Robert F. Holub

Nanometer and ultrafine aerosols from radon radiolysis

The ability of ionizing radiation to produce condensation nuclei aerosols in filtered air is well known. Recent studies have indicated that radiolysis results initially in the production of highly diffusive, nanometer-sized ( 5 nm) can then evolve by coagulation and growth processes. The nanometer nuclei are, however, poorly detected by condensation nuclei counters (CNCs) since CNC efficiencies drop sharply for particle sizes <5 nm. In this work, the formation of: (1) PoOx molecular cluster aerosols from the decay of radon, and (2) sulfuric acid nanometer nuclei and ultrafine aerosols from the radiolytic oxidation of SO2 in radon-air mixtures, were studied through wire screen-based size distribution measurements of the 218Po radioactivity associated with the aerosols. Comparisons with conventional diffusion battery-CNC derived number size distributions are also presented.

The reduction of airborne radon daughter concentration by plateout on an air mixing fan.

A series of experiments have been made in the U.S. Bureau of Mines Radon Test Chamber to study the effects of condensation nuclei, humidity and turbulence on the rapid deposition or plateout of radon daughter activity on the chamber walls. Under low humidity conditions the presence of a small fan reduced the working level by 41%. The activity was not deposited on the walls by the turbulent flow from the fan but actually became attached to the fan blades. High relative humidity (So%) totally inhibited this observed effect. A detailed mechanism for transport of the daughter species seems to be the critical factor in interpreting the experimental results.

Characteristics and geological significance of particles on fractures from the Dongshengmiao polymetallic pyrite deposit, Inner Mongolia, China

Fault gouge samples were collected from deep-seated fractures in the Dongshengmiao polymetallic pyrite deposit. Fault gouge particles were analysed by transmission electron microscopy. Many particles were identified with sizes of 200 nm or less, such as carbon-bearing, gold, Pb-bearing or Zn-bearing mineral particles. Carbon-bearing particles included graphite, carbonate, organic matter and carbonate mixed with organic matter. Gold particles were found in fault gouge samples in the form of natural gold, which had not been previously observed. Other particles, such as Pb- and Zn-bearing particles, directly reflect the ore-forming elemental characteristics of the Dongshengmiao deposit. Based on analysis of these particles, the following conclusions made: (1) carbon-bearing particles were deduced to be able to provide additional information related to the deposit formation; (2) fracture-induced stress acted on particles based on the observed lattice deformations in the gold, graphite, dolomite and Fe-bearing particles and the uneven edges of many particles; and (3) information about concealed ore bodies can be more easily obtained through the study of fault gouge particles, which will make ore body exploration more efficient.

Tracing Outdoor/Indoor Penetration of PM2.5, PM1.0 by 210Po/210Pb

Alpha activities of 210Po were determined in low-volume, 24-hour samples of 2 particulate matter (PM) size fractions indoors and outdoors in 3 localities in the centre of Prague during the winter periods of 2002-2003. High values of ventilation rates (0.34 0.12h 1) and penetration of outdoor aerosols into the indoor environment, which favours particles smaller than 1 m size, allows the application of a simplified equation of the indoor/outdoor (I/O) relationship. The slope of linear regression of indoors against outdoors for both mass concentrations and alpha activities as well as the I/O penetration factors Cmass, and Calpha, respectively were determined. While the Cmass ranged from 0.46 to 0.64, appropriate Calpha ranged from 0.57 to 0.95 being always greater and reflecting size selective particle penetration through the building envelope. Personal activities indoors had little effect on particle deposition indoors, which is in agreement with the finding that the majority (70%) of PM2.5 indoors is formed by PM1.0. For all 3 localities it was shown that outdoor PM concentrations determined indoor ones while probably the particle removal during infiltration through the building envelope is the most important aerosol loss mechanism.

Evaluation of MDA instant working level meters

The U.S. Bureau of Mines and the Mine Safety and Health Administration have evaluated, for accuracy and reliability, a commercially available Instant Working Level Meter (IWLM) used by the mining industry to measure short-lived 222Rn-progeny concentrations. Six evaluation parameters were determined experimentally. These included two alpha and two beta detector efficiencies for the short-lived 222Rn progeny and two internal conversion factors. The experimental procedure detailing the evaluation technique is described in the paper. The measuring accuracy of 13 instruments is as follows: average inherent uncertainty (at least 68% confidence interval) is +/- 18%; for counting statistics and rounding at 0.10 WL (2.1 microJ m-3), coefficients of variation range from +/- 15% at low gamma flux backgrounds to +/- 50% at gamma flux backgrounds of 0.39 microC kg-1 h-1 (1.5 mR h-1). All parameters were derived theoretically and measured experimentally. All tests were conducted at a sample flow rate of 2.5 L min-1. A sample air flow rate of 7.5 L min-1 can lower the counting statistics to more acceptable levels at 0.1 WL (2.1 microJ m-3).

Role of plateout in radon daughter mixture distributions in uranium mine atmospheres.

The Bureau of Mines has made a study of the magnitude of measured variations of radon daughter mixtures, with the objective of determining whether these variations reflect the existing physical conditions in uranium mine atmospheres or if they are merely random or systematic errors. To accomplish this, many data have been plotted using a triangular graphing technique which shows that plateout depletes RaA more than RaB or RaC, and that it is impossible to find simple correlations between working level ratios, radon daughter mixtures, and age of air. INTRODUCTION STUDIES OF radon daughter air concentration measurements show that mixtures of RaA, RaB and RaC vary in an unpredictable manner. Factors affecting these daughter product mixtures have been studied by several investigators (Br69; Co74; Lo76; Ro69) but the results appear to be inconclusive. This study explores several factors having an influence on the results of measurements of RaA, RaB and RaC in mine atmospheres, such as measurement method errors, daughter growth models and daughter plateout. A growth model is an idealized time development of radon daughter concentrations in systems containing air, radon, and airborne radon daughters. There are three growth models (Br69) for an enclosed volume: (1) ventilated with constant radon emanation, (2) unventilated with continuous radon emanation, and (3) unventilated with an initially pure radon concentration (Ev69). There are three radon daughters that plate out or change their concentration before or during the sampling, which results in a multivariate statistical problem. However, it is beyond the scope of the present investigation to try to unravel these naturally dependent statistical variables since it would require, in the most general case, a determination of 9 standard deviations and up to 36 correlation coefficients. DESCRIPTION OF THE PLOTTING METHOD The basis of the plotting is the triangular graph used in Figs. 1 4 . Any point within the triangle represents an airborne activity mixture of radon daughters normalized to 1 working level (WL). The lower left corner represents pure RaA with an activity of 956.3pCi, the upper right corner represents pure RaB with an activity of 193.9 pCi, and the upper left corner represents pure RaC with an activity of 263.7 pCi. Zero activity for RaA and RaB is at the

Evaluation and modification of working level measurement methods.

Abstract-Four working level measurement methods have been evaluated and optimized from the inherent and statistical error standpoint. Optimization with respect to various sampling and measurement yielded no marked improvement over the existing methods. However, when appropiate approximations are made and evaluated exactly, the two measurement methods can be reduced to simple formulas eliminating a need to use nomograms. These modified methods also have improved inherent error characteristics. A new method-a combination of two existing methods-with improved inherent and statistical error has been suggested.