Beta-delayed proton emission from heavy nuclei: (I). The observation of coincidences between protons and γ-rays

Coincidences have been detected between γ-rays and β-delayed protons emitted after the decay of very neutron-deficient nuclei. In the three cases studied the decay proceeds to the ground state with branches to the first excited (2⁺) state of the even daughter nucleus of (58±7) % (¹¹⁵Xe to 709 keV in ¹¹⁴Te), (14±3) % (¹¹⁷Xe to 679 keV in ¹¹⁶Te), and (50±10) % (¹⁸¹Hg to 158 keV in ¹⁸⁰Pt). Upper limits of 2 and 6 % can be placed on the branches to the 4⁺ states of ¹¹⁴Te and ¹⁸⁰Pt. For the cases of ^115,117Xe, coincidences with annihilation radiation were also observed; the measured positon/proton ratio determines the difference Q—B_p, between the energy available for electron capture and the proton separation energy for the daughter. For ¹¹⁵Xe the result is 6.20±0.13 MeV, for ¹¹⁷Xe 4.10±0.20 MeV.     

On the validity of dwba for deuteron stripping: (I). The Mitra three-body model

Previous work showing that there exists an exact formulation of the DWBA for stripping in the S-wave, separable potential, three-body model of Mitra is discussed and extended. The one-body equation obeyed by the c.m. wave function used in the reformulated DWBA is derived and compared with the equation obeyed by the wave function used in the standard formulation of DWBA, viz., the deuteron elastic scattering wave function. Results obtained by other workers on application of three-body methods to direct reactions are discussed in light of the fact that an exact DWBA exists for the separable potential model.     

Ultrasonic transducers: 3. Surface wave transducers

The many examples cited indicate the potential use of elastic surface waves in modern radar and communications signal processing. The use of surface waves reduces the physical size of most devices by factors as large as 10⁵ over their electromagnetic counterparts. An added attractive feature of elastic surface wave devices is that the fabrication techniques involved are compatible with integrated microcircuit techniques so widespread in general microwave technology.     

Ionic monolayers on metals: I. layers of like ions

We estimate the energy of a layer of like ions adsorbed on an atomically smooth face of a metal crystal. We consider only adions of large radius, so that the method of electrostatic images can be used in evaluating the energy. For periodic layers of high density, we find large deviations from the dipole approximation of Topping. Also, we estimate the increase in electrostatic energy accompanying disordering of a layer, and use the result to discuss thermal disordering of Na and Cs layers on W(110). We emphasize that the charge transfer to a layer of like ions must be small. For example, O and S anions of integral charge cannot form densely packed layers on metals.     

The weak coupling model applied to the nuclei with A = 16–19: (II). Gamma transitions and spectroscopic factors

We have formulated particle-hole states according to the weak coupling model where the particle and hole wave functions are respectively eigenfunctions of the particle-particle and hole-hole parts of the Hamiltonian. Previously the energy levels were found to be well given by this model and here we make an extensive comparison between theoretical predictions and experi- mental data on γ-transitions and spectroscopic factors for the nuclei with A = 16–19. Some discrepancies are found, particularly for the 3p-3h states in ¹⁶O, but on the whole the agreement is good and confirms the validity of the weak coupling model.     

A molecular orbital approach to chemisorption: I. Atomic hydrogen on graphite

We examine the use of Extended Hückel Theory, a semi-empirical molecular orbital approach, in treating chemisorption. The calculations include all valence electrons and overlap integrals. Adsorbate energy levels are self consistently determined. The substrate is represented by a relatively small number of atoms which is shown to be adequate for obtaining semi-quantitative results. The small representation permits investigation of adsorbate interactions with both ideal and imperfect surfaces. The binding energy, binding sites, and barrier to surface mobility exhibited by atomic hydrogen on a graphite basal surface are obtained. The experimentally observed formation of CH₄ on adsorption of hydrogen is also considered. Calculations on electrophilic adsorbates reveal the necessity for a more completely self consistent treatment in which all energy levels are adjusted.     

Tautochronic centrifugal pendulum vibration absorbers: General design and analysis

Since the 1930s, centrifugal pendulum vibration absorbers have been used in rotating and reciprocating machinery for the attenuation of torsional vibrations. A large variety of absorber types were suggested and the design was done by linearization theory until the introduction of the tautochronic bifilar pendulum absorbers. Since then, the performance and dynamic stability of this specific absorber type have been considered in analytical and numerical investigations. Different perturbations, e.g. nonlinear mistuning, were considered in order to optimize the system performance, but the characteristic bifilar design remained unchanged. In this paper, a general approach for the design of tautochronic pendulum vibration absorbers is proposed. As a result, it is possible to deal with a large variety of non-bifilar centrifugal vibration absorber designs which provide application-related optimal performance and resolve some of the existing design limitations.     

Magnetic interactions in corundum-hamatite solid solutions: An electron paramagnetic resonance study

EPR spectra of solid solutions between corundum and hematite in all their existence range have been examined. The dilute solutions of ferric oxide in corundum show only the EPR spectrum of isolated ferric ions. At higher concentrations this spectrum is gradually replaced by a strong Lorentzian signal which we attribute to clusters of ferric ions coupled by strong exchange interactions. The features of these signals change with iron concentration, revealing the development of magnetic interactions in solution.     

Comparison of feshbach and R-matrix reaction theories for C(n,n)C: (I). Shell model

The Feshbach and R-matrix approaches to nuclear structure calculations in the continuum have been applied to the elastic scattering of neutrons from ¹²C below the inelastic threshold. A simple shell model has been used for the positive-parity states of ¹³C and in contrast to the work of Lovas, the predictions of this model disagree significantly with experiment for both theories. The results for the two reaction theories have been compared.     

Elastic scattering and the K matrix: (II). Phase shifts,resonances and few-level approximations

The K-matrix expansions given in part I are applied to the scattering by a square-well potential. Their convergence proves very satisfactory from a physical point of view since few-level approximations allow very good approximations to the phase shifts and cross sections. It also appears that all the complex poles of K_l and the real ones with positive residue should undoubtedly be associated with physical resonances. As for the real ones with negative residue, i.e. the echo poles, they are obviously unrelated to resonances, but they provide a very good parametrization of the background part of the scattering. The time delay is given a major role in the argument. The possibility of having double poles is also discussed and sum rules are given for the energies and residues of the poles.     

Sound propagation in an anharmonic metal : III. The collision-free regime

The electron contribution to the phonon damping is calculated by solving the generalized transport equations derived in I. In particular, the collision-free regime and the transition from the collision-dominated to the collision-free regime are investigated. The solution of the transport equations is a generalization of the one given in II and it is valid also outside the collision-dominated regime. No single-relaxation-time approximation is used and the collision operator is taken into account in full. Certain higher-order relaxation times are taken into account only approximately. It is shown, however, that this approximation only affects the attenuation in a narrow frequency range around the transition from the collision-dominated to the collision-free regime. Even there, its influence is weak as demonstrated by some numerical results for potassium.     

Adsorption von Wasserstoff an platin: I. Adsorbierte menge,kinetik der ad- und desorption

Chemisorption of hydrogen on a platinum-foil has been studied by the flash-filament technique and by the capillary-flow method. Isobars were determined at temperatures between 140 and 600° K and at pressures between 10⁻⁴ and 10⁻⁶ torr. The dependence of the isosteric heat of adsorption E on the coverage σ is given by E = 16.3 −1.4 × 10⁻¹⁴σ (kcal/mole) with σ<2.5 × 10¹⁴ molecules/cm². At higher coverages E reaches values smaller than 5 kcal/mole. Adsorption and desorption at low coverages are second order processes. The initial sticking probability is 4.5 × 10⁻³. The results are discussed in terms of an atomic and a molecular state of the adsorbed hydrogen.