Short-lived Daughters Research Articles

Implication of Particle Sources in the Calculation of the Dose Arising from Exposure to Radon Progeny in Indoor Atmospheres

Radon is ubiquitous in the biosphere and present in soils and building materials. It accounts for about half of our total irradiation dose from natural sources. An association has been demonstrated in uranium miners between their exposure to radon and its decay products and an excess risk of lung cancer, however, any effect of domestic radon exposure in the production of lung cancer remains unclear. Epidemiologic and dosimetric approaches have been used to study the problem, but there is considerable variation between the results from each method. To better estimate the risk a European large-scale research programme has been conducted. One aim of the study was to better characterise the size distribution of particulates carrying radon progeny including their variation with time and ambient conditions. A methodology was developed to measure the particulate size distribution, unattached fraction and the equilibrium factor of 222Rn short-lived daughters. Measurements were made in a traditional dwelling built on a granitic soil in Brittany. Over 11 months, radon activity concentration was on average 1,420 Bq·m–3 (240–2,800 Bq·m–3), but it was concluded that such an approach only allows assessment of the dose as the sum of the unattached and attached forms.

Radiological Benchmarks for Effects on Aquatic Biota at the Oak Ridge Reservation

Radiological benchmarks for aquatic biota were developed for use at the U.S. Department of Energy's Oak Ridge Reservation as screening values to determine the spatial extent of potential ecological effects and to identify the need for additional site-specific investigation. The Point Source Dose Distribution approach was used to calculate water and sediment activities for selected radionuclides that result in a total dose rate to small and large fish of 1 Rad d−1, which is the National Council on Radiation Protection and Measurements recommended acceptable dose rate to natural populations of aquatic biota. These screening values incorporate internal and external exposures from parent isotopes and all short-lived daughter products. They also include exposures from all major alpha, beta, and gamma emissions for each isotope. Unlike exposures to chemicals, exposures to radionuclides are expressed as the dose rate received by the organism. Dose rates that account for the biological effects to the organism are additive. If the total dose rate from all radionuclides and pathways exceeds a recommended acceptable dose rate, further analysis is needed to determine the hazards posed by radionuclides. If, however, the total dose rate falls below an acceptable dose rate, radionuclides may be eliminated from further study.

Analysis of alpha-emitting isotopes in an inorganic scintillator

Large scintillating crystals are used in searches for dark matter and other elusive phenomena where the presence of trace radioisotopes is a major source of background. We describe a method for determining alpha-emitters present in concentrations very much less than 10 −12. The optimal filter for pulse shape discrimination, described by Gatti nearly 40 years ago, is implemented using modern digital techniques. Results are presented for a large NaI(Tl) scintillator; we give a detailed quantitative analysis of its radio-impurities, showing that the 235 U series is essentially absent and that both the 232 Th and 238 U series are far from equilibrium, the main contaminants being the radium isotopes and their short-lived daughters.

Mass Transfer of Diffusive Species with Nonconstant In-Flight Formation and Removal in Laminar Tube Flow. Application to Unattached Short-Lived Radon Daughters

This article deals with convective-diffusive aerosol transport with in-flight formation and removal and is applied to the unattached fraction of short-lived radon decay products. Two novel contributions to previous studies are given in this numerical and experimental work: on the one hand, we solve the mass-transport equations for all the short-lived radon daughters; on the other hand, we include the 218Po neutralization into the mass-transport equation of the first radon decay product. Concerning the mass-transfer of all short-lived radon daughters, numerical calculations lead to the development of simple correlations for the 214Pb and 214Bi penetration fractions. Those correlations can be used to determine the diffusion coefficient of 214Pb and 214Bi using the 2-filter method. In our experiments, a diffusion coefficient equal to 5 X 10-6 m2 s-1 is found for the 214Pb. Concerning the 218Po neutralization, better agreement is observed between our numerical and experimental results when 218Po neutralizatio...

Alpha-Particle Dosimetry Using Solid State Nuclear Track Detectors: Application to 222Rn and its daughters

We present a methodology for the determination of the detection efficiency of a solid state nuclear track detector for radon and its short-lived daughters. First, particular attention is paid to the α-particles having energies and angles of incidence that lead to observable tracks after an adapted chemical etching. These results are then incorporated in a mathematical model to determine the theoretical radon detection efficiency of a polymeric detector placed in a cylindrical cell. When applied to LR115 and CR39 detectors, the model reveals the influence of the position of the radon daughters inside the cell. Radon daughters tend to link up with natural atmospheric aerosols and then settle on the cell's inside wall. This model allows to determine, among other things, the cell size for which the detector response is independent of the fraction daughters plated out.

Three Decades of Track Detectors in Polish Metal-Ore Mines

The assessment of exposure caused by radon (222Rn) and its short-lived daughters (RnDP) in the air of Polish underground mines is reported. The first measurements were carried out in 1966; the active methods (Lucas cells) were used at that time. The results of the measurements pointed to a high probability of exposure at the level of 35 mJ.h.m-3 (10 WLM). In the early 1970s routine investigations were undertaken in Polish underground metal-ore mines. As a measuring device the passive, open-type dosemeter with Kodak LR-115 film was used. The first measurements were performed as environmental assessments but this changed in 1977 when individual dosimetry was introduced. The results here presented indicate that the average annual exposure to RnDP in Polish metal-ore mines has stabilised since the 1980s and equals approximately 1.4 mJ.h.m-3 (0.4 WLM).

Diurnal Variation in Radon Concentration and Mixing-Layer Depths

Variation of 222Rn, its short-lived daughters and 212Pb concentrations in the atmosphere, and conditions of the lower atmosphere were observed simultaneously at Kamisaibara Village in Japan. The variation of 222Rn concentration and the ratio of the concentrations of 212Pb and the short-lived daughters of 222Rn during nighttime is explained by sodar echoes and temperature profiles obtained by an instrumented tethered balloon. Depths of the convective mixing layer estimated using the 222Rn concentration, using the surface sensible heat flux, and obtained by low-level sondes are compared and found to be in approximate agreement.

Estimating Heat Generation Rates for Wastes Contaminated Primarily by 137Cs and 90Sr

A method is described to estimate the heat generation rate of various high-level waste (HLW) forms composed primarily of either a sludge (with a composition similar to that in the Hanford HLW tanks) or borosilicate glass. The main heat source is from radioactive decay and subsequent self-absorption of particles emitted from 137Cs, 90Sr, or their radioactive daughters contained in the waste form. The heat generation rate of the waste form is usually an important parameter in safety and performance assessments and will likely be a part of the specifications required for the vitrified waste. The heat generation rate depends on the size of the waste because larger waste forms will tend to absorb a greater fraction of the gamma radiation from 137mBa decays (a short-lived radioactive daughter of 137Cs). Because beta radiation from these two nuclides is short ranged (only a few tenths of a millimetre in water), assumption of complete self-absorption of beta radiation is justifiable. Previous work in this area estimated upper and lower bounds for the volume-averaged heat generation rate per litre of waste based on total (i.e., large-sized waste forms) and zero (i.e., small-sized waste forms) self-absorption of gamma radiation emitted from 137mBa. This analysis extends the previous work to more adequately estimate the heat generation rate of intermediate-sized waste forms based on the composition of the waste (either borosilicate glass or a simulated sludge), and the size of the waste as characterized by the surface-area-to-volume ratio. The analyses are based on runs of the MCNP version 4A code.

A-61 北海道におけるラドンならびに短寿命娘核種の放射能濃度に関する研究

A-61 北海道におけるラドンならびに短寿命娘核種の放射能濃度に関する研究

Transport of U- and Th-Series Radionuclides in Groundwater

The purpose of this study is to understand the behaviour of the actinides in groundwater by combining data on the distribution of both longlived and short-lived nuclides of the U and Th decay series in an aquifer with a model for the nuclide transport along aquifer flow lines. The groundwater concentrations of the short-lived nuclides, such as 222Rn, 224Ra and 234Th, provide information only on local aquifer conditions, while the concentrations of the long-lived nuclides reflect geochemical processes along extended flow paths. In an important study, Krishnaswami et al. (1982) calculated sorption rate constants for many of the decay series nuclides in an aquifer using a batch model. However, no study yet has combined the data provided by both long and short-lived radionuclides to study the transport mechanisms along a flow line. Furthermore, although colloidal phases have been found to be important carriers of U and Th in numerous natural aqueous systems, very few investigations have been conducted on their importance in the transport of naturally-occurring actinides in groundwater. The aquifer investigated here is the sandy unconfined Upper Glacial Pleistocene aquifer situated in Long Island, NY. Extensive information regarding the geology and the hydrology of the aquifer is available and numerous high quality and well-documented wells are available for sample collection. This aquifer is underlain by a discontinuous layer of impermeable clay, below which is a sandy confined aquifer, the Magothy, where reducing conditions prevail. Radionuclide data from several wells in this aquifer have been reported by Copenhaver et al. (1993). Samples from the Upper Glacial aquifer have been taken along two flow lines at three different depths and filtered through 0.45 gm filter cartridges. In addition, cross-flow ultrafiltration has been used to separate colloids >10 kD from ultrafiltered water that represents the dissolved load. This technique, described in previous papers, has proven to be successful in studying the association of uranium and other elements with colloids (e.g. Porcelli et al., 1997). The concentrations of the long-lived radionuclides :3SU, 234U and 23eTh have been measured by thermal ionization mass spectrometry and the short-lived radiogenic daughters 222Rn, 226Ra, 228Ra, 224Ra, 234Th by counting methods. In addition, the water samples have been analysed for pH and conductivity in the field, and for concentrations of major cations, anions and trace elements. Water samples from the Upper Glacial aquifer have pH values of 5.4 to 6.5 and TDS (Total Dissolved Solid) of 20 to 100 mg/l. The high Mn concentration in a deep sample of the shallow aquifer likely indicates a difference in redox conditions. The Magothy aquifer has TDS o f 50 mg/1, comparable to that of the unconfined aquifer, but much higher Fe and Mn concentrations. The 222Rn activities generally full within a restricted range throughout the Upper Glacial aquifer of 65 to 170 dpm/kg, with two peak values of 3 36 and 522 dprn/kg. The amount of Rn in the water represents -4 % of the Rn produced in the rock by decay. Assuming that the aquifer rock consists of solid spherical grains with uniform distribution of Ra, this amount of Rn can only be supplied by grains of ~ 0.1 ~tm in size and therefore cannot be produced by the aquifer which average grain size is ~1 mm. This has been observed previously (e.g. Copenhaver et al., 1993). High Rn concentrations have been observed and lead to the requirement that Rn is circulating through nanopores or that the source of Rn is on the surface. We observe that the dissolved Rn concentration is generally greater where the dissolved 226Ra concentration is lower, suggesting that higher Rn concentrations in the water are due to increased amounts of 226Ra on aquifer surfaces due to deposition of dissolved 226Ra. Therefore we infer that Rn concentrations here are controlled by the distribution of Ra on surfaces rather than by enhanced release from

Activation of the mec-3 promoter in two classes of stereotyped lineages in Caenorhabditis elegans

The mec-3 gene of Caenorhabditis elegans encodes a homeodomain protein and is expressed in one of two cells upon asymmetric cell division. As a result of asymmetric mec-3 expression, the two sister cells express different fates, so mec-3 is a likely target for the machinery that mediates asymmetric cell division. The unc-86 gene encodes a homeodomain protein of the POU family, which activates mec-3 by binding to its promoter. The ten mec-3-expressing cells are a subset of the anterior daughters of UNC-86-containing cells. Posterior daughters of UNC-86-containing cells do not express mec-3, even though the UNC-86 protein is distributed into both daughter cells. Lineages that express the unc-86 and mec-3 genes can be grouped into two types: in Type I lineages, UNC-86 protein is first made in the immediate parent of the terminal mec-3-expressing cell, while in Type II lineages, UNC-86 is first made in the grandparent of the terminal mec-3-expressing cell. The purpose of experiments presented here is to understand the relationship between the mec-3 expression patterns in each type of lineage, and to determine the fundamental activity pattern of the mec-3 promoter. We find that in the Type I V5.pa lineage, mec-3-lacZ is first synthesized in the terminal PVDR neuron, one cell division after unc-86 is expressed. mec-3 expression in PVDR can occur by transcriptional regulation alone; segregation of the mec-3 RNA or protein is not required to explain the asymmetric expression of mec-3. In the Type II Q lineage, the mec-3 promoter activity can be detected in the immediate anterior daughter of the first unc-86-expressing cell, but when this cell divides, mec-3 is expressed in only one of its daughters at later times. It seems likely that, in the short-lived immediate anterior daughter cell in Type II lineages, mec-3 product does not accumulate to levels that can influence subsequent events. Our results suggest that the mec-3 promoter is activated in all anterior daughters of unc-86-expressing cells.

The ratio of long-lived to short-lived radon-222 progeny concentrations in ground-level air

The ratio of 210Pb air concentration to the short-lived radon ( 222Rn) decay products concentration at ground level was investigated at a semi-rural location 10 km north of Munich, south Germany, for a period of 11 years (1982–1992). The average ratio from 132 monthly mean values has been found to be (7.5 ± 2.2) × 10 −5 (arithmetic mean ± S.D.). While the time series of the short-lived radon daughter concentration exhibit a distinct seasonal pattern with maxima mostly in October of each year, the course of 210Pb air concentration is characterized by high values from October through February. Consequently, high ratios of 210Pb to short-lived decay product concentration are often observed in the winter months of December–February. To study the influence of meteorological conditions on this behaviour, 210Pb and 214Pb concentrations were measured on a short-term basis with sampling intervals of 2–3 days from October 1991 to November 1992. The air concentrations obtained within those intervals were then correlated with actual meteorological parameters. On the base of this investigation the seasonal behaviour can essentially be explained by the more frequent inversion weather conditions in winter than in the summer months. At the same location, the average ratio of 210Po to 210Pb concentration in ground level air has been found to be 0.079 from 459 weakly mean values between 1976 and 1985. Hence, the corresponding average ratios of the short-lived radon daughters (EEC) to 210Pb and 210Po, were 1:7.5 × 10 −5 and 1:0.6 × 10 −5, respectively.

Radionuclides in Building Materials and Radon Indoor Concentrations

Radon concentrations in air and gamma dose rates were measured in a hundred and sixty-seven houses in Belgrade. Indoor radon concentrations determined by alpha scintillation counting were in the range from 10 to 200 Bq.m 3 and were roughly correlated with building materials corresponding to the age of the house. The vertical distribution of the mean radon indoor concentrations was also estimated. The annual effective equivalent dose for indoor radon and its short-lived daughters estimated for the mean radon in air concentration (58 Bq.m -3 ) was 1.3 mSv. The contents of natural radionuclides ( 232 Th, 226 Ra, 40 K) in raw building materials (gravel, quartz sand, cement, unhydrated lime) and final products (Siporex expanded concrete) were determined by standard gamma spectrometry.

An extended radon chamber model

The radon chamber model developed at the Paul Scherrer Institut (PSI) is covering differences in size between the different short-lived radon daughters by taking into account nuclide specific deposition and attachment rates. The resulting set of differential equations was analytically solved and the solutions were installed into a computer code. Different modes of operation of a radon chamber (continuous flow, pulse, and feedback) were analysed with the model. The influence of aerosol sampling on the chamber atmosphere was studied. Increasing the diffusion constant of the radon daughter clusters increases both attachment and deposition rates. As a consequence, the unattached concentration of the radon daughter with the shortest half-life, 218Po, is reduced relative to the radon progeny 214Pb and 214 Bi 214 Po , compared with calculations with equal mobilities of the radon progeny. The amount of 218Po activity deposited on the chamber walls also is increased relative to the other radon progeny if the size of 218Po is considered to be smaller.

Radon in soil and ground water survey around the Laguna Verde Nucleoelectric Facility, Mexico

Surveys of radon and short-lived daughters concentration levels have been performed in soil and groundwater around the Laguna Verde, Mexico, nuclear power facility. The soil monitoring was carried out at the power plant site, at a nearby aquifer, and at three localities where local seismic activity of low intensity occur. Groundwater samplings were performed at already existing wells. Solid State Nuclear Track Detectors (SSNTD) were used for radon in soil and groundwater determinations, while 214Pb and 214 Bi activities in soil and groundwater samples were obtained from the routine gamma spectrometry studies included in the Radiological Environmental Program of the plant. The results showed seasonal variations in the radon and daughters concentration levels, both in groundwater and in soil. The higher soil radon and daughters values are found at a nearby geologic fault. The radon potential of the zone can be considered low risk.

The Bronchial Dosemeter

It has been known for some decades that most of the radiation dose to the lung is due to the inhalation of the short-lived decay products of 222 Rn. Their deposition in the respiratory tract depends strongly on the attachment rate to aerosol particles present in indoor air and their plateout rate to surfaces. Instead of measuring the activity size distribution of the airborne decay products, knowledge of the respiratory tract retention has been incorporated in the design of a measurement system, called a bronchial dosemeter, to assess the lung dose directly. The simulation of the deposition characteristics of the short-lived radon daughters in the nasal cavity and the bronchial tree is based on the comparison of the model of the respiratory tract with results from screen penetration theory. A bronchial dosemeter consisting of three sampling heads has been built and calibrated.

Contribution of uranium to gross alpha radioactivity in some environmental samples in Kuwait

This study was done in connection with the use of uranium-tipped antitank shells during the Gulf War and possible contamination of the environment of Kuwait. It was found that uranium concentrations in the soil samples ranged from 0.3 μg/g to 1.85 μg/g. The average value of 0.7 μg/g was lower than the world average value of 2.1 μg/g for surface soils. Its contribution to the total natural alpha radioactivity (excluding Rn and its short-lived daughters) varied from 1.1% to 14%. The solid fall-out samples showed higher uranium concentration which varied from 0.35 μg/g to 1.73 μg/g (average 1.47 μg/g) but its contribution to the gross alpha radioactivity was in the same range, from 1.1 to 13.2%. The difference in the concentration of uranium in suspended air matter samples during the summer of 1993 and the winter of 1994 was found to be 2.0 μg/g and 1.0 μg/g, respectively. The uranium contribution to the natural alpha radioactivity in these samples was in the same range but lower for the winter period. The isotopic ratio of 235U to 238U for the measured samples was basically within an experimental error of ±0.001, close to the theoretical value of 0.007. The calculated total annual intake of uranium via inhalation for the Kuwait population was 0.07 Bq, e.g., 0.2% of the annual limit on intake.

Aerosols, Radon and Its Short-Lived Daughters

Aerosols, Radon and Its Short-Lived Daughters

Radon Concentrations in Rudas Thermal Bath, Budapest

Abstract Workers and visitors in thermal spas are exposed to radiation from radon and short-lived daughters. Radon concentrations in the premises of a thermal bath in Budapest were investigated; high radon concentrations (up to 7.15 kBq.m-3) were found in some rooms. Bronchial dose and effective dose equivalent values were estimated for the staff and the visitors. In some cases the effective dose was about or in excess of 20 mSv annual limit for the workers. Doses for the visitors were about 4 mSv per year, but exposure of the public from radon is still outside the scope of the system of dose limitation.

Alpha-beta discrimination liquid scintillation counting for uranium and its daughters

Advances in liquid scintillation counting (LSC) technologies, such as imporved scintillation cocktail formulations and alpha-beta radiation discrimination, make LSC suitable for applications in uranium process chemistry. Ease of use, low cost, and the huge dynamic range of LSC are distinct advantages for analytical support of actinide processing. All uranium isotopes decay primarily with alpha radiation emission. The immediate short-lived daughters of238U are234Th and234Pa. These nuclides are beta emitters having energy bands that overlap the uranium bands in a liquid scintillation spectrum. The resolution of these overlapping bands by alpha-beta radiation discrimination is useful for uranium quantification and purity verification. Protactinium-234 is a high-energy beta emitter that can be further identified and quantified from it's Cherenkov radiation. Energy spectra were collected on the Packard 2500AB liquid scintillator analyzer for uranyl solutions in diisopropylnaphthalene and pseudocumene based scintillator cocktails. Calibration curves were prepared for nitric, hydrochloric, and sulfuric acid media. Base titrations demonstrated the effect of acid quenching on those system. Ion exchange and water soluble polymer extraction studies are readily followed using liquid scintillation methods.