^(222)Rn calibration procedure for water analyses by liquid scintillation counting

Purpose Among the several methods to measure ^(222)Rn in water,the liquid scintillation counting(LSC)technique is one of the most sensitive and widely used when analysing non-saline waters by liquid extraction,providing excellent accuracy,precision and low-level detection limits.When using the liquid scintillation counter Tri-Carb 3170 TR/SL(Perkin-Elmer)it is not possible to make an automatic determination of the alpha/beta discrimination parameter,being necessary to evaluate the pulse decay discriminator(PDD)value manually to the ^(222)Rn determination.In this work,we describe the steps to perform the calibration of that type of equipment.Methods The method consists in the preparation of standard samples from a ^(226)Ra certified standard solution and the adjustment of the PDD value by hand until the percentage of alpha events reaches a plateau of a near-constant fraction of total events.The process consists in taking several measures between PDD 80 and 200 with 15 min counting time each.Within the plateau,the alpha/beta ratio was used to determine the plateau final range as well as the optimum PDD value.After that,the calibration standards and blanks were measured and the region of interest(ROI)was established by finding the maximum value for the figure of merit(FOM)in the upper and lower limits.Results The optimal PDD value of 148 was established by the alpha/beta ratio,and after that,it was possible to measure ^(226)Ra standards to perform the calibration.An efficiency of(9.758±0.035)×1^(0-1) was obtained.In routine measurements,a detection limit of about 0.50 Bq L^(-1) is achieved for a 120 min counting time.To evaluate the uncertainty budget,the uncertainties of the net count rate,the efficiency,the sample amount and the decay correction factor were considered.Conclusions A method was developed for the calibration of LSC Tri-Carb 3170 TR/SL with the optimization of the PDD using a ^(226)Ra standard solution.The acquisition to obtain the plot of the variation of the events fraction in each window(alpha and beta)in function of PDD allowed to evaluate a plateau where the fraction of events was at a minimum.Afterwards,it was possible to measure the set of ^(226)Ra standards after the equilibrium with ^(222)Rn and determine the efficiency for ^(222)Rn with a detection limit of about 0.50 Bq L^(-1) in routine analyses.

Standardization of tritiated water by the CIEMAT/NIST and TDCR methods

The activity of tritiated water has been standardized by two liquid scintillation counting methods:The CIEMAT/NIST method with the54Mn-standard efficiency tracing and the triple-to-double coincidence ratio(TDCR)method.The samples were prepared with Ultima Gold TM AB liquid scintillation cocktail in low-potassium glass vials.In the application of the CIEMAT/NIST method,the computer program EMILIA was used to calculate the efficiency of3H and54Mn according to the KL1L2L3M atomic rearrangement model.And the detection efficiency of the TDCR counter was calculated using TDCR07 code,which makes it possible to allow for the potential asymmetry between the three photomultiplier tubes.The influence of stopping power and k B factor is discussed in the paper.When a power approach is adopted for the stopping power for electrons below 1ke V and k B is chosen to be 0.0075 cm/Me V,the relative deviation will be only 0.3%between the two methods.

Uncertainty evaluation for determination of ^(14)C in urine samples by wet oxidation method

Objective:To figure out the source of uncertainty in the determination of ^(14)C activity concentration in urine samples,and to establish a complete expression of analysis results,in order to improve the accuracy of ^(14)C monitoring method.Methods:Four urine samples of normal people were collected,and wet oxidation method was used in the pretreatment of the samples,then the activity concentration of ^(14)C was determined by liquid scintillation counting(LSC).After the mathematical model was established,the uncertainty components were determined,the standard uncertainty was combined,and the extended uncertainty was calculated.Results:The relative uncertainty of 4 samples was 22.5%,17.0%,17.3%and 18.2%.The activity concentration of urine was(0.32±0.14),(0.60±0.20),(0.86±0.30)and(0.74±0.27)Bq/L,respectively.In the relative uncertainty of 22.5%,17.7%was from sample counting,13.6%from detection efficiency,2.1%from recovery rate,0.58%from sample volume,and 0.01%from sample weight.Conclusions:The main factors affecting the uncertainty include the error or deviation of sample counting,detection efficiency and recovery rate.The error of volume and weight also contributes to the measurement uncertainty.