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The aim of this work is to investigate, in a wide range of gamma-ray energies, the validity of the "Virtual Point Detector" (VPD) approach to evaluate Full-Energy-Peak Efficiency (FEPE) values for a Cerium-doped Lanthanum Bromide scintillator (LaBr 3 :Ce). With VPD approximation, the detector is assumed equivalent to a virtual point inside the crystal where all the interactions can be considered to occur. The distance of VPD from detector cap is evaluated through experimental point source measurements. The knowledge of the trend of VPD depth as a function of gamma radiation energy allows the evaluation of FEPE values starting from an experimental reference value. The validation of the procedure has been performed by applying the VPD approach to measurement geometries already characterized such as a disk source, an Havar foil irradiated inside a target of a medical cyclotron, and a parallelepided sample geometry, an atmospheric particulate paper filter reduced to 6 cm × 6 cm × 0.7 cm dimensions. FEPE values determined by VPD approach lead to radionuclide activities very close to the ones already obtained with measurements carried out with other detectors. • Validity of Virtual Point Detector approach for a LaBr 3 :Ce scintillator. • Efficiency evaluation for a LaBr 3 :Ce scintillator through a VPD approximation. • Experimental validation of VPD approach also for disk and volume sources. • Knowledge of the detector size and composition is not necessary. [ABSTRACT FROM AUTHOR]

A method for absolute measurements of the 225Ac activity in equilibrium with its progeny was developed. Measurements were performed using the triple-to-double coincidence ratio (TDCR) method in two different TDCR counters. The activity concentration of an 225Ac solution was determined and the solution was sent to the SIR system for a comparison. The half-life of 225Ac was determined by one of the TDCR counters and found to be 9.9150(63) days. • Detailed determination of the counting efficiency of the 225Ac in radioactive equilibrium with its progeny. • Description of the measurements of the activity of 225Ac sources using the TDCR method. • Result of activity comparison in the International Reference System (SIR) at BIPM. • Results of half-life determination of 225Ac at POLATOM compared to other published values. [ABSTRACT FROM AUTHOR]

Abstract The experimental characterization of an aged PIPS detector used in an alpha-particle spectrometry is performed using a standard mixed source of 238U, 234U, 239Pu, and 241Am. The variations in the detector efficiency and resolution (FWHM) at the main energy lines of the 238U, 234U, 239Pu and 241Am source were investigated at all possible source–detector distances under chamber air pressure of ∼ 1.33 Pa. Finding shows that on average, the counting efficiency data obtained from measurements are lower than those obtained by theoretical data and Monte Carlo simulation (SOLANG and AASI) methods. A combination of polymeric strippable coating and both traditional wiping and cleaning method for the detector decontamination works only show a significant reduction in the background activity. The counting efficiency improvement process by an increase of the higher voltages within the recommended range results in a good agreement in the counting efficiency comparison and a slight decrease of the detector dead layer thickness. Novel method to evaluate the dead layer thickness for PIPS detector via the variations in experimental energy loss with respect source to detector distance using alpha standard sources of 242Pu has been proposed. This method can help to predict a default dead layer thickness value which will be as close as it was originally, is less than 50 nm from the manufacturer. Highlights • Efficiency response of an aged PIPS detector was conducted. • Theoretical data and Monte Carlo simulation methods were involved for comparison. • Decontamination work shows an insignificant increase in the counting efficiency. • Novel method to evaluate the dead layer thickness for PIPS detector was developed. • An increase of the higher voltages can improve the counting efficiency and dead layer thickness. [ABSTRACT FROM AUTHOR]

Based on the principle of Mie scattering, we design a small flow optical sensor of particle counter. Firstly, laser illumination system was simulated and designed by ZEMAX optical design software, and the uniform light intensity of photosensitive area was obtained. The gas circuit structure was also designed according to the related theory of fluid mechanics. Then, the method of combining with MIST scattering calculation software and geometric modeling was firstly used to design spherical reflection system, on the basis of the formula of object-image distance. Finally, the test was conducted after the optical sensor placed in self-designed pre-amplification and high-speed processing circuit. The test results show that the counting efficiency of 0.3 μ m gear is above 70%, 0.5 μ m gear and 1.0 μ m gear are both reached more than 90%, and the dispersion coefficient of each gear is very nearly the same, compared with the standard machine of Kanomax 3886 under the particle spraying flow of 2.5SCFH, 3.0SCFH, 3.5SCFH. [ABSTRACT FROM AUTHOR]

In this work, the extrinsic counting efficiency and extrinsic sensitivity of a cylindrical source and a gamma camera with a rectangular detector were determined using homogeneous Tc-99 m . Scattered radiation effects were evaluated by both analyzing the energy spectrum of 99m Tc for the scatter fraction and plotting the extrinsic counting efficiency and sensitivity. It is found that the scattered fraction values increased with increasing source thickness. Calculated extrinsic sensitivity shows a gradually decreasing trend with increasing source thickness. The extrinsic efficiency decreases with increasing source thickness. It is concluded that increasing source to detector distances results with increasing extrinsic counting efficiency but decreasing extrinsic sensitivity. [ABSTRACT FROM AUTHOR]

In this study, a water-based compact handheld condensation particle counter (Hy-WCPC) is developed and its performance is evaluated. The Hy-WCPC is a small and light water-based CPC and the operating principle is the same as the conventional continuous flow conductive cooling alcohol-based condensation particle counters (CPC). This study presents the particle material dependent Hy-WCPC cut-off sizes and the particle concentration counting linearity between the Hy-WCPC and electrometer by generating silver, sodium chloride, zinc and paraffin particles. Moreover, the comparison between the Hy-WCPC and commercially available ultrafine CPC (TSI 3776) for ambient airborne particles is presented. The cut-off sizes of the Hy-WCPC for silver and paraffin particles are 3.61 nm and 5.30 nm, respectively. For sodium chloride and zinc particles, the Hy-WCPC lower detection limit is achieved less than 4 nm. Moreover, the particle concentration counting linearity between the Hy-WCPC and electrometer is presented. The excellent particle number concentration counting linearity agreement between the Hy-WCPC and electrometer is shown for the laboratory generated particles. Also, the particle concentration counting linearity between the Hy-WCPC and the TSI 3776 for outdoor ambient airborne particles is shown. The reasonable agreement between the Hy-WCPC and the TSI 3776 was obtained. In the long-term measurement of outdoor ambient airborne particles for 7 days, this agreement had been maintained, however, after 7 days, the TSI 3776 did not operate properly due to the high humidity, while the Hy-WCPC was operating without the problem. [ABSTRACT FROM AUTHOR]

A point source is used to investigate the effect of water phantom thickness and source-to-detector distance (SDD) on the sensitivity and counting efficiency of a rectangular detector gamma camera. The increase in water thickness resulted in an increase in scatter fraction, a decrease in sensitivity, and counting efficiency. The increase in SDD resulted in a decrease in sensitivity and an increase in counting efficiency. An SDD of 0.79±0.02 m is found to provide a good compromise for acceptable sensitivity and reasonable counting efficiency. [ABSTRACT FROM AUTHOR]

The Laboratory of Internal Dosimetry of the Center for Development of Nuclear Technology (LDI/CDTN) is responsible for routine internal monitoring of occupationally exposed individuals. The determination of photon emitting radionuclides in the human body requires calibration of the detector in specific counting geometries. The calibration process uses physical phantoms containing certified activities of the radionuclides of interest. The objective of this work was to obtain calibration efficiency curves of the Whole Body Counter in operation at the LDI/CDTN using a BOMAB physical phantom and Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Abstract: Standardization of 153Sm by 4π(LS)-γ coincidence and anticoincidence counting and the CIEMAT/NIST method in three LS-counters is presented. This short half-life radionuclide is applied in tumor therapy and bone pain palliation. A simplified disintegration scheme of 153Sm was applied in the calculation of the counting efficiency. Standard uncertainties of 0.4% for the 153Sm measurements by the 4π(LS)-γ coincidence and anticoincidence techniques and 0.7% by the C/N method were evaluated, respectively. An agreement of the standardization results by both methods within the respective uncertainties was obtained. The half-life of 153Sm of (1.92895±0.00024) days was determined during one month of measurements and correction for europium isotope impurities by the C/N method in the TriCarb 2910 LS-counter. [Copyright &y& Elsevier]

Abstract: A calibration setup has been established to calibrate or validate UN-ECE Regulation 83 compliant CPCs. A spark discharge generator (GFG 1000) is used to produce carbon particles. For charge conditioning an indirect photoelectric charger is combined with an electrostatic precipitator instead of the very common radioactive bipolar charger. The particle number concentration is determined with a Faraday cup electrometer. Detailed studies have been conducted to validate the calibration setup. The particle size classification was checked by a screen-type diffusion battery. Moreover the effect of multiple charged particles was investigated. Three independent measurements of the counting efficiency as well as the linearity of a typical regulation compliant counter were performed. The calibration setup was also compared with a similar system using a radioactive bipolar charger. The obtained results demonstrate that the counting efficiency can be measured in a particle size range from 13nm to 60nm with a high repeatability. A linearity check at a particle size of 55nm is possible in a concentration range of 1000–10000cm3. The effect of multiple charged particles produced by the indirect photoelectric charger was found to be negligible. Additionally, the difference between a CAST aerosol and a GFG aerosol as a calibration material is discussed. [Copyright &y& Elsevier]

Abstract: We measured 4π and 2π counting efficiencies for internal conversion electrons (ICEs), gross β-particles and also β-rays alone with various source conditions regarding absorber and backing foil thickness using e-X coincidence technique. Dominant differences regarding the penetration, attenuation and backscattering properties among ICEs and β-rays were revealed. Although the abundance of internal conversion electrons of 137Cs-137Ba is only 9.35%, 60% of gross counts may be attributed to ICEs in worse source conditions. This information will be useful for radionuclide metrology and for surface contamination monitoring. [Copyright &y& Elsevier]

• A bilateral comparison of particle number concentration (PNC) standards is reported. • Counting efficiency (CE) of optical particle counter (OPC) at 0.3 µm and 0.5 µm are compared. • Aerosol electrometers and inkjet aerosol generator are used as primary PNC standards. • The comparison of CE of OPC measured by two metrology institutes shows agreement within 1.5%. • Evidences for the equivalence of PNC standards of two metrology institutes have been shown. The first bilateral comparison of particle number concentration (PNC) standards via calibrating the counting efficiency (CE) of an optical particle counter (OPC) at high concentration of 1000 cm−3 is reported. An OPC (GRIMM 11-D) has been used as the transfer standard between NMC and NMIJ, with its CE being calibrated using monodisperse polystyrene latex (PSL) particles around 0.3 µm by the Faraday Cup Aerosol Electrometers (FCAE) of both metrology institutes. The CE of the OPC has been evaluated for a series of increasing concentrations to determine the highest concentration level which is free from coincidence loss. The OPC was also calibrated at 0.5 µm using an inkjet aerosol generator (IAG) and FCAE to compare its CE at different concentration levels. We have analysed the CE's stability at decreasing concentration levels from 1228 to 0.5 cm−3 to derive the evidence for the equivalence of CE at different concentration levels. The CE values of the OPC around 0.3 and 0.5 µm measured by two institutes have agreement within 1.5% (normalized error E n < 1), which can serve as evidence of the equivalence of the PNC standards of both metrology institutes for concentrations up to 1000 cm−3. The measurement setup, comparison results and uncertainty analysis for the OPC calibration have been presented. [ABSTRACT FROM AUTHOR]

Abstract: The new TSI Inc. Nano Water-based Condensation Particle Counter 3788 (N-WCPC Model 3788) is designed for counting particles down to a mobility diameter of . Published studies have shown that the use of water as a working fluid does not have a significant effect on the instrument performance. With the exception of a few specific substances, like emery oil or dioctyl sebacate which present a somewhat larger cut-point diameter, data in peer-reviewed literature suggests that the composition of the particles is not an issue as long as the particle diameter falls within the working range of the device. However, we have observed a very reduced counting efficiency from this water condensation particle counter for particles from a propane-rich fuel mixture (i.e. high carbon-to-oxygen ratio) generated by means of a Combustion Aerosol STandard burner (CAST). The percentage of detected particles decreases for an increasingly richer fuel mixture. The reduced efficiency is still present for particles well above the cut-point of the instrument. The 3788 N-WCPC counted only half as many particles when compared to two butanol based Condensation Particle Counters (CPC, models 3025A and 3022A, TSI Inc.), and the efficiency was even lower for smaller particles: only and for monodisperse particles with a mobility diameter of and , respectively. Preconditioning the polydisperse sample using a thermodenuder at 100 or even 250°C slightly increased the counting efficiency of the N-WCPC, but this still remained below the counts of the butanol CPC. No reduction in counting efficiency was detected for CAST particles from propane-lean fuel-mixtures (otherwise known as black soot) or for organic particles produced by the photo-oxidation of . For this reason, we believe that the effect is caused by the combination of the hydrocarbon rich composition of the particles and their low oxidation state. [Copyright &y& Elsevier]

Abstract: A 85Sr solution was measured in two liquid scintillation (LS) counters. Scintillation pulses from the delayed transitions in the 85Sr decay were by and large lost as the dead time of the LS-counter was much longer than the lifetime of the 85Rb excited level. The registration probability of these pulses has been defined and introduced into the counting efficiency calculation. The results of the 85Sr solution standardization by the CIEMAT/NIST and the TDCR methods relative to the results from the 4π(LS)-γ coincidence and anticoincidence method were 0.997±0.012 and 0.971±0.019, respectively. [Copyright &y& Elsevier]

Abstract: The detection and quantification of biological particles in the atmosphere is becoming an increasingly important field of study. One instrument designed for this purpose, known as WIBS-4, can measure individual particles and their number-size distributions in two pre-defined size ranges: (i) ∼0.3–12μm and (ii) ∼3–31μm (optical diameter, polystyrene latex equivalent) while also making measurements of fluorescence across two wavebands. It can also supply simultaneous information on particle asymmetry. Since particle number concentrations are provided by the technique, the counting efficiency of WIBS-4 needs to be defined. Therefore in the current study, a method for calibration suitable and necessary for use with single particle measuring instruments is described. The lower-end counting efficiency curve for the WIBS-4 was thereby defined in specific size regimes for the first time (D 50∼0.489μm and D 100∼0.69μm). Experiments were conducted at room temperature and atmospheric pressure using a range of different sized PolyStyrene Latex (PSL) microspheres. A TSI 3010 condensation particle counter, using butanol as a working fluid, was used as a reference particle counter. The results also demonstrated a relationship between fluorescence intensity and the calculated volume of the PSL particles, when λ ex=280nm and λ em∼310–400nm. To our knowledge the current study represents the first to provide the fluorescence particle sensor community with both the counting efficiency of the WIBS-4 and a relationship plot giving a fluorescence intensity-particle size correlation over a broad PSL size range. [Copyright &y& Elsevier]

Abstract: Four new, four re-calibrated and six used TSI 3790 condensation particle counters (CPC) were checked using soot particles produced by a mini CAST generator. One of the re-calibrated CPC was also checked with Emery oil (PAO 4) particles (evaporation-condensation method) and its counting efficiencies were in agreement with the manufacturer’s calibration data which were determined with Emery oil particles (electrospray method). However, the counting efficiencies with the soot particles were lower indicating the importance of the calibration material (chemical composition, morphology). Since UN-ECE regulation 83 for light duty vehicles does not specify the material to be used, the validation (check) should be conducted with the same material used by the manufacturer or the differences between the materials should be taken into account. Two used CPCs showed a ∼20% decrease in their counting efficiencies after 1.5 years of measuring engine exhaust aerosol. This drift could not be recognized by the status indicators of the instrument and could be attributed to a degradation of the CPC saturator (wick). Two CPCs also showed a non-linear response; a 7% difference was found between low (10cm−3) and high concentrations (10,000cm−3). A non-linear response (up to 40%) was also observed when the temperature difference between the saturator and the condenser was increased to decrease the cut-off size of the CPCs. [Copyright &y& Elsevier]

Abstract: The sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs—Grimm Model 1.109 and Palas Model WELAS 2100) as well as one high-resolution, non-commercial OPC were evaluated. The measured data were compared to scattering intensity calculations based on Mie theory. Additionally, the counting efficiency for all three counters was measured, as was the influence of coincidence effects for the OPC with the lowest (manufacturer specified) upper concentration limit. Beside the traditional polystyrene latex calibration, a little-known, very fast and precise “multimodal” calibration method was used, which is based on the simultaneous generation of up to eight sharp multiple-charge modes from polydisperse di-ethyl-hexyl-sebacate (DEHS) particles by electrical mobility classification. [Copyright &y& Elsevier]

Abstract: A triple-to-double coincidence ratio (TDCR) liquid scintillation counting system has been recently constructed at Australian Nuclear Science and Technology Organization (ANSTO). A description of the system and measured activities for sources such as 3H, 14C, and 241Am are presented. [Copyright &y& Elsevier]

Abstract: This paper studies the detection limit, selectivity and counting efficiency of an ultraviolet aerodynamic particle sizer spectrometer (UVAPS) with regard to aerosolized fungal spores. The study demonstrated the ability of the instrument for detection and measurement of fungal spores under controlled conditions. A reasonable correlation was found between the UVAPS and the AGI-30 impinger in measuring the aerosol fungal spore concentrations under investigation: Penicillium and Aspergillus niger (, and , , respectively). A linear relationship between total particle concentration and fluorescent particle concentration was found in the range from 0 to . Its lower detection limit was found to be . The dry generation method which was used for generating fungal spores has proved to be reproducible and easy to control, as well as simple and inexpensive. [Copyright &y& Elsevier]

Abstract: An experimental procedure has been developed for a rapid and accurate determination of the activity concentration of 210Pb in sediments by liquid scintillation counting (LSC). Additionally, an alternative technique using -spectrometry and Monte Carlo simulation has been developed. A radiochemical procedure, based on radium and barium sulphates co-precipitation have been applied to isolate the Pb-isotopes. 210Pb activity measurements were done in a low background scintillation spectrometer Quantulus 1220. A calibration of the liquid scintillation spectrometer, including its / discrimination system, has been made, in order to minimize background and, additionally, some improvements are suggested for the calculation of the 210Pb activity concentration, taking into account that 210Pb counting efficiency cannot be accurately determined. Therefore, the use of an effective radiochemical yield, which can be empirically evaluated, is proposed. 210Pb activity concentration in riverbed sediments from an area affected by NORM wastes has been determined using both the proposed method. Results using -spectrometry and LSC are compared to the results obtained following indirect -spectrometry (210Po) method. [Copyright &y& Elsevier]

Abstract: In this study calibration measurements of new TSI condensation particle counter models, using either butanol or water as working fluid, are described. Experiments were carried our at ambient, laboratory conditions for two particle materials, silver and sodium chloride. The obtained counting efficiency curves are presented. [Copyright &y& Elsevier]

Abstract: A Fast Integrated Mobility Spectrometer (FIMS) has been developed for sub-second aerosol size distribution measurements based on the description presented in the preceding paper (Paper I). The performance of FIMS was characterized using DMA classified aerosols in the size range 15–170nm. An excellent agreement was observed between the mean particle diameter measured by FIMS and the DMA centroid diameter. Comparison of particle concentrations measured by FIMS and a Condensation Particle Counter (CPC) shows that counting efficiency of FIMS is 100% for particles larger than 20nm, and higher than that of the CPC for particles with diameters less than 15nm. Experimentally determined FIMS mobility resolution ranged from 5 to 14 for particle diameters between 22 to 170nm, and agreed with theoretical predictions made using FIMS transfer theory, though there was some deviation observed at particle sizes that correspond to high theoretical mobility resolution. [Copyright &y& Elsevier]

Abstract: The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8–), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8- drops to 25% for 10- drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument''s inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations. [Copyright &y& Elsevier]

A Differential Mobility Particle Sizer (DMPS) system has been adapted and tested for reliable aerosol characterization at stratospheric pressures and temperatures in the AIDA aerosol chamber of Forschungszentrum Karlsruhe. To avoid partial or complete evaporation of volatile aerosol particles (e.g. solution droplets like sulfuric acid droplets), the DMA is operated at almost the same temperature and pressure as the AIDA aerosol vessel. In this study, we describe the experimental setup and technical modifications to the TSI standard DMA 3071 and CPC 3010 used for the DMPS system, discuss the results of low pressure Latex calibration and CPC counting efficiency measurements, and demonstrate the performance of the entire system in a case study with sulfuric acid aerosol. [Copyright &y& Elsevier]

Ionization quench function Q(E) introduces an important correction in the CIEMAT/NIST tracing method. In this paper we present a detailed analysis of the equations used to compute the counting efficiency of 55Fe. The counting efficiency of this radionuclide is very sensitive to the shape and values of Q(E) for this method. We demonstrate that the Birks equation and stopping power are not adequate to obtain low discrepancies between the experimental and computed efficiencies. An empirical procedure to compute accurate Q(E) functions is also given. [Copyright &y& Elsevier]

We have applied the MCNP Monte Carlo program to calculate γ-ray counting efficiencies and the separate influences of sample density and composition in two of our geometries. Using the detector characteristics given by the manufacturer in the input, it was possible to reproduce experimental spectra obtained with given activities of 152Eu and 137Cs in H2O. An equation for the self-absorption correction to be applied has been deduced as the ratio of the counting efficiency for a given sample to that of H2O. With a parameterization of this correction factor as a function of γ-ray energy and sample density, we could improve γ-ray spectrometry results for uranium concentrations in sedimentary Moroccan phosphates. These results were compared with those deduced by contact autoradiography using the solid state nuclear track detectors LR115 and CR39. [Copyright &y& Elsevier]

This paper gives a review of the development of the triple-to-double coincidence ratio (TDCR) method for standardizing pure β- and pure electron capture (EC)-radionuclides. The initial idea of Schwerdtel and practical realization and elaboration of the TDCR method by Pochwalski is presented. The main aspects and theoretical principle of the method are summarized and progress on the development of the theoretical model is presented. The details of the activity determination of pure β- and pure EC radionuclides are discussed, along with specific details in the application of the method in each case. The enhanced TDCR method based on the MAC3 electronic system developed in France is also discussed. Different applications of the TDCR method in metrology laboratories around the world are also pointed out. [Copyright &y& Elsevier]

In this study, we present a traceable method for determining the counting efficiency of optical particle size spectrometers (OPSS), also known as aerosol spectrometers. The primary standard consists of an aerosol generation setup, a vertical flow tube for particle homogenization and a reference optical particle counter. The OPSS under testing and the reference optical particle counter sample aerosol simultaneously through specially designed isokinetic sampling probes at number concentrations ranging from 0.5 cm−3 up to several hundred particles per cm3 (depending on the particle size). Calibration in terms of particle size relies by convention on the use of certified PS (polystyrene) spheres in the size range 100 nm - 10 μm. Here, the counting efficiency profiles of two commonly used OPSS, namely the Model 3330 OPS (TSI Inc., USA) and the 11-D monitor (Grimm GmbH, Germany) are presented for the first time and discussed within the context of the ISO 21501–1:2009 and 21501–4:2018 standards on the calibration of OPSS for indoor/outdoor measurements and optical particle counters (OPC) for clean rooms applications, respectively. We believe that this study can help manufacturers improve the design of their instruments, contribute to the further development of relevant national and international standards and pave the way for a standardised and traceable calibration of OPSS units installed at air quality monitoring stations and industrial/workplace environments. • A primary standard for the calibration of optical particle size spectrometers is described. • The calibration method covers sizes up to 10 μm and concentrations up to ≈1000 cm−3. • The counting efficiency profile of the TSI 3330 and Grimm 11-D spectrometers is presented. • The results are discussed within the context of the ISO 21401-1 and 21401-4 standards. • Recommendations for improving the relevant ISO standards are made. [ABSTRACT FROM AUTHOR]

Due to their sensitivity and ease of use, alpha-scintillation cells are being increasingly utilized for measurements of radon ( 222 Rn) in natural gas. Laboratory studies showed an average increase of 7.3% in the measurement efficiency of alpha-scintillation cells when filled with less-dense natural gas rather than regular air. A theoretical calculation comparing the atomic weight and density of air to that of natural gas suggests a 6–7% increase in the detection efficiency when measuring radon in the cells. A correction is also applicable when the sampling location and measurement laboratory are at different elevations. These corrections to the measurement efficiency need to be considered in order to derive accurate concentrations of radon in natural gas. [ABSTRACT FROM AUTHOR]

Abstract: This comment adds performance data for a modified version of one of the optical particle counters investigated in , namely the WELAS 2100. The new version was found to have a counting efficiency much closer to unity for larger particle sizes as well as some improvement in the lower 50% detection limit. [Copyright &y& Elsevier]