Piotr T. Wasiolek

A two‐particle‐size model and measurements of radon progeny near the Earth's surface

Measurements of radon progeny in the attached-to-aerosol and unattached-to-aerosol states were made in central New Mexico. Simultaneous measurements of attached and unattached progeny at 0.2 and 2 m were carried out over a range of meteorological and terrain conditions. The ratio of the average progeny concentrations at 2.2 to 0.2 m was 1.06 for total progeny and 1.35 for unattached progeny, indicating a net downward flux, with the unattached progeny dominating removal to the Earths surface. Progeny/parent activity ratios greater than 1 were clearly detected (for example, at 0.2 m, the average 214Pb/218Po ratio was 1.43 ± 0.10), providing partial support for some previous observations. A two-particle-size model for radon progeny is able to account for the observed gradients, progeny/parent activity ratios greater than 1, and some trends in the experimental measurements as a function of meteorological conditions.

Relaxed Eddy Accumulator for Flux Measurement of Nanometer-Size Particles

ABSTRACT An investigation of the relaxed eddy accumulation (REA) technique to measure the flux of ultrafine (∼1 nm in diameter) aerosol particles using unattached radon progeny as a tracer and the construction of a prototype system based on the REA principle is reported. The system consisted of a sonic anemometer with a response frequency of 21 Hz, three screen/filter holders, a custom-built electronic circuit to control three electromagnetic inlet valves for sampling the up-, down- and neutral vertical winds, a high-capacity air blower and a portable PC. A 635-wire mesh screen/fiberglass filter combination was used in each intake to provide a separate measure of the unattached-to-aerosol and attached-to-aerosol radon progeny. The 9 cm-diameter 635 mesh screen, combined with an air flow rate of 230 L min−1, resulted in 50% penetration for 2.7 nm-diameter particles. Corrections for a system response delay of 125 ms and the screen collection and alpha counting efficiencies were incorporated into the flux ca...

Measurements of the Activity-Weighted Size Distributions of Radon Decay Products Outdoors in Central New Mexico with Parallel and Serial Screen Diffusion Batteries

Interest in deposition of natural atmospheric tracers motivated study of the activity-weighted size distribution of radon (222Rn) decay products outdoors. High-flow, large area parallel, and serial screen diffusion batteries were constructed. The combination of a 25 L min−1 flow rate and a 9-cm-diameter collection area allowed measurements of activity-weighted size distributions at ambient radon levels. The measurements were performed outdoors at two field sites in semi arid south-central New Mexico. Spectra show the classical bimodal distributions with the first peak between 1 and 2 nm and the second one around 100 nm. No significant activity was detected in the cluster mode of 10 nm.

Influence Of Dust Loading On The Alpha-particle Energy Resolution Of Continuous Air Monitors For Thin Deposits Of Radioactive Aerosols

Abstract— Alpha-particle continuous air monitors must sometimes be operated in dusty environments where significant dust loading of the filter can be anticipated. It is important to understand how this dust loading affects the response of the continuous air monitors. Not only must a filter be changed if there is a reduction in airflow, but a change may be necessary if the energy resolution deteriorates and the continuous air monitor loses sensitivity and specificity for the radioactive aerosols of interest. A series of experiments were conducted to investigate alpha-particle energy resolution of continuous air monitor filters, particularly under dust loading conditions. Aerosol particles of various sizes were tagged with radon decay products to serve as surrogates for radioactive aerosols of interest such as plutonium or uranium. While the size of radioactive aerosols, filter type, and dust type affected the energy resolution, the thickness of an underlying (nonradioactive) dust layer did not show significant effect for the materials studied and a loading range of 0.01–10 mg cm−2. Our results indicate that it is possible for continuous air monitors to detect the release of radioactive aerosols with little deterioration in energy resolution under conditions of significant dust loading provided that the deposited layer of radioactive aerosols remains thin (≤ 0.1 mg cm−2).

Radon and Radon Progeny in the Carlsbad Caverns

ABSTRACT Measurements were made in July 1994 to determine air exchange rate, aerosol characteristics, radon concentrations, and radon progeny activity size distributions in the Carlsbad Caverns. The measured radon concentrations were stable at a level of 1821 ± 55 Bq m−3 (mean ±SD). Using a SF6 trace gas method, it was determined that stagnant air in the Caverns was exchanged once every 18 days. The stagnant air was a key factor in maintaining stable environmental conditions and radon concentration. The low air exchange and few aerosol sources inside the Caverns also contributed to the low aerosol concentrations of between 200 and 400 cm −3—orders of magnitude lower than mining, indoor, and outdoor environments. The alpha spectrum showed radon progeny but no thoron progeny, which may be a result of the long transport time for radioactive gases to diffuse from the deep rock to the cave. The activity size distribution of radon progeny showed typical bimodal distributions with higher unattached fractions [69...

Experimental and modeling studies of 220Rn decay products in outdoor air near the ground surface

Measurements of the concentrations of 220Rn gas and its short-lived decay products (216Po, 212Pb, 212Bi) in attached-to-aerosol and unattached states were carried out at a semi-arid field site in central New Mexico under varying atmospheric conditions. A high volume air sampler (100 L min−1), with a single 635 mesh stainless steel screen (50% penetration for 4 nm particles) and a glass fiber filter, were employed. Analysis of the 105 outdoor measurements yielded the following average values: 9 Bq m−3 for the 220Rn activity concentration; 22 nJ m−3 for the concentration of potential alpha energy, 0.03 for the equilibrium factor, 0.15 for the unattached fraction of potential alpha energy, and 14 nSv h−1 for the effective dose rate. The measurements were interpreted using the computer code TPOUT, which applies one-dimensional eddy transport to calculate the vertical concentrations of 220Rn and its decay products as a function of atmospheric stability, aerosol concentration, terrain roughness, and surface wind speed. This code successfully predicted the observed trends of unattached and attached decay products concentrations with height, and demonstrated the importance of the mixing height and the rate of vertical transport for controlling breathing level dose. Projection of the present results to conditions typical of temperate climates suggests an average annual outdoor effective dose from 220Rn decay products of about 0.025 mSv, which is a significant component of the total outdoor dose.

Y marks the spot

The caption to your photograph of the Very Large Array (VLA) radio telescope (October 1999 p9) states that it is located in Mexico.

High-resolution real-time optical studies of radiological air sample filtration processes in an environmental continuous air monitor

The need for a continuous air monitor capable of quick and accurate measurements of airborne radioactivity in close proximity to the work environment during waste management, site restoration, and D&D operations led to the Los Alamos National Laboratory development of an environmental continuous air monitor (ECAM). Monitoring the hostile work environment of waste recovery, for example, presents unique challenges for detector design for detectors previously used for the clean room conditions of the typical plutonium laboratory. The environmental and atmospheric conditions (dust, high wind, etc.) influence aerosol particle penetration into the ECAM sampling head as well as the build-up of deposits on the ECAM filter.

Investigation of techniques to improve continuous air monitors under conditions of high dust loading in environmental setting. 1998 annual progress report

Improvement in understanding of the deposition of ambient dust particles on ECAM (Environmental Continuous Air Monitor) filters, reduction of the alpha-particle interference of radon progeny and other radioactive aerosols in different particle size ranges on filters, and development of ECAMs with increased sensitivity under dusty outdoor conditions. As of May 1, 1998 (1/2 year into the project) the research-prototype 30-cm pulsed ionization chamber (PIC) is assembled and operational with an alpha particle energy resolution of better than 45 keV for 5-MeV alpha particles. Measurements of spectral resolution for alpha particles from radon decay products have been made as a function of filter type and dust loading conditions. So far, a study of ten filter types has found that the best combination of resolution and throughput is obtained with 3.0 265m Millipore fluoropore and 1.0 265m Corning FNMB filters. Experiments with gypsum and Portland cement dust in the size range 1 to 20 265m indicate significant degradation in alpha particle resolution for dust loading above about 0.5 mg cm{sup -2}. Study of metalized films for possible use as a PIC window indicate a minimum broadening of 5-MeV alpha particle peaks from 43 (no film) to 301 keV (with film) for AVR film type B8 (0.20 mg cm{sup -2} polycarbonate). A modified ECAM sampling head, equipped with an optical microscopy system feeding data to a high resolution video data capture and logging instrument, was constructed. This system will enable time-lapse study of dust build-up on ECAM filters and formation of dendrite structures that can reduce alpha-particle resolution.