Progeny Size Distributions Research Articles

Newly designed measurement system for the radon progeny activity size distribution based on screen diffusion battery

Accurate measurement of the activity size distribution of radon progeny is of importance for dose evaluation. To meet the increasing demand for field survey in China, a new measurement system consisting of 8 stages wire screen diffusion battery was developed, by which the unattached fraction, the fraction of particles larger than 2.5 μm, the activity size distribution and the activity concentration of each radon progeny could be measured simultaneously. To verify the activity size distribution measurement results of the new measurement system, a series of comparison experiments were carried out with an indirect measurement method in radon chamber and indoor environment. The results in radon chamber exhibited a good consistency between the two methods in activity size ranging from 73 nm to 297 nm with an average deviation of −1%, but the result measured by the new system was smaller at 551 nm due to the loss of large particles during the sampling process. Comparison results in indoors mostly showed a good agreement as the deviations were less than 10%, and some large deviations were also observed, which was mainly on account of the limitation of sensitivity and measurement uncertainty.

Radon Progeny Adsorption on Facial Masks.

The radioactive noble gas radon and its short-living progeny are inhaled during respiration, depositing their decay energies in the lungs. These progeny are considered responsible for more than 95% of the total effective dose and are, together with radon, classified as carcinogenic for lung cancer. Consequently, filtration of the progeny could reduce the dose to the lungs. In our study, we investigated the filtration properties of FFP2 versus surgical masks (II R) for radon and its decay products. The masks were attached to a measurement device, which enabled determination of the size distribution of radon progeny, ranging from unattached to clustered progeny. In parallel, it measured the radon activity concentration during experiments. By comparing background measurements without mask and experiments with masks, the percentage of retained unattached radon progeny was determined for FFP2 (98.8 ± 0.6%) and II R masks (98.4 ± 0.7%). For clustered progeny, the retained fraction was 85.2 ± 18.1% for FFP2 and 79.5 ± 22.1% for II R masks while radon was not filtered. We can show that masks are effective in filtering radon progeny and thus are capable of reducing the total effective dose to the lungs.

A computational algorithm for random particle breakage

Random breakage can be defined as the breakage patterns independent from the stressing environment and the nature of the broken particle. However, the relevant literature studies give contrary evidence against random breakage of particles. A simple way to detect random breakage is to evaluate the fragment (progeny) size distributions. Such distributions are estimated analytically or through numerical models. The latter models generally treat random breakage as a geometric statistical problem with prior assumptions on particle/flaw geometry and external stressing environment, which may violate the randomness of the breakage process. This study presents a random-breakage algorithm that does not require such assumptions. The simulated progeny size distributions were compared with the experimental size distributions by impact loading (drop-weight) tests. Random breakage events should yield number-weighted size distributions that is fitted well to the lognormal distribution function. Also, a mass-weighted (sieve) size distribution function is presented for random breakage. Nevertheless, the results refute the random breakage of clinker and other brittle particles after impact loading. Instead, the sieve size distribution of fragments may evolve due to crack branching/merging and Poissonian crack nucleation processes.

Size distribution of ambient and radioactive aerosols formed by the short-lived radon progeny

The survey of ambient airborne particle size distribution is important when the deposition of radioactive particles is considered in the human lung and the assessment of radiation hazard in occupational exposures or contaminated environments. CLOR (the Central Laboratory for Radiological Protection) in cooperation with CMI (the Central Mining Institute) performed simultaneous measurements of the activity size distribution of radon progeny and ambient aerosols using different types of aerosols. Measurements were performed in a radon chamber with a volume of 17 m3, where radon was generated by a radium-226 open source, and ambient aerosols by an oil candle, vax candle, and incense sticks. Such measurements were also made in an aerosol depleted atmosphere after cleaning the chamber air by means of a high-efficiency pump and filters. The size distribution of radioactive aerosols containing radon progeny was measured by RPPSS (Radon Progeny Particle Size Spectrometer) with the measuring size ranging from 0.6 nm to approximately 2500 nm. The key parts of this device are the impaction plates and diffusion screen batteries, which collect aerosols of different sizes, and semiconductor alpha detectors which detect the activity of the collected particles. The SMPS (Scanning Mobility Particle Sizer Spectrometer) and APS (Aerodynamic Particle Sizer) were applied to evaluate the size distribution of all aerosols with sizes from approximately 3 nm to 20 μm. Based on the results obtained by these spectrometers, the activity size distributions and related dose conversion factors (DCF) were evaluated both for the exposed workers and the general population.

Back-calculation of particle fracture energies using data from rotary breakage testing devices

Breakage probabilities and fracture energy distributions have now found application in several mathematical models that simulate both degradation during handling and comminution devices. Unfortunately, measurement of these at the range of sizes of interest, in particular in the case of fine sizes, is not a straight-forward task. The paper proposes a procedure to estimate breakage probability distributions over a wide range of particle sizes by combining direct measurements of fracture energies at a selected size to back-calculated values estimated on the basis of progeny size distributions from breaking single particles over a wider range. Whereas direct measurements of fracture energies were carried out in a short impact load cell device, energy-dependent progeny size distributions were conducted by propelling particles against a target in rotary breakage testing devices. The work demonstrates how the parameters that characterize the variation of particle fracture energies with size can be fitted in a stage-by-stage process, with successful application to characterizing breakage of a copper ore contained in the range from 37.5 to 0.25 mm.

Selective breakage of mineralised synthetic particles by high voltage pulses. Part 2: Interactions between mineralised particles in a multiple-particle system

Part 1 of this study presented evidence of high voltage pulse (HVP) selective breakage induced by metalliferous grain-embedded synthetic particles in a two-particle system. However, in reality, there are multiple particles containing minerals of varying conductivity in a pulse treatment zone and questions remain as to how this type of situation affects the HVP breakage characteristics. Consequently, an experimental study was conducted in a three-particle treatment system, consisting of two mineralised particles embedded with metalliferous grains of different electrical conductivities and one barren particle with no metalliferous grain, subjected to one pulse loading. It was found that the electrical breakdown channel travels preferentially through the particles containing the highest conductivity minerals, resulting in a higher probability of selective breakage, a finer progeny size distribution and a greater energy transfer efficiency for these particles, but impairing the breakage probability of the particles containing the less conductive minerals. The presence of multiple mineralised particles in the pulse treatment zone reduces the probability of misclassification of the barren particles, which means it could enhance the waste rejection rate in a multiple-particle treatment configuration using HVP technology for ore pre-concentration.

Size distribution of ambient and radioactive aerosols formed by the short-lived radon progeny

Abstract The survey of ambient airborne particle size distribution is important when the deposition of radioactive particles is considered in the human lung and the assessment of radiation hazard in occupational exposures or contaminated environments. CLOR (the Central Laboratory for Radiological Protection) in cooperation with CMI (the Central Mining Institute) performed simultaneous measurements of the activity size distribution of radon progeny and ambient aerosols using different types of aerosols. Measurements were performed in a radon chamber with a volume of 17 m3, where radon was generated by a radium-226 open source, and ambient aerosols by an oil candle, vax candle, and incense sticks. Such measurements were also made in an aerosol depleted atmosphere after cleaning the chamber air by means of a high-efficiency pump and filters. The size distribution of radioactive aerosols containing radon progeny was measured by RPPSS (Radon Progeny Particle Size Spectrometer) with the measuring size ranging from 0.6 nm to approximately 2500 nm. The key parts of this device are the impaction plates and diffusion screen batteries, which collect aerosols of different sizes, and semiconductor alpha detectors which detect the activity of the collected particles. The SMPS (Scanning Mobility Particle Sizer Spectrometer) and APS (Aerodynamic Particle Sizer) were applied to evaluate the size distribution of all aerosols with sizes from approximately 3 nm to 20 μm. Based on the results obtained by these spectrometers, the activity size distributions and related dose conversion factors (DCF) were evaluated both for the exposed workers and the general population.

Optimized graded screen array configuration for particle size distribution of radon progeny in standard chamber

Particle size distribution of radon progeny is one of the most important parameters and it needs to be measured accurately. Graded screen array measurement is the most frequently used method for analyzing the characteristics of radon progeny but it needs optimization due to its complex configuration. In this paper, collection efficiency of a single screen and the number of screen array were applied for optimization and simplification of the graded screen array configuration by a series of experimental measurements, theoretical calculations, and standard comparison research methods. When optimized in this way, an experiment was designed for radon progeny particle size distribution in a customized radon chamber. The experiment results indicated that the activity median diameter in unattached mode was 0.81 nm and 287.32 nm in attached mode, which were similar to the results obtained by other researchers. The results prove that the method can satisfy the requirements of graded screen array measurement.

The effect of strain rate on particle breakage characteristics

Strain rate has drawn great research attention in the area of material mechanics. However, thus far the effects of strain rate on the breakage characteristics of rocks or mineral particles were seldom studied. The applied strain rate is one of the key factors causing the variation in breakage environment, and hence the understanding of strain rate's effect on particle breakage is important to the development of a generic breakage model that isolates the rock properties from the breakage environment. This study systematically investigated the characteristics of single particle breakage at different strain rates. The rock samples from four narrow size fractions were used for carrying out impact and compression tests at variable energy input levels. The energy-size reduction relationships for impact and compression breakage were developed, respectively, and the appearance functions for these two breakage mechanisms were also developed based on previous and current work. The results suggest that the sample breaks easier at lower strain rates and the significance of the particle size effect strongly depends on the strain rate. It is demonstrated that the strain rate has an important influence on the progeny size distribution, but the significance of this influence reduces as the energy input increases. It is also found that the sample breaks with a higher energy efficiency at lower strain rates. The strain rate may affect the initiation and propagation of the cracks originate from small flaws and hence results in the difference in the breakage characteristics.

Particle size distribution of the radon progeny and ambient aerosols in the Underground Tourist Route “Liczyrzepa” Mine in Kowary Adit

Central Laboratory for Radiological Protection, in cooperation with Central Mining Institute performed measurements of radon concentration in air, potential alpha energy concentration (PAEC), particle size distribution of the radon progeny and ambient aerosols in the Underground Tourist-Educational Route “Liczyrzepa” Mine in Kowary Adit. A research study was developed to investigate the appropriate dose conversion factors for short-lived radon progeny. The particle size distribution of radon progeny was determined using Radon Progeny Particle Size Spectrometer (RPPSS). The device allows to receive the distribution of PAEC in the particle size range from 0.6 nm to 2494 nm, based on their activity measured on 8 stages composed of impaction plates or diffusion screens. The measurements of the ambient airborne particle size distribution were performed in the range from a few nanometres to about 20 micrometres using Aerodynamic Particle Sizer (APS) spectrometer and the Scanning Mobility Particle Sizer Spectrometer (SMPS).

Comparison of breakage models in DEM in simulating impact on particle beds

The discrete element method (DEM) has proven to be a powerful tool to simulate processes involving particulate material. When simulating materials handling operations that lead to mechanical degradation as well as several types of crushers and mills, description of particle breakage inside the DEM environment becomes indispensable, since flow of solids, energy transfer and size reduction are deeply intertwined. However, breakage modeling in DEM is still in an earlier stage of development and comparatively limited work has been carried out demonstrating the validity and limitations of the various models pursued in the literature and already available in commercial DEM packages. The work analyzed particle breakage using three models available in commercial DEM simulation platforms: the bonded-particle model (BPM), the particle replacement model (PRM) and the fast-breakage model (FBM). These were initially calibrated on the basis of the distribution of breakage probabilities of individual 6.3–4.75 mm copper ore particles and, whenever possible, progeny size distributions. Breakage of particles in beds by impact by a falling steel ball is an interesting case for testing breakage models, besides an important microprocess in some comminution operations, since particles interact with each other and with the grinding medium. As such, the potential of the three models to describe size reduction was demonstrated through comparison of unconfined particle bed breakage experiments and simulations. The models demonstrated different abilities to describe the various aspects of breakage. The work then identified opportunities for improvement in each of the models.

Characterization of Breakage and Washability of ROM Coal using X-ray Computed Tomography

ABSTRACTThe most critical parameters for the efficient design of coal processing operations depend on the assessment of coal breakage and washability characteristics of the coal resource. X-ray computed tomography (XCT) technology has been demonstrated to have the capability of analyzing washability and fragmentation parameters (particle size, energy, coal type). In this regard, progeny size distributions are obtained from sequential modified drop shatter tests (different input energy levels) and from XCT analysis. In this way, the breakage characteristics (selection and breakage functions) of coal particles are established and the prediction of particle size distribution (PSD) for different levels of energy input is demonstrated.

Investigating the effect of applied strain rate in a single breakage event

For successful mechanistic modelling of any size reduction equipment, an understanding of the fundamentals of the breakage mechanisms is essential. This understanding will allow the comparison of breakage events and the quantification of the effect of key factors such as applied strain rate, particle size, and particle shape while they are isolated. This paper uses the concept of analysing breakage of a single particle as a multi-stage process to compare different breakage mechanisms and to quantify the effect of factors such as applied strain rate. This approach regards a single breakage event as a process affected by three sub-processes; first (or primary) fracture, capture and spatial distribution of fragments. The first fracture is assumed to be independent of breakage mechanism and to be a characteristic of the ore type. On the other hand, capture and spatial distribution are influenced by the characteristics of breakage environment, the kinetic energy of fragments and their brittleness. The focus of this paper is to examine how each sub-process of a breakage event is influenced by applied strain rate and its impact on the size distribution of progeny. In this work, three rock types of widely different strength and brittle behaviour, i.e. LKAB magnetite ore, Beaudesert silicate and Bundaberg quartz, were tested at various energy levels using the impact and compression breakage mechanisms. To isolate the effect of spatial distribution of fragments, particles were forced to remain in the breakage zone. In this condition, similar progeny size distributions were generated from compression and impact mechanisms at similar energy levels. However, allowing natural distribution of fragments produced coarser progeny from the compression of silicate.

Linking impact-related progeny sizes of cement clinker to modes of single-particle breakage

Fragmentation of particulate solids is an important process in many industrial activities, particularly in the mineral, cement and glass industries to comminute the raw materials to a required size. Understanding of processes and mechanisms responsible for fragmentation of particulate solids is a hard task. This may bring great precision for designing and controlling the comminution process. This work aims to contribute to understanding fragmentation of cement clinker particles under impact loading. For this purpose, six narrow-size classes of Portland clinker were fragmented with varying specific impact energy levels in a drop weight test apparatus. Then, breakage probabilities and functions of these size classes were determined from the product size distributions. The calculated breakage functions show evidences for the modes of breakage (meridian cracks to oblique cracks and shattering) given in the literature. Results of this study indicate that self-similarity of progeny size distributions can only be achieved, regardless of particle size and impact energy, if the particles have the same breakage probability, that is the same mode of breakage.

Milling and Classification of Printed Circuit Boards for Material Recycling

Recycling of waste electric and electronic equipment (WEEE) is an emerging issue due to its hazardous nature. It is important to identify an appropriate environment-friendly process to recover the valuables and for safe disposal. The present work deals with the two-stage crushing process followed by a circulating air classifier for the separation of metals and nonmetals from the printed circuit boards (PCB). The two-stage crushing process is deployed to liberate the valuables for an appropriate progeny size distribution. The metal content decreases as the particle size decreases below 0.5 mm. However, it increases metal content above 500 µm up to 1,800 µm. It is concluded that the metals primarily enriched in the size range of −1.8 + 0.5 mm. The amount of metals and plastics present in each fraction is estimated. Among the classifier parameters, air flow velocity played a dominant role in metal enrichment. The material feed rate and rotating guide vane angle have no a significant effect on the enrichment of metals and nonmetals. The air flow velocity found was to be one of the crucial parameters for enrichment of metals. The superficial air flow velocity is optimized for efficient separation of metals and nonmetals of PCBs.

Indoor activity size distribution of the short-lived radon progeny

Activity size distribution of the short-lived radon progeny in indoor air was measured continuously over several weeks. Two different measurement techniques were used: a direct measurement with a low-pressure Berner cascade impactor for attached fraction of 214Pb and 214Bi (≥100 nm) and an indirect determination based on measurement with a wire screen diffusion battery (unattached fraction 0.5–5 nm, 218Po, 214Pb). In parallel, the meteorological parameters like temperature, humidity were registered. Measured activity size distribution of radon progeny can be approximated by a sum of three log-normal distributions modes (nucleation, accumulation and coarse). The greatest activity fraction was adsorbed on aerosol particles in the accumulation size range (100–1000 nm) with activity median aerodynamic diameters (AMADa) and geometric standard deviations (GSD a ) values of 250–500 nm, and 1.5–3.5, respectively. The influence of the weather conditions on the activity of the accumulation particles was not significant. In contrast to the results of measurements a small but significant fraction of the radon progeny (average value 5 %) was attached to coarse particles (>1000 nm). This fraction varied between 0 and 10 %. On the other hand, although the amount of unattached activities not more 10 % of the total activity, but is considered to yield about 50 % of the total radiation dose. The mean thermodynamic equivalent diameters of 218Po and 214Pb were determined to be 1.28 and 1.30 nm with relative mean geometric standard deviations of 1.30 and 1.24, respectively. Based on the obtained results of radon progeny size distributions (attached and unattached), the total deposition fractions of the human lung were evaluated by using a lung deposition model.

DEM modelling of non-spherical particle breakage and flow in an industrial scale cone crusher

Predictions of particle flow and compression breakage of non-round rock passing through an industrial scale cone crusher are presented. The DEM (Discrete Element Method) particle breakage model is generalised to allow non-round particles to be broken into non-round progeny. Particles are broken in this DEM model when the elastic energy of a contact is sufficiently high to initiate fracture. Progeny size distribution data from JKMRC Drop Weight Test (JKDWT) or JKMRC rotary breakage test (JKRBT) is used to generate the specific daughter fragments from each breakage event. This DEM model is able to predict the production of both coarser progeny which are resolved in the DEM model and finer progeny which are not. This allows the prediction of product down to very small sizes, limited only by the fineness of the fragments measured in the breakage characterisation. The predicted flow of material through the crusher, product size distribution and liner wear are discussed. The generalised breakage model demonstrated here is suitable for modelling all forms of crushers.

Effect of indoor activity size distribution of 222Rn progeny in-depth dose estimation

In this work, the attached and unattached activity size distribution of 222Rn progeny (214Bi and 218Po) were measured indoor. The fraction of attached progeny was collected using a low-pressure Berner cascade-impactor technique. A constructed wire screen diffusion battery was used for collecting the fraction of unattached progeny. Most of the attached activities for 214Bi progeny were associated with the aerosol particles of the accumulation mode. The active median aerodynamic diameter (AMAD) of this mode for 214Bi was determined to be 350nm with a geometric standard division (GSD) of 3. The GSD of unattached size distributions for 218Po was 1.3 with an active median aerodynamic diameter (AMTD) of 1.3nm. Given that dose estimation is sensitive to environmental conditions, an analytical method was introduced to compute the local energy deposition of 218Po alpha particles in a target volume of 1μm spheres located at different depths in bronchial epithelium. While the depth–dose distributions for nuclides uniformly distributed within the epithelium were found to be practically constant with depth, they decreased in an almost linear fashion with increasing depth for nuclides on the airway surface.

Dosimetric evaluation of thoron exposure in the three typical rural indoor environments of China

In order to evaluate thoron exposure in indoor environments, field measurements of both concentration and its size distribution were carried out in three typical rural residential houses in China, and exposure dose was evaluated using dosimetric method. Results show that the thoron progeny size distributions of rural indoor environments (AMAD: 76.5 nm; GSD: 2.7) are much smaller than those of urban (AMAD: 115 nm; GSD: 2.0), which makes the dose conversion factors of thoron in rural environments [307.4 nSv/(Bq m−3 h−1)] are much higher than those in urban [113.4 nSv/(Bq m−3 h−1)]. The highest thoron exposure (10.12 mSv a−1) was found in mud house of Yangjiang, the high radiation background area.

Thoron progeny size distribution in monazite storage facility.

Field experiments in the atmosphere of monazite warehouses with a high content of (220)Rn progeny concentration were conducted. Size distribution of aerosol particles was measured with the combined use of diffusion battery with varied capture elements and cascade impactor. Four (212)Pb aerosol modes were detected-three in the ultrafine region (aerosol median thermodynamic diameters ∼0.3, 1 and 5 nm) and one with an aerosol median aerodynamic diameter of 500 nm. The activity fraction of aerosol particles with the size <10 nm is nearly 20-25 %. The dose conversion factor for EEC₂₂₀Rn exposure, obtained on the basis of the aerosol size distribution and existing research data on lung absorption types of (212)Pb aerosols, is close to 180 nSv per Bq h m(-3).