Marvin H. Wilkening

Bio: Marvin H. Wilkening is an academic researcher. The author has contributed to research in topics: Radon & Eddy diffusion. The author has an hindex of 8, co-authored 9 publications receiving 556 citations.

Atmospheric pressure effects on 222Rn transport across the Earth-air interface

Abstract: 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.

Radon 222 from the ocean surface

Abstract: The flux of $sup 222$Rn from the ocean surface has been measured by the accumulation method off the windward coast of the island of Hawaii A figure of 74 +- 8 atoms m$sup -2$ s$sup -1$ was obtained, compared with a range of values from 11 to 116 atoms m$sup -2$ s$sup -1$ calculated from near-surface $sup 222$Rn concentration profiles in seawater obtained by other investigators If these results are representative, the total oceanic contribution to $sup 222$Rn in the global atmosphere is only about 2% of all $sup 222$Rn exhaled from continents Fluxes obtained by the accumulation method in shallow bay waters nearshore were intermediate between the very low value measured in the open ocean and the values obtained onshore

Daily and annual courses of natural atmospheric radioactivity

Abstract: Measurements of the radon-decay products in the atmosphere over a 6-year period have been made with a monitor which precipitates fine airborne particulate matter onto a moving metallic tape. A calibration of the apparatus showed that the mean value for radon content at Socorro, New Mexico, is 2.4×10−13 curie/liter, with an average diurnal fluctuation of a factor of 3.1 between maximum and minimum values. The diurnal variation is attributed to the amount of vertical mixing due to eddy diffusion in the lower atmosphere. The gustiness in air motion near the ground is taken as a measure of the mixing that occurs, and it is measured with a hot-wire anemometer. An annual variation in the atmospheric radioactivity is found which gives values during the fall months that are about twice those during the spring. This variation can also be explained in terms of the mixing that occurs at low levels as judged from mean wind-speed data. Values for the coefficient of vertical diffusion are calculated from measurements of the exhalation rate of radon from the ground and the concentration of radon near ground level as determined from the monitor data. The mean value of the height-independent diffusion coefficient is 6.7×104 cm2/sec. Maximum values of as high as 55×104 cm2/sec are found in the late afternoon of the month of April. Minimum values of the order of 2.0×104 cm2/sec are found in the early morning hours in the fall months.

Radon flux at the Earth‐air interface

Abstract: A radon condenser utilizing a trap cooled by liquid oxygen has been used to measure the radon content of the atmosphere and of the soil gases escaping through the surface of the earth. The average atmospheric-radon concentration at ground level in the Socorro area was found to be 0.24×10−12 curie/liter, and a measurement of the radon flux at the earth-air interface gave a result of 90×10−18 curie/cm2 sec. The radon content of the air showed a diurnal fluctuation, whereas the radon flux at the earth-air interface appeared to be relatively constant over a diurnal period. Diffusion theory is used to derive an expression for the radon flux in terms of the concentration of radon in the soil at depth. The flux value measured is consistent with a concentration of radon produced by 1.1×10−12 gram of radium per gram of soil.

Radon 222 concentrations in the convective patterns of a mountain environment

Abstract: Radon 222 concentrations have been measured in a mountain environment to learn more about radon 222 distribution and to test its usefulness in the study of certain features of convective cloud systems over a mountain range. Theoretical considerations make the use of radon 222 rather than its daughter products necessary in tracer applications of this kind. When the atmosphere is in a quiescent state, as generally occurs in the early morning hours, aircraft sampling gives radon concentrations varying from 0.43 pc/liter at 40 meters over a basin near the mountain ridge to 0.004 pc/liter at altitudes of nearly 8 km (MSL). The distribution over a mountain ridge follows that of potential temperature. Mountain slope heating is an important mechanism in the transport of air rich in radon 222 from the canyons and basins near the mountain to higher levels as solar heating progresses during the morning hours. Turbulence created by lee waves is another mechanism responsible for carrying radon 222 aloft. The first cumulus humilis clouds formed in the clear air above the mountains have a radon content in excess of their environment of approximately 25%. This appears to be supplied by air having a high radon content in updrafts below the cloud. Cumulus congestus exhibit patterns of activity that suggest an increase in radon flux into the cloud base over that found in the initial cloud development. Full-scale cumulonimbus systems may have an estimated total radon 222 content of the order of 1.5 curies in a volume of about 50 km3.

Ionizing Radiation: Sources and Biological Effects

Abstract: (1983). Ionizing Radiation: Sources and Biological Effects. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 43, No. 5, pp. 585-586.

Geochemistry of Atmospheric Radon and Radon Products

Abstract: The following topics are discussed: measurement of the radon-222 flux to the atmosphere; measurement of the lead-210 atmospheric flux; and the mean residence time of aerosols. A total global model is proposed for radon-222 and its daughters.

Radon transport from soil to air

Abstract: Radon generated within the upper few meters of the Earth's crust by the radioactive decay of radium can migrate during its brief lifetime from soil into the atmosphere. This phenomenon leads to a human health concern as inhalation of the short-lived decay products of radon causes irradiation of cells lining the respiratory tract. This paper reviews the factors that control the rate at which two radon isotopes, 222Rn and 220Rn, enter outdoor and indoor air from soil. The radium content of surface soils in the United States is usually in the range 10–100 Bq kg−1. The emanation coefficient, which refers to the fraction of radon generated in a material that enters the pore fluids, varies over a wide range with a typical value being 0.2. Radon in soil pores may be partitioned among three states: in the pore air, dissolved in the pore water, and sorbed to the soil grains. Except in the immediate vicinity of buildings, radon migrates through soil pores principally by molecular diffusion. Average reported flux densities from undisturbed soil into the atmosphere are 0.015–0.048 Bq m−2 s−1 for 222Rn and 1.6–1.7 Bq m−2 s−1 for 220Rn. Soil is the dominant source of radon in most buildings. Advective flow of soil gas across substructure penetrations is a key element in the transport process. The advective flow is driven by the weather (wind and indoor-outdoor temperature differences) and by the operation of building systems, such as heating and air conditioning equipment. A typical radon entry rate into a single-family dwelling of 10–15 kBq h−1 can be accounted for by weather-induced pressure-driven flow through moderately to highly permeable soils. The extent to which diffusion through soil pores contributes to radon entry into buildings is not known, but in buildings with elevated concentrations, diffusion is believed to be less important than advection.