General data analysis code for TDCR liquid scintillation counting

A non-radionuclide-specific computer code to analyze data, calculate detection efficiency and activity in a TDCR system is presented. The program was developed prioritizing flexibility in measuring conditions, parameters and calculation models. It is also intended to be well structured in order to easily replace subroutines which could eventually be improved by the user. It is written in standard FORTRAN language but a graphical interface is also available. Several tests were performed to check the ability of the code to deal with different decay schemes such as H-3, C-14, Fe-55, Mn-54 and Co-60.     

The Compton source efficiency tracing method in liquid scintillation counting: A new standardization method using a TDCR counter with a Compton spectrometer

We describe a new standardization method in liquid scintillation counting based on the use of a temporary virtual tracer source created inside the scintillator by Compton interaction. The Compton tracer source is measured by the triple coincidence liquid scintillation counter after selection of the Compton events by a gamma-ray detector. The paper describes the principle of the method, the experimental setup and presents the results obtained by this method for the standardization of a ³H solution. These results are compared with those obtained using the classical triple to double coincidence ratio method. Possible application of this new method for international comparisons is addressed.     

Standardization of Tc-99 by three liquid scintillation counting methods

The NMISA participated in the international key comparison of the pure beta-emitter Technetium-99, CCRI(II)-K2.Tc-99. The comparison solution was standardized using three methods, namely the TDCR efficiency calculation method, the CIEMAT/NIST efficiency tracing method and the 4π(LS)β–γ coincidence tracing method with Co-60 as tracer. Excellent agreement between results obtained with the three methods confirmed the applicability of the beta spectral shape given by the latest (2011) DDEP evaluation of Tc-99 decay data, rather than the earlier (2004) evaluation.     

A full digital approach to the TDCR method

Current state of the art solutions based on the Triple to Double Coincidence Ratio method are generally large size, heavy-weight and not transportable systems. This is due, on one side, to large detectors and scintillation chambers and, on the other, to bulky analog electronics for data acquisition. CAEN developed a new, full digital approach to TDCR technique based on a portable, stand-alone, high-speed multichannel digitizer, on-board Digital Pulse Processing and dedicated DAQ software that emulates the well-known MAC3 analog board.     

Half-life measurements of Rb by liquid scintillation counting

The specific activity of natural ⁸⁷Rb was measured by means of 4πβ liquid scintillation counting in a two-photomultiplier-tube spectrometer. ³H-efficiency tracing was used together with the CIEMAT/NIST method to obtain the detection efficiency. For this purpose a new parameterization of the shape factor for the third forbidden non-unique β-transition was performed. The hygroscopic behaviour of the salts used for sample preparation was studied. The half-life of ⁸⁷Rb was found to be T_1/2=4.967(32)×10¹⁰ y.     

Standardization of a 32P solution containing pure-beta impurities using the TDCR method in liquid scintillation counting.

The liquid scintillation counting standardization of pure-beta solutions containing pure-beta emitter impurities is a difficult task because, unlike that which can be achieved by using gamma-ray spectrometry, the continuous characteristics of beta spectra and the poor intrinsic resolution of LSC spectrometers do not allow an easy identification and precise determination of the activity concentration of these impurities. This problem was recently encountered in the standardization of a 32P solution in the framework of an international comparison, where the activity contribution of the impurities was over 10% of the main nuclide activity at the reference date. This paper describes the method used to identify the impurities in this 32P solution and the calculation of the detection efficiencies using the triple to double coincidence ratio model. Details on the calculation of the uncertainties of each activity and the covariances between these activities are given.     

On the stochastic dependence between photomultipliers in the TDCR method

The TDCR method (Triple to Double Coincidence Ratio) is widely implemented in National Metrology Institutes for activity primary measurements based on liquid scintillation counting. The detection efficiency and thereby the activity are determined using a statistical and physical model. In this article, we propose to revisit the application of the classical TDCR model and its validity by introducing a prerequisite of stochastic independence between photomultiplier counting. In order to support the need for this condition, the demonstration is carried out by considering the simple case of a monoenergetic deposition in the scintillation cocktail. Simulations of triple and double coincidence counting are presented in order to point out the existence of stochastic dependence between photomultipliers that can be significant in the case of low-energy deposition in the scintillator. It is demonstrated that a problem of time dependence arises when the coincidence resolving time is shorter than the time distribution of scintillation photons; in addition, it is shown that this effect is at the origin of a bias in the detection efficiency calculation encountered for the standardization of ³H. This investigation is extended to the study of geometric dependence between photomultipliers related to the position of light emission inside the scintillation vial (the volume of the vial is not considered in the classical TDCR model). In that case, triple and double coincidences are calculated using a stochastic TDCR model based on the Monte-Carlo simulation code Geant4. This stochastic approach is also applied to the standardization of ⁵¹Cr by liquid scintillation; the difference observed in detection efficiencies calculated using the standard and stochastic models can be explained by such an effect of geometric dependence between photomultiplier channels.     

Some remarks on photons statistics in the LS-counter

The available experimental data relating to processes in the liquid scintillation (LS) detector that lead to fluorescence have been analysed and the evaluated number of photons created are given. The evaluated global distribution of photons emitted from the LS-vial in the case of low-energy emitters is presented. The global distribution of photons is well fitted by the Polya distribution.     

Absolute activity of (133)Ba by liquid scintillation coincidence counting using the 4pi(e,X)-gamma extrapolation technique.

The Technical Committee for Ionizing Radiation (TCRI) of the Asia Pacific Metrology Programme (APMP) recently organized a regional key comparison of activity measurements of the radionuclide ¹³³Ba. This paper reports on absolute measurements made at the National Metrology Institute of South Africa (NMISA) by the coincidence extrapolation technique, with liquid scintillation counting (LSC) comprising the 4π channel. A detection efficiency analysis was undertaken to predict the maximum efficiency likely to be achieved and to confirm that the method does indeed provide the source disintegration rate for ¹³³Ba. Various experimental and data analysis difficulties to be aware of are discussed in the paper.     

Liquid scintillation counting of polycarbonates: A sensitive technique for measurement of activity concentration of some radioactive noble gases

This work explores the application of the liquid scintillation counting of polycarbonates for measurement of the activity concentration of radioactive noble gases. Results from experimental studies of the method are presented. Potential applications in the monitoring of radioactive noble gases are discussed.     

A sub-boiling distillation method for the preparation of low carbon content water from urine samples for tritium measurement by liquid scintillation counting

A new preparation method was developed for obtaining low carbon content water from urine samples for the measurement of tritium by a liquid scintillation counter. The method uses a simple and convenient subboiling distillation bottle. Many urine samples have been purified by this method and the change of tritium level in a tritium-handling radiation-worker was observed.     

jStudy of a Monte Carlo rearrangement model for the activity determination of electron-capture nuclides by means of liquid scintillation counting

A new Monte Carlo approach for the computation of the electron spectra of electron-capture nuclides is applied to obtain efficiencies in liquid scintillation counting for CIEMAT/NIST applications. The new method is applied to the radionuclides ¹⁰⁹Cd and ¹²⁵I by using a stochastic atomic rearrangement model, taking into account rearrangement processes including L-, M-, and N-subshells. The counting efficiencies were computed with the new code MICELLE which also comprises an approach for calculating the counting efficiency of a radionuclide in a gel phase sample. The calculated counting efficiencies are compared with experimental results.     

Radioactivity determination of individual radionuclides in a mixture by liquid scintillation spectra deconvolution

A spectrum deconvolution method has been applied to logarithmic liquid scintillation spectra containing more than one radionuclide, to determine the activity of the individual components. The shape of the sample spectrum has been used for resolving the various components in the sample by fitting the reference spectrum of each component to the measured composite spectrum. The procedure has been applied to environmental samples containing ⁹⁰Sr, ⁹⁰Y and ⁸⁵Sr, added as a tracer for the chemical recovery determination. Comparisons are made with results obtained using a modified window-based method and results obtained by measuring the ⁸⁵Sr activity by gamma-ray spectrometry and subtracting its contribution to the LS count rate. It is demonstrated that this treatment of the beta-particle spectra represents a rapid and reliable method of determining these radionuclides in a mixture, even at low activity levels.     

Absolute activity of Ba by liquid scintillation coincidence counting using the 4π(e,X)-γ extrapolation technique

The Technical Committee for Ionizing Radiation (TCRI) of the Asia Pacific Metrology Programme (APMP) recently organized a regional key comparison of activity measurements of the radionuclide ¹³³Ba. This paper reports on absolute measurements made at the National Metrology Institute of South Africa (NMISA) by the coincidence extrapolation technique, with liquid scintillation counting (LSC) comprising the 4π channel. A detection efficiency analysis was undertaken to predict the maximum efficiency likely to be achieved and to confirm that the method does indeed provide the source disintegration rate for ¹³³Ba. Various experimental and data analysis difficulties to be aware of are discussed in the paper.     

Analysis of detection-efficiency variation techniques for the implementation of the TDCR method in liquid scintillation counting

Detection efficiency variation is often used in liquid scintillation counting in order to evaluate a parameter in the detection efficiency calculation model. The aim of this paper is to compare the effects of three different detection efficiency variation methods in the activity measurement of three pure-beta radionuclides: ³H, ⁶³Ni and ¹⁴C. Some general conclusions concerning the TDCR method are drawn.     

Determination of plutonium isotopes in bilberry using liquid scintillation spectrometry and alpha-particle spectrometry

This paper presents α-particle spectrometry and liquid scintillation spectrometry methods to determine plutonium isotopes in bilberry. The analytical procedure involves sample preparation steps for ashing, digestion of bilberry samples, radiochemical separation of plutonium radioisotopes and their measurement. The validity of the method was checked for coherence using the ζ test, z-test, relative bias and relative uncertainty outlier tests. The results indicated that the recommended procedures for both measurement systems could be successfully applied for the accurate determination of plutonium activities in bilberry samples.     

Standardization of a 89Sr solution from a BIPM intercomparison using a liquid scintillation method.

A procedure to standardize 89Sr (as strontium chloride) solutions, within the frame of a BIPM intercomparison, by the CIEMAT/NIST method was presented for Instagel Plus, HiSafe III and Ultima Gold liquid scintillation cocktails. The stability was studied for two types of samples: those obtained by direct addition of the 89Sr solution and those by the extra addition of 0.5 ml of HCl (0.1 mol l(-1)) to the cocktails. The results only showed good stability with the three scintillants used when additional HCl was added to the cocktails. The activities per unit mass determined for 89Sr were: 26.344 kBq g(-1) for Instagel Plus; 26.335 kBq g(-1) for HiSafe III; and 26.310 kBq g(-1) for Ultima Gold (at a reference time of 2000.10.01, 00 h UT) with a total uncertainty of 0.5% in each case (k = 1).     

Comparative study of different methods for the activity quantification of H and C radionuclides in dual labeled samples using liquid scintillation analyzer

Different methods such as full spectrum DPM (FSDPM), dual isotope estimation and inclusion methods were studied for the activity quantification of ³H and ¹⁴C in dual beta labeled samples using liquid scintillation analyzer. A standardized Packard tritiated water was used as tritium source and ¹⁴C activity was standardized by CIEMAT/NIST method and compared with the results obtained by the above three methods. Minimum detectable activity was 2100 dpm/l for ³H and 1200 dpm/l for ¹⁴C with a counting time of 300 min. The accuracy of the results obtained was found to be within ±10% for ³H: ¹⁴C activity ratios 1:1, 1:2, 2:1, 6:1, 9:1, 13:1 and 18:1.     

Geochronology of lake sediments using 210Pb with double energetic window method by LSC: An application to Lake Van

In this study the age and sediment accumulation rates of the lake sediment were calculated by using the ²¹⁰Pb concentrations through the sediment core. The specific activity of ²¹⁰Pb for each sediment section was determined by LSC with double energetic window method which relies on the direct determination of ²¹⁰Pb without waiting for the in growth of ²¹⁰Po from ²¹⁰Pb. For the successful determination of this radionuclide two counting windows were optimized to eliminate the overlapping of the beta spectra of ²¹⁰Pb and ²¹⁰Bi.