Table of contents

Extensive air showers have been recorded at sea level over a period of nine months. The data show a fairly good correlation between the shower rate and the air temperature at about one cascade unit above the apparatus, e.g. at the 950 mb. level. A temperature coefficient of -(0.38±0.11)% per °C. at this level is indicated. This may be explained by the dependence of the lateral spread of an extensive shower on the air density.

The disintegration by π^--meson capture of the elements helium and carbon is discussed. Two types of meson theory, scalar and pseudo-scalar, are considered. The relative probabilities of the various modes of disintegration of helium are calculated and the energy spectra of the most likely one, viz. proton emission, are shown. The disintegration of carbon into two α-particles and one singly charged particle is considered, using a simple α-particle model. The energy spectra and angular correlations of the α-particles obtained by a direct transition and by a transition via an excited state of ⁸Be are compared.

The range-energy relationship for protons of energies up to 12 MeV. in Ilford C2 dry emulsion has been determined with an accuracy better than 0.5% in energy. The particles were produced by bombarding a thin beryllium foil with deuterons having an energy of 8 MeV. The energy of the incident deuterons was obtained by a method which involves the measurement of the two angles of emission at which the two proton groups of longest range from the reaction ⁹Be(d, p)¹⁰Be have the same energy.

In an attempt to account theoretically for the lateral and angular development of the penetrating particles in high energy cosmic-ray showers, we have developed a method for deriving the differential from the total cross section, in the laboratory frame of reference. An integral equation is set up for the differential cross section, and solved assuming that the differential cross section in the centre-of-mass frame of reference is of the form R+S' cos² θ, where R and S' are functions of the incident and scattered energies only. Using a form of the total cross section derived from the analysis of high-energy cosmic-ray experiments, the mean square angle of scatter in a nucleon-nucleon collision has been calculated and found to be inversely proportional to the energy of the incident particle. The results are compared with experiments.

The radiation from a hollow-cathode tube containing rhodium was passed four times through an atomic beam of rhodium. Absorption was found in eight lines, four of which showed hyperfine structure doublets of separation 0.023 cm^-1. The splitting could be ascribed to the ground state 4d⁸ 5s ⁴F_9/2 It was concluded with certainty that the spin of the rhodium nucleus ¹⁰³₄₅Rh has the value I = ½. The relative intensities of the components show that the magnetic moment is negative. The observed splitting leads to an estimated value of μ = -0.10 nuclear magneton The values of I and μ indicate a configuration (5g_9/2)⁶3p_1/2 for the last seven protons of the rhodium nucleus in the Goeppert-Mayer model

Consideration is made of the predictions of the Bloch spin wave model within its region of approximate validity, for the magnetic scattering of very slow neutrons by a ferromagnetic It is found that observable peaks of intensity in the angular distribution of scattered neutrons occur due to spin wave absorption Neutrons are also scattered with phonon absorption and by an analogous calculation it can be shown that similar peaks occur due to this vibrational scattering. A possible method is suggested of differentiating between the two kinds of scattering in order to provide a check of the Bloch model

The Bethe method for order-disorder is applied to a lattice of magnetic dipoles with antiferromagnetic nearest-neighbour interactions. Magnetization and entropy are calculated for all values of temperature and magnetic field, and an anti-parallel ordered phase is found below a definite transition curve The computed curves agree qualitatively with those observed experimentally with certain paramagnetic salts at low temperatures.

Silver crystal surfaces which had been prepared by either electrolytic etching or electrolytic polishing were studied by means of the electron diffraction reflection technique. It was found that fine structure effects, in the form of split spots or streaks through spots, gave information concerning the topographies of the various surfaces of the crystals. The fine structure effects showed certain asymmetries which do not immediately follow from the Laue diffraction theory The possible causes of these asymmetries are discussed, and it is concluded that they were probably due to distortion of the silver crystals, but that some might have also been due to refraction effects.

A very general calculation has been made by Fröhlich giving the dielectric constant of a material in terms of the spontaneous fluctuations of the electric moment of the material which would occur in a field-free region. This calculation is now extended one step further so as to include the first term in the field dependence of the dielectric constant. By way of illustration the general theory is applied to Kirkwood's model for a dipolar liquid. (In order to preserve continuity of argument it has been found necessary to reproduce much of Fröhlich's work)