Radon Diffusion Coefficient Research Articles

Emanation investigation of the structure microheterogeneities of Fe-S, Co-S and Ni-S melts

Liquid-liquid structural transitions have been investigated by means of the emanation method in Fe−S, Co−S, Ni−S melts near the eutectic point. Both polythermal and isothermal conditions were used in the experiments. The superheating values were 0–300 ° above the melting temperature. In order to calculate the diffusion coefficient of220Rn in melts a model connecting the emanation level with the diffusion coefficient of radon was employed. Using the diffusion coefficient vs. viscosity relationship /the Stokes-Einstein relation/ the viscosity of melts as a function of the composition and temperature was obtained. Cluster-formation in sulphide melts was estimated theoretically, the particle number in a cluster as a function of the composition was determined, and a correlation was established between viscosity and particle number in clusters vs. composition.

Alpha-particle autoradiography in CR-39: The determination of the microdistribution of activity and trace element analysis

New and elaborate techniques for alpha-particle autoradiography of thick specimens based on the plastic nuclear track detector CR-39 have been developed. These permit a full analysis of both trace element and microdistribution of alpha-active nuclides present. The important features of the techniques are: 1. (1) reliable low level counting down to 10 −15Ci g −1, 2. (2) high resolution alpha-particle spectroscopy in CR-39, 3. (3) determination of the absolute abundance of alpha active nuclides present in the specimen, 4. (4) determination of the distribution of emission with height up to 30 microns above the surface of the autoradiograph, 5. (5) the local determination of the radon diffusion coefficient in the specimen which is needed to calculate the activity levels of 222Rn and daughter nuclei, 6. (6) the analysis of small and large clusters of alpha-particle activity recorded on the autoradiograph. These techniques are briefly discussed.

Diffusion of Radon through Soils: A Pore Distribution Model

AbstractA mathematical model was developed for calculating radon diffusion coefficients from water contents and pore size distributions of soil materials. The model accounts for radon diffusion in the air‐filled and the water‐filled pore space, for radon solubility in water, and for Knudsen diffusion in extremely small air‐filled spaces. The model considers soil pores to be composed of all possible serial combinations of the size increments from a measured pore size distribution. Diffusion coefficients for the resulting composite pores are computed and then used to calculate the overall diffusion coefficient of the soil by assuming parallel diffusion through all of the pore combinations. The resulting diffusion coefficients increase with the median pore diameter, and decrease with increasing soil water contents and with increasing widths of the soil pore size distribution. The model diffusion coefficients compare well with measured coefficients and with empirical calculations and are useful in evaluating the required soil cover thickness for uranium mill tailings reclamation.

The determination of the diffusion coefficient of radon in a porous material by injecting radon and measuring the exhalation

A means of measuring the diffusion coefficient of radon in a porous medium has been developed and demonstrated. It is applicable whether or not the medium has a distributed radon source. Radon exhalation is measured from a pair of parallel, planar surfaces as a function of time after the sample has been externally impregnated with radon and, if a distributed source is present, after the sample has developed its own radon. The exhalation has been measured by means of grab samples taken with small, flow-through scintillation cells. The method is free of approximations within the limits of the model. The model includes the porosity of the medium, the adsorption of radon on the solid matrix, and the radon absorption on any pore moisture.

A technique for discrimination of radon ( 222Rn) and thoron ( 220Rn) in soil-gas using solid state nuclear track detectors

A technique for discrimination of radon ( 222Rn) and thoron ( 220Rn) in soil radon emanometry using SSNTDs has been described. It is based on the large ratio of their half lives and consequent difference in their diffusion lengths. It can be computed that a length of about 25 cm of an air column is adequate to eliminate thoron almost completely while radon is not much affected. Theoretical and experimental curves demonstrating the discrimination of radon and thoron using Kodak Pathe LR-115 cellulose nitrate films have been presented. The design of a sonde for the estimation of radon as well as thoron in soil gas for uranium exploration is given. Diffusion coefficient of radon in air at room temperature has been determined experimentally.

Effect of Moisture Content on Radon Emanation from Uranium Ore and Tailings

A study was made of the effect of moisture on the emanation coefficient and radon flux from uranium mill tailings. A sharp rise in emanation coefficient occurred as the moisture content was increased from the absolutely dry state to 2% water by weight. The emanation coefficients from water-saturated tailings were about four times those from absolutely dry materials. Radon flux was measured from columns of dry, moist and water-saturated tailings. The highest flux came from the column filled with moist tailings. This can be explained by the effect of moisture content on the emanation coefficient. Water-saturated tailings gave the lowest flux because of the much lower diffusion coefficient of radon through water.

The microdistribution of α-active nuclei in the human lung I - techniques

ABSTRACT We present further developments of our technique for high sensitivity high resolution α-particle autoradiography of human lung tissue using CR-39 plastic. High resolution measurements of α-track length and dip angle on the auto radiograph are made. The distributions of these quantities allow the distribution of α-active elements present to be calculated. Any localisation of height emission up to 30 μm above the plastic surface can also be found. Using a distribution of distance to nearest neighbour of α-tracks on the autoradiograph the Radon diffusion coefficient is measured. This information is necessary in order to calculate the thickness of tissue sampled for Rn222 and daughter nuclei.

Effective diffusion coefficient of radon in concrete, theory and method for field measurements.

Abstract A linear diffusion model serves as the basis for determination of an effective radon diffusion coefficient in concrete. The coefficient was needed to later allow quantitative prediction of radon accumulation within and behind concrete walls after application of an impervious radon barrier. A resolution of certain descrepancies noted in the literature in the use of an effective diffusion coefficient to model diffusion of a radioactive gas through a porous medium is suggested. An outline of factors expected to affect the concrete physical structure and the effective diffusion coefficient of radon through it is also presented. Finally, a field method for evaluating effective radon diffusion coefficients in concrete is proposed and results of measurements performed on a concrete foundation wall are compared with similar published values of gas diffusion coefficients in concrete.

Radon-222 in the Lunar Atmosphere

THE concentration of polonium-210 has been measured in the Solar Wind Composition (SWC) experiment foils which were exposed on the surface of the Moon by the Apollo 11 and Apollo 12 astronauts. These data permit a direct calculation of the equilibrium lunar atmospheric content of radon-222 which Kraner et al.1 had estimated to be 4 disintegrations cm−2 s−1 using terrestrial values of the radon diffusion coefficient and uranium concentration and assuming a lunar surface porosity of 0.25. In 1969 Yeh and Van Allen2 set upper limits for the alpha-particle emissivity of the Moon which indicated the radon-222 concentration was at least an order of magnitude lower than the provisional estimates of Kraner. Their calculations were based on alpha flux measurements made by a totally depleted gold–silicon surface barrier detector on the Moon-orbiting spacecraft, Explorer 35.