岩石土壤及沉积物样品中₂₁₀Pb-₂₁₀Bi-₂₁₀Po联测技术的研究与应用

【作者】 王玉学；

【导师】 郭冬发；

【作者基本信息】 核工业北京地质研究院 ， 矿产普查与勘探， 2013， 博士

【摘要】 铀系核素²¹⁰Pb、²¹⁰Bi、²¹⁰Po在铀矿地质勘查、沉积年代学研究、海洋地球化学研究、大气环境学研究、油气勘查、自然地质灾害勘查、地下水及温泉勘查、土壤侵蚀研究、放射卫生学研究等诸多领域具有重要应用。目前多采用相对独立的分析方法对三核素分别进行测定，并存在一些技术缺陷需要解决。外文文献报道的三核素连续测试技术除了仍然存在一些技术问题需要解决外，较为突出的问题是均需要使用价格昂贵的检测设备或者难于获取且价格不菲的放射性示踪剂、闪烁液，目前国内难以普及应用。本文详细研究了²¹⁰Bi、²¹⁰Po同步且定量恒温自沉积于铜箔和镍箔的最佳抗干扰制源条件，分析了212Bi/²¹⁰Bi比值、212Bi/²¹⁰Po比值、²¹⁰Bi/²¹⁰Po比值、226Ra/²¹⁰Pb比值、²¹⁰Bi/²¹⁰Pb比值等在测量过程中的影响，首次建立了双样-铜箔恒温自沉积制源-总α、总β同时计数法快速联测岩石土壤及沉积物样品中²¹⁰Pb、²¹⁰Bi、²¹⁰Po的分析技术，以及双样-镍箔恒温自沉积制源-总α、总β同时计数法快速联测岩石土壤及沉积物样品中²¹⁰Pb、²¹⁰Bi、²¹⁰Po的分析技术。研究表明，当制源介质为0.5mol/L HCl+3.5mol/L NaCl溶液，初始体积为20mL，制源温度为90℃，制源振速为140r/min，振幅为20mm，0.6g抗坏血酸存在下，制源70min，²¹⁰Bi、²¹⁰Po可同步且定量恒温自沉积于铜箔（直径20mm，厚度0.15mm）。当制源介质为0.1mol/L HCl+2.9mol/L NaCl溶液，初始体积为25mL，制源温度为90℃，制源振速为160r/min，振幅为20mm，0.5g抗坏血酸存在下，制源60min，²¹⁰Bi、²¹⁰Po可同步且定量恒温自沉积于镍箔（直径20mm，厚度0.15mm）。大量共存元素和核素不干扰自沉积，自沉积制源可以在无示踪且不附加分离手段的情况下进行。放置衰变法可以消除212Bi和218Po等短寿命天然放射性核素对测量产生的影响。系统分析了各核素比值在测量过程中的影响并给出了精密测量时的校正公式，讨论了可以酌情忽略影响时需要满足的条件:当212Bi/²¹⁰Bi≤10、212Bi/²¹⁰Po≤10，样品源放置10h后测量时，212Bi对²¹⁰Bi、²¹⁰Po测量产生的正干扰均低于1.2%；当²¹⁰Bi/²¹⁰Po≤5，样品源测量中间时刻与样品源制备中间时刻的时间间隔小于30h时，²¹⁰Po的生长与衰变修正系数小于1.0224；当²¹⁰Bi/²¹⁰Po≥0.2时，²¹⁰Bi测量值的串道修正系数小于1.0276；当226Ra/²¹⁰Pb≤10，2份样品制源时间间隔为15天时，²¹⁰Pb测量结果的偏高程度小于0.74%。采用双份样品间隔自沉积制源，能够避免采用单份样品两次自沉积制源时被测核素在容器上吸附以及还原剂的氧化和水解产物对制源或测量带来的影响。通过低本底α/β测量仪对两份样品源分别进行总α、总β同时计数，根据Bataman公式建立联立方程并求解，本文建立的测试技术能够准确给出样品取样时刻的三核素比活度。测试精度优于5%，全程加标放化回收率在99.5%～100.5%之间。采用铜箔自沉积制源方式时，²¹⁰Pb、²¹⁰Bi、²¹⁰Po三核素的检出下限分别为7.1、7.1和0.87Bq/kg。采用镍箔自沉积制源方式时，三核素的检出下限分别为14.2、14.2和1.74Bq/kg。完成三核素联测的典型检测周期少于2周。本文建立的测试技术检测精度高，检出下限低，制源方式简单快速，检测流程容易掌握，所用试剂和仪器全部国产化（只需要1台国产低本底α/β测量仪即可快速完成三核素联测），检测成本经济，满足国情，容易推广。更多还原

【Abstract】 Uranium series nuclides²¹⁰Pb,²¹⁰Bi,²¹⁰Po are widely used in many fieldssuch as the geological exploration of uranium, the deposition geochronology, themarine geochemistry,the atmospheric environmental science, the petroleumexploration,the natural geologic hazard exploration, the underground water and hotspring exploration, the soil erosion science,the radiation hygiene,and so on.Measurement techniques of these nuclides are relatively independent at the moment inmost cases, and there are some technical issues need to be addressed.Among someinsufficiencies still exist in the successive measurement techniques of these nuclidesreported in the foreign literatures, the most prominent problems are that all thetechniques either needing some kinds of expensive testing apparatus or someradioactive tracers and cocktails which are difficult to obtain domestically. As a result,these testing techniques are hard to popularize and apply in China.In this paper, the optimum and anti-interference spontaneous depositionconditions of²¹⁰Bi,²¹⁰Po on Cu-foil and Ni-foil simultaneously and quantificationallyare studied in detail，the influences of the nuclide activity ratios of212Bi/²¹⁰Bi,212Bi/²¹⁰Po,²¹⁰Bi/²¹⁰Po,226Ra/²¹⁰Pb,²¹⁰Bi/²¹⁰Pb on measurement are discussed，and thetwo kinds of conjoint measurement techniques for²¹⁰Pb,²¹⁰Bi,²¹⁰Po are set up.Thefirst one is “Conjoint Determination of²¹⁰Pb,²¹⁰Bi,²¹⁰Po in Rock, Soil andSediment Samples by Constant Temperature Spontaneous Deposition on Cu-foil withGross α and β Counting and Double Samples”,the other one is “ConjointDetermination of²¹⁰Pb,²¹⁰Bi,²¹⁰Po in Rock, Soil and Sediment Samples by ConstantTemperature Spontaneous Deposition on Ni-foil with Gross α and β Counting andDouble Samples”.It is found experimentally that under the conditions of the concentration of HClbeing0.5mol/L, the concentration of NaCl being3.5mol/L,the initial volume ofsolution being20mL, the constant experiment temperature being90℃, the vibrationfrequency being140r/min, the vibration amplitude being20mm,0.6g ascorbic acidbeing added, and the deposition time being70min,²¹⁰Bi and²¹⁰Po can spontaneouslydeposit on Cu-foil（diameter=20mm,thickness=0.15mm） simultaneously andquantificationally. Under the conditions of the concentration of HCl being0.1mol/L, the concentration of NaCl being2.9mol/L,the initial volume of solution being25mL,the constant experiment temperature being90℃, the vibration frequency being160r/min, the vibration amplitude being20mm,0.5g ascorbic acid being added,andthe deposition time being60min,²¹⁰Bi and²¹⁰Po can spontaneously deposit onNi-foi（ldiameter=20mm，thickness=0.15mm）simultaneously and quantificationally.Lots of coexisting elements and nuclides do not produce interference to thespontaneous deposition for²¹⁰Bi and²¹⁰Po,and allow the spontaneous depositionprocess without spiking or any extra separation procedures from interferences.Theeffects of some short half-time natural radionuclides such as212Bi and218Po on testingwill decrease or exterminate while standing the foils for a certain length of timebefore measuring.The influences of various nuclide activity ratios on the measurement process areanalysed systematically and some appropriate correction formulas are given in orderto make accurate measurement results,and conditions to be met if these influencescan be neglected discretionally are discussed.In case of212Bi/²¹⁰Bi≤10,212Bi/²¹⁰Po≤10，and the foils have been put aside for10h before measuring, the disturbancedegree of212Bi to²¹⁰Bi and²¹⁰Po respectively lower than1.2%. In case of²¹⁰Bi/²¹⁰Po≤5, the intervals of time between measuring and depositing lower than30h,correction factor caused by²¹⁰Po growth and decay lower than1.0224. In case of²¹⁰Bi/²¹⁰Po≥0.2, correction factor caused by crosstalk that from²¹⁰Po to²¹⁰Bi lowerthan1.0276. In case of226Ra/²¹⁰Pb≤10, the intervals of time between the doublesamples deposition being15d, over-estimated²¹⁰Pb measuring result caused by226Ralower than0.74%.The method of double samples-twice spontaneous deposition used in theconjoint measurement techniques proposed in this paper will be helpful to avoidcontainer adsorption of²¹⁰Bi and²¹⁰Po，and eliminate any negative effects caused byoxygenization or hydrolysis products of ascorbic acid on spontaneous deposition ormeasurement which occurred in the method of single sample usually.After simultaneous counting the net gross α and β for two deposited foils,thatcomes from the double samples respectively,by means of the low background α/βcounter, a set of simultaneous equations are built up according to the Batamanformula and the net gross α&β counting rates, then specific activity of²¹⁰Pb,²¹⁰Bi,²¹⁰Po at sampling time can be calculated through solving these equations. Degree of precision of the measurement techniques is higher than5%,total spikerecovery rate reaches99.5%～100.5%.The limit of detection for²¹⁰Pb,²¹⁰Bi,²¹⁰Po of the proposed techniques is7.1,7.1and0.87Bq/kg respectively for Cu-foil spontaneous deposition method, and14.2,14.2and1.74Bq/kg respectively for Ni-foil spontaneous deposition method.The typicaloperation period should be shorter than2weeks.The two conjoint measurement techniques proposed in this paper have manycharacteristics of high testing precision, low detection limit, and fast and simple soucepreparation.The test programs are easy to learn, all reagents and test instruments usedin them are produced domestically (accomplish rapid conjoint measurement of²¹⁰Pb,²¹⁰Bi,²¹⁰Po only need one set of home-made low background α/β counter),operatingcosts are low. So they meet the China national situation and strength, and will be easyto popularize and apply.更多还原