Table of contents

The method is based on the simplifying features of helium-like ions and on the rapid establishment of equilibrium between the processes of populating and de-populating the 2³P₂ level The specific mtensity of the emission line 2³S₁-2³P₂ can then be deduced as a function of the electron temperature. In order to test the basic assumption that the electron velocity distribution is Maxwellian for the very fast electrons which produce the atomic excitation, more than one member of the iso-electronic sequence must be studied. Also, an expression containing the relative emission from two members of the sequence eliminates the electron concentration which can only be estimated at present.

The intensities of C V and BIV lines from SCEPTRE IIIA were measured with a combination of a monochromator and a photomultiplier. A carbon arc was used to calibrate the intensities absolutely, and the spatial intensity distribution was determined by means of the Abel integral equation. For typical discharge conditions, the maximum electron temperature attained was in the range (2-3) × 10⁵degK The electron temperature was unaltered by the introduction of the methane. The results suggest that any existing departure from a Maxwellian distribution of electron velocities did not seriously affect the value of electron temperature derived by this method.

A simple and rapid procedure is described for the correction of line shapes observed in any branch of spectroscopy, for distortions governed by the equation

f(x₀) = ∫^∞_-∞g(x)h(x₀ - x)dx

where f(x) is the observed line shape, g(x) the true line shape and h(x) an instrumental or intrinsic broadening function, provided that the moments of h(x) are finite As an illustration the method is applied to the case of the distortion, inherent in the modulation technique, of magnetic resonance spectra. Formulae for the correction of moments of lines are also given.

A measurement is described of the polarization in neutron-proton scattering at an effective neutron energy of 77 MeV. The beam of polarized neutrons was produced by proton irradiation of a beryllium target. The neutrons emerging at a production angle of 55° were 23.7 ± 1 8% polarized, the beam polarization being measured by using the calculable polarization dependence of small angle scattering from uranium. In the neutron-proton experiment, an angular range from 20.6° to 159.2° was covered detecting either scattered neutrons or recoil protons. The polarization effects are large and there is a marked difference between the present results and those obtained previously at 95 MeV. A broad neutron spectrum was used extending from 50 MeV to 130 MeV but arguments are advanced to establish that the spectrum does not seriously vitiate the validity of the results.

It is shown how the Hamiltonian equations for a ray in an anisotropic medium can be used on an electronic computer to calculate ray paths in three dimensions in a model ionosphere. A programme has been written for a digital computer and some ray paths have been calculated.

Electron diffraction patterns have been taken from a large variety of natural single crystals of α-Fe₂O₃ (haematite) which had previously been heated to 500°C. Some of these showed additional patterns similar to those observed by Finch and Sinha in 1957. Measurements of the basic plane spacings associated with the extra patterns showed that these differed considerably from the corresponding basic plane spacings of α-Fe₂O₃. This result is in contradiction to the findings of Finch and Sinha who claimed that the basic plane spacings associated with the extra patterns approximated closely to those of α-Fe₂O₃. There is therefore no justification for assuming that a new form of Fe₂O₃ (β-Fe₂O₃) exists.

Experiments were also carried out on crystals of α-Fe₂O₃ which had been heated to temperatures between 700° and 1000°C. In some cases oriented layers of Fe₃O₄ (magnetite) were observed but no evidence was found for the presence of γ-Fe₂O₃ (maghemite) in contrast to the results of Finch and Sinha These investigators claimed that γ-Fe₂O₃ was formed when α-Fe₂O₃ crystals were heated in air to temperatures above 700 C.

The stability of a cylindrical jet of incompressible inviscid liquid in the presence of a longitudinal electric field is investigated. It is shown that the electric field increases the stability of the jet. For given values of electric field, the wavelength of the disturbance at which the instability sets in and the wavelength which has maximum rate of instability are calculated.

The stopping powers of atomic hydrogen towards beams of protons, neutral hydrogen atoms and negative hydrogen ions are computed for beam energies up to 100eV.

The properties of high pressure neon flash-tubes suitable for the detection of cosmic rays are described. The tubes have high efficiency for flashing after traversal by ionizing particles, short sensitive time and low rate of spurious flashing A search for an ageing effect has been made by subjecting each of a batch of tubes to 10⁶ flashes; no important deterioration in performance has been found.

Using simple assumptions, the expected efficiency of neon flash-tubes (Conversi counters) is calculated as a function of time delay and numerical results are given, subject to one adjustable parameter. Satisfactory agreement with experiment is obtained, and the diffusion coefficient for thermal electrons in neon at 1 atmosphere and 20°C is found to be 1800±100 cm² sec^-1.

Resistivity values, and some absolute thermoelectric powers, for pure metals and semiconductors at and above the melting point are collected and tabulated. Theories of the change in resistance on melting are discussed in relation to the subdivision of the melting entropy into vibrational and structural parts.

The principles underlying Moffitt's method of atoms in molecules and Hurley's intra-atomic correlation correction are examined with the minimum of mathematical analysis, initially by reference to a wave function not involving configuration interaction (the simplest wave function for the lowest ¹Σ⁺_u state of the hydrogen molecule). Because of variational difficulties in more complex systems, and difficulties of interpretation in all systems, it is suggested that the evidence which Hurley has presented in support of asymptotic energy adjustments, convincing though it seems, should not be taken to justify the use of the intra-atomic correlation correction as a means of improving molecular wave functions.

An assessment is given of the various types of thermonuclear device based on shock heating. The classical shock heating process in which the mean free path in the shocked gas is much smaller than the dimensions of the apparatus is analysed and it is shown that shock heating alone is unlikely to yield temperatures in excess of the order of 3 × 10⁶ deg K with present day techniques. The temperature may be increased in principle to a value required for power production by isentropic compression after the shock heating phase. The so-called Z pinch types of apparatus are limited by the growth of instabilities whereas the θ pinch devices are limited by the difficulty of recovering energy without undue ohmic losses.

In a previous paper (Champion 1958) a calculation was made of the optical anisotropy due to shearing a simple liquid. A coaxial cylinder apparatus suitable for the measurement of the streaming birefringence of pure liquids at very high velocity gradients (50 000 sec^-1) was constructed in order to test this calculation experimentally. A new experimental technique to enable a weak birefringence to be measured was developed, the liquid being sheared for the shortest possible time (similar 10 sec), so that the heating effects within the liquid were negligibly small. Measurements on ethyl cinnamate, chloroform and carbon tetrachloride are described and for the tetrahedral molecule (CCl₄) there is a favourable agreement between experiment and theory. This agreement shows that the assumptions made and the conclusions drawn in the previous paper are reasonable.

In the instrument described, collimated light from the lens which is being tested is directed into a triangular path interferometer in which the two beams are sheared by tilting a single, parallel plate, while the path difference between them is varied linearly with time, over a range of one wavelength, by means of a polarizing system. The modulus and argument of the frequency response of the lens are obtained directly from the amplitude and phase of the resultant sinusoidal variation of the total flux in the interference pattern.