222Rn Flux Research Articles

A field experiment on Rn flux from reclaimed uranium mill tailings.

Design and construction techniques are described for a 1.6 ha experimental reclamation plot consisting of a 1-m-thick slab of uranium mill tailings covered with various depths of overburden. A passive, activated charcoal device was developed and used for measurements of Rn flux at the soil surface. Observations on Rn flux vs overburden depth indicated that tailings covered with 1.5 m of revegetated or 0.3 m of bare overburden had Rn exhalation rates comparable to background. Vegetated subplots exhibited a significantly higher (often an order of magnitude) flux than the bare subplots. A positive correlation was observed between precipitation quantities and Rn flux.

Radon entry into houses having a crawl space.

The transport of 222Rn from soil, through a vented crawl space, and into the living space of single-family residences was studied. Two houses were monitored in detail for periods of 5 and 7 weeks. With crawl space vents open, the average indoor 222Rn concentrations were 1.2 and 0.6 pCi 1.-1 (44 and 22 Bq m-3); with the vents sealed the averages rose to 2.2 and 1.0 pCi 1.-1 (81 and 37 Bq m-3). The data suggest that, of the Rn released into the crawl space from the soil beneath the house, a significant fraction, perhaps 50% or more, enters the living space. The effect of 3 meteorological parameters--wind speed, indoor-outdoor temperature difference, and rate of barometric pressure change--on Rn concentration and entry rate were examined. In 1 of the houses a higher temperature difference corresponded to a higher indoor concentration, suggesting that the increased infiltration rate is more than compensated by an increase in the Rn entry rate. On the other hand, a high wind speed tended to reduce the indoor concentration, presumably by increasing both cross-ventilation of the crawl space and the infiltration rate of the living space. Results suggest that Rn transport into the crawl space of at least 1 of the houses occurred by pressure-driven flow, rather than solely by molecular diffusion. The diffusion coefficient of 222Rn through polyethylene sheeting, such as was present on the ground beneath this house, was measured in the laboratory and found to range from 0.65 X 10(-7) cm2 s-1 at 11 degrees C to 1.6 X 10(-7) cm2 s-1 at 25 degrees C, implying that the maximum diffusive flux through the sheet was many times smaller than that necessary to account for the rate of Rn entry into the house. A third house was studied using a tracer gas injected into the crawl space at a controlled rate. The fraction of air leaving the crawl space that entered the living space ranged from 0.3 to 0.65, in good agreement with results for Rn transmission in the other 2 houses, assuming that the 222Rn flux into the crawl space was comparable to that which would have resulted from molecular diffusion from soil having a 222Rn diffusion length of 1.0 m. By sealing leaks in the floor of this house, the average infiltration rate was reduced by 25%, but the indoor concentration of the tracer gas remained constant.

An Experimental Study on Diffusion and Exhalation of <sup>222</sup>Rn and <sup>220</sup>Rn from Building Materials

Results of measurements of the diffusion coefficients of 222Rn in commercial building materials, their dependence on porosity, and of 222Rn and 220Rn exhalation rates from building materials are presented. The surface on one side of the material under investigation was exposed to a high radon concentration. After a constant concentration gradient was established, the resulting activity flux of 222Rn at the unexposed side of the slab was determined by electrostatic deposition of 218Po ions. This procedure was also used in order to determine the natural 222Rn and 220Rn exhalation rates from these materials. The values of the 222Rn diffusion coefficients covered a range of between 2.8 x 10-6 m2.s-1 (gypsum) and 6.8 x 10-9 m2.s-1 (heavy concrete), and were strongly dependent on the porosity of the material. The measurements of the exhalation rates showed values in the range of 0.5 x 10-4 to 50 x 10-4 Bq.m-2.s-1 for 222Rn and 10-1 to 10-2 Bq.m-2.s-1 for 220Rn. Investigations of the emanating power revealed strong differences between 222Rn and 220Rn. The 220Rn emanating power was found to be on average about a factor of five smaller than that of 222Rn. The measured transport parameters were applied to estimate the effective dose equivalent by inhalation of short lived 222Rn and 220Rn daughters due to the 222Rn and 220Rn exhalation from walls.

Radiochemical observations on manganese nodules from three sedimentary environments in the north Pacific

Decay-series isotopes were measured on manganese nodules from three sedimentary environments, characterized by substrates of red clay (R), siliceous ooze (S) and hemipelagic clay (H). Growth rates of nodules are shown to be site dependent: 1–2 mm/Myr at site R, 3–8 mm/Myr at sites S, and 20–50 mm/ Myr at site H. Correlation between growth rate and the parameter Mn/Fe 2 suggests that regional diagenetic variations control the compositions and growth rates of the nodules. The frequency of nodule turnover and the period of their growth are assessed from the “top” vs. “bottom” distributions of several nuclides. Based on the 230Th, 231Pa and 226Ra data, turnover times of 10 3 to 10 5 years are estimated and they vary with relative size and shape of the specimens at a given site. The presence of unsupported 210Pb and 228Th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years, despite their old ages. The data also indicate that turnover rates are not more frequent than once every several years or decades. The 230Th- 226Ra, 226Ra- 210Pb and 232Th- 228Th disequilibrium relationships in the nodules allow the migratory behavior of 226Ra, 222Rn and 228Ra and their fluxes to be deduced: thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites R and S. At site R there is a net loss of radium to the sea; the opposite is true at site S. Surface nodules at site H trap radium from both sides, probably due to more intense diagenetic input of radium from sediment pore water. The effective diffusivities of 226Ra in nodules vary from 3 × 10 −12 to 8 × 10 −14 cm 2/s, dependent on the textural variation of the nodule material, which crudely reflects the growth rate and hence sedimentary environment. 222Rn diffuses out of nodules from all sides, with an effective diffusivity of ca. (2–6) × 10 −8 cm 2/s . At all sites nodules serve as a more effective source of 222Rn to sea water than their adjacent sediments. The outward flux of 222Rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments, an effect caused by the fact that Mn-rich nodules from more reduced environment act as a more efficient trap for 226Ra.

Radon 222 from the ocean surface

The flux of 222Rn from shallow water off the bay of Málaga has been measured by the accumulation method. The mean value of 67 atoms m−2 s−1 was obtained, compared with a range of values from 11 to 116 atoms m−2 s−1 calculated from near‐surface 222Rn profiles in seawater obtained by other investigators. Quantitative relations between the flux of 222Rn and 222Rn concentrations in surface water and the temperature of seawater were found. A correlation was also found between the flux of 222Rn and the wind speed at the moment of taking the sample.

Measurements of the effect of cyclic atmospheric pressure variation on the flux of 222RN from the soil

A continuous recording accumulator method has been employed to study the effect of natural pressure cycles such as due to the passage of cyclonic weather systems on the time‐averaged flux of 222Rn from the soil. Results indicate a modest net enhancement of flux (∼10%) for pressure variation with standard deviations on the order of 0.2 in Hg.

230Th, 226Ra and 222Rn in abyssal sediments

A model that predicts the flux of 222Rn out of deep-sea sediment is presented. The radon is ultimately generated by 230Th which is stripped from the overlying water into the sediment. Data from many authors are compared with the model predictions. It is shown that the continental contribution of ionium is not significant, and that at low sedimentation rates, biological mixing and erosional processes strongly affect the surface concentration of the ionium. Two cores from areas of slow sediment accumulation, one from a manganese nodule region of the central Pacific and one from the Rio Grande Rise in the Atlantic were analyzed at closely spaced intervals for 230Th, 226Ra, and 210Pb. The Pacific core displayed evidence of biological mixing down to 12 cm and had a sedimentation rate of only 0.04 cm/kyr. The Atlantic core seemed to be mixed to 8 cm and had a sedimentation rate of 0.07 cm/kyr. Both cores had less total excess 230Th than predicted. Radium sediment profiles are generated from the 230Th model. Adsorbed, dissolved, and solid-phase radium is considered. According to the model, diffusional losses of radium are especially important at low sedimentation rates. Any particulate, or excess radium input is ignored in this model. The model fits the two analyzed cores if the fraction of total radium available for adsorption-desorption is about 0.5–0.7, and if K, the distribution coefficient, is about 1000. Finally, the flux of radon out of the sediments is derived from the model-generated radium profiles. It is shown that the resulting standing crop of 222Rn in the overlying water may be considered as an added constraint in budgeting 230Th and 226Ra in deep-sea sediments.

Atmospheric pressure effects on222Rn transport across the Earth-air interface

The effect of large-scale atmospheric pressure changes on the 222Rn flux across the soil-air interface is investigated. Field data collected during 1972 and 1973 show that pressure changes of 1–2% associated with the passage of frontal systems produce changes in the 222Rn flux from 20 to 60%, depending upon the rate of change of pressure and its duration. A simple model of molecular diffusion combined with pressure-induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra-bearing sand. On the basis of this model, pressure changes of 10–20 mbar occurring over a period of 1–2 days produce Darcy velocities of the order of 10−4 cm s−1 near the surface of a soil having a permeability of 10−8 cm2. The corresponding variations in the 222Rn flux predicted by the model are in agreement with those observed from valley alluvium in central New Mexico.