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The ¹⁴N(α, γ)¹⁸F reaction has been examined from 1.2 to 2.2 MeV bombarding energy. Two narrow resonances have been found; their positions have been measured, and upper limits obtained for their total widths. The cascade schemes at each resonance have been partly elucidated, and the position of another level involved in these cascades has been measured. The partial radiation widths of these resonances have been determined, except for a statistical factor. Some of the angular distributions have been studied, and conclusions have been drawn about the possible values of the spins and parities of the levels concerned.

The effect of the finite nuclear size on the scattering of high energy electrons depends upon the ratio of the small to the large radial Dirac function inside the nuclear charge distribution. An approximate expression for this ratio is given, valid for energies of the order of 150MeV. The result is used to discuss the model independence of the scattering for the case of uniform and shell charge distributions.

The transition integrals corresponding to the 2pπ_u-2sσ_g, 2pπ_u-3sσ_g, 2pπ_u-3dσ_g and 3dπ_g-3pσ_u, 3dπ_g-4pσ_u, 3dπ_g-4fσ_u perpendicular type transitions of H₂⁺ are computed from the exact two-centre wave functions.

A modified variational method is used to obtain approximate wave functions for the 2sσ_g and 3dσ_g states of H₂⁺. Their accuracy is assessed by comparing various quantities computed using them with the exact values of these quantities. The dependence of the kinetic and potential energies on the nuclear separation is briefly discussed.

An approximate covariant solution of the Salpeter-Bethe equation is obtained by a modification of the Fredholm theory. This solution is developed to the point where only numerical substitutions are required to obtain the scattering amplitudes and differential cross sections for elastic nucleon-nucleon collisions, for any energy and any spins of the incident and scattered particles.

The times of arrival of 17 665 local and 2526 extensive penetrating showers have been recorded. The showers penetrated various thicknesses of lead from 17.5 cm to 97.5 cm. A variation of the rate of local showers with solar time which is correlated with the small diurnal pressure variations appears to be statistically established. This variation seems to have a much larger barometric coefficient than that derived from the large pressure changes associated with the weather. No significant variation of the rate of local showers with sidereal time was found.

Possible variations of the rates of penetrating extensive showers with solar and with sidereal time are discussed.

The lower excited electronic states of some unsaturated hydrocarbon radicals and ions are discussed in terms of molecular orbital theory, taking account of electron interaction. The following results emerge:

1. In the absorption spectrum of an alternant radical there should appear two long wavelength bands. These arise jointly from excitations of electrons into and out of the singly occupied orbital. The lower frequency band should be weak, and the higher frequency band relatively strong. The existence of a low-lying quartet level is also predicted.

2. The absorption spectra of the corresponding anion and cation should be closely related, the lowest two excited states being for both types of ion a triplet and a singlet.

3. The singlet-triplet separation in the ions should be roughly equal to the separation of the two low-lying doublets of the radical.

These generalizations are supported by the experimental data for certain triaryl-methyl systems.

The electronic spectrum of a composite alternant hydrocarbon R-S is discussed theoretically in relation to the excited electronic states of the separate fragments RH and SH. The lowest excited states of RS are interpreted as arising from two types of excited configuration. In the first type an electron is raised from an occupied orbital of one fragment to an unoccupied orbital of the same fragment, and in the second, an electron is transferred from one fragment to the other. The self-consistent molecular orbital theory is used to evaluate the interactions between the various configurations, and the molecules butadiene, biphenyl and styrene are examined quantitatively. The following results are worthy of mention: (i) In butadiene the near ultra-violet transition arises primarily from an in-phase combination of local excitations in the two double bonds. (ii) In biphenyl a similar situation arises, there being strong configurational interaction in the perpendicular as well as in the planar conformation.

In all three molecules there is quite good agreement between the observed and calculated spectra.

This paper is a supplement to the discussion by Kinsey of the fluorescence yields of the L sub-shells in the heavy elements; it suggests the use of experimental measurements other than those which he discussed for the calculation of these quantities. New observations are reported and collated with existing information. The fluorescence, Auger and Coster-Kronig yields of Bi are re-calculated. Suggestions are made about further experimental work.

The numerical results are, for the fluorescence yields of Bi, ω₁ = 0.12 ± 0.01, ω₂ = 0.32±0.04, ω₃ = 0.40 ± 0.05, for the Auger yields a₁ = 0.11 ± 0.03, a₂ = 0.62 ± 0.14, a₃ = 0.60 ± 0.05, and for the Coster-Kronig yield f₁₂ = 0.19 ± 0.05, f₁₃ = 0.58 ± 0.05, f₂₃ = 0.06 ± 0.14.

A discussion is added on some aspects of the radioactive disintegration of RaD.

The results of several underground measurements of the positive temperature effect are examined in order to obtain some information about the attenuation length of high-energy π-mesons in air. It is shown that this quantity can hardly be smaller than the attenuation length of the primary component. If this is so, competition between disintegration and nuclear capture of the π-mesons can account for but a very small part of the positive temperature effect which has been observed at sea level.

Using the Rayleigh-Ritz variational method, the ¹σ states of the hydrogen molecule arising from the [H(1s), H(2s or p)], [H⁺, H^-(1s)²] and [H(1s), H(3s, p or d)] configurations are investigated in the region of transition from ionic to homopolar character. Potential energy curves are given for these regions. It is shown that the admixture of configurations has a very considerable effect on the potential energy curves even at large nuclear separations. The ionic content is defined and calculated for [H(1s), H(3s, p or d)] states and found to vary rapidly in the transition region. The bearing of this result on collision theory is discussed briefly.

Using scintillation-counter detection and pulse-height analysis, the angular distributions of the neutron groups from the reaction ¹¹B(d, n)¹²C leading to the ground state and first excited state of ¹²C, have been determined at a deuteron bombarding energy of 600 keV. The results are compared with those predicted by the stripping theory and with those expected if the reaction proceeds by compound nucleus formation. The stripping mechanism appears to be important even at low bombarding energies for the ground-state group, but for the excited state the interpretation is less certain.