Comparison of two direct LS methods for measuring 222Rn in drinking water using α/β liquid scintillation spectrometry

Direct liquid scintillation (LS) methods are widely used for surveying ²²²Rn in drinking water. Two direct methods are used that differ in sample composition. In a two-phase sample, water lies below a water-immiscible cocktail, while in a homogeneous sample water is mixed with an emulsifying cocktail. Although these methods were developed in the late 1970s, their performances have not been simultaneously tested. Here, the methods were compared in two ways: by preparing both types of sample similarly from ²²²Rn-bearing groundwater in one emulsifying and in three organic cocktails, and by calibrating the methods with a ²²⁶Ra standard according to their respective procedures. The samples were measured using α/β LS spectrometry. The standard deviations of parallel samples and the repeatability of the measurements were excellent for both methods, except two-phase ²²⁶Ra samples, whose efficiencies decreased slightly over time. This instability was due to interference from ²¹⁰Pb, ²¹⁰Bi and ²¹⁰Po, which accumulated in the ²²⁶Ra standard, and possibly also to the migration of ²¹⁴Pb and ²¹⁴Bi into the aqueous phase and deficient transfer of ²²²Rn from the water to the cocktail.     

226Ra 228Ra 210Pb和210Po在水生生物及食物链中转移规律的探讨

目的 为了解天然放射性核素²²⁶Ra、²²⁸Ra、²¹⁰Pb与²¹⁰Po在水生物及食物链中转移和蓄积情况。方法 定点采集养殖水产品及栖息环境中水与底质沉积物, 按不同的实验需要, 每个鲜样分别剥取肉, 骨(壳),鳞片和胃肠。烹饪样品, 洗净、称重、清炖, 熟后分离出骨(壳),余为食物。样品分别测定²²⁶Ra、²²⁸Ra、²¹⁰Pb和²¹⁰Po含量。数据按统计学要求处理, 配对数据, 作了配对显着性检验。结果 ²²⁶Ra、²²⁸Ra和²¹⁰Pb主要沉积于骨(壳)中, 浓集系数为10²～10³,肉中为10⁰～10².²¹⁰Po主要蓄积在水生物胃肠中, 浓集系数在10²～10⁴,鱼类胃肠与贝类肉中可达10⁴.水产食品烹饪加工过程²²⁶Ra、²²⁸Ra和²¹⁰Pb在食物链中转移不明显, 经配对显着性检验, 差异无显着性(P0.05);然而210Po在淡水鱼类和虾类中转移是明显的, 肉配对检验有非常显着性差别(P<0.01).结论水生物对²²⁶Ra、²²⁸Ra、²¹⁰Pb和²¹⁰Po有很强浓集能力。     

Evaluation of uncertainty and detection limits in Pb and Po measurement in water by alpha spectrometry using Po spontaneous deposition onto a silver disk

An easy and accurate method for the determination of ²¹⁰Pb and ²¹⁰Po in water using ²¹⁰Po spontaneous deposition onto a silver disk is proposed and assessed for its detection capabilities according to the ISO Guide for the expression of uncertainty in measurement (GUM) and ISO Standard 11929-7 concerning the evaluation of the characteristic limits for ionizing radiation measurements. The method makes no assumption on the initial values of the activity concentrations of ²¹⁰Pb, ²¹⁰Bi and ²¹⁰Po in the sample to be analyzed, and is based on the alpha spectrometric measurement of ²¹⁰Po in two different aliquots: the first one measured five weeks after the sampling date to ensure radioactive equilibrium between ²¹⁰Pb and ²¹⁰Bi and the second after a sufficient time for the ingrowth of ²¹⁰Po from ²¹⁰Pb to be significant. As shown, for a recommended time interval of seven months between ²¹⁰Po measurements, the applicability of the proposed method is limited to water samples with a ²²⁶Ra to ²¹⁰Pb activity ratio C_Ra/C_Pb≤4, as usual in natural waters. Using sample and background counting times of 24 h and 240 h, respectively, the detection limit of the activity concentration of each radionuclide at the sampling time for a 1 L sample typically varies between 0.7 and 16 mBq L⁻¹ for ²¹⁰Pb in water samples with an initial activity of ²¹⁰Po in the range 0-200 mBq L⁻¹, and between 0.6 and 8.5 mBq L⁻¹ for ²¹⁰Po in water samples with an initial activity of ²¹⁰Pb in the same range.     

Determination of 210Pb and 226Ra/228Ra in continental water using HIDEX 300SL LS-spectrometer with TDCR efficiency tracing and optimized α⧸β-discrimination

An analytical method for determination of ²¹⁰Pb, ²²⁶Ra and ²²⁸Ra is presented based on adsorption on 3M Empore RadDiscs, and measurement applying liquid scintillation spectrometry (LSC) after elution. The LSC measurement was performed with optimized α⧸β-discrimination and isotope standardization using the triple to double coincidence ratio (TDCR). The consistency of measurement results between radioactive parent–daughter pairs ²¹⁰Pb/²¹⁰Bi, ²²⁶Ra/²²²Rn and ²²⁸Ra/²²⁸Ac was checked in long-term counting experiments and the influence ofinterference of in-growing daughters from ²²⁶Ra into the β-spectrum of ²²⁸Ra+²²⁸Ac was studied as well. Recommendations for optimized LSC ²²⁸Ra measurement besides presence of ²²⁶Ra are given.     

Morphological features of the microdistribution of naturally occurring 210Pb/210Po and 226Ra in the teeth of children and juveniles

Purpose: To examine the microdistribution of natural α‐radioactivity in deciduous teeth of children and the permanent teeth of juveniles extracted for orthodontic purpose from across the UK.

Materials and methods: The microdistribution of ²¹⁰Pb‐supported ²¹⁰Po and ²²⁶Ra in 708 deciduous and permanent teeth and 32 foetal teeth was measured on 1442 TASTRAK α‐particle track detectors.

Results: Of the various findings, a number are of special interest. Around half of the ²¹⁰Pb activity in the outer enamel of deciduous teeth appears to have been acquired in utero as a result of transplacental transfer. In deciduous and permanent teeth, ²²⁶Ra is concentrated mainly in the circumpulpal region, while the highest levels of ²¹⁰Po are on the highly calcified outer enamel surface. Furthermore, activity concentrations recorded on this surface were ln‐normally distributed.

Conclusions: ²¹⁰Pb‐supported ²¹⁰Po activity on the outer enamel surface of permanent teeth constitutes an assay of cumulative environmental exposure with which to assess exposure in bone, both in utero and in childhood. Such assessment can be used to study geographical variations in the α‐activity in teeth. More work is also required to determine the concentrations of both ²¹⁰Po and ²¹⁰Pb in the foetal skeleton.     

Spatial Distribution of Naturally Occurring 210Po and 226Ra in Children's Teeth

Deciduous and permanent teeth extracted from juveniles for orthodontic purposes have been analysed using α-sensitive plastic track detectors for the spatial distribution of total α-activity and naturally occurring ²¹⁰Pb-supported ²¹⁰Po and ²²⁶Ra. The distribution of these radionuclides is nonuniform, with ²¹⁰Po being primarily associated with outer enamel and ²²⁶Ra with the pulp. The observations suggest that ²¹⁰Pb/²¹⁰Po concentrates at the interface of enamel with saliva or blood, by means of unidirectional ionic exchange with calcium. In contrast, ²²⁶Ra concentrates in the predentine band at the interface with pulp and with systemic blood circulation, where its uptake is permitted by the incomplete calcification in this band. Activity concentration was measured in 900 teeth. Total concentration on the outer enamel surface of deciduous teeth, permanent teeth from children ?10 years and permanent teeth from children > 10 years give respective mean values of 8·63±0·26, 5·76±0.48 and 7·00±0·15 Bq kg^?1. ²²⁶Ra concentration on the corresponding longitudinal sections comprising pulp, dentine and annular enamel give respective mean values of 0·715±0·055, 0·418±0·083 and 0·514±0·029 Bq kg^?1. Mean activity concentration in 32 foetal teeth was 2·05±0·31 Bq kg^?1. The results form the basis of more detailed studies of (1) age-dependent uptake of α-radionuclides in teeth and their microdistribution, and (2) the geographical variation in activity concentration with respect to environmental factors such as domestic radon exposure.     

Simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by using the liquid scintillation counter-suspension gel method.

A method for the simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by liquid scintillation counting was developed. Radium and lead were separated together from the samples as Ba(Ra) x PbSO4 co-precipitate, which was centrifuged and dissolved with 0.1 M EDTA solution (pH 9.0). Radium was separated as Ba(Ra)SO4 co-precipitate by adding ammonium sulfate and adjusting the pH of the solution to 4.2. Lead remaining in the solution was separated as PbSO4 precipitate by adding 9 M sulfuric acid. These Ba(Ra)SO4 and PbSO4 precipitates were purified with EDTA solution and used for measurement. To save time and to make counting samples simpler, direct counting of Ba(Ra)SO4 and PbSO4 precipitates instead of the phosphoric acid fusion method was attempted. Ba(Ra)SO4 and PbSO4 precipitates were suspended in the scintillation gel, and measured. Two liquid scintillation cocktails, Instagel XF and UltimaGold AB were used to prepare the counting samples. A mixture of water (40%), Instagel XF (40%) and UltimaGold AB (20%) formed a stable gel. Activities of 226Ra and 210Pb were calculated from the alpha spectrum of Ba(Ra)SO4 and beta spectrum of PbSO4, respectively. The long-term stability of the suspension gel was good. The analytical results of 226Ra and 210Pb in spiked groundwater samples were in good agreement with the known concentrations of 226Ra and 210Pb. The analytical values of 226Ra and 210Pb in the soil reference samples were within 11.5 and 1.6% of the relative error from the reference values, respectively.     

Standardisation of 210Pb

The standardisation of ²¹⁰Pb is complicated by the presence of the daughters, ²¹⁰Bi and ²¹⁰Po. In addition, the low energies of the beta emissions from ²¹⁰Pb make it difficult to obtain high detection efficiencies in an atmospheric proportional counter and hence produce the need for large extrapolations with consequential large uncertainties when extrapolating to unit efficiency with the conventional 4π(PC)-γ-coincidence technique. In order to produce a reliable standardisation, it is necessary to remove the daughter products. A solution of ²¹⁰Pb was therefore chemically separated from its daughters and then standardised using the conventional 4π(LS)-γ-coincidence technique. The low energy (46 keV) and low emission probability (4%) of the associated photon emissions effectively rules out the possibility of using ionisation chambers as secondary standard transfer instruments for this nuclide. A germanium spectrometer therefore was calibrated for this purpose using ²⁴¹Am as a normalising agent.The results of this work are presented together with an analysis of the standardisation uncertainties that can be achieved in practice.     

Geochronology of lake sediments using 210Pb with double energetic window method by LSC: An application to Lake Van

In this study the age and sediment accumulation rates of the lake sediment were calculated by using the ²¹⁰Pb concentrations through the sediment core. The specific activity of ²¹⁰Pb for each sediment section was determined by LSC with double energetic window method which relies on the direct determination of ²¹⁰Pb without waiting for the in growth of ²¹⁰Po from ²¹⁰Pb. For the successful determination of this radionuclide two counting windows were optimized to eliminate the overlapping of the beta spectra of ²¹⁰Pb and ²¹⁰Bi.     

Relationship between radioactivity of radium and concentrations of barium and lead in hokutolite

Hokutolite consists of barite (BaSO₄) and anglesite (PbSO₄), and contains significant amounts of radium isotopes as a radioactive mineral. Photon activation and gamma-ray spectrometry were employed to determine Ba, Pb and ²²⁶Ra contents in hokutolite samples and to investigate the correlation between ²²⁶Ra activity and both Ba and Pb content. ²²⁶Ra activity in 30 hokutolite samples were estimated in the range of 40–65 Bq/g and was positively related to Ba content (r=0.859, p<0.001), but independent of Pb content (r=−0.236, p=0.217). Experimental results implied that ²²⁶Ra preferably precipitated with Ba over Pb. The ²²⁶Ra activity in hokutolite from the Peitou Hot Spring was experimentally estimated based on the Ba/Pb ratio and expressed as ²²⁶Ra (Bq/g)=14.67 (Ba/Pb)_molar+14.13.     

The natural radioactivity in Guarani aquifer groundwater, Brazil.

The measurements of gross alpha and gross beta radioactivity in groundwater samples from Guarani aquifer in Brazil are reported in this paper together with the activity concentration of the natural dissolved radionuclides (40)K, (238)U, (234)U, (226)Ra, (222)Rn, (210)Po, (210)Pb, (232)Th, (228Th), and (228)Ra. Most of the gross alpha radioactivity values were below the critical level of detection corresponding to 1mBq/L, however, the whole data set for the gross beta radioactivity and radionuclides (40)K, (238)U, (234)U, (226)Ra, (222)Rn, (210)Po, (210)Pb, and (228)Ra was submitted to a statistical treatment, considering class intervals arranged in geometric progression, because of the great variability of the activity. The analysis indicated lognormal distribution of the data, as usually observed in samples taken from the natural context. An inverse relationship between the gross alpha and gross beta activity has been identified and is related to an increase in the K content in the water. The mobility coefficient has been estimated for (238)U, (226)Ra, (232)Th and (228)Ra in Guarani aquifer and the results indicated that the radioelement solubility in the studied system varies according to the following order: radium>uranium>thorium. The implications of the data obtained in terms of standards established for defining the drinking water quality have also been discussed.     

Morphological features of the microdistribution of naturally occurring 10Pb/2l0Po and 226Ra in the teeth of children and juveniles

PURPOSE: To examine the microdistribution of natural alpha-radioactivity in deciduous teeth of children and the permanent teeth of juveniles extracted for orthodontic purpose from across the UK. MATERIALS AND METHODS: The microdistribution of 210Pb-supported 210Po and 226Ra in 708 deciduous and permanent teeth and 32 foetal teeth was measured on 1442 TASTRAK alpha-particle track detectors. RESULTS: Of the various findings, a number are of special interest. Around half of the 210Pb activity in the outer enamel of deciduous teeth appears to have been acquired in utero as a result of transplacental transfer. In deciduous and permanent teeth, 226Ra is concentrated mainly in the circumpulpal region, while the highest levels of 210Po are on the highly calcified outer enamel surface. Furthermore, activity concentrations recorded on this surface were In-normally distributed. CONCLUSIONS: 210Pb-supported 210Po activity on the outer enamel surface of permanent teeth constitutes an assay of cumulative environmental exposure with which to assess exposure in bone, both in utero and in childhood. Such assessment can be used to study geographical variations in the alpha-activity in teeth. More work is also required to determine the concentrations of both 210Po and 210Pb in the foetal skeleton.     

Determination of 210Pb and 210Po in water using the extractive scintillation cocktail Polex™

Method validation was performed to achieve the accreditation for our determination method of ²¹⁰Pb and ²¹⁰Po in water. A Pb(NO₃)₂ carrier is added to the sample and lead is precipitated with Na₂SxH₂O. ²¹⁰Po is co-precipitated and the extractive scintillation cocktail Polex^™ is used to determine ²¹⁰Po and ²¹⁰Pb. Uranium is also extracted by Polex^™. It can be removed by washing the precipitate with 1% HNO₃. The ingrowth of ²¹⁰Pb from ²²²Rn during transportation time must be calculated. It has to be subtracted from the original ²¹⁰Pb in the sample and taken into account for the calculation of the lower limit of detection.     

伽玛能谱仪分析226Ra的部分影响因素的研究

目的通过对γ能谱分析226Ra的部分影响因素进行有针对性的测量, 进一步优化γ能谱针对226Ra活度的分析方法, 以求得到更为精准的测量结果。方法利用实验室高纯锗γ能谱仪, 开展样品密封时间的跟踪测量、铅室本底波动影响测量, 分析方法与子体核素特征γ射线能峰选择等方面研究。结果样品密封12 d后, 226Ra-222Rn衰变系基本达到平衡。测量屏蔽铅室本底中222Rn昼夜波动明显且无明显规律, 向铅室内注入氮气的方式可降低或避免本底波动影响。针对31份密封23 d后测量的土壤样品, 采用效率曲线法分析的结果表明, 351.9 keV能峰计算的226Ra结果普遍高于609.3 keV能峰, 高出的比例范围为8.0%～20.7%;采用相对比较法分析的结果表明, 两能峰偏差的比例范围为-4.1%～10.3%。结论在样品密封后第12天进行测量时, 建议考虑由衰变系平衡因素引入约4%的不确定度。通过铅室内注入氮气避免本底波动时, 须注意铅室内腔体积与氮气注入流量的匹配关系。采用效率曲线法分析226Ra活度时, 214Bi(609.3 keV)能峰存在级联符合相加影响, 应避免选用;采用相对比较法...     

食品中的铅-210

本文报道了30种常用食品²¹⁰Pb含量, 它们是在样品中²¹⁰Pb～²¹⁰Po接近放射性平衡后, 用银片自沉积法测定²¹⁰Po, 计算出²¹⁰Pb含量。粮食、蔬菜和肉类的²¹⁰Pb平均浓度分剐为0.14, 15.08和1.26×10^-14Ci/g。     

Transfer of 238U, 230Th, 226Ra,and 210Pb from soils to tree and shrub species in a Mediterranean area

The soil-to-plant transfer factors of natural uranium isotopes (²³⁸U and ²³⁴U), ²³⁰Th, ²²⁶Ra, and ²¹⁰Pb were studied in a disused uranium mine located in the Extremadura region in the south-west of Spain. The plant samples included trees (Quercus ilex, Quercus suber, and Eucalyptus cameldulensis) and one shrub (Cytisus multiflorus). All of them are characteristic of Mediterranean environments. The activity concentrations in leaves and fruit were determined for the tree species at different stages of growth. For the shrub, the total above-ground fraction was considered in three seasons. For old leaves and fruit, the highest activity concentrations were found in Eucalyptus cameldulensis for all the radionuclides studied, except in the case of ²³⁰Th that presented similar activity concentrations in all of the tree species studied. In every case, the transfer to fruit was less than the transfer to leaves. In the shrub, the results depended on the season of sampling, with the highest value obtained in spring and the lowest in autumn. Important correlations were obtained for ²³⁸U and ²²⁶Ra between the activity ratio in soils with that in leaves or fruit.     

Activity size distributions for long-lived radon decay products in aerosols collected in Barcelona (Spain)

The activity median aerodynamic diameters (AMADs) of long-lived radon decay product (²¹⁰Pb, ²¹⁰Po) in aerosols collected in the Barcelona area (Northeast Spain) during the period from April 2006 to February 2008 are presented. The ²¹⁰Po mean AMAD was 420 nm, while the ²¹⁰Pb mean AMAD was 500 nm. The temporal evolution of ²¹⁰Pb and ²¹⁰Po AMADs shows maxima in autumn and winter and minima in spring and summer. ²¹⁰Pb AMAD are being used to estimate the mean-residence time of atmospheric aerosols.     

Estimation of annual effective dose due to ingestion of natural radionuclides in foodstuffs and water at a proposed uranium mining site in India

Abstract

Purpose: To study the distribution of ²¹⁰Po, ²²⁶Ra, ²³⁰Th and U(nat) (naturally occurring radioisotopes of uranium [²³⁴U, ²³⁵U and ²³⁸U]) in food and water around the Bagjata uranium mining area in India.

Materials and methods: Radionuclides were analyzed in food samples of plant and animal origin after acid digestion. Intake and ingestion dose of the radionuclides were estimated.

Results: ²¹⁰Po, ²²⁶Ra, ²³⁰Th and U(nat) in all the dietary components ranged widely from < 0.2–36, < 0.02–1.58, < 0.01–2.8 and < 0.017–0.39 Bqkg^-1, respectively. The range of ²²⁶Ra and U(nat) in water was < 3.5–206 and < 12.6–693 mBql^?1, respectively. The intake of radionuclides considering food and water was calculated to be 760 BqY^?1 while the ingestion dose was 601 μSvY^?1. The estimated doses reflect the natural background dose via route of ingestion, which is below the 1 mSvY^?1 limit set by the International Commission on Radiological Protection (ICRP). However, the doses are more than the dose constraint of 300 μSvY^?1 as suggested by the ICRP for members of the public for planned disposal of long-lived radioactive waste.

Conclusion: The study confirms that current levels of radionuclides do not pose significant radiological risk to the local inhabitants, but they need close investigation in the near future.     

Radiometric determination of 210Pb in powder samples by the method of standard additions

The method of standard additions is a well known procedure in chemistry for the measurement of trace substances. The use of this method is described in the radiometric determination of ²¹⁰Pb activity via the γ-ray at 46.5 keV emitted in about 4% of the decays. Standard additions of ²¹⁰Pb activity are adsorbed on anion exchange resin which is then mixed with the sample. The procedure used to extract the area of the photopeak from the continuum on which it is superimposed, is described in detail. The value of the ²¹⁰Pb activity is calculated using the slope and intercept of the best straight line fitting the count-rate data plotted against added activity. Results obtained on four standard ore samples indicate that this method yields results of comparable accuracy to other methods such as β-ray spectrometry of the prompt ²¹⁰Bi daughter. This method, however, avoids the tedious chemical separations required.     

Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry.

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists of the evaluation of the alpha-spectrum that is composed of the strongly overlapping peaks of 226Ra, 233U, 237Np, 222Rn and 218Po in the energy range of 4.60-6.00 MeV and the single 214Po peak at 7.69 MeV. The alpha-peaks are analysed by a special peak fit function that considers the deviation of the alpha-peak at the low energy side from the pure Gaussian shape. First 237Np is determined using its daughter 233Pa by analysing the beta-spectrum in the range 150-570 keV. 226Ra follows from the alpha-spectrum that is measured 6 weeks after sample preparation, i.e., 226Ra is determined from the radioactive equilibrium with its short-lived daughters 222Rn, 218Po and 214Po. Finally the 233U activity results from the fitted spectrum in the range of 4.4-4.8 MeV by subtracting the activity of 226Ra and 237Np. Knowing the exact energy position of the LS-peaks an alternative evaluation consists in the accurate deconvolution of the first three peaks that are formed by 226Ra and 233U (maximum of both at channel 700), 237Np (maxima at channels 700 and 725) and 222Rn (maximum at channel 737). In these two ways 226Ra, 233U and 237Np can be determined in mutual activity ratios of 1:50 with a relative standard deviation of less than 4% for the major activity and 9% for the minor activity.