Liquid Scintillation Measurements Research Articles

Жидкосцинтилляционная спектрометрия. Современное состояние в России

An overview of the existing instrument fleet of liquid scintillation (LS) spectrometers of both foreign and Russian production is presented. A comparative analysis of their design features and characteristics was carried out. The current situation with spare parts of equipment and consumables for LC analysis was studied. A review of software for processing the results of liquid scintillation measurements was carried out. The areas of application and prospects of LC spectrometry are described.

Study on Measurement Method of β Radioactivity in Environmental Water by Liquid Scintillation Spectrometers

Compared with other methods for measuring radioactivity in water, liquid scintillation measurement has the outstanding advantages of fast sample pretreatment, simple measurement method and high detection efficiency. Based on liquid scintillation spectrometer (SIM-MAX LSA3000B), 14C and 90Sr-90Y are selected as typical nuclides to study the change of TDCR quenching correction curve under different activity concentrations, and the basic method for measuring radioactive water samples with different activity concentrations is proposed, which is applied to the measurement of lake water, mountain spring water, tap water, mineral water and rainwater. The measurement results show that the total time of this method is less than 60 minutes, and the measurement error is less than 20%, which is obviously superior to the existing water sample radioactivity measurement method under nuclear emergency conditions.

Validation of carbonization as a part of benzene synthesis for radiocarbon measurement

Carbonization, i.e., turning organic sample to carbon, was validated for the benzene synthesis for the radiocarbon liquid scintillation measurement. Tests of sample preparation by combustion, carbonization followed by combustion and carbonization followed by a direct reaction with lithium were performed. Wood and charcoal samples were good for carbonization followed by direct reaction with lithium, while collagen obtained from bones had to be combusted. Direct reaction of carbonized sample with lithium required three times less amount of lithium than the combusted sample.

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.

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.

Evaluation of the accidental coincidence counting rates in TDCR counting

This paper presents analytical and experimental methods to evaluate the accidental coincidence counting rates in a Triple-to-Double Coincidence Ratio (TDCR) Liquid Scintillation (LS) measurement. The experimental method we propose is based on the analysis of the distribution of the time delays between the first detected events in each photomultiplier tube. The underlying assumption is that events separated by several microseconds in time are not correlated, thus the accidental coincidence counting rates could be determined from the time interval distribution of uncorrelated events. The analytical evaluation of the accidental coincidence counting rates is based on the conditional probabilities for the occurrence of uncorrelated events within the same coincidence resolving time. The analytical and experimental evaluations of the rate of accidental coincidences give consistent results for TDCR measurements of 3H, 55Fe and 14C. The two methods were used to evaluate corrections for accidental coincidences for Monte Carlo (MC) generated list-mode files of 3H measurements with increasing activities. The counting rates, corrected for accidental coincidences using the analytical method, are within 0.29% of the MC reference up to 100 kBq and the corrected, using the experimental method, are within 0.21% up to 200 kBq.

Preliminary Investigation of Pretreatment Methods for Liquid Scintillation Measurements of Environmental Water Samples Using Ion Exchange Resins

Preliminary Investigation of Pretreatment Methods for Liquid Scintillation Measurements of Environmental Water Samples Using Ion Exchange Resins

Liquid xenon scintillation measurements and pulse shape discrimination in the LUX dark matter detector

Weakly Interacting Massive Particles (WIMPs) are a leading candidate for dark matter and are expected to produce nuclear recoil (NR) events within liquid xenon time-projection chambers. We present a measurement of the scintillation timing characteristics of liquid xenon in the LUX dark matter detector and develop a pulse shape discriminant to be used for particle identification. To accurately measure the timing characteristics, we develop a template-fitting method to reconstruct the detection times of photons. Analyzing calibration data collected during the 2013-16 LUX WIMP search, we provide a new measurement of the singlet-to-triplet scintillation ratio for electron recoils (ER) below 46~keV, and we make a first-ever measurement of the NR singlet-to-triplet ratio at recoil energies below 74~keV. We exploit the difference of the photon time spectra for NR and ER events by using a prompt fraction discrimination parameter, which is optimized using calibration data to have the least number of ER events that occur in a 50\% NR acceptance region. We then demonstrate how this discriminant can be used in conjunction with the charge-to-light discrimination to possibly improve the signal-to-noise ratio for nuclear recoils.

An investigation about natural radioactivity, hydrochemistry, and metal pollution in groundwater from Calabrian selected areas, southern Italy

The increasing interest in radioactivity has brought about the need for an assessment of human exposure to radiation. It is, therefore, necessary to examine naturally occurring radioactivity in the environment, especially its occurrence in groundwater. The aim of this work was then to study the levels and behavior of the most significant natural radionuclides, also in order to improve the knowledge of the hydrochemical processes involved in the selected groundwater systems. Natural radioactivity in fifteen Calabrian groundwaters for human use was investigated through high-resolution gamma spectrometry (with a negative-biased Ortec HPGe detector) and liquid scintillation measurements. Particular attention was given on those radionuclides (3H, 238U, 226Ra, and 228Ra), which contribute in a significant way to the overall effective dose received by members of the public due to the intake of drinking water originating from groundwater systems. The activity concentration of 238U varied from 1 to 51 mBq/L, as a result of the geology of the investigated area and of the oxidizing conditions that favored U dissolution. 226Ra presented a broad range of activity concentrations (0.011–0.14 mBq/L), lower than uranium ones because radium occurs in groundwater under reducing conditions. Some heavy metals (Cd, Pb, Be, Hg, Ag, As, Tl, Sb, Se, and Ni) were also investigated through ICP-MS measurements and compared with the limits set by the Italian Legislation. Metals are released into the environment by both natural and anthropogenic sources; they leach into underground waters, moving along water pathways and eventually depositing in the aquifer.

Determination of low-level tritium concentrations in surface water and precipitation in the Czech Republic

Past tests of nuclear weapons in the atmosphere, nuclear energy facilities and tritium of natural origin are main sources of tritium in the environment. Thanks to its presence in environment and its favourable properties, tritium is used as a radiotracer. Since stopping of atmospheric nuclear tests, tritium in precipitation has been decreasing towards natural levels below 1 Bq l−1 and precise analyses of low level tritium activities are necessary. This paper focuses on tritium development at sites not influenced by any technogenic release of tritium in Elbe River basin (Bohemia) in the Czech Republic using liquid scintillation measurement with electrolytic enrichment.

Liquid scintillation counters calibration stability over long timescales

Liquid scintillation spectrometry is widely used for the analysis of alpha and beta emitting radionuclides. Robust calibration of liquid scintillation (LS) spectrometers is fundamental to accurate LS measurement but at the same time is time consuming and costly, particularly if a wide range of radionuclides are analysed by the laboratory. The frequency of the calibration varies in different laboratories and is based on many practical and operational factors. This work summarizes the observations regarding variations in 1220 Quantulus spectrometers efficiency calibrations performed annually using various radionuclides: 3H 63Ni, 55Fe, 36Cl, 45Ca, 147Pm, 241Pu, 99Tc for a period of 9 years and discusses the implication to calibration frequency.

Activity determination of 60Co and the importance of its beta spectrum

The activity concentration of a 60Co solution was measured by means of two 4πβ-γ coincidence counting systems using a liquid scintillation counter and a proportional counter (PC) in the beta channel, respectively. Additional liquid scintillation measurements were carried out and CIEMAT/NIST efficiency tracing as well as the triple-to-double coincidence ratio (TDCR) methods were applied to analyse the data. The last two methods require computed beta spectra to determine the counting efficiencies.The results of both 4πβ-γ coincidence counting techniques are in very good agreement and yield a robust reference value. The initial activity concentration determined with liquid scintillation counting was found to be significantly lower than the results from 4πβ-γ coincidence counting. In addition, the results from TDCR and CIEMAT/NIST show some inconsistency.The discrepancies were resolved by applying new beta spectrum calculations for the dominant allowed beta transition of 60Co. The use of calculations which take screening effects as well as the atomic exchange effect into account leads to good agreement between all four methods; the combination of these techniques delivers an important validation of beta spectra.

Measurement of radon in air using a radon-218Po calibration curve determined by an absorptive non-volatile liquid scintillator

This work reports a novel method for determining 222Rn (radon) in air using a radon-218Po calibration curve constructed by an absorbable non-volatile liquid scintillator (NVLS). The ability of this method to detect low natural concentrations of radon was confirmed from linear extrapolation of the curve between 500 and 8000 Bq/m3. The calibration curve was created from data obtained from measurements performed in a radon calibration chamber at the National Institute of Radiological Science (NIRS) by using the least-squares method. The line had high precision and stability, and the required detection time was less than that of 214Po. An absorptive NVLS was used to collect radon and was found to be highly advantageous for α-spectrometry liquid scintillation measurements. Variations of the Ostwald coefficient due to changes in temperature and humidity, which affect radon absorption, were investigated and discussed.

Comparison of Tritiated-Water Standards by Liquid Scintillation for Calibration of a New Standard Reference Material

A new National Institute of Standards and Technology (NIST) tritiated-water ((3)H-labeled oxidane) standard was prepared and calibrated. It is the 17th in a series of linked standards since 1954 and will be disseminated as Standard Reference Material® SRM 4927G, having a massic activity of 544.2kBqg(-1), with an expanded (k=2) relative standard uncertainty of 0.96%, at a Reference Time of 1200 EST, 1 May 2015. The calibration is based on relative liquid scintillation (LS) measurements using quench-varied efficiency tracing with two previous 1999 issues, viz., SRM 4927F and 4926E. Measurement comparisons were also made with respect to a 1994 tritiated-water French national standard and to a tritiated-water solution measured by 19 laboratories as part of an international measurement comparison organized by the Bureau International des Poids et Mesures (BIPM) in 2009. Confirmatory measurements for the massic activity of both SRM 4927F and 4927G by a triple-to-double coincidence ratio (TDCR) technique were also made.

Comparison of tritiated-water standards by liquid scintillation for calibration of a new Standard Reference Material®

A new National Institute of Standards and Technology (NIST) tritiated-water (3H-labeled oxidane) standard was prepared and calibrated. It is the 17th in a series of linked standards since 1954 and will be disseminated as Standard Reference Material® SRM 4927G, having a massic activity of 544.2kBqg−1, with an expanded (k=2) relative standard uncertainty of 0.96%, at a Reference Time of 1200 EST, 1 May 2015. The calibration is based on relative liquid scintillation (LS) measurements using quench-varied efficiency tracing with two previous 1999 issues, viz., SRM 4927F and 4926E. Measurement comparisons were also made with respect to a 1994 tritiated-water French national standard and to a tritiated-water solution measured by 19 laboratories as part of an international measurement comparison organized by the Bureau International des Poids et Mesures (BIPM) in 2009. Confirmatory measurements for the massic activity of both SRM 4927F and 4927G by a triple-to-double coincidence ratio (TDCR) technique were also made.

Optimization of liquid scintillation measurements applied to smears and aqueous samples collected in industrial environments

Search for low-energy β contaminations in industrial environments requires using Liquid Scintillation Counting. This indirect measurement method supposes a fine control from sampling to measurement itself. Thus, in this paper, we focus on the definition of a measurement method, as generic as possible, for both smears and aqueous samples’ characterization. That includes choice of consumables, sampling methods, optimization of counting parameters and definition of energy windows, using the maximization of a Figure of Merit. Detection limits are then calculated considering these optimized parameters. For this purpose, we used PerkinElmer Tri-Carb counters. Nevertheless, except those relative to some parameters specific to PerkinElmer, most of the results presented here can be extended to other counters.

A new determination of the 209Po half-life

A substantial 25% error in the then-known and accepted (102 ± 5) year half-life of 209Po was reported on in 2007. This error was detected from decay data from two separate primary standardizations of a 209Po solution standard, which were performed approximately 12 years apart. Despite author claims that this observation was not a new half-life determination, it was nevertheless included in subsequent nuclear data evaluations and compilations to obtain a currently tabulated value of (115 ± 13) a, computed from the median and range of the two half-life reports. A third primary standardization on the identical 209Po solution has since been performed to derive a new half-life value of (125.2 ± 3.3) a. This half-life determination was obtained from 30 distinct data sets over a period of 20.7 years, encompassing over 700 liquid scintillation measurements with nearly 50 counting sources all prepared from the same solution, and as obtained over a very broad range of measurement conditions (composition of cocktails, characteristics of counters, time sequencing) during five periods in 1993, 1994, 2005, and 2013.

Direct measurement of tritium production rate in LiPb with removed parasitic activities: Preliminary experiments

Liquid scintillation (LS) technique applied to direct measurement of tritium activity produced in LiPb eutectic in Frascati HCLL TBM mock-up neutronic experiment has been tested so far in the case of LS measurement after long period since irradiation. LiPb samples irradiated in neutron filed show, except of tritium, meaningful activity of other radioisotopes (parasitic). Parasitic activity, mainly from isotopes of lead (209Pb, 204mPb, 203Pb) calculated with the use of FISPACT, exceeds ca 5 times tritium activity 1.4h after irradiation. We propose to remove disturbing radioisotopes in a chemical way to avoid long “cooling” of the irradiated samples before tritium measurement. Samples (1g of LiPb) irradiated in reactor fast neutron flux were diluted and metallic cations removed by chemical precipitation. For this purpose we used: potassium iodide (KJ), strontium chloride (SrCl2), APDC (C5H8NS2·NH4), NaDDTC (C5H10NNaS2·3H2O), and PAN (C15H11N3O). Precipitation procedure in each case lasted ca 5–25min, and the following filtration next 10–20min. In each filtrate (ca 120ml) we measured Pb concentration in total reflection X-ray fluorescence (TXRF) analyzer and parasitic activity (left after 21-day “cooling”) applying HPGe gamma spectrometer. Pb cations precipitated by SrCl2 and than by PAN lowered activity of Pb isotopes to less than 1% of the initial tritium activity. Another combination of reagents: NaDDTC followed by SrCl2 in a single and double step filtration reduced Pb concentration 102 and 104 times, respectively. Reduction of this order allows tritium radiometric measurement ca 3h after irradiation with acceptable accuracy. This time can be shortened by applying correction for decay of known parasitic activity. Input of 76As and other less abundant radioisotopes can be eliminated using high purity LiPb. Tritium activity of the filtrates measured in LS spectrometer showed no dependence upon used reagent being, within measurement error, the same as for analyzed LiPb samples.

Rapid method for plutonium-241 determination in soil samples.

A simple and rapid procedure for the determination of plutonium isotopes in the environment is presented. The procedure combines alpha spectrometry, solvent extraction and liquid scintillation measurements to ensure that both alpha- and beta-emitting isotopes are determined. Of five tested extractants, bis-(2-ethylhexyl) phosphoric acid was found to be the best choice. The procedure was applied to soil samples contaminated with Chernobyl fallout.

Primary activity standardization of 99Tc by three different absolute methods

The activity concentration of a solution of 99Tc was absolutely determined by liquid scintillation measurements based on the triple-to double-coincidence ratio method (TDCR) and compared with the results given by 4πβ(LS)-γ(NaI) live-timed anticoincidence (with extending dead-time) and classical 4πβ(PC)-γ(NaI) coincidence counting systems based on using 60Co as the efficiency-tracing radionuclide. The results of anticoincidence and coincidence counting are, respectively, 0.18% and 0.66% higher than the result from TDCR measurements, but they are consistent within uncertainties.