Table of contents

Measurements have been made of the mechanical reaction on a source of heat in liquid helium II. On the two-fluid model this reaction is due to the inertia of the fluids. The results are consistent with the predictions of the two-fluid model, although the conditions of the experiment were chosen so that dissipative effects were present which are not given by that model in its present form. This result gives experimental justification for retaining the two-fluid model under such conditions.

It is shown that many of the properties of liquid He₃, including its two changes of state, are predicted semi-quantitatively by a model in which one applied corrections of van der Waals type to the free energy of a perfect Fermi gas. Various other models are also discussed in the light of available experimental evidence.

Calculations are made of the first anisotropy coefficient K₁ and of the spectroscopic splitting factor g for nickel, based on the collective electron theory of the corresponding effects due to Brooks and the calculations of the author of the N(E) curve for the 3d electrons in nickel. Brooks' theory is reviewed, the underlying assumptions and approximations examined, some minor errors are corrected and it is extended to provide a formula for the gyromagnetic ratio g'. The value of - 5×10⁷ erg cm^-3 obtained for K₁ is considerably larger than the best available experimental value of - 8×10⁵ ergs cm^-3 for nickel at 0°K and Brooks' estimate of - 8×10⁵ erg cm^-3. The values of 2.14 and 1.84 are obtained for g and g' respectively as compared with experimental values of 2.19-2.42 and 1.93. Possible reasons for the discrepancies are discussed. Finally Brooks' theory is formally extended to remove one of the major approximations.

A method has been developed for estimating traces of light water in heavy water. The transmission of slow neutrons through a sample of the water is compared with that through a standard sample. The method gives an accuracy to 0.006% in the heavy water content after 3 hours' counting.

The magnetic susceptibility of nitric oxide enclosed in a β-quinol lattice has been measured at temperatures from 10°K to 300°K. The susceptibility, which obeys Curie's law at room temperature, approaches a temperature-independent value at low temperatures. This behaviour is compared with that predicted for the free gas by Van Vleck.

The emission spectra of GaF and InF may be excited conveniently in hot hollow-cathode tubes, the cathode containing a mixture of the respective metal with aluminium trifluoride. The emission spectra are similar to those observed in absorption, but many more bands of the ³Π-¹Σ systems of InF have been observed. The Ga isotope effect in GaF has been resolved, and improved constants are derived for the two molecules.

The oscillator strengths associated with the 1sσ_g-3pσ_u, 1sσ_g-4pσ_u, 1sσ_g-4fσ_u, 2pσ_u-2sσ_g, 2pσ_u-3sσ_g and 2pσ_u-3dσ_g transitions of H₂ + are computed from the exact two-centre wave functions. It is found that some of the transition integrals vary rapidly with the internuclear separation. The significance of this in connection with the calculation of relative intensities in band systems is briefly discussed. A comparison is made with the values of the oscillator strengths obtained using the 1.c.a.o. approximation.

The electron-capture decay of ²⁰⁷Bi has been studied by scintillation counter coincidence techniques. Gamma-rays of energy 0.57, 1.07, 1.76 and 2.47 MeV were found in the relative abundances 1.57: 1: 0.16: 0.0072. `Prompt' coincidences were observed between the three former and the K-capture x-ray. The following percentages of the gamma-rays were prompt: 0.57: 19%; 1.07:6%; 1.76:7%. There is some evidence for a prompt gamma-ray of 1.46 MeV. The 1.76 and 1.07 MeV gamma-rays are in coincidence with the 0.57 MeV gamma-ray. The results are discussed in relation to the level scheme of ²⁰⁷Pb.