Radon progeny in Egyptian underground phosphate mines

In addition to the workers in uranium mines, the staff of other underground mines, such as workers in underground phosphate mines, can be exposed to 222Rn and its progeny. In this study the individual radon progeny concentrations were measured in three Egyptian underground phosphate mines to estimate the occupational exposure of the workers at those sites. A filter method was used to measure individual radon progeny concentrations (218Po, 214Pb and 214Po). The reported mean values of radon progeny concentrations exceed the action levels which are recommended by ICRP 65 (1993). Based on the measured individual radon progeny concentrations (218Po, 214Pb and 214Po) in these mines, the annual effective dose for the workers has been calculated using the lung dose model of ICRP 66 (1994). According to the obtained results, some countermeasures were recommended in this study to minimise these exposure levels.     

Bimodal unattached 218Po Radon progeny and the influence of enhanced deposition effect at high-radon levels

Unattached fraction (218)Po airborne particle size distributions from graded screen array diffusion batteries are analysed for bimodal constituents. The analysis is for the high (222)Rn concentration range from 10 to 50 kBq m(-3) where the recently reported enhanced deposition effect is in transition. We find that the single unattached fraction is distributed nominally at an arithmetic mean diameter (AMD) of 0.8-1.0 nm, and consists of two (218)Po molecular species with AMD congruent with 0.756 and 1.101 nm, respectively. In unfiltered room air the 0.756 nm species is the least stable, decreases monotonically in concentration magnitude beginning at 12 kBq m(-3) and disappears completely at approximately 32 kBq m(-3) (at a relative humidity of 54%). The AMD congruent with 1.101 nm mode does not become unstable until it reaches approximately 32 kBq m(-3) (222)Rn level and completely disappears at approximately 50 kBq m(-3). Similar behaviour is observed for filtered air but with some distinct differences. This work supports the bimodal findings for the (218)Po unattached fraction of Porstendorfer and co-workers and provides further details of the high-radon enhanced deposition effect.     

Indicatrices of the earth's surface reflection from Landsat MSS data

A method of obtaining an indicatrix or a scattering diagram of the earth's surface is developed. When we regard the earth's surface as a kind of irregular surface, the indicatrix of scattered radiation is a way of effective representation of its surface roughness. The indicatrices of radiation over the sands of a seashore, a downtown area of Tokyo, and some of its suburban areas are obtained from Landsat MSS data. The radiant intensity decreases within the range of 32 degrees to 65 degrees of scattering angles in accordance with the degree of urbanization. Experimental results obtained by a remote sensing simulator are compared with those of Landsat MSS data analysis.     

Radon progeny microdosimetry in human and rat bronchial airways: the effect of crossfire from the alveolar region

The objectives of the present study were (1) to present a comprehensiveanalysis of the microdosimetric quantities in both human andrat bronchial airways and (2) to assess the contribution ofthe crossfire alpha particles emitted from the alveolar regionto bronchial absorbed doses. Hit frequencies, absorbed dosesand critical microdosimetric quantities were calculated forbasal and secretory cell nuclei located at different depthsin epithelial tissue for each bronchial airway generation fordefined exposure conditions. Total absorbed doses and hit frequencieswere slightly higher in rat airways than in corresponding humanairways. This confirms the a priori assumption in rat inhalationexperiments that the rat lung is a suitable surrogate for thehuman lung. While the contribution of crossfire alpha particlesis insignificant in the human lung, it can reach 33% in peripheralbronchiolar airways of the rat lung. The latter contributionmay even further increase with increasing alveolar ²¹⁴Po activities.Hence, the observed prevalence of tumors in the bronchiolarregion of the rat lung may partly be attributed to the high-linearenergy transfer crossfire alpha particles.     

Radon progeny size distributions and enhanced deposition effects from high radon concentrations in an enclosed chamber

Prior work studying radon progeny in a small enclosed chamber found that at high (222)Rn concentrations an enhanced surface deposition was observed. Subsequent measurements for unfiltered air showed minimal charged particle mobility influence. Progeny particle size measurements reported here, performed at the US Department of Energy Environmental Measurement Laboratory (now with Home Security Department), using the EML graded screen array (GSA) system show in unfiltered air that the high (222)Rn levels causes a reduction in the attached (218)Po progeny airborne particulates and formation of additional normal sized unattached ( approximately 0.80 nm) and also even smaller (218)Po below 0.50 nm. At a (222)Rn level of 51 kBq m(-3), 73% of all (218)Po are of a mean particle diameter of about 0.40 +/- 0.02 nm. At this (222)Rn level, the ratio of (218)Po to (222)Rn airborne concentrations is reduced significantly from the concentration ratio at low (222)Rn levels. Similar reductions and size reformations were observed for the (214)Pb and (214)Bi/Po progeny. The particle size changes are further confirmed using the plateout rates and corresponding deposition velocities. The Crump and Seinfeld deposition theory provides the corresponding particle diffusion coefficients. With the diffusion coefficient to ultrafine clustered particle diameter correlation of Ramamurthi and Hopke, good agreement is obtained between EML GSA and deposition velocity data down to 0.40 nm. Strong evidence is presented that the progeny size reduction is due to, as a result of air ionization, the increased neutralization rate (primarily from electron scavenging of OH molecules) of the initially charged progeny. This is shown to increase with the (1/2) power of (222)Rn concentration and relative humidity as well as increased air change rate in the chamber. These results imply that at (222)Rn levels above 50 kBq m(-3), at relative humidity of 52%, a considerable reduction in lung dose could occur from preferential deposition of the progeny in the nasal and oral passages.     

Estimating seasonal deformations in the earth's crust in correcting for effects on the deter-mination of the earth's rotational parameters

Estimates are made of the vertical deformations in the Earth's crust produced by variable loads on regions having characteristic dimensions of the order of thousands of kilometers, which arise from the development and displacement of cyclones and anticyclones and also from the accumulation of snow and the passage of floods on large rivers. It is found that the total deformation in Siberia can attain 30 cm. It is necessary to correct for the periodic displacements in observational points in the service for determining the Earth's rotational parameters. Suggestions are made on organizing experiments on the deformations. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 5–7, March, 1994     

Inversion of the seismic parabolic Radon transform and the seismic hyperbolic Radon transform

Reflection seismology is a method of exploration of the hidden structure of the earth subsurface by processing received seismograms. For a long time, this processing utilizes the so-called slant stack transform, or line Radon transform. More recently, two generalizations of the slant stack transform have been introduced to extract new features of the seismic data and to improve their treatment. These transforms are the parabolic and hyperbolic seismic Radon transforms. The first transform maps a given function to its integrals over parabolas with a fixed axis direction, whereas the second one maps a function to its integrals over hyperbolas (more generally also over ellipses and circles) of fixed axis directions. We show how they can be converted to a line Radon transform, and thereby obtain their inversion formulas. Numerical simulations for each transform were performed and commented to illustrate the suggested algorithms.