Single-particle Studies Research Articles

Electromagnetic form factors of odd-A rotational nuclei.

We present a systematic study of single-particle and collective transverse current multipoles in the ground-state band of odd-A axially symmetric deformed nuclei. We analyze the interplay between single-particle and collective contributions to the total transverse form factors for elastic and inelastic scattering in a number of nuclei ${(}^{169}$Tm, $^{177}$,179Hf, $^{239}\mathrm{Pu}$), which exemplify different possibilities of ground-state ${k}^{\ensuremath{\pi}}$ bands ((1/${2}^{+}$,(7/${2}^{\mathrm{r}\mathrm{\ensuremath{-}}}$,(9/2+) and of odd-Z or odd-N character. We also discuss the dependence of form factors and static moments on the mean field used to generate the ground-state wave function. The dominant contribution is found to come from the odd nucleon, except in the low momentum transfer region (q<1 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$) where the core is manifest through its interference with the single-particle amplitude.

Polarized Light Scattering by Small Particles

All of the polarized light scattering properties of single particles and suspensions of particles are contained in the 16-element Mueller matrix. For single-particle studies the particle is electrostatically suspended, the light scattering functions are measured, and the particle is then extracted from the suspension chamber by placing it on the point of a needle. The particle is examined subsequently with an electron microscope to determine precisely its size and shape. Results will be presented for single polystyrene spheres, sphere multiplets, approximately cubic NaCl crystals, and cubes of MgO. Recent studies of suspensions have concentrated on oceanic hydrosols. Some results and general features of these hydrosols will be presented.

The structure of small, vapor-deposited particles: I. Experimental study of single crystals and particles with pentagonal profiles

The crystallographic structure of small gold particles vapor-deposited on NaCl substrates was investigated using high resolution,0 selected-zone dark field (SZDF), Bragg reflection imaging (BRI), moiré fringe imaging, and strong beam and weak beam dark field (WBDF) transmission electron microscopy (TEM) imaging techniques. Those particles that exhibit uniform contrast in bright field (BF) and have a distinct triangular shape are perfect single crystals with a face-centered cubic (fcc) structure. The particles with pentagonal profile were determined to be regular decahedra composed of five identical tetrahedral building units of non-fcc structure. Each unit has a body-centered orthorhombic crystal symmetry, slightly distorted from the fcc structure. The experimental evidence for this new particle model and for the conclusion that the older model based on fcc tetrahedral building units does not apply includes (a) SZDF-BRI micrographs demonstrating the nonexistence of gaps between the tetrahedral units; (b) WBDF images showing thickness fringes that exclude nonuniform lattice strains that would result from an fcc model with closed gaps; and (c) micrographs exhibiting characteristics moiré fringes in well-defined parts of the composite particles.

A study of particle motion induced by two-dimensional liquid oscillations

The motion of single particles in liquids undergoing two-dimensional oscillations has been studied both experimentally and theoretically. By imposing combined vertical and horizontal oscillations on a liquid, particle mean motion can be controlled so that individual particles either rise against gravity or fall. The one dimensional equation of particle motion was modified to suit this situation and numerical solutions were used to predict the occurrence of the rising motion although agreement with experiment was only qualitative. A dimensional analysis approach combined with experiments allowed prediction of particle behaviour within the range of variables of this study. Extension of the single particle studies to mixtures of quartz and galena in various flowing liquids allowed prediction of the conditions under which separation and upgrading of minerals could occur and this was verified experimentally.

Mathematical model of drying in a brown coal mill system. 1. Formulation of model

Brown coals, because of their high as-mined moisture contents, are dried as they are transported through the drying system of a power station mill, by hot gas taken from the boiler combustion chamber. In this paper, a mathematical model of the drying process that occurs in this system is developed and tested. In the first part of the paper, drying experiments on single coal particles in hot gas streams are described and a model of the drying of a single particle is developed. From the single-particle study, a rate equation is obtained which is used in the formulation of a model of the mill drying process. The basic assumptions necessary for the development of the drying-process model are discussed. Modifications to a simple model are proposed to account more realistically for gas-particle interactions.

Single particle studies of binary and ternary cation exchange kinetics

AbstractExtensive ternary ion‐exchange rate data for cases where particle‐diffusion is important are presented. Experimental rate data, using a single‐particle radioactive‐tracer technique, were obtained for the following systems in Dowex 50W‐X8 resin: Mn‐Cs‐Na, Ba‐Mn‐Na, and Sr‐Mn‐Cs. Nernst‐Planck equations have been used to describe the ternary ion‐exchange kinetics. The Nernst‐Planck model, when used for the correlation of binary and various types of ternary exchange data obtained under unfavorable equilibrium conditions, usually cannot afford to disregard liquid‐film resistance. The model incorporating the film effects correlated satisfactorily most of the experimental data, and even in cases where the correlation was not good, it interpreted adequately the trend of the results.

Stability studies of single catalyst particles

Criteria for the stability of single catalyst particles, which have previously been given in terms of the multiple solution region, are investigated by examining the dynamic behaviour in these regions. In general, the limits of stability given by steady state analyses are expected to be conservative and the results presented here confirm this. It is shown that it is feasible for catalyst particles to pass transiently into a region which would correspond to temperature runaway in the steady state, and then to return to the initial state. The conditions under which this is possible depend on the characteristics of the perturbation as well as on the initial steady state, since these determine the length of time spent in the region of potential temperature runaway. Although it does not seem possible at the present time to predict quantitatively the bounds on the amplitude and frequency of the disturbance which will lead to a stable response, it is shown that any particular system can be conveniently examined on a phase plot of fluid temperature against pellet temperature.

An evaluation of the pneumatic transport reactor

AbstractIn a pneumatic transport reactor, a dilute suspension of the reacting solid particles is conveyed by the gas stream through the reactor. The system is characterized by very short particle residence times. The relative flow rates of gas and solids are determined by the thermodynamic and kinetic requirements of the reacting conveyed systems.Design considerations for co‐current gas and solids flows are presented and a comparison between co‐gravity and counter‐gravity flow reactors is discussed for the case of iron ore reduction by hydrogen. Kinetic data from single particle studies have been used to predict the performance of a pilot‐scale reactor.

Single particle studies of cation‐exchange rates in packed beds: Barium ion‐sodium ion system

Single particle studies of cation‐exchange rates in packed beds: Barium ion‐sodium ion system

Combustion studies of single aluminum particles

Ignition and combustion of single aluminum particles at atmospheric pressure in ammonium perchlorate-fuel flames