Table of contents

The optical model of the nucleus has been used with the phase shift method of calculate the scattering of 340 MeV neutrons and protons in carbon and lead, and of 4, 14, 36 and 100 MeV neutrons in nitrogen, for different forms of potential well and with different amounts of nuclear absorption. The results are used to establish the range of validity of the approximations of Born, of Montroll and Greenberg, and of Fernbach, Serber and Taylor. The latter gives remarkably accurate values over a wide energy range for the total elastic and absorption cross sections and forward elastic scattering. It is the only approximation which gives a satisfactory account of the effect of absorption. Unfortunately it does not give the angular distribution simply, and the most accurate approximation which does so, that of Montroll and Greenberg, has a very limited range of validity. Comparison with the experimental angular distributions of 340 MeV protons in carbon and lead leads to limited conclusions about the nuclear potential. An approximate calculation of the angular distribution of the scattering of 22 MeV α-particles in silver and lead indicates that the optical model can account for the observed results in terms of a rounded-off potential well.

The photoelectrically measured intensities and depolarization ratios of the Raman lines of liquid benzene, hexadeuterobenzene and sym.-trideutero-benzene are interpreted in terms of the normal coordinates and the polarizability gradients. Preferred choices are indicated, where sign ambiguities lead to alternative solutions, and the polarizability gradients are:

partial differentialαxx/partial differentialS1= +6.7A2	partial differentialαzz/partial differentialS1= +1.9A2	partial differentialαxx/partial differentialS2= +4.7A2
partial differentialαzz/partial differentialS2= +0.3A2	partial differentialαxx/partial differentialS6a= +1.16A2	partial differentialαxx/partial differentialS7a= +1.17A2
partial differentialαxx/partial differentialS8a= -1.14A2	partial differentialαxx/partial differentialS9a= +0.25A2	partial differentialαx*z*/partial differentialα10a = +0.050A2

Tables show the agreement between experiment and calculation. Bond polarizability gradients are deduced and the reasons for incomplete agreement are discussed.

When measuring elastic scattering of gamma rays, the secondary radiation from the scatterer, such as bremsstrahlung from photo- and Compton electrons and annihilation radiation, must be considered. It is shown that this secondary radiation is predominant in many experiments reported on elastic scattering of gamma rays.

A measurement of the large angle scattering of 1.33 MeV gamma rays by lead is described. It is found that the elastic scattering cross sections at 90° and 120° are, without corrections, 1.7×10^-28 cm² sterad^-1 and 1.6×10^-28 cm² sterad^-1 respectively.

The first result is already below the combined effect of Rayleigh and Thomson scattering as calculated by Bethe, and both must contain contributions from bremsstrahlung etc. that can be estimated only roughly but are appreciable. The present experiments therefore support the destructive interference of Delbruck scattering with the Rayleigh and Thomson components.

In the augmented plane wave method, and in an earlier related method, both due to Slater, the wave functions in a crystal are expressed in terms of spherical harmonics and radial functions around each atom, and of plane waves between the atoms. Convergence in these two methods with respect to the addition of l values near the atoms is discussed in the light of a variation principle which involves an arbitrary parameter. It is shown that this convergence is likely to be improved by calculating the matrix elements in a way slightly different from that given by Slater. This is illustrated by a simple example. A new method, of the same general kind, is suggested, which has some advantages over the other two methods.

A method for calculating the x-ray emission intensity from thick targets as a function of the target atomic number, accelerating voltage and angle of emission has been devised, and applied to the emission of the radiation from Ag, Cu, Cr and Al. These calculations have involved a discussion of the penetration of electrons into metals and a convenient expression for the range of low energy electrons has been obtained. The theoretical emission of Cu Kα radiation has been compared with some experimental observations on emission at small angles to the target surface, with results which are satisfactory within certain limits. The bearing of these results on the design of x-ray sources, particularly for low-angle diffraction apparatus is discussed.