Rocky Soil And Sediment Samples In ₂₁₀ Pb- ₂₁₀ Bi- ₂₁₀ Research And Application Po Joint Measurement Technology

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.