Activity Median Aerodynamic Diameter Research Articles

Determination of the physical and chemical properties, biokinetics, and dose coefficients of uranium compounds handled during nuclear fuel fabrication in France.

The introduction of new ICRP recommendations, especially the new Human Respiratory Tract Model (HRTM) in ICRP Publication 66 led us to focus on some specific parameters related to industrial uranium aerosols collected between 1990 and 1999 at French nuclear fuel fabrication facilities operated by COGEMA, FBFC, and the CEA. Among these parameters, the activity median aerodynamic diameter (AMAD), specific surface area (SSA), and parameters describing absorption to blood f(r), s(r) and s(s) defined in ICRP Publication 66 were identified as the most relevant influencing dose assessment. This study reviewed the data for 25 pure and impure uranium compounds. The average value of AMAD obtained was 5.7 microm (range 1.1-8.5 microm), which strongly supports the choice of 5 microm as the default value of AMAD for occupational exposures. The SSA varied between 0.4 and 18.3 m2 g(-1). For most materials, values of the absorption parameters f(r), s(r), and s(s) derived from the in vitro experiments were generally consistent with those derived from the in vivo experiments. Using average values for each pure compound allowed us to classify UO2 and U3O8 as Type S, mixed oxides, UF4, UO3 and ADU as Type M, and UO4 as Type F based on the ICRP Publication 71 criteria. Dose coefficients were also calculated for each pure compound, and average values for each type of pure compound were compared with those derived using default values. Finally, the lung retention kinetics and urinary excretion rates for inhaled U03 were compared using material-specific and default absorption parameters, in order to give a practical example of the application of this study.

Summary of stationary and personal air sampling measurements made during a plutonium glovebox decommissioning project.

Workplace air sampling was performed during the decommissioning of a previously active plutonium glovebox facility located at Argonne National Laboratory. Personal air samplers (PAS) were used to measure breathing zone activity concentrations of workers engaged in size-reducing contaminated gloveboxes. Stationary air samplers (SAS) were used to measure the work area activity concentrations and test their application in providing representative sampling of breathing zone activity concentrations. The relative response of these samplers (PAS:SAS) was tracked during the course of the decommissioning work, with results yielding favorable agreement to within a factor of +/-5. A cascade impactor was used to determine the particle size distribution of workplace aerosols. The average activity median aerodynamic diameter (AMAD) was estimated to be 3.0 microm, with a corresponding geometric standard deviation of 2.4. A gas-flow proportional counter was utilized to measure the gross alpha activity collected on both the SAS glass fiber and the PAS cellulose fiber filters. A subset of this filter group was subsequently analyzed using an alpha spectrometer post radiochemical processing and isotopic separation. The quantity of alpha activity measured on the SAS filters was generally within +/-30% of the alpha spectrometry measurements. However, measurements made of the activity present on the PAS cellulose fiber filters were consistently underestimated using a gas-flow proportional counter, suggesting a small correction factor of 15-20% to account for the absorption of alpha particle emissions.

241Am as a metabolic tracer for inhaled plutonium nitrate in external chest counting.

The plutonium (Pu) treated in the nuclear fuel cycle is usually accompanied by 241Am produced from 241Pu by beta disintegration, which emits gamma rays of 60 keV with the emission rate of 0.36, being more penetrating than the L X rays from Pu. The 241Am could imprve the detection limit of chest counting of Pu, if it was being used as a metabolic tracer for Pu in lungs. Young adult male Wistar rats were exposed to polydisperse aerosols of Pu(NO3)4 with 0.6 microm in activity median aerodynamic diameter. They were periodically killed and the radioactivity of 241Am was cleared from the lungs at almost the same rate as the Pu at least for half a year post-inhalation, which proved the validity of 241Am as a metabolic tracer for inhaled Pu nitrate in external chest counting.

Dose to lung from inhaled tritiated particles.

Tritiated particulate materials are of potential hazard in fission, fusion, and other tritium handling facilities. The absorbed fractions (fraction of energy emitted that is absorbed by the target region) are calculated for tritiated particles deposited in the alveolar-interstitial (AI) region of the respiratory tract. The energy absorbed by radiologically sensitive tissue irradiated by tritiated particles, in regions of the lung other than in the AI region, is negligible. The ICRP Publication 71 assumes the absorbed fraction is unity for tritium deposited in the AI region. We employed Monte Carlo methods in a model to evaluate the energy deposition in the wall of the alveolar sac from particles of tritiated beryllium, tritiated graphite, titanium tritide, tritiated iron hydroxide and zirconium tritide. For the five materials examined, the absorbed fraction in alveolar tissue ranged from 0.31 to 0.61 for particles of 1 microm physical diameter and 0.07 to 0.21 for 5 microm diameter particles. The dose to alveolar tissue, for an acute inhalation of tritiated particles by an adult male worker, was calculated based on the ICRP 66 lung model and the particle dissolution model of Mercer (1967). For particles of 5 microm activity median aerodynamic diameter (AMAD), the committed equivalent dose to alveolar tissue, calculated for the five materials, ranged from 32-42%, respectively, of the committed equivalent dose derived assuming the absorbed fractions were unity.

Internal dosimetry for inhalation of hafnium tritide aerosols.

Metal tritides with low dissolution rates may have residence times in the lungs which are considerably longer than the biological half-time normally associated with tritium in body water, resulting in long-term irradiation of the lungs by low energy beta particles and bremsstrahlung X rays. Samples of hafnium tritide were placed in a lung simulant fluid to determine approximate lung dissolution rates. Hafnium hydride samples were analysed for particle size distribution with a scanning electron microscope. Lung simulant data indicated a biological dissolution half-time for hafnium tritide on the order of 10(5) d. Hafnium hydride particle sizes ranged between 2 and 10 microns, corresponding to activity median aerodynamic diameters of 5 to 25 microns. Review of in vitro dissolution data, development of a biokinetic model, and determination of secondary limits for 1 micron AMAD particles are presented and discussed.

Measurements of thorium–B ( [formula omitted]) in the outdoor environment and evaluation of equivalent dose

The activity size distribution of unattached as well as attached 212 Pb to aerosol particles was measured in the open air of El-Minia City, Egypt. The samples were collected using a wire screen diffusion battery technique and a low pressure cascade impactor. The mean activity median thermodynamic diameter (AMTD) of unattached 212 Pb was determined to be 1.4 nm with a relative mean geometric standard deviation ( σ g) of 1.55. A mean unattached fraction ( f p ) of 0.03±0.007 was obtained at a mean aerosol particle concentration of 32×10 3 cm −3. Sometimes the f p values were less than the detection limit of 0.008. The mean concentration of activity of 212 Pb was found to be 9.6±1.1 mBq m −3. The mean activity median aerodynamic diameter (AMAD) of the accumulation mode of attached 212 Pb was determined to be 360 nm with a mean ( σ g) of 2.7. The mean value of specific air activity concentration of 212 Pb associated with that mode was determined to be 303±12 mBq m −3. With a dosimetric model calculation (International Commission on Radiological Protection. Human respiratory tract model for radiological protection. Oxford: Pergamon Press, ICRP Publication 66, 1994) the total deposition fractions as well as total equivalent and effective dose have been evaluated considering the obtained parameters of the activity size distributions. At a total deposition fraction of about 97% for unattached activities the total equivalent and effective doses to the lung were determined to be about 0.18 and 0.02 μSv, respectively, while total equivalent and effective doses of about 0.45 and 0.05 μ Sv, respectively, were determined at a total deposition fraction of about 23% for the attached activities.

Activity Size Distributions of Short Lived Radon Progeny in Indoor Air

The activity size distributions of both unattached and attached fractions of short-lived radon progeny ( 218 Po, 214 Pb and 214 Bi) were measured in indoor air of El-Minia University, Egypt. The measurements were performed with a wire screen diffusion battery and a low pressure cascade impactor (Berner type). The results for parameters of derived distributions demonstrate that the distributions for the unattached 218 Po and 214 Pb are similar. The mean diffusion equivalent diameters (d e ) of 218 Po and 214 Pb were determined to be 1.73 and 1.69 nm with relative mean geometric standard deviations (σ g ) of 1.63 and 1.69. respectively. The distributions of the attached 214 Pb and 214 Bi are also similar. Most of the attached activities were associated with the aerosol particles of accumulation mode. The mean activity median aerodynamic diameters (AMAD) of this mode for 214 Pb and 214 Bi were determined to be 0.32 and 0.34 μm, respectively, with the same relative mean geometric standard deviation of 2.7, Based on the obtained results of radon progeny size distributions (unattached and attached), the deposition fractions in each airway generation of the human lung were evaluated by using a deposition model of Koblinker and Hofmann.

Performance Evaluation of the Sampling Head and Annular Kinetic Impactor in the Savannah River Site Alpha Continuous Air Monitor

ABSTRACT This paper describes evaluation and testing of the Savannah River Site (SRS) impactor-type alpha continuous air monitor (CAM) to determine the particle delivery and collection efficiency in the device using fluorescence-labeled, polystyrene latex spheres and liquid droplet aerosols. Particle sampling efficiency through the dome-shape sampling inlet for particles with aerodynamic diameters of 6.2 and 10 μm was 98% at 20 cfm (566 L/min), 90% at 32 cfm (906 L/min), and 87% at 40 cfm (1132 L/min) sampling flow rates. Internal delivery efficiency through the CAM was > 94% at 20 and 32 cfm for 0.5-, 1.1-, 2.2-, and 3.2-μm particles and > 90% for 6.2-μm particles. For 10-μm particles, the internal delivery efficiency was 91% at 20 cfm and decreased to 83% at 32 cfm and 77% at 40 cfm. The 50% cutoff aerodynamic diameter for the impactor was 3.2 μm at 20 cfm, 2.6 μm at 32 cfm, and 2.3 μm at 40 cfm. For a typical radioactive aerosol in the workplace (activity median aerodynamic diameter of 5 μm with a geometric standard deviation of 2), these cutoff diameters provide collection efficiencies of 74% at 20 cfm, 83% at 32 cfm, and 87% at 40 cfm. The normal grease layer of 1.5 mg that is routinely applied to the planchet of the SRS CAM was adequate to quantitatively retain all collected particles with diameters of 3.2 μm or less at flow rates of 20, 32, and 40 cfm. For particle sizes of 6.2 and 10 μm, approximately 80–85% of the particles were retained on the impactor planchet and 15–20% were re-entrained into the exhaust airstream due to particle bounce. The delivery and collection efficiencies in the SRS CAM can be combined to give overall efficiencies for detection of airborne actinide aerosols as a function of particle size. For 6.2 and 10 μm aerodynamic diameter particles, the total collection efficiency of the SRS CAM at 20, 32, and 40 cfm exceeds the conservative assumption of 50% efficiency for plutonium particle collection that has been traditionally used at SRS.

Exposures from thorium contained in thoriated tungsten welding electrodes.

Information provided in this article can be used for estimating the radiation dose associated with the use of thoriated tungsten electrodes in tungsten inert gas welding. Area and breathing zone concentrations of 232Th generated by welding and electrode sharpening along with particle size information; isotopic composition of electrodes from two domestic manufacturers and one European manufacturer; and process variables and estimates on the number of thoriated tungsten electrodes manufactured are presented. Past literature is reviewed and compared with the results of this study. Isotopic analysis of a nominal 2% thoriated electrode found 0.6 ppm +/- 0.4 ppm 230Th and less than 0.1 ppm 228Th. Analysis of a ceriated tungsten electrode and a lanthanated tungsten electrode for 232Th found 124 ppm and 177 ppm, respectively. Electrode consumption during welding was primarily the result of tip sharpening. Less than 3% of the weight loss was attributable to the welding process. The in-mask concentration of respirable thorium particulate in the welder's breathing zone was 0.002 x 10(-12) microCi 232Th/mL. The concentration of respirable thorium particulate from electrode sharpening was 1.3 x 10(-12) microCi 232Th/mL. The measured sharpening time was 20 sec per electrode. Estimates of the activity median aerodynamic diameters for the respirable fraction of the welding and electrode sharpening aerosols were 3.5 and 5 microns, respectively, when measured in the breathing zone at 0.3 m (12 inches) from the point of operation. The respirable fraction of the total welding and sharpening aerosols was 45 and 60%.

Re-entrainment of 239PuO2 Particles Captured on HEPA Filter Fibres

Filter performance is very important not only before use but also in use. In addition to particle collection, particle retention or dispersion rate should be evaluated. Re-entrainment of 239 PuO 2 particles collected on HEPA filter fibres was investigated under various conditions of air flow direction, air flow rate, air flow pattem and dust loading. Plutonium aerosols with an activity median aerodynamic diameter of 0.45 μm and a geometric standard deviation of 2.0 were used. Dispersion rate per hour, which is defined as activity ratio on the sampling filter downstream to that on the source filter under forward flow, was measured as less than 2.3 X 10 -7 h -1 . Under reverse flow, higher dispersion rates were observed, but the dispersion decreased with repeated sample runs. A high air flow rate increased the dispersion rate. There was no significant differences among air flow patterns. Dispersion rate depended strongly on the dust loading level. For example, at 2.9 times the loading of atmospheric aerosols compared with the initial pressure drop the dispersion rate was increased by approximately 100 times to 10 -2 h-'.

Assessment Of Physico-Chemical And Biokinetic Properties Of Uranium Peroxide Hydrate UO4

Comprehensive studies on the radiotoxicological risk of an intermediate compound UO4, which is not specified in ICRP Recommendations, were motivated by its increased use in the nuclear fuel cycle and the lack of information such as physico-chemical and biokinetic properties. The aim of this work was to give an experimental basis for assessing the appropriate limits on intake for workers exposed to UO4 and to provide guidance for the interpretation of personal monitoring data. Particle size measurement of the UO4 dust indicated a geometric diameter D of 0.5 microm, which corresponds to an activity median aerodynamic diameter (AMAD) of 1.1 microm. In vitro experiments conducted in culture medium showed that UO4 is a soluble compound with 66.2% dissolved in 1.9 d and 33.8% in 78 d. Results of dissolution obtained with macrophages showed a significant decrease of 50% at 1 d in terms of solubility. Biokinetic data in the rat obtained from two in vivo studies involving intratracheal instillation in rats indicated half-times in the lung of 0.5 d (96.6%) and 27 d (3.4%) for an initial lung deposit (ILD) of 195 microg, and 1.2 d (90.3%) and 38 d (9.7%) for an ILD of 7.6 microg. Absorption parameters to blood as defined in the ICRP Publication 66 human respiratory tract model were calculated with the specific software GIGAFIT and led to the rapid fraction fr (0.800 to 0.873), the rapid rate sr (0.525 to 0.928 d(-1)), and the slow rate ss (1.57 x 10(-2) to 2.42 x 10(-3) d(-1)). Effective dose coefficients by inhalation for this UO4 compound using the in vivo experimental results were calculated to be between 0.52 and 0.70 x 10(-6) Sv Bq(-1). Comparison of these values with effective dose coefficients defined in ICRP Publication 68 for workers showed that UO4 could be considered as a fast soluble compound of Type F.

Dose Coefficients and Assessment of Intake After Inhalation of Contaminated Dusts from Palomares

The inhalation of dust particles bearing 230 Pu and 241 Am resulting from the aviation accident at Palomares in 1966 is still a potential health hazard for persons living or working in the vicinity. The dose coefficient for the dust and the behaviour of these actinides in members of the public have been predicted by combining absorption parameters from the lungs into blood derived from animal studies with human data from the most recent age-dependent biokinetic models published by the International Commission on Radiological Protection. For an aerosol of I μm activity median aerodynamic diameter it is concluded that the most appropriate dose coefficients for adults, 10 year old and I year old children are 2.3×10 -5 , 2.6×10 -5 and 4.8 × 10 -5 Sv.Bq -1 respectively. For assessing intakes of the dust, measurements of 239 Pu in urine could be used with advantage provided fission track or mass spectrometric methods of analysis were used.

Characterisation of Enriched Uranium Dioxide Particles from a Uranium Handling Facility

A case study was conducted on approaches for using a prospective measurement of the particle size distribution of a process powder in a uranium handling facility to assign an appropriate annual limit on intake (ALI) for potential inhalation exposures of workers to that powder. The aerodynamic size distribution was determined for particles to which workers might be exposed during dispersion of dusts in an enriched uranium casting operation. Bulk powders were obtained during cleaning of the casting crucibles. The material was 0.846 uranium by mass, which corresponds to the theoretical uranium mass fraction for U 3 O 8 . The material was aerosolised using a DeVilbis dry powder blower and separated by aerodynamic diameter using a five-stage aerosol cyclone train. Approximately 0.08 of the total mass processed in the casting operation was retained as residual oxide, and approximately 0.01 of that mass was less than 10 μm aerodynamic diameter. Assumptions from ICRP 30 and from ICRP 68 and 69 were used to calculate the appropriate dose coefficients, depending on the fraction of the bulk powder that might be suspended into the workplace. Using the assumptions of ICRP 30 for Class D material, the potential location of particle deposition in the respiratory tract has little influence on assignment of an appropriate dose; using the actual particle size distribution of the powder reduced the ALI to about 90% of the value based on assuming that all re-suspended material had an activity median aerodynamic diameter of I μm. Using the assumptions of ICRP 30 for Class W and Y materials, the ALI was increased by a factor of 2.4, 6.3, 9.2, or 10.9 depending on whether the suspended material was limited to particles of aerodynamic diameter less than 10 μm, 20 μm, 50 μm, or all measured particle sizes, respectively. Using the assumptions of ICRP 68 and 69 the ALI for powders of Type F is more dependent on particle size than the ALI for Class D material and would be increased by a factor of 1.1, 1.5, 1.6, and 1.6 over the ICRP 30 model values for the four assumptions of particle size. The ALI for Type M material was changed by factors of 0.8, 1.8, 2.4, and 2.2 (an overall factor of 3) for the four assumptions of available particle size. For Type S material, the ALI changes by factors of 5.0, 10.4, 13.5, and 12.2 (again, an overall factor of about 3) compared to the ICRP 30 values for the four assumptions of particle size. Thus, the potential radiation doses to workers can vary substantially for Type M and Type S materials depending on which size fractions of the bulk powder are suspended into the breathing zone. The approaches and results of this case study provide insight into when prospective studies of particle size and solubility should be used to improve worker protection.

Population exposure to airborne thorium at the high natural radiation areas in India

High natural radiation areas in the coastal and peninsular India were studied for airborne thorium and resultant population exposure due to inhalation. Four locations covering three states viz., Ayiramthengu and Neendakara in Kerala, Kudiraimozhi in Tamil Nadu and Bhimilipatnam in Andhra Pradesh were investigated. External gamma radiation fields 1 m above the monazite ore bodies ranged from 200 to 3000 nGy h -1. Soil samples showed 232Th specific activity varying from 0·1 to 1·5 Bq g -1 with surface alpha activity in the range of 1·0–12·5 Bq cm -2. Suspended particulates in the samples ranged from 60–140 μg m -3 with 232Th showing a wider variation of <0·03–0·3 mBq m -3. There was poor correlation between suspended particulates and long-lived alpha airborne activity ( r=−0·3). The resuspension factors for 232Th were in the range of 1·5×10 -8–7·9×10 -7 cm -1. Higher resuspension was correlated with dry sand dunes. The upper limits for Committed Effective Dose (CED) due to inhalation of airborne 232Th at the respective high natural radiation areas were estimated to range from 50±30 to 300±130 μSv (5–30 mrem) per year per adult member of public assuming an activity median aerodynamic diameter of 1 μm for the airborne particulates.

A Study on Radon and Radon Progeny in Surface Air of El-Minia, Egypt

Activity concentrations of 222 Rn gas and its long-lived progeny ( 210 Pb, 210 Bi) attached to aerosol particles were determined in surface air of El-Minia (ARE). Fluctuations of activity concentrations were observed during the measurements. An electroprecipitation method was used for the determination of 222 Rn gas concentration while a high volume air sampler was used for collecting the attached 210 Pb and 210 Bi. A mean activity concentration of 4.8 ± 0.74 Bq.m -3 was determined for 222 Rn gas while mean values of 0.25 ± 0.04 and 0.142 ± 0.02 mBq.m -3 were determined for 210 Pb and 210 Bi, respectively. From the ratio between the activity concentrations of 210 Pb and 210 Bi a mean residence time of aerosol particles in the air of 12.7 ± 2.2 d could be estimated. A mean aerosol mass concentration of 33.6 ± 7.4 μg.m -3 was also determined during the measurements. Small fractions of attached 210 Pb and 210 Bi were observed at higher aerosol mass concentrations while the majority of attached activities were associated with lower mass concentrations. In addition, activity size distributions of short lived radionuclides 214 Pb and 214 Bi were determined using a Berner impactor as a sampling device. The activity size distribution of both radionuclides could be described by one log-normal distribution (accumulation mode). Activity median aerodynamic diameters of 330 and 316 nm with relative geometric standard deviations of 2.45 and 2.35 were determined for the two radionuclides, respectively. The total and regional deposition in the human respiratory tract due to inhalation of attached 214 Pb and 214 Bi were evaluated using the ICRP lung deposition model.

ＩＣＲＰの内部被ばく線量評価モデルに基づく｀２３９´Ｐｕのモニタリング量の計算

Plutonium (Pu) is one of the most important elements from the viewpoint of radiotoxicology and protection. The International Commission on Radiological Protection (ICRP) recently revised the respiratory tract model and biokinetic models for selected elements, including Pu. The monitoring quantities for inhaled 239Pu such as lung retention and daily excretion rate have been computed. The aerosols of 5μm Activity Median Aerodynamic Diameter (AMAD) and 1μm AMAD were treated by using these new models. The conversion coefficients from the monitoring quantities to the effective dose of 239Pu have been obtained. Besides the graphical representation, the computed monitoring quantities have been approximately represented by a summation of exponential functions. The present results provide useful data for the design of monitoring programs and for the interpretation of the monitoring results in occupational exposure.

Dynamic calibration of an aerosol monitor with natural and artificial alpha-emitters

Measurement of airborne artificial /spl alpha/-activity concentrations in the presence of naturally occurring radionuclides requires reliable subtraction of the natural contribution and precise calibration. Therefore, the commercially available aerosol monitor LB150D-R was calibrated dynamically at the IPSN/CEA in Saclay, France. Aerosols with activity median aerodynamic diameters of 0.4 /spl mu/m and 4 /spl mu/m labelled with /sup 239/Pu were generated and isokinetically sampled by the aerosol monitor. The response to /sup 239/Pu activity concentrations and detection limits in the presence of radon progeny were determined. The retention of aerosols and their distribution on the filter was investigated using fluoresceine labelled aerosols.

Effects on Dose Coefficients for Workers of Recent Changes in Internal Dosimetry

The International Commission on Radiological Protection (ICRP) has recently reviewed and updated, in ICRP Publications 56, 67 and 69, some of the biokinetic models of ICRP Publication 30. As well as this, ICRP has adopted a new model for the human respiratory tract, the details of which were issued as ICRP Publication 66. A compendium of dose coefficients (dose per unit intake values) for workers based on the new lung model, and some new recommendations on systemic models, has been issued in ICRP Publication 68. Doses for inhalation of 1 and 5 µm Activity Median Aerodynamic Diameter aerosols and for ingestion are given here for a selection of important nuclides, using the latest lung and systemic models. The results are compared with those of previous models. The new Absorption Types F, M, S (Fast, Moderate and Slow) are compared with the old inhalation Classes D, W, Y (for retention periods Days, Weeks, Years). It is found that generally the dominating factors for Types F and S is the lower overall deposition in the new model, leading to lower doses. Type M material is retained in the lung for much longer that Class W material of the ICRP Publication 30 model. This overrides the lower deposition and lung doses are higher in most cases. For 5 µm aerosols (the new default for occupational exposure) the activity reaching blood for Types F and M is similar to that for 1 µm (the previous default) Class D and W aerosols. However, the amount for Type S is only around 10% of that for Class Y. Doses to systemic tissues are reduced accordingly. A detailed investigation of systemic uptake is given in the Appendix. Further changes in systemic tissue doses are caused by some substantial changes to biokinetic models. Committed effective doses are generally lower although there are some exceptions. Differences in doses by ingestion are more simply explained by changes to systemic models and some other relatively minor changes.

Particle Size Distributions of Radioactive Aerosols in the Environment

Published measurements of Activity Median Aerodynamic Diameter (AMAD) of environmental aerosols were surveyed in order to determine a realistic default value for estimating doses to members of the public (i.e. the value to be used in dose assessments in the absence of specific information). Reported AMADs for artificially produced radioactive aerosols ranged from 0.3 to 18 µm and on fitting a single log-normal function gave a median value of 1.5 µm. The distribution did, however, show some evidence of being bimodal. Most of the measured AMADs fell into two distinct categories: aerosols released into the atmosphere by the Chernobyl accident and those produced by resuspension of radioactive material deposited on the ground or released into the sea. The distributions of measured AMADs for each category were well fitted by single log-normal functions with median values of 0.6 and 6µm respectively. The distribution of AMADs for 7Be, a natural radioactive aerosol produced in the atmosphere by cosmic gamma rays, had a median value of 0.6 µm. It is concluded that for exposure of the public to radioactive aerosols in the environment a 1 µm AMAD, as recommended by ICRP in Publication 66, is a realistic rounded default value. However, public exposures arising from inhalation of material resuspended into the atmosphere are more realistically represented by a 5 µm AMAD, as recommended by ICRP for workplace exposures.

再処理施設の設備更新に伴い発生する放射性エアロゾルの粒径分布

Some of the superannuated equipment were replaced in the nuclear fuel reprocessing plant at the Tokai-works of the Power Reactor and Nuclear Fuel Development Corporation (PNC). The authors have been investigating the airborne particle sizes of radiological materials in the decommissioning process using Andersen samplers. This paper describes information on the particle sizes during the cutting processes. The activity median aerodynamic diameters (AMAD) of the aerosols ranged from 2 to 4μm, and their geometric standard deviations were in the range of approximately 2-3.