Table of contents

For the evaluation of the so-called vibrational overlap integral in the theory of the relative intensities in a band system of a diatomic molecule various approximate methods have been proposed for obtaining the vibrational wave functions. The ` distorted wave ' method of Gaydon, Pearse and Pillow is here discussed. For the case of Morse oscillators an approximate method is suggested that enables the integrals to be evaluated semi-analytically. The method is applied to the calculation of the relative intensities of the second negative bands of O₂⁺ studied recently experimentally by Feast. A procedure for applying the WKB method to find the vibrational wave functions of an anharmonic oscillator is also given. A general exact relation involving the vibrational wave functions of two electronic states and their potentials is given which may be used as a check for the accuracy of the approximate wave functions obtained by various methods.

An approximate method has been used to calculate the elastic total and differential cross sections for p-d scattering, at incident proton energies of 150 and 240 MeV A nuclear interaction has been assumed of a type suggested by Jastrow, containing an infinite repulsive core in singlet two-body states Of the various phenomenological interactions, this agrees about the best with the high energy n-p and p-p scattering data The calculated angular distribution near 90°, in the centre-of-mass system, is found to be of the right order of magnitude, but agreement with experiment in the forward and backward directions is poor An explanation of this result is suggested.

The coherent scattering of high energy gamma-rays by bound electrons in light atoms is investigated. The bound intermediate states of the electron are expanded in terms of free states and potential scatterings. It is found that not only the zero-order term of this expansion, but also the first-order term, must be kept, and that the latter is actually the larger of the two for large momentum transfer.

Expressions are derived theoretically for the angular distribution of γ-radiation from a deuteron stripping reaction, measured in coincidence with a fixed direction of the emitted particle.

An electrostatic analyser of high accuracy has been used to measure and control the energy of a proton beam accelerated by an electrostatic generator. By using a deflecting angle of π/2radical2 radians, a wide incident beam was focused on to a narrow exit slit

Target currents of 10 μA were obtained homogeneous in energy to one part in a thousand The beam energies were also measured absolutely to this accuracy

The instrument was used to determine the energy of the ⁷L1(p,γ) resonance, which was found to be 441 5±0 5 keV with a half width of 12 2±0 5 keV The energies of two sharp resonances in fluorine were found to be 340 4±0 4 and 483 1±0 5 keV, with half widths 2 9±0 2 keV and 2 2±0 2 keV respectively

The neutron total cross sections of Be, Na, Mo and Hg have been measured in the energy region 1 eV to 10 keV, and of Th between 1 eV and 1 keV, using the Harwell linear accelerator time-of-flight spectrometer The energy resolution is better than in previously reported work on these elements, and several resonances have been more clearly resolved.

The emission of particles from a nucleus following the capture of a negative μ-meson is discussed using evaporation theory Assuming a reaction of the form μ^- + P → N + μ⁰, it is possible to calculate a distribution of nuclear excitation from which the mean probability of charged particle emission is evaluated

In the relation between excitation U and nuclear temperature τ the exponent of τ is given the values 2 and 3 The usual law U = λτ² is found to predict results for proton emission which are far less than those experimentally observed

In order to investigate this energy-temperature relationship data from low energy photo-disintegration experiments (U ≃ 20 MeV) have been compared with theoretical values Combination of the limited evidence available with very high energy data suggests a variation of excitation with the cube of the nuclear temperature

The Q-values of the reactions ³²S(α, p)³⁵Cl and ³⁵Cl(n, α)³²P were measured as -2 02±0.11 MeV and +1.07±0 15 MeV respectively. From these Q-values and from the β-decay energy of ³²P the difference in mass excess of ³²S and ³⁵Cl was calculated in two independent ways, giving 1 96±0 11 MeV and 1 98±0 15 MeV.

In the investigation of the (α, p) reaction the nuclear emulsion technique was used in conjunction with α-particles from ThC'. An ionization chamber was used to measure the α-particle energy in the case of the (n, α) reaction which was excited by fast neutrons obtained from the D-D process

Investigations on the M_IV and M_V absorption edges of four of the `light' rare earth elements are described, using a bent crystal focusing spectrometer. In particular, close attention has been paid to the occurrence of fine structure (`white lines') on the long wavelength side of the edge Such white lines are found at both edges for ⁵⁹Pr, ⁶⁰Nd, and ⁶²Sm, but for ⁶³Eu, while a white line is found at the M_V edge, it is absent or very weak at the M_IV edge

By the solution of Bloch's equation for the density matrix, a development is obtained suitable for the exact evaluation of the second virial coefficient near absolute zero Assuming a molecular interaction of the Lennard-Jones type, it is shown that the virial coefficient for helium is -{½(πβ)^3/2+31 15πβ+O(1)}ų, πβ=38 04/T

General formulae are given for fluids the molecules of which satisfy Bose or Fermi statistics

The thermal conductivities of polycrystalline alumina, beryllia and graphite have been measured between 2° K and room temperature The first two are dielectric solids but, even in the graphite specimens, the electronic contribution to the heat conduction is very small

It is shown that the phonon mean free path is limited by scattering at the crystallite boundaries at sufficiently low temperatures For sintered specimens of alumina and beryllia, in which the density is near the single crystal value, it appears that the mean free path can become greater than the crystallite size On the other hand there is no evidence that the mean free path can increase above the crystallite size in the graphite specimens, although in this case the interpretation of the results is more difficult

As a consequence of this restriction on the mean free path, graphite specimens with small crystallites are extremely good heat insulators at low temperatures, being better than a glass at temperatures below 5 to 10° K

A brief review is given of experimental results on the oriented overgrowth of very thin deposits of alkali halides evaporated on to cleavage surfaces The theoretical implications of some of these results are considered

On the assumption that second sound can be propagated through media other than helium II, its velocity is calculated for non-ideal gases, insulators, conductors, superconductors and ferromagnets