Table of contents

The theory of the absorption of light by photo-excitation of the valency electrons in cubic metals is developed. The matrix elements vanish when calculated with respect to the Wigner-Seitz approximate wave functions for the occupied states in the first band, and free electron wave functions for the states in the higher bands. Calculations of the contribution to the absorbing powers of the alkali metals due to photo-excitation are made, using the approximation of nearly free electrons to obtain all the unperturbed wave functions. The calculated values for sodium, potassium and rubidium agree quite well with those observed if the first non-vanishing Fourier coefficient of the self-consistent potential field has the values 0.323, 0.305 and 0.350 eV. respectively.

A method previously used for `distorting' the wave functions of a simple harmonic oscillator to fit the potential curve for a particular electronic state has been modified, giving wave functions for the vibrational states which are close approximations to those of Morse, with comparatively little labour The transition probabilities obtained from these functions are compared with experimental values for the first negative bands of N₂⁺, the Swan bands of C₂, the CN violet bands, and the α-system of BO.

Some theorems concerning the free energy of the electric double layer of a collodial particle in a dilute sol are developed by making use of the Poisson-Boltzmann equation. It is shown that this free energy can be derived by employing the fictitious process of charging the excess ions in the double layer and that the surface density of ions may be an arbitrary function of the degree of charging. By integrating with respect to the charging parameter at constant surface density of ions we obtain an alternative form for the free energy which is expressed in terms of the electrostatic energy of the double layer and the excess osmotic pressure in the diffuse layer. The latter expression for the energy can also be derived by attributing to each volume element in the diffuse layer an energy term due to the thermal motion of the ions and an (electrostatic) field energy term.

The conversion and Auger electrons of Radium D have been studied in a lens β-ray spectrometer with a post-focusing electron accelerator. The number of conversion electrons due to the 46.7 keV. γ-ray is found to be 59.2 ± 5 per hundred disintegrations but reasons are given which suggest that this value be regarded as a lower limit. The Auger electrons have been compared with those resulting from the ThB-ThC transition.

A proton recoil chamber with a thick polythene layer was used to determine the angular distribution of the neutrons from thick targets of various light elements bombarded with 8 MeV. deuterons. In all cases a pronounced forward maximum in intensity was found, the half width of the distribution decreasing with increasing atomic number. The absolute intensity of neutrons in the forward direction decreases as the atomic number increases but the dependence on atomic number is not a smooth function. Most elements show the presence of multiple forward peaks. In a few elements the effect of reducing the incident deuteron energy was investigated.

Neon gas of normal isotopic constitution was bombarded by 7.8 MeV. deuterons from the Liverpool University cyclotron Photographic plates were used as detectors, enabling the protons from the reactions ²⁰Ne(d, p) and ²²Ne(d, p) and alphaparticles from ²⁰Ne(d, α) and ²²Ne(d, α) to be studied, as well as a group of inelastically scattered deuterons

Results are presented both for the fluctuation and distribution of electrons in electron-photon cascade shower theory. The results were obtained in approximation A and are for the case of a single primary electron giving rise to the shower

A calculation has been made of the ferromagnetic properties of a system of electrons using plane wave functions and Bloch exchange integrals. Our results show that below a critical temperature T_c the spontaneous magnetization decreases slowly with increasing temperature. At T_c the magnetization drops suddenly to zero as if a change of phase were taking place and there is therefore a latent heat of demagnetization at this temperature. Above T_c the model is paramagnetic. The reasons for the differences between the results and those obtained by experiment and on Stoner's theory of collective electron ferromagnetism are discussed, and the possibility that they may be due to the neglect of positional correlations among the electrons is considered.

The velocity u₁ of ordinary sound in liquid helium has been measured in the temperature range from 1.2° K. to 4.2° K Its value extrapolated to 0° K. is compared with the velocity u₂ of second sound at 0.1° K. and a slight departure from the Landau relation u₂ = u₁/√3 is indicated. The behaviour of u₁ in the neighbourhood of the λ-point has been studied in detail

A study has been made of the isothermal, pressure-induced flow of liquid helium II through glass capillaries of bore between 2.6 × 10^-3 and 4 × 10^-2 cm. The critical velocity is found to be less than 1 cm. sec^-1 except, possibly, in the case of the finest capillary. The theory that there is a force of mutual friction between the normal and superfluid components predicts the correct order of magnitude for the flow velocities, but there are discrepancies which suggest the existence of some other source of friction.