Table of contents

Reports a natural all-order decorrelation procedure for the interaction of a single two-level atom with all modes of the radiation field which replaces the semiclassical boson approximation for the atom by an exact fermion treatment. In consequence, the spontaneous emission of the semiclassical theory is extended to include stimulated emission, a semiclassical Lamb-type shift is explicitly replaced by a shift satisfying the Bethe formula manifestly due to vacuum fluctuations, and there can be two intensity-dependent terms, one of which generalizes the Bethe formula.

See abstr. A704 of 1971. The recent findings of the Sydney air shower group concerning the existence of high-transverse-momentum events in air shower cores are disputed. It is shown that the multiple cores which are interpreted as large-transverse-momentum events are likely to be simulated by the detection fluctuations quoted by the Sydney group itself.

Shows in which way the conditional probability of light diffused by particles suspended in a turbulent fluid can yield direct information on spatial velocity correlation functions.

A first-order differential equation, derived from the Schrodinger equation, is used to outline a numerical method for calculating the energy eigenvalues for a local potential.

The two-meson-exchange peripheral model has been used to explain the observed backward production features of the reaction K^-p to K⁺ Xi ^- in the intermediate energy region.

A simple, exact analytic expression is derived for the effective spectral linewidth of laser intensity fluctuations as a function of output power. Relevance of the work to the general theory of second-order phase transitions is pointed out.

An earlier result concerning the rate of entropy production for an isolated system near equilibrium is partially extended to the case when the system is well away from equilibrium.

E2/M1 mixing ratios have been measured for transitions from the second (3/2⁺), third (7/2⁺) and fourth (5/2⁺) excited states of ²⁷Si. A discrepancy in the magnitudes of the mixing ratios for the 5/2⁺ to ground state transition in ²⁷Al and ²⁷Si is confirmed, and is used to estimate the ratio of the isovector to the isoscalar components of the E2 matrix element for the transition.

Spin states analogous to the coherent states of the linear harmonic oscillator are defined and their properties discussed. They are used to discuss some simple problems (a single spin in a field, a spin wave, two spin ¹/₂ particles with Heisenberg coupling) and it is shown that their use may often give increased physical insight.

The partition sum (the diagonal element of the one-particle density matrix) of a gas of non-interacting boltzons in a random potential is calculated. It is shown that the author's formula for the averaged density matrix must be subject to a minor modification, being multiplied by a correction factor. A considerable simplification of the formula is achieved in a limiting case which was not dealt with previously but may be important enough if one has in mind electrons in amorphous semiconductors.

The problem of alpha decay of deformed even nuclei is treated by assuming the barrier to be the usual anisotropic electrostatic potential superimposed by a nonlocal alpha -nuclear potential. With certain assumptions a formula for the hindrance factor (H.F.)_l is derived. From straightforward calculations, and with a single value of epsilon ₈ for different nuclei, the values of (H.F.)₈ are found to be within 50% of the empirical values, whereas the values from the shell-model theory or from a purely Coulomb or static barrier hypothesis show large discrepancies. Similarly, for l<or=6, overall agreement for an average epsilon _l is better than obtained previously. For the best-fit values of an epsilon _l varying slightly with nuclear mass A and charge Z one obtains exact agreement (within 10%) with all the empirical (H.F.)_l values discussed.

The angular distribution of photoelectrons emitted from the K shell of lead and platinum by 483 keV linearly polarized photons has been studied. At forward emission angles the photoelectrons are emitted predominantly in the plane of polarization of the photons, but at an emission angle of 72 degrees a crossover effect is observed and the preferred plane of emission is orthogonal to the polarization plane of the photons. Although the crossover effect is expected from theoretical considerations it is observed to occur at a smaller emission angle than predicted by theory.

The neutron spectrum at sea level has been measured in the kinetic energy range 0.4-1.2 GeV using the charge exchange reaction n+p to p+n. In this energy range the vertical intensity of neutrons is found to be consistent with the value calculated from the work of Hughes and Marsden (abstr. A19942 of 1966) who estimated the global spectrum of neutrons from indirect measurements of the multiplicity distribution of neutrons in a neutron monitor.

A number of groups have observed air showers in the atmosphere at large zenith angles. The possibility of explaining these showers in terms of muon bremsstrahlung is examined; the expected shower size spectrum for this process is calculated and the method enables the sensitivity of shower frequency to high-energy muon intensity to be examined rather simply. Some problems associated with comparison of prediction with the experimental results are indicated. A tentative comparison indicates that when allowance is made for the effect of uncertainties in recorded shower size it is likely that the majority of the showers can be explained by muon bremsstrahlung.

A simple relationship is derived between L_c the critical length for amplified spontaneous emission, and L_T, the threshold length of gas that must be excited for laser action to occur in a cavity of loss delta _l. The relationship is experimentally verified and the semiclassical laser theory of Stenholm and Lamb is re-verified in a new way.

General results are developed for the Green function appropriate to radiation or diffraction in anisotropic media. The formulae may be evaluated from a knowledge of the geometry of the wavevector surfaces. The results allow the calculation of radiation fields in anisotropic media in both the Fresnel and Fraunhofer region. The case of optical radiation in a uniaxial medium is treated in detail.

The calculation is made in cylindrical geometry using a model similar to that introduced in 1968 by Arsenin and Chuyanov. A diffuse plasma is considered and the effect of varying the locations of the sensing and suppressing systems is examined in the following cases: both suppressor and sensor outside the plasma, only the sensor inside the plasma, and finally both sensor and suppressor inside the plasma. The density threshold is improved by factors of 4, 12 and 36 in the three cases. A sharp boundary plasma is also considered but phase shift and frequency response are included in the feedback terms. The Nyquist method is used to find a frequency response giving improved stability.

The flow rates of hydrogen, helium, argon, nitrogen, carbon dioxide, krypton and water vapour through both glass and silver parallel-plate channels have been measured for values of the ratio of the plate separation to the mean free path between 0.02 and 0.5. An equation for the diffusive flow is derived which takes account of the mode of scattering at the channel surface, which when compared with the experimental results shows that the scattering off the silver surfaces is diffusive, whereas that off the glass surfaces is mainly diffusive but with some specular reflection.

Precision measurements of the relative permittivity of n heptane at pressures up to 3334 bar and over a temperature range from 0 to 100 degrees C are reported. Similar data for carbon tetrachloride up to 1118 bars and at temperatures from 25 to 54 degrees C have also been obtained. The data have been fitted to various empirical and theoretical expressions involving relative permittivity, making use, where necessary, of densities determined by other workers.

The velocity and attenuation of sound and zero sound have been measured at a frequency of 120 MHz. The velocity increases by 5.6+or-0.3 m s^-1 over a temperature range centred on 34+or-3 mK, while the attenuation rises to a maximum value of 700 cm^-1. These results are comparable with those of Abel et al. at 15 and 45 MHz, and in agreement with the Landau theory with the parameter F₂ approximately equal to zero. A comparison of the values for the velocity with previous values for the impedance at 122 MHz shows that the fractional change in the impedance at the transition is larger than the fractional change in the velocity. This result appears inconsistent with the Bekarevich-Khalatnikov treatment of the impedance.

Starting from the appropriate equation of state for the liquid medium and taking a suitable form of the interaction potential, general expressions have been derived relating the velocity of sound to density, compressibility, and molecular weight of the liquid. The general relations reduce to the empirical relations of Wada and Rao as a special case.

A recent expression of Saksena and Sharma for the thermal conductivity of polyatomic gas mixtures has been presented in a well known form after Wassiljewa. The utility of the modified form has been tested by calculating the thermal conductivity of dry air, considered as a binary mixture, and comparing the values with experimental results.