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This is the text of a tutorial talk on the use of electron paramagnetic resonance (EPR) as a "microscopic" tool in the study of radiation-produced defects in semiconductors. The basic concepts of EPR and its general applicability to point defects in semiconductors are outlined. As an illustrative example, the study of a p-type (aluminum doped) silicon sample is described from 20.4°K irradiation with 1.5 MeV electrons through various annealing stages. By analysis of the EPR spectra, it is shown that the major defects can be identified and the annealing mechanisms determined.

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1. The bulk rate constant for the recombination of nitrogen atoms on ternary collision has been measured. 2. It has been shown that the nature of the third particle (impurities in molecular nitrogen) influences the value of the constant for ternary collisions. 3. The bulk rate of recombination of nitrogen atoms, according to the ternary collision law, is much greater than the rate of recombination taking place on clean glass walls of the vessel at pressures from 1 mm and above. 4. It has been found that TiO2 is an effective catalyst on which the recombination of nitrogen atoms takes place readily at a velocity proportional to the square of the concentration of atoms. 5. The coefficients of adhesion and the rate constants for the recombination of nitrogen atoms on a clean glass wall and on pure TiO2 catalyst have been measured.

A novel guide-magnet configuration has been devised which makes possible the acceleration of all charge-to-mass ratios from 0.04 to 1. A concentric storage ring, with the associated beam-switching equipment, allows for the extension of beam duty factor to essentially 100%. The storage ring can also be used in a bootstrap acceleration of heavy ions in which the ions are injected at low e/m, accelerated to a moderate velocity, stored while the accelerating ring returns to minimum field, stripped to maximum e/m, and re-injected for further acceleration. With a pressurized 2.5 MV Cockcroft-Walton injector, the proposed system is capable of accelerating all ions from protons to uranium--to energies up to 1.5 BeV for protons and 0.3 to 0.5 BeV/nucleon for the heavier ions. Intensities of 1012 to 1013 nucleons/sec for the lighter ions (M ? 128) are anticipated. The heavy-ion charge-exchange probabilities determine the vacuum requirements of this system. To minimize these requirements and to increase beam intensity, a 60/sec cycling rate has been chosen. The vacuum requirements and the special rf resonator and beam-switching problems attendant with the high cycling rate are discussed.

A transient plasma is located within the Fabry-Perot resonator of a dc hydrogen cyanide laser. Plasma tuning sweeps the resonator modes through the emission line of the HCN molecules and produces pulses of far-infrared output radiation. Pulse production by hydrogen, nitrogen, helium, and argon pulsed plasmas is discussed.

The argument that Ti3+ ions produce 12 magnetic complexes when substituted for Al3+ in CsAl (SO4)2∙12H2O (Cs alum) is supported neither by experimental evidence nor a realistic physical model. The uniform intensity of the superhyperfine structure in Rb(TiAl) alum disproves the idea that titanium nuclei are involved because the natural abundance of nuclear magnetic isotopes is only 13%. In addition, the magnitudes of the splittings are too small to represent electron–nuclear spin interactions within the Ti3+ ions.

The polarization factor for the interference between Rayleigh scattering and Mossbauer scattering from 57Fe is shown to be cos θ for both an unsplit scatterer and a non-aligned split scatterer, a result which differs from that recently published by Wong. Polarization factors have no effect on the ratios of the absorption cross sections for the hyperfine components of a non-aligned split scatterer.

Separate abstracts were prepared for 36 of the 39 papers included. Three other papers on multiparticle excitation in the intermediate compound state, Ca/sup 41/ and Ca/sup 49/ shellmodel levels, and (p,t) and (He/sup 4/,He/ sup 6/) reactions on Mg/sup 26/ were previously abstracted in NSA. (D.C.W.)

In this paper there is contained a full elaboration of two previously published short notes on the subject of magnetic scattering of neutrons together with a comprehensive treatment of certain sides of this problem which have already received some attention from other authors. After presenting the state of the problem in the introduction and discussing in detail our reasons for the choice of an interaction function between neutrons and electrons, and the nonmagnetic interaction between neutrons and nuclei, the various possible cases of coherent and incoherent scattering and depolarization phenomena are treated. Later applications to the theory of ferromagnetic scattering are kept in mind. The general expression for the cross section due to magnetic interaction is obtained and applied to various classes of phenomena (scattering by free, rigidly aligned, and coupled magnetic ions). The influence of the elastic form-factor is treated quantitatively with the aid of a simple model for the current distribution in the ion. Finally a series of performed or suggested experiments is discussed mainly from the point of view whether they will permit theoretical interpretation. Arrangements are described which will allow one to obtain a reliable value for the neutron's magnetic moment and also give insight into the magnetic constitution of the scatterer (ion or crystal) which will exceed the knowledge obtainable from macroscopic magnetic experiments.

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Some ion-probe source mass spectrometers which have been constructed, but are not referred to in Long's 1965 paper, are briefly mentioned. These embody certain features he discusses. In addition, mention is made of an interesting instrument that utilizes the neutral species produced by ion bombardment rather than the ions, and thereby achieves a considerable reduction of the differences in sensitivity from element to element observed in secondary-ion spectra.

Kay's method of deducing the stage of ionization from which atomic spectral lines are emitted is found to be unsatisfactory on several grounds.

The apparent detachment rate observed by Hackam and Lennon in O2-N2 mixtures is most likely not due solely to collisional detachment by N2 molecules.

The difference in the ionization rates of holes and electrons in Si results in different properties of n+-p-p+ and p+-n-n+ TRAPATT diodes. An approximate analysis is presented which shows these differences and indicates superior performance in the n+-p-p+ structure.

I agree very much with Dr Walsh that a satisfactory knowledge of effective atomic electronegativities is very important and that we should concentrate on obtaining such knowledge. The effective electronegativity of an atom varies, of course, in different circumstances. This appears to be the explanation of the difference in strength (length and force constant) of the C—H bonds in methane and acetylene. The effective attraction of the carbon atom for the electrons in a C—H bond in methane is a resultant of the attraction of the carbon nucleus plus Is core and the repulsion of the electrons associated with the other three C—H bonds. In acetylene the effective attraction of the carbon atom for the electrons in the C—H bond is the resultant of the attraction of the nucleus plus core and the repulsion of the electrons in the triple bond. Because these last six electrons are drawn away into the triple bond on the far side of the carbon atom from the C—H bond it seems that their repulsion on the electrons in the C—H bond is less than that of the six electrons in the three other C—H bonds in methane which are relatively nearer.

Polymer films may grow on ion bombarded surfaces due to cross-linking of hydrocarbon molecules adsorbed from a vacuum atmosphere. Electron-induced polymer formation has been studied intensively, but only limited information exists on the role of ions (their mass and energy) in promoting the growth of similar films. Attention is drawn to a recent paper in the journal, and it is suggested that polymer growth during argon ion bombardment may have arisen also from secondary electrons returned to the target.

The motion of electron–hole drops is analysed when nucleated in a non-uniform density of free excitons. The exciton condensation on the drop surface gives rise to a driving force towards regions with lower densities. This force and the internal friction of the exciton gas lead to a drift velocity which is proportional to the drop radius. In typical excitation geometries this motion is more important than drop diffusion, and the flight towards low density regions influences strongly the drop growth. It is pointed out that very large drops can be formed in a local minimum of the exciton density. Es wird die Bewegung der Elektron–Loch-Tropfchen in einem Exzitonengas mit inhomogener Dichte berechnet. Die Kondensation von Exzitonen auf der Tropfchenoberflache verursacht eine Kraft in Richtung niedrigen Exzitonendrucks. Diese Kraft und die Reibungskraft des Exzitonengases ergeben eine Geschwindigkeit, die dem Radius der Tropfchen proportional ist. Es wurde gefunden, das die entsprechende Bewegung in typischen Anregungsgeometrien viel wichtiger als die Diffusion ist und die Flucht nach Bereichen mit niedrigerer Dichte einen grosen Einflus auf das Wachsen der Tropfchen hat. Sehr grose Tropfchen werden erwartet, wenn die Exzitonendichte ein lokales Minimum hat.

Dieke and Hopfield showed that the absorption bands of H 2 , which are located in the extreme ultra-violet (about 1000-1500 Å. U.) were due to transitions up from the ground level of H 2 , which they called A, to two higher electronic levels which they called B and C respectively. Two years ago I found the emission bands which go down to the B level and some of them were described and partially analysed in this journal. In a series of papers Dr. Davidson and I have been able to show that these bands comprise a large number of distinct band systems and contain a very large part of the total strength of the visible emission spectrum of H 2 . In previous papers I have called this B level of Dieke and Hopfield 2 1 S as it has an effective principal quantum number in the neighbourhood of 2 and its properties are those of an S level. In view of recently proposed changes in the nomenclature for band spectra I propose in this paper to denote this B or 2 1 S level by the symbol 2 p 1 ∑. In this notation 2 denotes the principal quantum number and p indicates that the azimuthal or equivalent quantum number of the excited electron is 1. ∑ means that the component of the total angular momentum (or equivalent quantized quantity) about the internuclear axis is 0 and the prefix 1 that the state is a singlet state. Various attempts have been made from time to time to discover bands in this spectrum which end on Dieke and Hopfield’s C level, but, until recently, nothing at all convincing has resulted from these efforts. I have now found a number of band systems which end on this C state.

The present paper is a continuation of the work on the spectra of selenium, carried out by the authors partly in Professor Fowler’s Laboratory at the Imperial College and partly in Professor Siegbahn’s Laboratory at Uppsala. A detailed account of the experimental part of the investigation together with the analysis of Se IV and Se V has been given in a previous communication. As already reported in ‘Nature’ the experimental data there described have led to the identification of the system of energy levels characteristic of the spectrum of doubly-ionized selenium. It is the purpose of the present paper to give an account of the structure of this spectrum so far as it is revealed by a study of the spectrograms of selenium under different conditions of excitation. The lines of the spectrum in question appear when discharges, even of moderate intensity, are passed through selenium vapour contained in a capillary tube. In the ordinary spark in air, the spectrum is represented only by a very few of the stronger lines which could be ascribed to Se III, but with strong discharges through capillary tubes, the lines are considerably enhanced and the complete spectrum is easily photographed. In the region of very short wave-lengths, below λ 1500, the source found suitable for the excitation of the spectrum was the spark in vacuum between aluminium poles tipped with metallic selenium. With this source, excited by a 50 K. V. transformer, it was found necessary to include an inductance of about 0·5 m. h. to elicit lines of Se III and Se II. At the same time, a study of the spectra excited with and without inductance in series in the secondary circuit has greatly facilitated the assignment of the lines to the various stages of ionization of the element. Reference may be made to a reproduction of the spectra in the previous paper by the authors ( hoc . cit .), where the method of measurement and the instruments employed for photographing the various regions of the spectrum have also been described.

It is recognised as a result of numerous independent experiments that ionisation by X-rays is the result of corpuscular radiation liberated by the X-rays. In a recent paper it was shown by the author that, in the case of carbon and oxygen compounds, the corpuscular radiation liberated by a beam of X-radiation was an “atomic” phenomenon, i. e . that the number of corpuscles given out by an atom of carbon or oxygen in a beam of X-rays is the same whether the atom is in combination or not the resulting ionisation is not, however, “atomic”, the ionisation produced in different gases or vapours by a given amount of corpuscular radiation being dependent on the nature of the gas or vapour. In the present paper an attempt has been made to test whether this “atomic” law holds good for other elements of higher atomic weight. These, given much larger ionisations than the lighter elements, also allow of greater accuracy in the observation, although as the absorption is corresponding increased, large absorption corrections are rendered necessary in some cases.

In the ‘Proceedings’ of the Royal Society, A, vol. 84, p. 209, I gave an account of experiments with Potassium vapour, which had for their object the determination of the dispersion curve for the vapour. The effect of the first three pairs of lines of the principal series was quantitatively estimated, and it appeared that certain conclusions could be drawn as to the numbers of systems taking part in the absorption of light. The present communication deals with further experiments of the same kind with vapours of Sodium and Rubidium, and again with the vapour of potassium, as far as regards a temperature effect, which will be discussed later. The experiments were made possible by a grant from the Royal Society, which enabled me to obtain metallic rubidium, and I am glad to take this opportunity of thanking the Government Grant Committee. In a former paper I gave results of the measurements of wave-length of the principal series lines for rubidium obtained in the absorption spectrum. This spectrum was obtained by heating rubidium chloride with metallic potassium; enough vapour was formed to give an absorption spectrum showing 25 lines of the series. With metallic rubidium it is easier to get the absorption spectrum, and the list of lines has been extended to include 30 members. A better reading microscope has been available since the original measurements, so that the complete series of lines has been remeasured. The method adopted was the same as that described in the paper referred to, so that there is no need for further description.