Table of contents

The energy levels of the magnesium isotopes of mass 25 to 28 inclusive have been measured with a broad-range magnetic spectrograph using a variety of deuteron and triton induced nuclear reactions. The following is a list of the reactions used to study each magnesium isotope together with the number of levels observed below a particular excitation energy:

25Mg	24Mg(d, p)25Mg	54 levels below 7.64 MeV
	27Al(d, α)25Mg	54 levels below 7.64 MeV
26Mg	25Mg(d, p)26Mg	49 levels below 8.617 MeV
	24Mg(t, p)26Mg	63 levels below 9.370 MeV
	27Al(t, α)26Mg	87 levels below 10.515 MeV
27Mg	26Mg(d, p)27Mg	18 levels below 5.017 MeV
	25Mg(t, p)27Mg	42 levels below 7.031 MeV
28Mg	26Mg(t, p)28Mg	19 levels below 6.759 MeV

The ground state Q-values of the above reactions were also measured.

Crystals of β-In₂ S₃ have been studied under the polarizing microscope and by x-ray diffraction. Optical examination has shown that the crystals are twinned, and the relative orientations of the twin components have been determined by rotation and oscillation x-ray photographs. The diffraction data have also confirmed the body-centred tetragonal cell proposed by Rooymans. Assuming that the material has a spinel structure, deficient in cations, it follows that twinning takes place when a redistribution in the tetrahedrally occupied sites occurs.

Modifications to the Manchester counter spectrograph are described which have permitted the momentum measurement of single cosmic ray particles to a maximum detectable momentum of 1000 GeV/c. The measured output of the instrument was 20 particles per day of which approximately 50% had momentum exceeding 10 GeV/c and 2% exceeding 100 GeV/c.

The momentum spectrum of single cosmic ray muons arriving at sea level in the north-south plane at 57° N geomagnetic latitude has been measured for near vertical incidence. Results are given which cover the momentum range 5 GeV/c<p< 1000 GeV/c, and together with the earlier work of Owen and Wilson form a continuous spectrum from 0.5 GeV/c to 1000 GeV/c. The high momentum work is based on 1800 particles of momentum greater than 10 GeV/c.

The charge ratio of single muons arriving at sea level has been measured, for near vertical incidence, to an upper momentum limit of 100 GeV/c. The measurements are compared with those of other workers and together show evidence for a maximum in the sea level charge ratio in the momentum range 3 GeV/c to 7 GeV/c.

Germanium shows at liquid helium temperature a very strong rise in conductivity with field strength at about 2 v cm^-1. This process has been investigated theoretically on the basis of electron temperature concept. The variation of the density of electrons with field is calculated considering excitation of donors into the conduction band by impact ionization and phonon absorption as well as reverse processes. It is shown that the current, though strongly field dependent, is always stable and an expression for current density as an explicit function of the field strength is obtained. Good agreement with experiments supports the validity of this theory.

It is shown that Bloch's solution for the nth order perturbation of the energy and the eigenvector in the Rayleigh-Schrödinger perturbation theory of non-degenerate, discrete levels can be expressed in a different form, of a kind suggested by Brueckner, and some advantages of the latter form are presented.

A résumé is given of how accurately perturbation theory (using a ground-state hydrogen-like atom perturbed by a point charge) predicts the 1sσ and 2pσ energies of H₂⁺ and HeH²⁺. Corresponding delta-function models are discussed; here it is possible to test the convergence of the perturbation expansions. The models indicate that the series for the 1sσ energy is divergent for H₂⁺ at large values of the internuclear separation R but convergent for HeH²⁺; this explains why the H₂⁺ series is inaccurate and the HeH²⁺ series accurate. Both series converge for small R. The 2pσ energies are represented by divergent series which are asymptotically convergent if R is sufficiently large. A `resonance' correction is justified for the H₂⁺ series, giving an accurate 1sσ energy for all R and an improved 2pσ energy.

This paper is concerned with the derivation of the radial equations for positron-hydrogen atom collisions from the continuous state Hartree - Fock equations. The angular coefficients are expressed in terms of vector addition coefficients and Racah coefficients for any angular momentum state of the atomic systems: positronium and atomic hydrogen.

The boundary conditions are written in terms of the S-matrix and expressions are obtained for total and differential cross sections.

The univalent ions Fe¹⁺, Co¹⁺ and Ni¹⁺ have been produced by ultra-violet or X-irradiation of impure MgO crystals. The electron spin resonance spectra of these ions are compared with those of the isoelectronic ions Co²⁺, N1²⁺ and Cu²⁺ which they resemble closely. The spectra of Fe¹⁺, Co¹⁺ and Ni²⁺ show line-width effects which may be interpreted as being due to the presence of small distortions in the cubic crystal lattice. A detailed report of the 3d⁹ configuration in a cubic field is given. There is a transition at low temperature from an isotropic to an anisotropic spectrum, presumably due to the `freezing in' of Jahn-Teller distortions. Observation of hyperfine structure from ⁶¹Ni has made it possible to estimate the nuclear moment by comparison with the observed hyperfine structure from Co¹⁺. The ease of formation and stability of these univalent ions is shown to be related to the concentration of positive ion vacancies and to the concentration of trapped hole centres.

The experimental conditions which have to be satisfied in order to measure ionization coefficients accurately at high values of the parameter pd (pressure x gap distance) are assessed. In an apparatus designed to fulfil these conditions, precision measurements were carried out for uniform electric fields E in air at values of the parameter pd up to 2300 mm Hg cm, which corresponds to a sparking potential of about 80 kv, thus extending the range so far investigated by Llewellyn Jones and Parker in 1950 and 1952. The results show that prebreakdown ionization growth in air is due to the action of primary (α) and secondary (ω) ionization processes modified by the process of attachment a, and that significant space charge effects were absent. At a value of pd of 2300 mm Hg cm the sparking potential calculated (81 ± 1.5 kv) from the criterion (expressed in terms of the ionization and attachment coefficients) which gives the static sparking potential was in agreement, within the experimental error, with that (79 ± 0.7 kv) observed. It was also shown that the state of the cathode surface had a marked influence on the secondary ionization even at these higher values of pd.

For 35 less-than-or-eq, slant E/p less-than-or-eq, slant 40 v cm^-1 (mm Hg)^-1 and pressures between 400 and 1000 mm Hg, the apparent secondary ionization coefficient ω/(α-a) was found to be a function of E/p alone, whereas the apparent primary ionization coefficient (α-a)/p showed a small, just detectable decrease with increasing pressure at a given value of E/p.

When a feebly ionized gas is compressed until the mean distance between atoms decreases down to approximately less than ten times an atomic radius, the positive charge is not carried by the ion in motion but rather jumps resonantly from atom to atom. This statement is arrived at by comparing the mean time of flight of the positive ion between two collisions with the resonant transfer time of the electron from the atom to the next positive ion.

The measured rotational intensity distribution of N₂⁺ First Negative bands excited by 1 MeV protons indicates that the rotation of the molecules is not greatly affected by the collisions. Measured rotational temperatures compare favourably with laboratory temperatures. Similar observations on N₂⁺ bands excited by 1 to 3 keV Li⁺ ions show that these collisions appear to cause a marked departure from Boltzmann distribution of rotational energies. Energy levels of high and of low quantum numbers are enhanced in population.

Polycrystalline thin films of a number of face-centred cubic metals have been prepared by evaporation on to rock-salt, followed by annealing. In a number of cases, transmission electron diffraction patterns show, in addition to the normal face-centred cubic rings, some extra rings which fit well with those which would be expected from a hexagonal close-packed form of the metals. No hexagonal close-packed rings are observed with aluminium films, and this is correlated with the absence of stacking faults on transmission electron microscope images of aluminium films.

A short summary is given of a variation of the Michelson stellar interferometer. This is an adaptation of part of the principle of the radio-frequency phase-sensitive interferometer developed by the author in 1958 and it enables the phase component associated with the structure of the source to be determined. The technique may also be used to determine the correct relative amplitude of the visibility function of the star at two spacings even when phase and amplitude errors are present.

The ultra-violet absorption spectrum of indium vapour has been photographed by means of a 3-metre grating spectrograph. Lines of the series 5²P_1/2⁰-n²S_1/2 (n=9 to 27), n²D_3/2 (n=7 to 33), 5²P_3/2⁰-n²S_1/2 (n=10 to 29), n²D_3/2 (n=8 to 19), n²D_5/2 (n=8 to 34), have been measured against good wavelength standards. A short sixth series is identified as 5²P_1/2⁰-n²P_1/2⁰. The accepted value for the ionization potential has been confirmed. From a consideration of the character of the perturbations in the n²D series we conclude that the sp²²D term lies above the ionization limit, instead of, as formerly supposed, below.

Experimental data and theoretical calculations on neon and argon are analysed to yield consistent sets of electric dipole oscillator strengths. The derived oscillator strengths are used with known values for hydrogen and helium to calculate the van der Waals energies between all pairs of atoms selected from hydrogen, helium, neon and argon. The results are summarized in the Table. The probable error is less than 10%.

One system of bands comprising thirty-two bands of the BiF molecule has been obtained in absorption in the region λλ2400-2180. Three of these bands were previously observed in emission by Rochester. The bands have been analysed and can be represented by the following formula: ν_{ν'νdouble prime} = 44222.0+615.0 (ν'+½) -2.50 (ν'+½)² - 512.0(νdouble prime+½) + 2.25 (νdouble prime+½)².

A discussion regarding the electronic states involved in the transition shows that the ground state is a triplet state, whereas the upper one a single state and not otherwise as suggested by Rochester.