Geochronology of Lake Baikal from Pb and Cs radioisotopes

Two box cores of near surface sediments were obtained from Lake Baikal in Southeastern Siberia, Russia. The cores were taken from the northern and southern basins of the lake during a joint American–Russian research expedition in the summer of 1994. The cores were analyzed for ²¹⁰Pb, ¹³⁷Cs and total organic carbon (TOC). Organic carbon is an indicator of photosynthetic production by phytoplankton, taking place primarily in the euphotic zone of the water column. Accumulation rates of TOC may be used as indicators of paleo-productivity when sedimentation rates are determined using the ²¹⁰Pb dating method and combined with both the density of sediment and organic carbon content. Accordingly, the lake is characterized by changes in accumulations of TOC, which may be linked to rates of sedimentation. Accumulations of TOC and sedimentation rates were higher in the southern basin site than in the northern basin site. The southern station core was taken from an area in close proximity to the Selenga River delta, which carries 50% of the water input to Lake Baikal. Productivity should thus be higher in this region due to the high nutrient input and sediment accumulation higher due to influx of riverine sediment input. Traces of ¹³⁷Cs (an anthropogenic product) were found in both cores. However, activities of ¹³⁷Cs were significantly higher in the southern basin, likely due to the input of the Selenga River in the southern region, which extends to a region in Mongolia in close proximity to the area of the Chinese atomic-bomb atmospheric testing of the 1970s. Application of a quantitative inverse model to the ²¹⁰Pb profiles yielded the following results: (i) station 12, near the Selenga Delta, had an accumulation rate of about 0.38 cm/y in 1957 but this rate was halved by 1980 to about 0.22 cm/y and has been roughly steady since that time; ¹³⁷Cs values are consistent with the age-to-depth determination from ²¹⁰Pb for station 12; (ii) since about 1960, station 5A in the northern basin had an accumulation rate lower by a factor 2–4 than that of the station near the Selenga Delta; the ¹³⁷Cs values are consistent with the ²¹⁰Pb age-to-depth determination for station 5A; (iii) the ¹³⁷Cs activities for station 12 systematically increase with time towards the present day and are about a factor 6–10 higher than ¹³⁷Cs activities recorded for station 5A, which do not show a corresponding systematic increase with time.     

Geochronology of Lake Baikal from 210Pb and 137Cs radioisotopes

Two box cores of near surface sediments were obtained from Lake Baikal in Southeastern Siberia, Russia. The cores were taken from the northern and southern basins of the lake during a joint American–Russian research expedition in the summer of 1994. The cores were analyzed for ²¹⁰Pb, ¹³⁷Cs and total organic carbon (TOC). Organic carbon is an indicator of photosynthetic production by phytoplankton, taking place primarily in the euphotic zone of the water column. Accumulation rates of TOC may be used as indicators of paleo-productivity when sedimentation rates are determined using the ²¹⁰Pb dating method and combined with both the density of sediment and organic carbon content. Accordingly, the lake is characterized by changes in accumulations of TOC, which may be linked to rates of sedimentation. Accumulations of TOC and sedimentation rates were higher in the southern basin site than in the northern basin site. The southern station core was taken from an area in close proximity to the Selenga River delta, which carries 50% of the water input to Lake Baikal. Productivity should thus be higher in this region due to the high nutrient input and sediment accumulation higher due to influx of riverine sediment input. Traces of ¹³⁷Cs (an anthropogenic product) were found in both cores. However, activities of ¹³⁷Cs were significantly higher in the southern basin, likely due to the input of the Selenga River in the southern region, which extends to a region in Mongolia in close proximity to the area of the Chinese atomic-bomb atmospheric testing of the 1970s. Application of a quantitative inverse model to the ²¹⁰Pb profiles yielded the following results: (i) station 12, near the Selenga Delta, had an accumulation rate of about 0.38 cm/y in 1957 but this rate was halved by 1980 to about 0.22 cm/y and has been roughly steady since that time; ¹³⁷Cs values are consistent with the age-to-depth determination from ²¹⁰Pb for station 12; (ii) since about 1960, station 5A in the northern basin had an accumulation rate lower by a factor 2–4 than that of the station near the Selenga Delta; the ¹³⁷Cs values are consistent with the ²¹⁰Pb age-to-depth determination for station 5A; (iii) the ¹³⁷Cs activities for station 12 systematically increase with time towards the present day and are about a factor 6–10 higher than ¹³⁷Cs activities recorded for station 5A, which do not show a corresponding systematic increase with time.     

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.     

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.     

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。     

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.     

A sequential method for the determination of 210Pb, 226Ra,and uranium and thorium radioisotopes by LSC and alpha-spectrometry

A procedure for the determination of ²¹⁰Pb, and alpha-emitting radioisotopes of uranium, thorium, and radium from the same aliquot of a sample has been proposed. The key step consisted in the recovery of Pb(II) and Ra by precipitation of insoluble Pb(NO₃)₂, the uranium and thorium radioisotopes remaining in solution. Afterwards, the fractions were handled by specific, well consolidated procedures. Lead-210 was determined by the LSC technique while the uranium, thorium, and radium radioisotopes were measured with silicon alpha-spectrometers. The procedure was applied to a reference sample and several environmental samples obtaining satisfactory results.     

Evaluation of the chromium contamination at Ribeirão dos Bagres,Franca (SP), Brazil,by the 210Pb method

This paper presents a chronological study focusing the use of ²¹⁰Pb in four sediment cores collected at Ribeirão dos Bagres in the region of Franca, São Paulo State, Brazil. When evaluating the sedimentation rate by using the ²¹⁰Pb method, it was possible to monitor historical changes occurring in the concentrations of chromium present in the sediments. In order to do so, several specific parameters were determined in sediments, as chromium concentration, major oxides, organic matter, grain size, and chemical and physical–chemical parameters of waters. The sediments possessed a Cr concentration range of 0.83–26.25 mg/kg that is below the world's average of shales. The sedimentation rates obtained from the ²¹⁰Pb analysis were between 0.07 and 0.77 g cm⁻² year⁻¹, while the linear sedimentation rate was from 0.6 to 3.2 cm/year. The adoption of the CIC (Constant Initial Concentration) ²¹⁰Pb model allowed characterize older sediments, aged 177 years, and younger sediments, aged 4 years. The organic matter in the sediments was more abundant in the first few centimeters of practically all profiles, and the analysis of oxides showed that silica is the major constituent of the sediments, in which there is predominance of sand and silt. In addition, the analysis of the physical and chemical parameters of waters indicated that they are suitable for navigation and natural harmony landscape.     

2017—2020年北京地区大气气溶胶中7 Be和210 Pb放射性活度浓度监测与分析

目的 监测与分析2017—2020年北京地区大气气溶胶中⁷Be和²¹⁰Pb放射性活度浓度变化情况,为有效防治空气污染提供科学依据。方法 利用大流量空气气溶胶采样器（SnowWhite）采集气溶胶样品1 074份,其中春季、夏季、秋季和冬季分别采集275、266、262和271份。使用低本底高纯锗伽马谱仪（ORTEC）分析气溶胶样品中⁷Be和²¹⁰Pb放射性活度浓度。结果 2017—2020年北京地区大气气溶胶中⁷Be放射性活度浓度的变化范围为0.56~14.84 mBq/m³,平均值为6.84 mBq/m³。²¹⁰Pb放射性活度浓度的变化范围为0.01~9.37 mBq/m³,平均值为3.19 mBq/m³。2017—2020年北京大气气溶胶⁷Be和²¹⁰Pb放射性活度浓度在春、夏、秋、冬四季中差异均有统计学意义（F=32.66、93.93,P<0.05）,其中⁷Be放射性活度浓度春季最高,秋季次之,夏季和冬季最低,²¹⁰Pb放射性活度浓度由高到低分别为冬季、秋季、春季、夏季。结论 2017—2020年北京地区大气气溶胶中⁷Be和²¹⁰Pb放射性活度浓度处于正常涨落水平范围内。     

The Uptake of 210Pb by Resting and Growing Hair

Summary

The incorporation of ²¹⁰Pb into resting and growing hair has been studied in rabbits. It was found that in the telogen (resting) hair the concentrations of ²¹⁰Pb were from 7 to 137 times lower than in the anagen (growing) hair. The concentrations in the anagen hair were dependent both on the total dose of injected ²¹⁰Pb and on the mode of dose fractionation.     

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.     

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.     

Calibration of the direct LSC method for radon in drinking water: Interference from 210Pb and its progenies accumulated in 226Ra standard solution

The standard ASTM method is the most commonly applied method for determining ²²²Rn in drinking water. The method is calibrated with a ²²⁶Ra standard solution that usually contains variable amounts of ²¹⁰Pb, ²¹⁰Bi and ²¹⁰Po if the standard has not recently been purified. Until now it has not been experimentally confirmed that these progenies do not interfere when the method is calibrated. In this study, interference was examined using three different organic cocktails and α/β liquid scintillation spectrometry to separately assess the effect of three radionuclides. The interference from ²¹⁰ Po was 4% for one of the cocktails if the ²²⁶Ra standard had been purified 5 years earlier. The interferences from ²¹⁰Pb and ²¹⁰Bi were negligible compared to that of ²¹⁰Po.     

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。     

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.     

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.     

Results of an IAEA inter-comparison exercise to assess 137Cs and total 210Pb analytical performance in soil

Fallout radionuclides (FRNs) such as ²¹⁰Pb and ¹³⁷Cs have been widely used to assess soil erosion and sedimentation processes. It is of major importance to obtain accurate analytical results of FRNs by gamma analysis before any data treatment through conversion model and to allow subsequent comparison of erosion and sedimentation rates from different case studies.Therefore, IAEA organized an inter-comparison exercise to assess the validity and reliability of the analytical results of ¹³⁷Cs and total ²¹⁰Pb using γ-spectrometry in the various laboratories participating in the IAEA Co-ordinated Research Project on “Assess the effectiveness of soil conservation measures for sustainable watershed management using fallout radionuclides”.Reference materials were distributed to 14 participating laboratories and, using a rating system, their analytical results were compared to the reference values assigned.In the case of ¹³⁷Cs, the analytical results were satisfactory with 66% of the laboratories producing acceptable results. Only the sample with low ¹³⁷Cs activity (2.6±0.2 Bq kg⁻¹) gave less accurate results with more than 25% not acceptable results. The total ²¹⁰Pb analysis indicated a clear need for corrective actions in the analysis process as only 36% of the laboratories involved in the proficiency test was able to access total ²¹⁰Pb with occurrence (bias ⩽10%). This inter-laboratory test underlines that further inter-comparison exercises should be organized by IAEA or regional laboratories to ensure the quality of the analytical data produced in Member States. As a result of the above-mentioned proficiency test, some recommendations have been provided to improve accurate gamma measurement of both ¹³⁷Cs and total ²¹⁰Pb.     

Radon measurements—discussion of error estimates for selected methods

The main sources of uncertainties for grab sampling, short-term (charcoal canisters) and long term (track detectors) measurements are: systematic bias of reference equipment; random Poisson and non-Poisson errors during calibration; random Poisson and non-Poisson errors during measurements. The origins of non-Poisson random errors during calibration are different for different kinds of instrumental measurements.The main sources of uncertainties for retrospective measurements conducted by surface traps techniques can be divided in two groups: errors of surface ²¹⁰Pb (²¹⁰Po) activity measurements and uncertainties of transfer from ²¹⁰Pb surface activity in glass objects to average radon concentration during this object exposure. It's shown that total measurement error of surface trap retrospective technique can be decreased to 35%.     

低本底γ能谱实验室铅室放射性本底变化分析探讨

目的 探讨γ能谱仪本底中天然放射性核素净计数率的变化规律,为降低本底涨落对样品测量的影响提供科学依据。方法 收集两台高纯锗γ能谱仪在2013-2017年间不定期测量的本底谱,记录天然放射性核素²¹⁰Pb、²³⁴Th、²¹²Pb、²¹⁴Pb、²⁰⁸Tl、²¹⁴Bi、²²⁸Ac和⁴⁰K特征峰的净计数率,运用统计学方法分析其净计数率的变化。结果 谱仪本底中²¹⁰Pb、²³⁴Th、²¹²Pb、²¹⁴Pb、²⁰⁸Tl、²¹⁴Bi、²²⁸Ac和⁴⁰K的净计数率不同,其中²¹⁴Pb、²¹⁴Bi和⁴⁰K的净计数率明显高于²¹⁰Pb、²³⁴Th、²¹²Pb、²⁰⁸Tl和²²⁸Ac。2013-2017年间,8种天然放射性核素的各自净计数率差异无统计学意义（P>0.05）,但是²¹⁴Pb和²¹⁴Bi的净计数率变异系数均在50%以上。结论 用γ能谱仪测量样品中天然放射性核素的活度浓度,当活度浓度较低时,须用近期测量的本底进行扣除,以保证结果的准确性。     

Natural radionuclides in volcanic activity

Natural radionuclides of ²²²Ra, ²¹⁰Pb and ²¹²Pb present in the magma are emitted during the eruption of volcanoes. Depletion of ²²²Rn in pumices and in lava showed that significant amounts of ²²²Rn were released from erupting magmas. Atmospheric ²¹⁰Pb originating from the 1991 eruption of Mt. Pinatubo was detected in Japan and in Korea as a temporal increase in the atmospheric concentration after the eruption. Atmospheric ²¹²Pb originating from the 2000 eruption of Mt. Miyake-jima was also detected as an abrupt rise in atmospheric concentration after the event.