Table of contents

The elastic scattering of neutrons by deuterons at energies less than 166 MeV incident neutron energy has been calculated using a scattering equation similar to that of Buckingham and Massey and a central nuclear potential with Gaussian form. Five values of the effective range are considered, covering all values of physical significance. For analytical convenience, a deuteron wave function consisting of two Gaussians is used, the deuteron binding energy being minimized with respect to three parameters. S and P phases for several energies were evaluated with the aid of electronic computers (Pilot ACE and DEUCE) for Serber, ordinary and symmetrical exchange forces. From the total cross section below 2 MeV it appears that the potentials of larger effective range agree best with experiment, although the doublet scattering length considerably exceeds the experimentally estimated value for all these potentials, probably because of polarization effects at low energies. From the P phases, conclusions are drawn about the validity of the Born approximation used by Christian and Gammel. The problem is then resolved for the short range potential using an adaptation of the variational methods of Hulthén and Kohn. The results at low energies compare favourably with the exact solution obtained previously. It therefore seems that the variational method may be used successfully when polarization of the deuteron is explicitly allowed for, and further calculations including this effect and using the Kohn method are in progress.

We have derived from the Boltzmann equation a new integral equation governing the slowing down of neutrons in a homogeneous mixture of atoms. The new equation reflects a view of the neutrons as propagating down the energy scale, whereas the Boltzmann equation expresses a collision balance. Unlike the Boltzmann equation the new equation lends itself to approximate solution by iteration and to the construction of an accurate variational principle for p, the resonance escape probability. Some numerical results are given.

The available theoretical values of the oscillator strengths of dipole transitions from the ground state of helium are modified so that they satisfy four different sum rules. They are then employed to evaluate the refractive index, the Verdet constant, the diamagnetic susceptibility, the Lamb shift, the average energy loss for fast particle impact and the van der Waals interaction between two helium atoms, good agreement being obtained with experimental data where comparison is possible.

The Landau-Zener formula for the transition probability arising from the pseudo-crossing of potential energy curves is used to investigate charge transfer processes of the type A + B³⁺ → A⁺ + B²⁺ involving neutral helium atoms and triply charged ions of Be, Li, Al and Mg.

In addition, a method based on the Landau-Zener formula involving one experimentally determined parameter is used to calculate cross sections for processes of the type A + B²⁺ → A⁺ + B⁺. Good agreement is found with the cross sections obtained in the laboratory by Hasted and Smith for N²⁺ ions in He and Ne, and for A²⁺ ions in Ne.

A technique is described in which a heavily loaded flash discharge is employed as a background source for observation of absorption spectra, when the absorbing gas column is strongly excited and, therefore, itself brightly luminous. Examples of the absorption spectra of the plasmas of several arc discharges, of both open and screw-stabilized type, are reproduced. Photometric determination of the total absorption under a number of lines, combined with relative emission intensities, yield values of line-reversal temperatures; some first results are reported for copper arcs.

A study has been made of some of the active products from the high energy bombardment of carbon, nitrogen, oxygen and fluorine. The ratios of cross sections to the ¹²C(p, pn)¹¹C cross section were found and the excitation functions estimated. Deviations from a monotonic decrease of cross section with energy for some reactions have been found and are discussed. Evidence exists for a marked dependence of the (p, pn) cross section on the energy level structure of the residual nucleus.