Alpha Air Sample Counting Efficiency Versus Dust Loading: Evaluation of a Large Data Set.

Dust loading on air sample filters is known to cause a loss of efficiency for direct counting of alpha activity on the filters, but the amount of dust loading and the correction factor needed to account for attenuated alpha particles is difficult to assess. In this paper, correction factors are developed by statistical analysis of a large database of air sample results for a uranium and plutonium processing facility at the Savannah River Site. As is typically the case, dust-loading data is not directly available, but sample volume is found to be a reasonable proxy measure; the amount of dust loading is inferred by a combination of the derived correction factors and a Monte Carlo model. The technique compares the distribution of activity ratios [beta/(beta + alpha)] by volume and applies a range of correction factors on the raw alpha count rate. The best-fit results with this method are compared with MCNP modeling of activity uniformly deposited in the dust and analytical laboratory results of digested filters. A linear fit is proposed to evenly-deposited alpha activity collected on filters with dust loading over a range of about 2 mg cm to 1,000 mg cm.

Radon Levels Measured at a Touristic Thermal Spa Resort in Montagu (South Africa) and Associated Effective Doses.

Radon activity concentrations (in water and in air) were measured at 13 selected locations at the Avalon Springs thermal spa resort in Montagu (Western Cape, South Africa) to estimate the associated effective dose received by employees and visitors. A RAD-7 detector (DURRIDGE), based on alpha spectrometry, and electret detectors (E-PERM®Radelec) were used for these radon measurements. The primary source of radon was natural thermal waters from the hot spring, which were pumped to various locations on the resort, and consequently a range of radon in-water analyses were performed. Radon in-water activity concentration as a function of time (short term and long term measurements) and spatial distributions (different bathing pools, etc.) were studied. The mean radon in-water activity concentrations were found to be 205 ± 6 Bq L (source), 112 ± 5 Bq L (outdoor pool) and 79 ± 4 Bq L (indoor pool). Radon in-air activity concentrations were found to range between 33 ± 4 Bq m (at the outside bar) to 523 ± 26 Bq m (building enclosing the hot spring's source). The most significant potential radiation exposure identified is that due to inhalation of air rich in radon and its progeny by the resort employees. The annual occupational effective dose due to the inhalation of radon progeny ranges from 0.16 ± 0.01 mSv to 0.40 ± 0.02 mSv. For the water samples collected, the Ra in-water activity concentrations from samples collected were below the lower detection limit (~0.7 Bq L) of the γ-ray detector system used. No significant radiological health risk can be associated with radon and progeny from the hot spring at the Avalon Springs resort.

Indoor radon monitoring near an in situ leach mining site in D G Khan, Pakistan.

Indoor radon and its decay products are considered to be the second leading cause of lung cancer after cigarette smoking. This is why extensive radon surveys have been carried out in many countries of the world, including Pakistan. In this context, 25 spots were selected at workplaces in the vicinity of the uranium mining site in Dera Ghazi Khan District for indoor radon measurement. For this purpose, CR-39 based radon detectors were installed at head height and were exposed to indoor radon for 60 days. After retrieval, these detectors were etched in a 6 M solution of NaOH at the temperature of 80 °C for 16 h in order to make the alpha particle tracks visible. The observed track densities were related to the indoor radon concentration using a calibration factor of 2.7 tracks cm(-2) h(-1)/kBq m(-3). The measured indoor radon concentration ranged from ∼386 ±161 to 3028 ± 57 Bq m(-3) with an average value of 1508 ± 81 Bq m(-3) in the studied areas of Dera Ghazi Khan District. The mean annual effective dose ranged from 2.22 ± 0.93 to 17.44 ± 0.33 mSv yr(-1), with an average of 8.68 ± 0.47 mSv yr(-1). The effect of the seasonal correction factor (SCF) on the annual average radon concentration has also been considered. Results of the current study show that, for the majority of the workplaces studied, indoor radon levels exceed the action levels proposed by many world organisations.

[Depending on exposure, functional state of left ventricle in combined cardiovascular disease among chronic uranium intoxication patients].

State of left heart contractility in patients having IHD and AH during long-term period of chronic uranium intoxication depends on duration of exposure to toxic radiation factor. The authors revealed left ventricle myocardium weight decreased by 11.7% on exposure up to 10 years and that decreased by 18.9% on the exposure over 10 years, when compared to the reference group. Longer length of service was connected with higher share of patients with pathologic remodelling of left ventricle, mostly due to increased concentric remodelling.

NORM workers: a challenge for internal dosimetry programmes.

The mining, milling and processing of uranium and thorium bearing minerals may result in radiation doses to workers. The control of occupational exposures from these natural sources of radiation imposes a challenge to regulators and radiation protection advisers. A survey pilot programme, which included six mines in Brazil and a monazite plant, was established, consisting of the collection and analysis of concentrations of uranium, thorium and polonium in urine, faeces and air samples. Results from workers were compared to background data from their families living in the same area and from residents from the population of Rio de Janeiro. Positive exposure results were identified among the coal miners, the niobium miners and the monazite sand workers. Difficulties in the application of internal dosimetry programmes are discussed in relation to the control of NORM workers.

Estimate of the dose-increment due to outdoor exposure to gamma rays from uranium progeny deposited on the soil around a coal-fired power plant in Ajka Town, Hungary.

Brown coal unusually rich in uranium is burnt in a coal-fired power plant that lies inside the confines of a small industrial town named Ajka, Hungary, and has been operational since 1943. The 238U (226Ra) activity discharged to the atmosphere per unit electrical energy produced was about 330-400 GBq (GW y)(-1), which is 66-80 times more than that was estimated by UNSCEAR (1988) as a characteristic value for old type coal-fired power plants [5 GBq (GW y)(-1)]. The objective of this study was the experimentally established assessment of the artificial increment in the dose from external exposure to gamma rays of terrestrial radionuclides outdoors. Soil samples were collected in and near Ajka from 81 locations. The samples were investigated by Ge(Li) gamma spectrometry. Considerably elevated concentrations of uranium and its progeny have been measured in most of the samples that were collected near to the plant. Concentrations of 238U and 226Ra in the top (0-5 cm depth) layer of undisturbed soil at public areas inside town were 4.7 times higher, on average, than those in the uncontaminated deeper layers. Dose rate in air (air kerma) from external exposure to terrestrial gamma rays outdoors at a height of 1 m and effective doses were estimated from the measured activity concentrations using some relevant literature data. The estimated artificial increment in the dose rate in air was, on average, 32.8, 10.3, and 102.1 nGy h(-1) at public areas, vegetable gardens, and backyards, respectively. The mean artificial increment in the annual per caput effective dose from external exposure to terrestrial radionuclides outdoors is 21.8 microSv y(-1). The collective dose commitment per unit energy generated from outdoor exposure to the deposited uranium progeny is about 8.0-9.1 person Sv (GW y)(-1), which is 67-76 times more than that evaluated by UNSCEAR (1988) for a typical "old" coal-fired power plant [0.12 person Sv (GW y)(-1)]. Ajka is a suitable place for studying the dosimetric consequences of the utilization of coal for energy production experimentally.

Improvements in modeling sagebrush concentrations of radioiodine released from the Hanford site.

The Hanford Environmental Dose Reconstruction Project estimated the radiation dose to individuals from historical emissions of radioactive materials from the Hanford Site in Washington State. Project validation studies using predicted activity concentrations of 131I on sagebrush (Artemisia tridentata) showed a systematic underestimation against historical data during cold weather months, indicating a need for sagebrush model improvement. A deposition model for semi-volatile organic materials presented by Komp and McLachlen (Environ. Sci. Tech. 31 (1997) 886-890) is adapted here for gaseous iodine onto sagebrush. The deposition model includes a temperature-dependent term based on an integrated van't Hoff equation. Calibration data for the model are obtained from a release of 131I in 1963. Modeling results for releases in 1946 show a good match between historical data and predicted results using the new model. The new model shows improvement over interception-fraction type models, but requires plant-type-specific calibration data.

Aerial measurements on uranium ore mining, milling and processing areas in Germany.

The paper describes aerial measurements at several sites containing residues from uranium mines, waste rock dumps and tailings ponds of the Wismut company in Saxony and Thuringia. For the measurements, a computerized gamma-ray spectrometer equipped with a HPGe-detector and a NaI(Tl)-detector array with a volume of 121 was used. Radioactive anomalies from natural radionuclides have been detected and mapped. The activity concentrations of 226Ra, 228Th and 40K in areas with elevated radioactivity from natural radionuclides were determined from aerial measurements. Ground-based measurements--as far as available--confirmed these results. The mean 226Ra activity concentrations in the different waste rock dumps were found to be in the range 370 to 1600 Bq kg-1. The highest mean 226Ra activity concentrations were measured for the tailings ponds with values up to 1300 Bq kg-1. For 40K and 208Tl, activity concentrations of 860 and 40 Bq kg-1, respectively, were obtained as averages of all measurements. These values are commonly found in the environment. In general, there is reasonable agreement between the results measured with different detectors and measuring methods.

Full-spectrum analysis of natural gamma-ray spectra.

In this paper, a new system to measure natural gamma-radiation in situ will be presented. This system combines a high-efficiency BGO scintillation detector with full-spectrum data analysis (FSA). This technique uses the (nearly) full spectral shape and the so-called 'standard spectra' to calculate the activity concentrations of 40K, 232Th and 238U present in a geological matrix (sediment, rock, etc.). We describe the FSA and the determination of the standard spectra. Standard spectra are constructed for various geometries and a comparison in intensity and shape will be made. The performance of such a system has been compared to a more traditional system, consisting of a NaI detector in combination with the 'windows' analysis. For count rates typically encountered in field experiments, the same accuracy is obtained 10-20 times faster using the new system. This allows for shorter integration times and hence shorter measurements or a better spatial resolution. The applicability of such a system will be illustrated via an example of an airborne experiment in which the new system produced results comparable to those of much larger traditional systems. This paper will conclude with a discussion of the current status of the system and an outlook for future research.

Extraction of full absorption peaks in airborne gamma-spectrometry by filtering techniques coupled with a study of the derivatives. Comparison with the window method.

In this paper, an adaptation of a spectral profile analysis method, currently used in high-resolution spectrometry, to airborne gamma measurements is presented. A new algorithm has been developed for extraction of full absorption peaks by studying the variations in the spectral profile of data recorded with large-volume NaI detectors (16 l) with a short sampling time (2 s). The use of digital filters, taking into consideration the characteristics of the absorption peaks, significantly reduced the counting fluctuations, making detection possible based on study of the first and second derivatives. The absorption peaks are then obtained by modelling, followed by subtraction of the Compton continuum in the detection window. Compared to the conventional stripping ratio method, spectral profile analysis offers similar performance for the natural radioelements. The 137Cs 1SD detection limit is approximately 1200 Bq/m2 in a natural background of 200 Bq/kg 40K, 33 Bq/kg 238U and 33 Bq/kg 232Th. At low energy the very high continuum leads to detection limits similar to those obtained by the windows method, but the results obtained are more reliable. In the presence of peak overlaps, however, analysis of the spectral profile alone is not sufficient to separate the peaks, and further processing is necessary. Within the framework of environmental monitoring studies, spectral profile analysis is of great interest because it does not require any assumptions about the nature of the nuclides. The calculation of the concentrations from the results obtained is simple and reliable, since only the full absorption contributions are taken into consideration. A quantitative estimate of radioactive anomalies can thus be obtained rapidly.

Radon exposure in Slovenian spas.

Radon and gamma dose rates were surveyed in five Slovenian spas, at Rogaska Slatina, Radenci, Moravci, Podcetrtek, and Catez. Due to effective ventilation systems, the indoor air radon concentration rarely exceeds 200 Bq x m(-3) and is usually lower. Uncer the present operationsal conditions and working regimes of the spas, there is no basis for concern about elevated exposure of personnel to radon.

Enhanced airborne radioactivity during a pine pollen release episode.

A single episode of pine pollen release in the highly contaminated area of Novozybkov, Russian Federation, which led to enhanced atmospheric concentrations of 137Cs is discussed. The pollen grains were sampled by a rotating arm impactor and analysed by gamma-spectrometry for 137Cs activity and by image analysis for their size. In the vicinity of a forest, a maximum concentration of 4.5+/-0.4 mBq m(-3) was measured, and a mean activity per pollen grain of 260+/-80 nBq was determined. The emission rate of the Novozybkov mixed pine forest was estimated to be approximately 400 Bq m(-2) per year. Because of the large size of pine pollen grains (about 50 microm) and the short emission period of 5-8 days per year, the estimated potential annual inhalation doses are very low. Biological emissions including pollen release may be a source of increased airborne radionuclide concentrations at larger distances from the source areas as well.

Evaluation of continuous air monitor placement in a plutonium facility.

Department of Energy appraisers found continuous air monitors at Department of Energy plutonium facilities alarmed less than 30% of the time when integrated room plutonium air concentrations exceeded 500 DAC-hours. Without other interventions, this alarm percentage suggests the possibility that workers could be exposed to high airborne concentrations without continuous air monitor alarms. Past research has shown that placement of continuous air monitors is a critical component in rapid and reliable detection of airborne releases. At Los Alamos National Laboratory and many other Department of Energy plutonium facilities, continuous air monitors have been primarily placed at ventilation exhaust points. The purpose of this study was to evaluate and compare the effectiveness of exhaust register placement of workplace continuous air monitors with other sampling locations. Polydisperse oil aerosols were released from multiple locations in two plutonium laboratories at Los Alamos National Laboratory. An array of laser particle counters positioned in the rooms measured time-resolved aerosol dispersion. Results showed alternative placement of air samplers generally resulted in aerosol detection that was faster, often more sensitive, and equally reliable compared with samplers at exhaust registers.

Radiation data input for the design of dry or semi-dry U tailings disposal.

Before discussion of design criteria for the handling of dry or semi-dry tailings, it is necessary to obtain an insight into the radiation levels associated with the tailings particles and to study the basic physical properties of dry tailings. This article presents the experimental results of assessing Ra and specific alpha-activity distribution with respect to particle size of the Ranger (RUM) and Nabarlek (QML) uranium mines dry tailings samples. The variation of Rn emanation coefficient versus particle size of dry tailings has also been measured. The nuclear-track detection technique, gamma spectrometry and alpha counting were used for the above measurements. Surface Rn flux from the hypothetical Nabarlek semi-infinite dry tailings pile is 32 Bq m-2 s-1 and the Rn flux for Ranger is 10 Bq m-2 s-1. The theoretical exposure rates for 1 m above these hypothetical tailings piles are 0.95 microC kg-1 h-1 and 0.28 microC kg-1 h-1, respectively. The derived air alpha-contamination limits (DAAC) for the tailings dust were calculated to be 1.2 Bq m-3 for workers and 0.034 Bq m-3 for a member of the public. The limit for workers corresponds to the air tailings dust concentration of 0.79 mg m-3 for QML tailings and 2.2 mg m-3 for RUM tailings. The DAAC limit for the public corresponds to the air tailings dust concentration of 0.022 mg m-3 for QML tailings and 0.064 mg m-3 for RUM tailings.

Radiological health implications of lead-210 and polonium-210 accumulations in LPG refineries.

Radon-222, a naturally occurring radioactive noble gas, is often a contaminant in natural gas. During fractionation at processing plants, Radon tends to be concentrated in the Liquified Petroleum Gas (LPG) product stream. Radon-222 decays into a number of radioactive metallic daughters which can plate out on the interior surfaces of plant machinery. The hazards associated with gamma-emitting short-lived radon daughters have been investigated previously. The present work reports an analysis of the hazards associated with the long-lived daughters; Pb-210, Bi-210, and Po-210. These nuclides do not emit appreciable penetrating radiation, and hence do not represent a hazard as long as they remain on the inside surfaces of equipment. However, when equipment that has had prolonged exposure to an LPG stream is disassembled for repair or routine maintenance, opportunities for exposure to radioactive materials can occur. This paper reports a series of measurements made on an impeller taken from a pump in an LPG facility. Alpha spectroscopy revealed the presence of Po-210, and further measurements showed that the amount on the impeller surface was well above the exempt quantity. Breathing zone measurements made in the course of cleaning the impeller showed that an inhalation exposure equivalent to breathing Po-210 at the Maximum Permissible Concentration (MPC) for 60 hours could be delivered in less than half an hour. It was concluded that maintenance and repair work on LPG and derivitive product stream equipment must be carried out with the realization that a potential radiological health problem exists.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental effects of natural radionuclides from coal-fired power plants.

The assessment of the environmental effects of natural radionuclides contained in fly ash released from a coal-fired power plant was carried out and the following results were obtained. Mean concentrations of U, Th and K in 28 kinds of domestic and foreign coals were 1.0 ppm, 3.3 ppm and 2300 ppm, respectively. A good correlation between U and Th concentrations appears evident. Natural radionuclide concentrations of bottom and fly ashes were approximately equal in both ashes, and the values were the same as those calculated by concentration in coal divided by ash content. Release rates of 40K and radionuclides of each decay chain of U or Th were evaluated in the range of 2 to 40,000 pCi/sec for model coal-fired power plants of 1000 MW and 250 MW. The natural radionuclide concentration in air in a plume at the maximum concentration point was 5 X 10(-9) to 5 X 10(-3) pCi/m3, and these values were below 1/200 of those of natural origin.

The assessment of human exposure to radionuclides from a uranium mill tailings release and mine dewatering effluent.

This study provides an assessment of human exposure to radiation from a river system contaminated by radionuclides of the 238U decay series released through a dam break at a uranium mill tailings pond and by the continuous discharge of dewatering effluent from 2 uranium mines. The in vivo analyses of radionuclides in 6 Navajo Indians who lived near the river indicate no detectable elevations above background concentrations. Dose estimates for inhalation of suspended river sediment indicate a maximum annual 50-yr dose commitment of 204 mrem to the endosteum. Estimates of doses (50-yr dose commitments) from the ingestion of livestock range between 1 mrem (to liver) and 79 mrem (to bone) suggest that the major contribution to human exposure is from mine dewatering effluent that has been continuously released into the river system for many years. Although the estimated exposures do not exceed existing state or federal regulations, their magnitude justifies further measurement of radionuclides in animals and in the natural environment and the consideration of strategies to reduce radiation exposure to humans and animals.

On the escaping radioactivity from coal power plants (CPP).

The escaping radioactivity from Greek coal power plants (CPP) was studied. For the case studied the radioactivity is due to the uranium series. The major part (99%) escapes as very fine particles, while the rest is fly ash. The total escaping 226Ra activity is of the order of 40 Ci/yr. The particulate dispersion of fly ash in sites around the stacks of CPP is described. The hazards from the escaping radioactivity are evaluated.