a propagation of density waves. On the assumption that the coupling between these waves is weak, a simple expression for the specific heat is obtained in fair agreement with experiment. On account of coupling the waves are damped; the rate of damping is derived by low-order perturbation theory. The result is used for deriving the mean product of the intermolecular force at different times (correlation function). The time integral of the correlation function plays the part of a friction constant in Kirkwood's theory of transport processes. This constant is calculated and found to be in accordance with estimates from experiment. In addition, the use of density waves as dynamical variables is examined critically. It is found that for movement in one dimension the amplitudes of these waves are canonical variables of standard type.

In a previous paper a trial wave function of the form ψ = DII_i<if(x_ij) was used variationally to calculate the ground-state energy of an interacting electron gas, D being a determinant of plane waves and f(x_ij) a correlation function. In this work attention is focused on the nature of the wave function; in particular, the correlation function f(x_ij) and the pair distribution function are calculated and numerical results are presented for two widely different densities. In the course of this work, further light is thrown on the approximations made in the earlier energy calculations. Finally, the use of a wave function of the type ψ = II_i<jf(x_ij) in the calculation of the ground-state energy of a system of charged bosons is discussed and the exact high-density result of Foldy obtained.

To supplement Huby's rules in the Rayleigh-Schrödinger perturbation theory of non-degenerate discrete levels, an expression for the total number of terms contained in the nth order is derived. The number of terms in the nth order having v + 1 disconnected factors is also found.

The absorption coefficient of evaporated zinc sulphide has been measured between 0.27 and 0.60 μm. A kink has been found at 0.332 μm. The effects of cooling at liquid-air temperature and of ageing at 200 °C on the absorption curve have been measured. A comparison has been made with other published results. The Urbach rule for the long-wavelength tail of the absorption curve was found to be followed only by the average curve.

The influence of the Townsend-Ramsauer effect on the electron mobility, diffusion coefficient, mean energy and Townsend's alpha of hydrocarbon gases has been examined theoretically. In general it is shown that the Townsend-Ramsauer effect causes the mobility to decrease sharply with increase in electron mean energy giving rise to a drift velocity which is almost independent of the applied field; this plateau-like behaviour was experimentally observed by McGee and Jaeger in 1928. In the region in which the Townsend-Ramsauer effect prevails, the diffusion coefficient tends to remain constant and independent of the electron mean energy or the applied field. It is shown that, for gases exhibiting a Townsend-Ramsauer effect, the determination of reliable mean energy values as a function of E/p from swarm experiment data requires a knowledge of the total collision cross section and the electron energy distribution. The use of a Druyvesteyn distribution instead of a Maxwellian one appreciably reduces the mobility but hardly affects the diffusion coefficient. It is concluded from this and experimental evidence that the Maxwellian distribution does not hold for methane but may become more applicable as the molecular complexity of the hydrocarbons increases. The reasons for some of the discrepancies between theory and experiment are discussed.

Diffraction theory is applied to the case of the back-scattering of radio waves from rough surfaces, and leads to a mathematical formulation which expresses the amount of power scattered back towards the transmitter as a transform of the autocorrelation function of the wave reflected from the surface. The formulation is somewhat similar to that for the case of diffraction by a thin phase-changing screen, but differs in detail and in application. When applied to the case of the scattering of radio waves by the lunar surface it is found that agreement can be obtained with the experimental data, but this requires the inclusion of a `uniformly bright' component which is consistent with shadowing. The statistical distribution of the lunar surface, which is not normal, is derived from the analysis, and, though the radio results are complementary to the other observations at optical wavelengths, they are shown to be in general agreement.

A simple statistical model of the large-scale irregularities of the moon's surface is described, which gives agreement with the main features of lunar radio reflections.

Space-charge-limited current in solids has been studied experimentally in crystals of cadmium sulphide. Accurate compensation of trapping defects has been achieved and the fundamental Child's square law for solids has been verified experimentally over a temperature range from 77° to 400 °K.

Under space-charge-limited conditions the density of charge carriers available for current is independent of temperature; current is proportional to carrier mobility and provides a means of studying this quantity directly. By observing Child's law over the whole temperature and voltage range of interest it may be ensured that true space-charge-limited conditions are existing and consequently that reliable and accurate information is obtained.

An insulator crystal provided with an emitting contact and a collector contact forms a dielectric diode. The emitting contact is a space-charge cloud of mobile carriers which is experimentally reproducible and is amenable to quantitative theoretical description; accordingly, the experimental characteristics of the diode are determined by the physical nature of the collector contact which is made in the normal manner. It is therefore possible to investigate experimentally the properties of a single contact. Rectification characteristics have been measured and compared with theory for a number of diodes over ranges of current covering nine orders of magnitude. The straightforward concept of a contact as two different sets of energy levels simply butted together is remarkably well vindicated.

The magnetic susceptibilities, electrical resistivities and lattice parameters of a range of binary alloys of palladium containing up to 20 at.% of vanadium, niobium, tantalum, zirconium or molybdenum have been measured and the results are compared with the predictions of a simple band model.

An examination is made of the effects of heating chlorophaeite extracted from Icelandic rocks to around 600 °c. The mineral is shown to be transformed to a more strongly magnetic form in the heating process. The evidence suggests that this is due to the breakdown of the chlorophaeite to an impure haematite.

Chlorophaeite extracted from some Indian lava flows is shown to behave in a similar manner. Several of the criteria and techniques of rock magnetism are critically examined in the light of these results.

The authors have studied the change in modulation of an amplitude-modulated electromagnetic wave in a Lorentzian plasma by using the geometrical-optics approximation as well as the wave equation. Expressions for the quadratic dependence of the conductivity on the amplitude of the electric vector have been obtained and used in the present investigation. A critical comparison of the results obtained by the two methods has been made.

The methods used to determine the shape of the imaginary (or absorbing) part of the nuclear optical potential by phenomenological analyses of the experimental data on nucleon-nucleus elastic scattering are critically examined. A detailed analysis is made of the data on the elastic scattering of 7.5 and 9.75 MeV protons by copper, and it is found that the radius of the absorbing part of the potential is about one fermi greater than that of the real part. All the low-energy data reviewed are consistent with this, and with the theoretical calculations of the absorbing potential. Phenomenological optical model analyses are insensitive to the absorption in the nuclear interior, and at present are not sufficiently accurate to determine it.

The coefficients of viscosity and thermal conductivity of the binary gas mixtures argon-neon, argon-helium and neon-helium, have been determined over the full range of composition of each mixture at a pressure of 70 cm of mercury and at a temperature in the range 18.0 to 18.3 °C. The experimental values are compared with theoretical values based on the Lennard-Jones (6-12) potential of interaction between molecules. There are small discrepancies between some of the measurements given here and those of other workers. Agreement between the experimental and theoretical results is not complete.

Expressions have been derived for the optical birefringence and elastic moduli of an idealized semicrystalline polymer in terms of the molecular orientation. The predicted birefringence and moduli show qualitative agreement with previous experimental data for polyethylene at low extension ratios. A result of particular interest is that this treatment predicts the observed minimum in the Young's modulus with increasing orientation.