Table of contents

A distinction is made between the surface Helmholtz free energy F, and the surface tension γ. The surface energy is the work necessary to form unit area of surface by a process of division: the surface tension is the tangential stress (force per unit length) in the surface layer; this stress must be balanced either by external forces or by volume stresses in the body.

The surface tension of a crystal face is related to the surface free energy by the relation γ=F+A(dF/dA), where A is the area of the surface. For a one-component liquid, surface free energy and tension are equal. For crystals the surface tension is not equal to the surface energy. The standard thermodynamic formulae of surface physics are reviewed, and it is found that the surface free energy appears in the expression for the equilibrium contact angle, and in the Kelvin expression for the excess vapour pressure of small drops, but that the surface tension appears in the expression for the difference in pressure between the two sides of a curved surface.

The surface tensions of inert-gas and alkali-halide crystals are calculated from expressions for their surface energies and are found to be negative. The surface tensions of homopolar crystals are zero if it is possible to neglect the interaction between atoms that are not nearest neighbours.

The effect of temperature on the counting rate-voltage characteristics of self-quenching Geiger-Müller counters with internal and external cathodes (in this paper denoted as counters Nos. 1 and 2) has been investigated within the temperatures ranging from 8° to 60° C.

It is found that the average counting rate remains independent of temperature (within the statistical error limits), and this constancy is better in the case of the external cathode counter than with the other. As counter No 1 shows a greater increase in slope at higher temperatures, the rate appears to be greater at higher applied potentials. Further, it is noticed that the plateau decreases and disappears at lower temperatures in the case of counter No 1, while counter No 2 does not show this effect. This is partly explained by the formation of semiconducting paths between the central wire and the cathode, the discharges along which give rise to spurious counts in the case of counter No 1, and the absence of these in the case of counter No 2.

It is also observed that the slope of the plateau increases and the width decreases with rise of temperature in both cases, though the increase in slope is more marked with counter No 1 than with counter No 2. The increase in slope is probably due to the presence of a greater number of multiple discharges or spurious counts at higher-temperatures, an important point which is under study.

The investigation also brings about the advantage of the external cathode in the construction and design of G-M counters, especially when reliable observations are desired with a counter under widely changing temperature conditions.

The relation between the line-width of the 0-3 vibration-rotation band of HCN at 10380 Å. and the pressure of the HCN gas, as well as the pressure resulting from the addition of different extraneous gases, was investigated. In the P and R branches of the band a relation was found between the half-line width and the rotational quantum number, J, which differs for the broadening due to self-pressure and the broadening resulting from pressure of extraneous gases. The results could be explained, according to London's theory, in the former case as an effect due to the combined action of rotational resonance alignment, and in the latter case to alignment alone. Measurements made with the addition of DCN suggest that the chain association of the hydrogen bridge bonds also has an effect on the half-width value.

The 2-0, 3-0 and 4-0 bands of ¹H¹⁹F, the 4-0 and 5-0 bands of ¹H³⁵Cl and ¹H³⁷Cl, the 4-0 band of ¹H⁷⁹Br and ¹H⁸¹Br, and the 4-0 band of ¹H¹²⁷I were photographed under great dispersion in the infra-red. The molecular constants have been calculated and are summarized in a table.

A new numerical procedure, based on relaxation methods, for calculating the correction for instrumental broadening in x-ray diffraction lines has been evolved. The corrected integral breadth and the true line profile are obtained without restrictive assumptions. The calculations for a practical example are given.

The absorption due to the inversion spectrum of ammonia has been studied at pressures up to 6 atmospheres between wavelengths of 8 cm. and 8 mm. The resonant frequency is found to shift downwards from 0.78 cm^-1 as the pressure rises, becoming substantially zero above 2 atmospheres. The line width rises less rapidly than the pressure in the transition region, but ultimately becomes proportional to the pressure with an effective ` collision diameter ' of 7.7 A. These effects are attributed to multiple collisions, which become dominant at the higher pressures; the resonant inversion is then destroyed by the molecular interaction.

In the methyl halides the inversion frequency is virtually zero owing to the low probability of tunnelling through the barrier, but the absorption line is spread out to the centimetre wave region by the collision process. The collision diameters are found to be 7.7 A. and 9.0 A. for methyl chloride and bromide respectively.

The neutrons from deuteron bombardment of a separated ⁶Li target have been studied by the photographic plate method. The energy release for the reaction ⁶₃Li + ²₁D → ⁷₄Be + ¹₀n has been shown to be 3.40 ± 0.05 MeV., and evidence is given for the existence of a level in ⁷Be at 450 ± 60 keV. This is identified with the level at 430 keV. found in work on the reaction ¹⁰B(pα)⁷Be.

Nuclear evaporation theory predicts that the mean energy of the protons evaporated from disintegration stars should increase with star size. It is shown that the calculated rate of increase is in agreement with experimental results.

The scattering and the consequent depolarization of a polarized beam of neutrons by an unpolarized proton gas is suggested as a means of obtaining information about the interaction potential between a neutron and a proton. It is found that the interaction, if it were spherically symmetrical, could be determined from a knowledge of the polarization and scattering differential cross sections. A similar analysis with non-central interaction has not yet been carried out. In this case, however, the polarization depends also on the azimuth Φ of scattering. This dependence of polarization on Φ is calculated for (a) very low energies, (b) very high energies. The maximum azimuthal variations for incident neutrons of energy 1 MeV. and 100 MeV. are about 1% and 50% respectively.

It is hoped that in future experimental techniques for the production and measurement of a polarized beam of fast neutrons will be developed, since these would give important information about the interaction potential between a neutron and a proton.

The general direct coupling between four fermions is studied. It is a linear combination of the five invariants used in β-decay theory. Altering the order of the particles in the Hamiltonian changes only the coefficients of the linear combination. The formalism of charge conjugation is used with the ordinary theory or the Majorana abbreviated theory for neutral particles. This is applied to the study of the decay of the μ-meson into an electron and two neutrinos.

A new isotope of dysprosium, identified as ¹⁶⁶Dy, has been studied. It has been shown that it is formed by thermal neutron capture in the 140 minute isomer of ¹⁶⁵Dy, the capture cross section being about 1,200 barns. It decays with a half-life of 82 hours and is the parent of 27 hour ¹⁶⁶Ho. It emits beta-particles, the energy of which was found by absorption in aluminium to be 0.22 MeV., and gamma rays of less than 50 keV. energy.

Another new isotope, ¹⁵⁹Dy, has been made both by slow neutron irradiation of dysprosium and by deuteron bombardment of terbium. It decays by orbital electron capture, with a half-life greater than 50 days. It will be described in a later paper.