Table of contents

Total cross sections have been measured for the elements H, D, Li, C, O, Al, Cu, Sb and Pb and absorption cross sections for C, Al, Cu and Pb for neutrons of an effective energy of 765 ± 30 Mev. The neutrons were detected by observing the Cerenkov light from charged secondaries produced in a cylinder of Perspex. Large corrections must be applied to the measured absorption cross sections and these are strongly dependent upon the differential cross section assumed. The results are compared with an optical model with a potential distribution indicated by electron scattering measurements, and with an imaginary central potential and a real spin-orbit potential. The results can be adequately represented by assuming that at this energy the imaginary potential is given by the free nucleon-nucleon total cross sections and that the nuclear potential size and shape agree with the charge density size and shape. The spin-orbit coupling parameter required to fit the results is somewhat less than that found at lower energies.

The angular distributions of neutrons scattered by protons at effective energies of 96, 130 and 137 Mev and at angles between 19.3° and 78.1° in the centre-of-mass system have been measured using photographic emulsions.

The differential cross sections have been normalized to the absolute scale by deducing the energy spectrum of the neutrons. The results confirm that at 130 and 137 Mev the cross sections for scattering at angles within 60° of the forward direction in the centre-of-mass system are less than those for a similar range of angles in the backward direction.

Using a thin gas target, the differential cross sections for the two most energetic proton and alpha groups have been measured; an expansion in the form Σa_nP_n (cosθ) has been fitted to the results. In no case was the value of a_n significant for n > 3, indicating that deuteron stripping is not important below 1 mev bombarding energy.

A single crystal scintillation spectrometer has been utilized to detect the triple summing, in the crystal, of three coincidence radiations. It has been shown that in an electron capture isotope the triple sum of two cascade γ-rays and K x-ray, which precedes the emission of γ-rays, can be used to calculate the ratio P_L/P_K for the transition to the second excited state of the daughter isotope. The ratio P_L/P_K can also be calculated by recording triple coincidence rate with two coincidence spectrometer units, by detecting the sum of two γ-rays in one and K, x-rays in the other unit. These methods have been used to calculate the decay energy of ¹⁹⁶Au. The decay energy has been found to be 911_-25⁺⁵⁵kev

It is shown that the 56kev γ-ray observed from natural tungsten irradiated in the pile does not arise from the decay of ¹⁸⁵W as was suggested by Bisi, Terrani and Zappa (1955). The γ-ray peak at 125kev probably arises from a 0.005% branching ratio to the 125 kev excited level in ¹⁸⁵Re. The continuous photon spectrum is interpreted quantitatively as internal plus external bremsstrahlung.

The dielectric constant of an ionized medium is decreased not merely by the presence of electrons but also by that of other free carriers, the positive and negative ions. In a highly electronegative gas discharge, the effect of the ions cannot be neglected and sometimes their contributions may swamp that of the electrons.

Under such conditions, measurements of the recombination coefficient between positive and negative ions have been made in the afterglow following pulsed radio-frequency discharges in iodine and bromine vapours.. The recombination coefficient α_i was found to be 1.47 × 10^-8 cm³ sec^-1 for iodine molecular ions and 1.85 × 10^-8 cm³ sec^-1 for bromine at room temperature. α₁ was constant over an extended pressure range and was found to be temperature dependent.

Absolute differential cross sections are given for the elastic scattering by silicon of 9.45 MeV, 9.28 MeV, 8.96 MeV, 8.55 MeV and 7.97 MeV protons for an angular range of 15°-156° (centre-of-mass coordinates). The angular distributions show characteristic maxima and minima, the patterns varying slowly with energy as might be expected for scattering by a complex potential. Absolute differential cross sections for the inelastic scattering of protons at these five energies from the 1.78 MeV level of ²⁸Si are also given. All the inelastic angular distributions are asymmetric about 90° with a forward peaking. The magnitude of the asymmetry varies with energy and is greatest at 8.96 MeV.

The paper describes the development of a crossed beam method suitable for measuring ionization cross sections of unstable gases such as atomic hydrogen.

Results obtained in He and H₂ are compared with those of Tate and Smith. The method makes use of a narrow band amplifier associated with a beam chopper and phase sensitive detector, to eliminate the current due to ionization of the background gas. The electric field in the collision region is such that limitation of the beam crossover volume can make the uncertainty in electron energy much smaller than is otherwise possible, without resorting to magnetic collimation or pulsed collection. An analysis of the sources of error due to the collection of spurious currents at signal frequency is given.

A finite set of possible Slater determinants with spatial part constructed from an orthonormal complete one-electron set of associated Laguerre functions in the radial coordinates, and Legendre functions in the angular coordinates, has been introduced into the minimal sequence of the Ritz variational principle applied to the (2s)² state solution (L = 0) of the two-electron wave equation for infinite nuclear mass. The sequence converges on a certain limiting eigen-function of the energy state. The numerical solution of the function and the corresponding energy value are given for helium as well as the negative hydrogen ion. The identification of certain helium lines in the vacuum ultra-violet is discussed.

The fine structure of the K Auger spectrum is discussed and the positions and intensities of the K-LL and K-LM Auger lines calculated for different values of Z using a non-relativistic theory and assuming intermediate coupling between the two inner shell vacancies of the atom in the final states. In regions of intermediate atomic number the usual six-line K-LL spectrum expected on the basis of j-j coupling is modified into a nine-line spectrum and the relative intensity of the various lines varies markedly with Z. The effect of inter-configuration terms on the K-LL spectrum is also discussed. The observed position and relative intensities of the K-LL lines can be understood when reasonable allowance is made for relativistic effects but the interpretation of the rather meagre experimental data on the K-LM spectrum is less clear, although there is qualitative agreement with the theoretical predictions.

A programme developed by Altmann for a high-speed computer to carry out cellular computations for close-packed hexagonal metals has been applied to titanium. The eigenvalues and eigenfunctions corresponding to all states for k=0 have been determined and the effect on these results of the type of potential field used has been investigated.

A small thin NaI(Tl) scintillator has been used as both source and detector of photoprotons produced in sodium by ⁷Li(p, γ) radiation. This technique provides photoproton energy spectra of good resolution and high statistical precision. Spectra were obtained with both resonance and non-resonance radiation from the ⁷Li(p, γ) reaction which permit identification of protons produced by the 17.6 MeV component of the incident radiation. These protons correspond to transitions to states in ²²Ne at energies of 0 (0.31 mbn), 13 (2.5mbn), 3.3 (0.6 mbn), 4.4 (0.9 mbn), 5.4 and 5.7 MeV (approximately 2mbn for both).

This experiment establishes the existence of ²²Ne levels at the three highest energies. Previous evidence for a level between 4 and 5 MeV is discussed and is found to be compatible with the present results.

The Cerenkov radiation emitted by a fast charged particle moving through one medium and in the vicinity of another medium has been theoretically investigated, employing the invariance of the phenomenological electrodynamic equations of Maxwell. A simple geometry has been considered, this being the case of two coaxial dielectrics and permeable cylinders with a common cylindrical interface and a charged particle moving along their common axis. The results obtained have been discussed with special reference to the case of Cerenkov radiation at microwave and radio-frequency regions. The effect of the phenonema and coherence on the output of the emitted radiation in these cases has been briefly outlined.

Polarization of the cell Ta|Ta₂O₅|Solution|Pt sets up a very high electric field strength in the oxide and ionic conduction (resulting in growth of the oxide film) occurs with negligible electronic conduction. With this cell measurements of field strength and current density have been made in the temperature range -63 to + 90°C. These results are incompatible with single barrier control in which space charge is neglected but are consistent with a theory proposed by Dewald in 1955 in which space charge due to ions in transit causes the field in the oxide to vary through its thickness, so that barriers near the metal interface and within the oxide both play a part in controlling the rate of oxide formation.

Pure polycrystalline samples of indium phosphide have been prepared Point contact experiments have shown useful rectification on both n- and p-type samples, as well as transistor effects with power gains up to 20 times. The infra-red transmission spectrum has been extended to 20 μ, and the effective mass of electrons has been estimated as 0.02m. Previous work on general properties has been revised and extended.

An investigation has been made of the trap distributions in a single crystal of calcium tungstate as revealed by thermoluminescence and current `glow' curves. The resulting distribution agrees reasonably well with the results of a theoretical analysis of the photocurrent and phosphorescence decay after irradiation with ultra violet light or gamma rays from a ⁶⁰Co source.

The resistivity, Hall coefficients and low field magnetoresistance coefficients associated with current flow in the cleavage planes have been measured at 77°K on a number of n-type specimens of bismuth telluride. The resistivity and Hall coefficient measurements were extended up to room temperature. The experimental results are given and are shown to be reasonably consistent with a many-valley model of the band structure in which the energy minima are situated on the reflection planes. The parameters associated with this model are evaluated and used to relate the two Hall coefficients to the density of carriers. These relations are used to obtain the conductivity mobility of electrons for current flow in the cleavage planes. This mobility varies as T^{-1 68} over the temperature range 150°K to 300°K and has a value of 1250 cm²sec^-1V^-1 at room temperature.

A theory of yielding in iron is developed which includes the effect of the continued reduction with time under load of the restraint offered to the motion of dislocations by atmospheres of solute atoms. The manner in which this reduction comes about, namely by decrease in atmosphere density consequent on the bending of the dislocations, is analysed and is shown to lead to the existence of stress and temperature-dependent delay times and to the presence of microstrain prior to yielding. Qualitative and to some extent quantitative agreement is found between the predictions of the theory and the experimental evidence.

The Manchester University Mk I computer has been used to calculate accurately the viscosity cross section for hydrogen molecules, and its dependence on the symmetry of the wave function for binary collisions. The calculations assume a central intermolecular potential of (exp, 6, 8) type, and cover reduced temperatures in the range 0.05 ⩽ T^* ⩽ 2.0.

Comparison is made with estimates of the relative difference in viscosity cross sections for para-para and para-ortho collisions derived from Becker and Stehl's measurements. Assuming elastic collisions only, fairly good agreement is found at 15°K, but at higher temperatures the theoretical results become increasingly too small. A central interaction is seemingly inadequate to explain the relatively large ortho-ortho cross sections observed; in this connection the effect of an increased range of interaction is briefly discussed and shown to be unimportant.

Negative magnetoresistance in n-type InSb at 4.2°K has been investigated gated for several specimens prepared by different techniques from single crystals of differing purity. The results indicate that this phenomenon is not a bulk property of the material but is largely due to the method of preparation of the specimens.

Oscillations in the magnetoresistance as a function of magnetic field have been observed in samples having a balanced donor concentration of less than 10¹⁶ cm^-3 and the results are discussed in detail for two samples.

The emission spectrum of SiF has been examined in the Schumann and infra-red regions. The system B-A (ν_{0, 0} = 11850.8 cm^-1) is strong, and rotational analysis shows that both states are ²Σ. A new rotational analysis of the 0, 0 band of the α-system, A-X²π, although in substantial agreement with earlier work, confirms the view that state A is ²Σ⁺, and not ²π (case-b), as has previously been supposed. Violet degraded bands which have tentatively been ascribed to five systems, all with X²π as the ground state, are found, partly superimposed, in the region 51 000 to 53 500 cm^-1. Three of the excited states of SiF appear to form a Rydberg series of ²Σ⁺ states leading to the ground state... π⁴σ², ¹Σ⁺ of SiF⁺. The ionization potential is found to be 7.2₈ eV. Evidence about the dissociation energy is briefly considered; the best value seems to be D₀double prime(SiF) similar 125 kcal.

The contribution of lattice vibrations to the infra-red spectrum of diamond in the 2 to 6 μ region has been calculated from the vibrational frequency distribution where second nearest neighbour central forces are taken into account. It is assumed that this absorption is associated with two-phonon processes arising from second-order terms in the electric moment. Certain general selection rules are determined. Most of the details of the observed spectrum are reproduced in the calculated spectrum.

The lateral distribution of ionizing particles in extensive showers over the approximate range of size 5 × 10⁴ < N < 5 × 10⁵ particles has been studied using a core-locating device (already described) to select showers, and unshielded `probing' counter trays to estimate particle density at measured distances from the located shower axis. The distribution is determined with useful accuracy for four ranges of shower size. For the three greatest size ranges examined, the distribution is generally in accord with that of other workers and confirms the observation that for these showers structure does not vary significantly with shower size. For the range corresponding to the smallest showers, which are of a size for which accurate structure measurements have not previously been reported, it is found that the lateral structure shows evidence of significant ageing of the effective cascade.

Corrections to 1958 Proc. Phys. Soc.71 177

Corrections to 1957 Proc. Phys. Soc. A 70 908.