

ARTICLE 

Year : 2011  Volume
: 34
 Issue : 3  Page : 190192 


Analysis of triplelabeled samples by multivariate liquid scintillation counting
PJ Reddy, S.P.D. Bhade, D.A.R. Babu, DN Sharma
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India
Date of Web Publication  27Sep2012 
Correspondence Address: P J Reddy Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra India
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/09720464.101717
The radioassay of samples containing three pure beta emitters having various activity ratios has been performed by using the most probable value theory applied to liquid scintillation detection. The principle of the technique is based on experimentally generating simultaneous equations more than the radionuclides to be analyzed. This technique requires a liquid scintillation counter and sets of quenched radionuclide standards. The present technique has been applied successfully to the case of ^{3} H ^{35} S ^{36} Cl in composite mixtures. Keywords: CIEMAT/NIST, composite mixture, liquid scintillation counting, most probable value theory, transformed spectral index of external standard
How to cite this article: Reddy P J, Bhade S, Babu D, Sharma D N. Analysis of triplelabeled samples by multivariate liquid scintillation counting. Radiat Prot Environ 2011;34:1902 
How to cite this URL: Reddy P J, Bhade S, Babu D, Sharma D N. Analysis of triplelabeled samples by multivariate liquid scintillation counting. Radiat Prot Environ [serial online] 2011 [cited 2019 Sep 21];34:1902. Available from: http://www.rpe.org.in/text.asp?2011/34/3/190/101717 
1. Introduction   
Conventionally, liquid scintillation counting (LSC) is used for the activity estimation of single and dual radionuclides. However, in present LSC systems, it is possible to analyze multilabeled radionuclides. Several methods are available for the radioassay of multilabeled nuclides, ^{[1]} in the sample using LSC. However, in the present study, the most probable value theory was applied for activity estimation in a sample containing triplelabeled betaemitting radionuclides. The fundamental principle of this technique is based on the construction of a number of simultaneous equations that exceeds the number of radionuclides. This technique can also be applied for more than three combinations of radionuclides. This technique eliminates the timeconsuming chemical separation and needs only a set of quench standards for each radionuclide. Composite samples containing ^{3} H (E _{max.} 18.6keV), ^{35} S (E _{max.} 167keV), and ^{36} Cl (E _{max.} 714keV) were successfully analyzed using this method.
2. Materials and Methods   
Aqueous standard solutions of ^{3} H from Packard (primary standard) and ^{35} S and ^{36} Cl from the Board of Radiation Isotopes and Technology (BRIT) were used. Using nitromethane as a chemical quencher, quench standards of ^{3} H, ^{35} S, and ^{36} Cl were prepared gravimetrically by adding the required amount into polyethylene vials containing 10 mL of Optiphase HiSafe III scintillator. Measurements were carried out using the Packard TriCarb Model 2900TR Liquid Scintillation Counter. The quenchindicating parameter tSIE (transformed spectral index of external standard) was obtained from ^{133} Ba inbuilt gamma source. The composite samples ( ^{3} H, ^{35} S, and ^{36} Cl) were counted in three counting regions, namely, 02 keV, 24 keV, 46 keV, 68keV, 820 keV, 20100 keV, 100200 keV, and 200400 keV. The counting times were decided to get a total of 10,000 counts in each of the abovementioned regions for each quenched standard to keep the error minimum.
2.1 Standardization of ^{35} S and ^{36} Cl by CIEMAT/NIST method
^{35} S and ^{36} Cl standards were prepared by adding the solutions into 20 mL polyethylene vials gravimetrically, each containing 10 mL Optiphase HiSafe III scintillator. The CIEMAT/NIST method developed by Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (CIEMAT) and the National Institute of Standards and Technology (NIST) was used for the standardization of radionuclides with liquid scintillation analyzer. Visual Basic CN2004 program ^{[2]} was used to determine algorithmically the counting efficiency of the radionuclide to be assayed using tritium as a tracer. In this method, the quenchindicating parameter, tSIE and figure of merit (FOM) were used to construct the universal curve [Figure 1]a which is basically independent of the radionuclide. [Figure 1]b depict the relationship between FOM and the theoretical efficiency for ^{35} S and ^{36} Cl, respectively. The counting efficiencies for ^{35} S and ^{36} Cl using the universal curve and the relationship between FOM and theoretical efficiency were 91 and 99.4% for tSIE values 460.18 and 531.63, respectively. These were used to determine the absolute disintegration rates of ^{35} S and ^{36} Cl individually. The method has been described in detail in the earlier studies. ^{[3],[4],[5]}  Figure 1: (a) Universal curve of FOM Vs tSIE using 3H standard using CIEMAT/NIST standardization technique (b) FOM Vs theoretical efficiencies for ^{35}S and ^{36}Cl
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2.2 Experimental procedure for the most probable value theory
To resolve ^{3} H (E _{max} =18.6keV), ^{35} S (E _{max} =167keV), and ^{36} Cl (E _{max} =714keV) activities in a composite mixture, three counting regions 02 keV, 24 keV, 46 keV, 68 keV, 820 keV, 20100 keV, 100200 keV, and 200400 keV were selected. These counting regions were selected on the basis of a higher efficiency of each radionuclide in the mentioned regions as well as with maximum contribution of lowest energy radionuclide ( ^{3} H) in the maximum counting regions.
Tritium standards were prepared by adding 0.01mL of ^{3} H into polyethylene vials containing 10 mL of Optiphase HiSafe III scintillator gravimetrically. In the same way, ^{36} Cl standards of 0.01 mL were prepared by dispensing the same volume of scintillator. In all cases, adequate amounts of nitro methane (0.010.05mL) were added to obtain increasing quench.
All the quench standards were counted in the counting regions as defined earlier. Quenchcorrection curves were prepared in these regions to obtain the efficiencies corresponding to the tSIE value [Figure 2]a c. Composite samples with varying activity ratios 1/1/1/ to 1/1/10 were prepared to evaluate the performance of the multivariate technique. The count rate of composite samples in the above three counting regions are defined by the following normal equations:  Figure 2: (a) Calibration curves fro H3 in different counting regions (b) Calibration curves fro S35 in different counting regions (c) Calibration curves fro Cl36 in different counting regions
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Where N _{1,} N _{2,} N _{3} are the count rates of a sample in respective counting regions, A,B,C are the activities of ^{3} H, ^{35} S, and ^{36} Cl, respectively and a _{1,} a2 , a _{3} are respective efficiencies in the counting regions. From the series of above equations and following the derivations as given by Matsui and Takiue, ^{[6]} the activities of ^{3} H, ^{35} S, and ^{36} Cl were obtained. The individual activities thus obtained were then compared with the absolute activities obtained by the CIEMAT/NIST standardization method [Table 1].  Table 1: Activity obtained for ^{3}H, ^{35}S, and ^{36}Cl from multivariate method and the percentage deviations as compared to the CIEMAT/NIST standardization technique
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3. Results   
The activities of triplelabeled radionuclides in a mixture for various activity ratios 1/1/1 to 10/1/1, 1/10/1, and 1/1/10 clearly indicate that the measured values are in good agreement with the percentage deviation within ±9.3% compared with the activity obtained by the CIEMAT/NIST standardization method which is acceptable in all radiationprotection measurements.
4. Conclusion   
Simultaneous determination of activities using LSC in multilabeled samples provides easy sample preparation as compared to the timeconsuming conventional chemical separation method. The approach used in this present study can also be used for more than three combinations of radionuclides.
References   
1.  Noor A, Zakir M, Rasyid B, Maming, L'Annunziata MF. 1996. Cerenkov and Liquid Scintillation Analysis of the Triple Label ^{86} Rb ^{35} S and ^{33} P. Appl Radiat Isot 1996;47:65968. 
2.  Günther E. What can we expect from the CIEMAT/NIST method? Appl Radiat Isot 2002;56:35760. 
3.  Kulkarni DB, Reddy PJ, Bhade SPD, Narayan KK, Narayanan A, Krishnamachari G, et al. 2006. Comparision of efficiency tracing and zero detection threshold techniques with CIEMAT/NIST standardization method under different quench conditions with Liquid Scintillation Spectrometer. Current Science,90;837. 
4.  Malonda AG, GarciaTorano. Evaluation of counting efficiency in liquid scintillation counting of pure beta ray emitters. Appl Radiat Isot 1982;33:24953E. 
5.  Reddy PJ, Kulkarni DB, Bhade SPD, Narayan KK, Narayanan A, Krishnamachari G, et al. Activity determination of Beta emitting Radionuclides by different methods using Liquid Scintillation Spectrometry. Nucl Radiochem Symp 2005;6812. 
6.  Matsui, Takiue M. Liquid Scintillation Radioassay of Multilabeled Betaemitters. Int J Radiat Isot 1991;42:8415. 
[Figure 1], [Figure 2]
[Table 1]
