Triple-to-double Coincidence Ratio Research Articles

TDCRPy: A python package for TDCR measurements

The TDCR (Triple-to-Double Coincidence Ratio) measurement technique is a primary standardization method used by metrology laboratories to accurately determine the activity of radioactive solutions, particularly for radionuclides unsuitable for traditional coincidence counting methods, such as pure beta emitters. The TDCR method leverages a liquid scintillation counter equipped with three photomultiplier tubes (PMTs). This paper introduces TDCRPy, a novel Python package developed by the BIPM, designed to calculate detection efficiency of liquid scintillation counters using Monte Carlo simulations and decay data evaluations from the Decay Data Evaluation Project (DDEP). The software simulates particle interactions within the liquid scintillation counter, utilizing pre-calculated probability distributions for energy deposition. Comparisons with the PENNUC/NUR code and tests with measurement from the BIPM.RI(II)-K1.Co-60 key comparison demonstrate the potential of TDCRPy. This open-source package is distributed at https://pypi.org/project/TDCRPy and available for collaborative development on GitHub https://github.com/RomainCoulon/TDCRPy, where detailed user documentation can be found.

Activity standard and calibrations for 227Th with ingrowing progeny

Thorium-227 was separated from its progeny and standardized for activity by the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting. Confirmatory liquid scintillation-based measurements were made using efficiency tracing with 3H and live-timed anticoincidence counting (LTAC). The separation time and the efficiency of the separation were confirmed by gamma-ray spectrometry. Calibrations for reentrant pressurized ionization chambers, including commercial radionuclide calibrators, and a well-type NaI(Tl) detector are discussed.

Liquid scintillation efficiencies, gamma-ray emission intensities, and half-life for Gd-153

Gadolinium-153 was standardized for activity by live-timed anticoincidence counting and an ampoule was submitted to the international reference system (SIR). Absolute emission intensities for the main γ rays were determined with calibrated high-purity germanium (HPGe) and lithium-drifted silicon (Si(Li)) detectors. A revised decay scheme is indicated, with no probability of direct electron capture to the 153Eu ground state. Triple-to-double coincidence ratio (TDCR) efficiency curves indicate that the revised decay scheme is consistent with experiment. Half-life measurements agree with a previous NIST determination and show no sensitivity to chemical environment.

Primary standardization and half-life determination of [formula omitted]Ac at NRC

A solution of 225Ac was standardized by NRC using the triple-to-double coincidence ratio (TDCR) method. The counting efficiencies were calculated assuming a counting efficiency of 100% for alpha decays and those calculated using the MICELLE2 Monte Carlo code for beta decays and was approximately 500% for the NRC TDCR system. The relative uncertainty for the activity concentration was determined to be 0.25%. This agreed with measurements performed using gamma spectroscopy and a predicted calibration factor for the Vinten 671 ionization chamber as calculated using an EGSnrc model, implementing radioactive decay. Finally, the half-life of 225Ac was determined from long-term measurements using ionization chambers and liquid scintillation counting. The NRC measured half-life for 225Ac was found to be 9.914(4) days and is consistent within an expanded uncertainty coverage of k = 2 with the most recent (Kossert et al., 2020; Pommé et al., 2012) measurements of this decay parameter.

Activity standardisation of 32Si at IRA-METAS

This work explores the primary activity standardisation of 32Si as part of the SINCHRON project that aims at filling the geochronological dating gap by making a new precise measurement of the half-life of this nuclide. The stability of some of the radioactive test solutions, providing 32Si as hexafluorosilicic acid (H232SiF6), was monitored over long periods, pointing to the adequate sample composition and vial type to ensure stability. These solutions were standardised using liquid scintillation counting with the triple to double coincidence ratio (TDCR) technique and the CIEMAT-NIST efficiency tracing (CNET) method. Complementary backup measurements, using 4πβ-γ coincidence counting with 60Co as a tracer, were performed with both liquid and plastic scintillation for beta detection. While 60Co coincidence tracing with a liquid scintillator predicted activities in agreement with the TDCR and CNET determinations, using plastic scintillation turned out to be unfeasible as the addition of lanthanum nitrate and ammonia to fix the silicon during the drying process generated large crystals that compromised the linearity of the efficiency function.

Activity standardization of 60Co and 106Ru/106Rh by means of the TDCR method and the importance of the beta spectrum

Atomic and nuclear data represent an important input for the accuracy of primary activity measurements based on liquid scintillation. In particular, the reliability of β-spectrum computation has been investigated for several years through experimental and theoretical studies providing solid evidence for the need to consider the atomic effects. In the present study, the activity standardization of two β-emitting radionuclides (60Co, 106Ru/106Rh) was carried out by means of the 4πβ−γ coincidence and Triple-to-Double Coincidence Ratio (TDCR) methods. The comparison between the activity concentrations given by both primary techniques presents new evidence that a better agreement is obtained when the exchange and screening effects are included in the β-spectra implemented in the model of light emission for TDCR measurements. A new development of a stochastic model based on Geant4 simulations for TDCR calculations is also presented.

Measurement of the activity and determination of the half-life of 225Ac at POLATOM

A method for absolute measurements of the 225Ac activity in equilibrium with its progeny was developed. Measurements were performed using the triple-to-double coincidence ratio (TDCR) method in two different TDCR counters. The activity concentration of an 225Ac solution was determined and the solution was sent to the SIR system for a comparison. The half-life of 225Ac was determined by one of the TDCR counters and found to be 9.9150(63) days.

A bilateral comparison between LNHB and PTB to determine the activity concentration of the same 125I solution

A bilateral comparison to determine the activity concentration of the same 125I solution was organized. As electron-capture radionuclide with a rather high atomic number, 125I must be regarded as difficult to measure. The situation is partly exacerbated by the fact that some established standardization methods, like photon-photon coincidence counting, can no longer be applied due to the unavailability of appropriate equipment and expertise.One aim of this work is to compare modern liquid scintillation counting methods for the standardization of 125I. Both participating metrology institutes have used their custom-built triple-to-double-coincidence ratio (TDCR) counters and the determined activity concentrations are in excellent agreement even though the ways to analyze the data and to compute counting efficiencies were widely independent. The results also agree with the outcome of 4π-γ counting that was carried out at LNHB.In both laboratories, the measurements were complemented by measurements with several secondary standardization methods which even allow to establish a link to the CCRI(II)–K2.I-125(2) comparison started in 2004. A good agreement between the TDCR results and the key comparison reference value of the 2004/2005 comparison was obtained.

Development of FPGA-based standalone, portable TDCR system

A standalone, lightweight, portable, FPGA-based triple to double coincidence ratio (TDCR) system is developed. The optical chamber of the system is fabricated in a dual, coaxial cylindrical geometry, with the inner cylinder made up of Teflon and the outer one of aluminium. Three square PMTs, each having an active cathode area of 2.3 cm × 2.3 cm, are housed in the optical chamber. The variation in detection efficiency to identify the optimum kB (ionization quenching parameter) value is achieved by changing the vial position vertically with respect to the centre line of the PMTs. The coincidence analyzer implemented in a field programmable gate array (FPGA) transfers the pulse counts and associated parameters in real time to a Raspberry Pi single board computer (SBC). The TDCR algorithm to compute the efficiency is implemented in the SBC. In addition, the SBC is interfaced with a local 7” touchscreen to provide an intuitive graphical user interface (GUI) for operating the standalone instrument. The system performance is validated with 3H and 14C radionuclide standards.

An FPGA-based automated approach for identification and setting of the single electron response threshold voltage in portable TDCR systems

The threshold voltage setting of the pulse counting discriminator corresponding to each of the three photomultiplier tubes (PMTs) is crucial in a Triple to Double Coincidence Ratio (TDCR) system for accurate measurement of the activity of a radionuclide. The discriminator threshold voltage of each PMT signal processing channel is required to be set before the single electron response peak and after the thermal noise to allow the detection of a single photoelectron from the photocathode of the PMT. The portable TDCR systems, when subject to different field environments for accurate in-situ activity measurements, may need the re-setting of the discriminator threshold of the PMT channels. However, such miniaturized systems have minimal access to the circuit components for the sake of compactness. Therefore, an automatic solution to obviate the need for access to the circuit components (test connectors/test points) and the measuring instruments in the field is preferred. A Field Programmable Gate Array (FPGA) based automated methodology for identifying and digitally controlling the discriminator threshold voltage in standalone, portable TDCR systems is discussed.

Test of a digitizer to process the pulse signal from the 3 photomultiplier tubes of a TDCR liquid scintillation counter

The BIPM is developing a new service for international key comparisons in radionuclide metrology. The system, called ESIR, is based on a liquid scintillation counter using the Triple-to-Double Coincidence Ratio (TDCR) technique. The aim is to produce an international reference that can be reproduced over several decades of time in order to compare the calibration capabilities of National Metrology Institutes (NMIs). The maintainability of the electronics performing the signal processing is a challenge. To ensure the long-term sustainability of the electronics, the strategy is to set up redundant systems including at least one digital electronics module. The analogue modules developed in the 1990s and 2000s are less and less maintained and digital electronics are increasingly available on the market. In this context, a digitizer was tested and its suitability for the TDCR measurements compared to the currently used module based on an analogue front-end. This first implementation directly linking the photomultiplier anode to the CAEN digitizer without any analogue preconditioning shows a significant loss of detection efficiency and a lower signal to noise ratio observed on distributions of single photoelectrons. Although the TDCR method can correct for these efficiency losses, the loss of symmetry between the channels is too great to provide a sufficiently robust measurement. The use of low-pass filters upstream of the ADC will be considered to make this digital measurement system more reliable.

Primary standardization of 212Pb activity by liquid scintillation counting

An activity standard for 212Pb in equilibrium with its progeny was realized, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. A Monte Carlo-based approach to estimating uncertainties due to nuclear decay data (branching ratios, beta endpoint energies, γ-ray energies, and conversion coefficients for 212Pb and 208Tl) led to combined standard uncertainties ≤ 0.20 %. Confirmatory primary measurements were made by LS efficiency tracing with tritium and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting. The standard is discussed in relation to current approaches to 212Pb activity calibration. In particular, potential biases encountered when using inappropriate radionuclide calibrator settings are discussed.

Development of 4πβ(LS)-γ digital coincidence counting system at NIM

A new 4πβ(LS)-γ digital coincidence counting (DCC) system has been developed at NIM. The system equipped with a triple-to-double coincidence ratio (TDCR) counter in the β-channel and a NaI(Tl) scintillation detector in the γ-channel. A dedicated DCC software was designed for off-line implementation of 4πβ(LS)-γ coincidence counting method. The software consists of three modules: software-based circuits module, dead-time and resolving-time correction module and efficiency extrapolation module, respectively. The performance of the newly developed 4πβ(LS)-γ DCC system was demonstrated by a comparison measurement of Co-60 solution with the conventional 4πβ(PC)-γ DCC system.

Development of FPGA-based coincidence module for TDCR counting system

A new coincidence module for the Triple-to-Double Coincidence Ratio (TDCR) counting system has been developed at KRISS. The module is developed based on the Field-Programmable Gate Array (FPGA) to replace the MAC3, a well-known coincidence module developed by the LNHB for a TDCR system. A cRIO controller equipped with a Zynq-7020 FPGA from the National Instrument is used to develop the FPGA code that emulates the functionality of the MAC3. The performance of the new module was tested by comparing the output count rates of the new module with the output from the MAC3 module. A comparison in activity measurement of 3H and 14C was also performed between the two modules. A good agreement was observed with a difference of less than 1.0% between the new module and the MAC3 module, confirming the ability of the new module to replace the MAC3.

Performance of portable TDCR systems developed at LNE-LNHB

The triple to double coincidence ratio (TDCR) liquid scintillation measurement technique is commonly used in national metrology institutes (NMIs) to perform standardization of pure beta emitters. The LNE-LNHB historical device, RCTD1, is a quite large device, which has been developed and commonly used over the past 30 years with its associated electronics for measurements of various radionuclides. During the last 4 years LNE-LNHB has developed two new portable TDCR devices. Such portable instrumentation gives end-users access to a reference measurement method that can be used for a large number of radionuclides. It addresses a wide range of industrial and medical applications for radionuclide metrology, including calibrations of solutions containing short-lived radionuclides, avoidance of radioactive source transportation, and performing on-site comparison to promote radionuclide metrology harmonization. In this paper, we will present the newly developed portable TDCR liquid scintillation measurement systems. Two kinds of devices have been developed and designed at LNE-LNHB and built using fused deposition modelling (FDM) 3D printing: a mini-TDCR (25 cm diameter, 10 cm height) and a micro-TDCR (16 cm diameter, 10 cm height). After a detailed discussion of the design and the possibilities offered by 3D printing for their conception, this paper will present the performance of the devices obtained for several radionuclides. The results will be compared with the RCTD1 in order to validate the performance of the new devices. They exhibit improved performance, such as higher detection efficiency, and include various useful tools for proper on-site metrology. The first tests, which were performed in Orsay Hospital (CEA/SHFJ) and in another laboratory (IRSN), allowed us to show the very good overall performance of the systems including their outstanding linearity, which was tested in the range from 430 000 s−1 down to 160 s−1 in the double coincidences channel. Applications of the developed systems for high and low activity measurements are also discussed. Finally, the portable device has been used for half-life measurements in order to check for impurities in a radio-pharmaceutical solution.

Simultaneous determination of actinides and 90Sr in large-size soil and sediment samples

A simultaneous analytical method for sequential separation and determination of actinides and 90Sr in large-size environmental samples has been developed. In this method, successive co-precipitation steps were firstly conducted to remove matrix elements, then sequential column separation method was applied for simultaneous separation and purification of actinides and 90Sr/90Y. By using vacuum box technology, the total analytical time was minimized and batch processing allowed analyzing 12 samples in four days. The activity of 90Sr was obtained immediately by measuring its daughter radionuclide (90Y) with triple-to-double coincidence ratio (TDCR) Cherenkov counting, while the concentrations of Pu isotopes and 241Am could be measured by alpha spectrometry and mass spectrometric techniques. The overall recoveries of Pu, Am, Sr and Y were higher than 70% for the entire procedure, while the recovery ratios of Sr/Y were between 0.95 and 1.04 before chromatographic separation. The developed method was verified using 20 g and 50 g of environmental soil samples spiked with certified reference materials IAEA-384 or IAEA-385 and standard solution of 90Sr/90Y, and good agreement between the expected values and measured results has been achieved.

Standardization of 129I using the movable 4πβ(LS)-X(NaI(Tl)) system

The 129I standardization, using the movable 4πβ(LS)−X(NaI(Tl)) coincidence system, was performed for two 129I radioactive sources – one was dissolved in 0.1M NaOH solution and the other in 0.1M HNO3 solution. The system incorporates three movable PM tubes for a β–counter placed on a plane and a X-ray detector that can be moved up to the bottom of the vial.The β-efficiency depending on the amount of radioactive solution was investigated with 14 liquid scintillation samples prepared by gravimetrically dispensing 4.4–145 mg of 129I radioactive solution. The β-efficiencies above 90% were observed at less than 56 mg, but it was at most 70% at 145 mg. This occurred regardless of the activity of the sample or the type of chemical solution used to dissolve 129I source. The activity concentration of each 129I source was determined by efficiency-extrapolation method for samples with an activity range of 0.28–4.5 kBq. The β-efficiency points were derived over 10 intervals by moving 3-PM tubes in fine steps of about 1 mm from the sample. The highest value for β-efficiency was 95%. The combined uncertainty were 0.25% and 0.26%, respectively. The stated precision obtained using the system is better than that previously reported in the literature obtained by the triple to double coincidence ratio (TDCR) or the CIEMAT/NIST efficiency tracing method.

Development of multi-systems for measurement of radionuclide absolute activity

The development of a multi-systems triple-to-double coincidence ratio (TDCR) and coincidence 4pb-g methods, based on liquid scintillation to radionuclide standardization is presented in this work. The adjustments of multi-systems were made using standards of 3H and 14C and 60Co. The initial stage was performing measurements of pure beta-emitters 3H, 63Ni, and 90Sr90Y standard solutions by TDCR. The results were consistent within the standard uncertainty. Measurements will be performed with a beta-gamma 60Co in a comparison to the SIR / BIPM to assess the multi-system's performance.

A New DCC Software for 4πβ(LS) – γ Coincidence Counting

Coincidence counting (CC) is a widely applied method for radionuclide activity measurement. The 4πβ( LS) -γ coincidence counting is a type of CC that is applied to determine the activity of radionuclides that undergo β-γ decay. A liquid scintillation (LS) counter has the advantages of no self-absorption and simple sample preparation. Hence, this study focuses on the 4πβ( LS) -γ method to measure the activity of LS sources with a standard triple-to-double coincidence ratio (TDCR) system for LS measurements in the β channel and a NaI(Tl) scintillation detector in the γ channel. In this study, high-accuracy digital coincidence counting (DCC) software was developed to determine the activity of radionuclides using this 4πβ( LS) -γ coincidence counting method. The software is characterized by the application of the living time method during true event discrimination and the TDCR technology to estimate the effect of system noise and after-pulses in the β channel. The developed software was validated by comparing the results obtained using the software with standardized <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co activity measurement at the National Institute of Metrology (NIM) applying previously validated methods. The results showed that the activity measured by the developed DCC software had a tolerable error. It has good potential activity measurement, and it is expected to be applied to calibrate radionuclides with more complex decay diagrams in the future.

Activity standardisation of 223Ra

We report here on the primary activity standardisation of a223Ra dichloride solution in equilibrium with its decay daughters. Both the triple-to-double-coincidence-ratio (TDCR) method with an in-house TDCR detector and the CIEMAT-NIST efficiency tracing (CNET) technique with a commercial counter were used. The liquid scintillation efficiencies for both methods are about 6 while the activities they predict with about 0.4% relative standard uncertainty agree within 0.15%. For backup, the solution was also standardised with 4πγ NaI(Tl) integral counting with a well-type NaI(Tl) detector, and efficiencies computed by Monte Carlo simulations using the GEANT code. This simple technique, unused previously for this nuclide, yielded an activity concentration compatible with, but 1% lower than, the one determined by liquid scintillation counting.