Liquid Scintillation Measurements Research Articles

Activity determination of 229Th by means of liquid scintillation counting

Liquid scintillation measurements of 229Th in radioactive equilibrium with its progenies were carried out. The counting efficiency was determined by means of a free parameter model. The measurements were made in a custom-built triple-to-double coincidence ratio (TDCR) system. In addition, a new portable mini-TDCR system with three channel photomultipliers and two commercial counters were tested. The decay of the short-lived 213Po requires great care, since it often occurs during the dead time of the counter systems. Also the rather short-lived 217At may decay during the dead time caused by 221Fr decay events. The overall counting efficiency of the TDCR system of PTB was found to be about 700% (depending on the degree of chemical quenching) and the relative standard uncertainty of the activity concentration was found to be about 0.23%. The determined activity concentration was compared with the outcome of alpha spectrometry under defined solid angle and excellent agreement was found. The TDCR efficiency calculations can be easily adapted to activity determinations of 225Ra or 225Ac in equilibrium with their progenies.

Reinvestigation of the irregularities in the 3H decay

Having in mind the potential impact of the results presented by Veprev and Muromtsev (2012) [13] on our knowledge of the universe, we reinvestigated the liquid scintillation measurement of the count rate variations of 3H. Making use of the sophisticated Quantulus liquid scintillation spectrometer, we found that the measurement of the high-energy tail of 3H spectrum may be significantly influenced by instrumental instability. Thus, the possible explanation for the relatively high count rate variations of Veprev and Muromtsev (2012) [13] can be attributed mainly to the walk of the cut-off in the integrated spectrum, although weak variations of different origin could be masked by such cut-off drifts. In our experiment we have also registered the oscillatory behavior of measured high-energy tail of 3H spectrum, but with very small amplitude (less than 0.5%), which cannot be easily explained only by instrumental instability. When the total 3H spectrum was measured, no significant variations in the count rate were found.

Systematic study of particle quenching in organic scintillators

Among the different factors that affect measurements by organic scintillators, the majority of attention has been focused on those related to the scintillator (i.e., ionization, chemical, color and optical quenching), and less attention has been paid to the loss of energy before the particle (i.e., alpha or beta) arrives at the scintillator (i.e., particle quenching). This study evaluates the effect of particle quenching in different scintillation methods (i.e., using two plastic scintillation microspheres (PSm1 and PSm2), liquid scintillator and gel scintillator) by measuring solutions that contain increasing concentrations of NaCl, BaCl2 and glycerin. The results show the importance of particle quenching in PSm measurements because detection efficiency decreases with increasing concentrations of the quenching component, although the spectrum position and external standard parameter remain constant. The results have shown evidence of particle quenching, although at a lower magnitude, in the liquid scintillation or gel scintillation measurements. Moreover, the use of two PSm with different diameters and salty compound that alters the equilibrium of the liquid and gel emulsions also exemplified the importance of the transmission of optical photons through different scintillation media (i.e., optical quenching). Improvement and deterioration of the optical conditions on the scintillation media is manifested as a movement of the spectrum to higher and lower energies, respectively. The results obtained with PSm were confirmed by Monte Carlo simulation.

Determination of oil reservoir radiotracer (S14CN−) in a single step using a plastic scintillator extractive resin

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S14CN−. Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS.The objective of this study is to develop a PS resin for the determination of 14C-labelled thiocyanate radiotracer in water samples.For this purpose, the immobilisation procedure was optimised, including optimisation of the proportion of PS microspheres:extractant and the use of a control blank to monitor the PS resin immobilisation process. The breakthrough volume was studied and the detection and quantification limits for 100mL of sample were determined to be 0.08BqL−1 and 0.31BqL−1, respectively. The established procedure was applied to active samples from oil reservoirs and errors lower than 5% in the sample determinations were obtained.

Activity determination and nuclear decay data of 113mCd

The radionuclide (113m)Cd was extracted from a Cd component, which has been irradiated in a research reactor during its routine operation. A validated separation procedure was then used to obtain a (113m)Cd solution of high radiochemical purity. The solution was measured by means of liquid scintillation counting for activity determination. To this end, the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence (TDCR) counting technique were used. Measurements in a low-background gamma-ray spectrometer were applied to identify any potential photon-emitting impurities and to measure the 263.7 keV photons from the isomer transition. A gamma emission probability of 0.01839(29)% was determined for this line. The liquid scintillation measurements were also used to evaluate the half-life of (113m)Cd. The decay was followed for about 11 months and a half-life T(1/2)=13.97(13) years was obtained.

Application of a stochastic TDCR model based on Geant4 for Cherenkov primary measurements

Cherenkov measurements can be advantageously carried out using a counting instrumentation dedicated to liquid scintillation. In the case of radionuclide measurements, the interest of this technique is largely described in the literature. For instance, it is generally quoted that the possibility to measure directly the activity of aqueous solutions makes the sample preparation easier. Based on a three-photomultipliers apparatus, the Triple to Double Coincidence Ratio (TDCR) method is implemented in National Metrology Institutes for liquid scintillation measurements. Knowing the decay scheme associated with the radionuclide to be standardized, a free parameter model of light emission is constructed to determine the counter detection efficiency using the experimental TDCR value. Contrary to liquid scintillation, Cherenkov emission is characterized by a directional behavior. Instead of using an additional free parameter to take this effect into account, a stochastic modeling based on the Monte Carlo code Geant4 is proposed in order to extend the TDCR method to Cherenkov counting. The purpose of this model is to simulate the different optical processes of Cherenkov photons leading to the production of photoelectrons in the three-photomultipliers counter. The validation of this stochastic approach of the TDCR method for Cherenkov counting is carried out in the case of (90)Y activity measurements.

Investigation into the standardization of 99Tc

The standardization of (99)Tc by several primary methods was investigated. This was performed to support a new (99)Tc transfer standard that has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as Standard Reference Material SRM 4288B. The standardization for the (99)Tc content of the solution was based on 4pibeta liquid scintillation (LS) measurements with (3)H-standard efficiency tracing (CIEMAT/NIST method). Confirmatory determinations were performed by 4pibeta(LS)-gamma(NaI) live-timed anti-coincidence (LTAC) counting and an LS-based 4pibeta triple-to-double coincidence ratio (TDCR) method.

Background Tritium Concentrations of River and Lake Waters in Japan

The levels of tritium in the atmosphere nowadays are those of natural origin before the nuclear test. Nuclear power stations, nuclear reprocessing plants and fusion facilities are observed as a further occurrence source. Then, in order to appraise the influence of nuclear facilities and long distance transport from the continent where tritium level is relatively high, it is necessary to investigate background levels of tritium.Tritium concentrations of 34 river waters and 6 lake waters in Japan were determined by low background liquid scintillation measurement system combined with the electrolysis using solid polymer electrolyte.Tritium concentrations of river and lake water were 0.36-2.66 Bq/l (average 1.06±0.60 Bq/l) and 0.48-1.43 Bq/l (average 0.81±0.37 Bq/l), respectively. The entire mean value was 1.03±0.57 Bq/l. This mean value equals 43% of the mean value which was measured in 1982. It was possible to calculate 11 years as an apparent half-life.

Investigation of radioactivity in selected drinking water samples from Maryland

In 2004, levels of radioactivity exceeding federal drinking water standards were found by state laboratories in two separate areas of Maryland through gross alpha and beta screening measurements. It was desired to know which radionuclides were responsible for the activity and what effect water softener systems installed in individual households had on the mitigating problem. Non-destructive gamma-spectrometry and gross alpha-beta liquid scintillation measurements, as well as chemical separations followed by measurements of 222Rn, 226Ra and 228Ra, uranium and thorium isotopes, 210Po, and 210Pb were carried out by National Institute of Standards and Technology (NIST). The results of the studies indicated disequilibrium among the decay products in the Th and U decay chains had a major influence on the radionuclide content. Unsupported 210Po was found to be the predominant radionuclide in drinking water at one of the locations. Furthermore, the influence of the use of water softeners was found to be much more effective for radium than for uranium.

63Ni, its half-life and standardization: Revisited

Recent liquid scintillation (LS) measurements at the National Institute of Standards and Technology (NIST) and at the Laboratoire National Henri Becquerel (LNHB) on a standardized 63Ni solution that has been tracked for nearly 40 years have resulted in several important findings: (i) a 63Ni half-life value of 101.2±1.5 a has been determined with the present decay data. This value is consistent with a previous specific activity determination and with an earlier value from decay measurements; and it appears to be more satisfactory than a recent data evaluator's recommended value of 98.7 a. (ii) All solution standards of 63Ni as disseminated by NIST for the past 38 + years are internally consistent with past and recent standardizations. (iii) Primary LS standardizations of 63Ni by the triple-to-double coincidence ratio (TDCR) method and by CIEMAT/NIST 3H-standard efficiency tracing (CNET) appear to be comparable, although the latter methodology is believed to be inherently inferior. (iv) There is excellent measurement agreement between NIST and LNHB for 63Ni primary standardizations.

A liquid-scintillation-based primary standardization of 210Pb

A new radioactivity solution standard of 210Pb has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as standard reference material (SRM) 4337. This new 210Pb solution standard is contained in a 5 mL flame-sealed borosilicate glass ampoule, consists of (5.133±0.002) g of a nominal 1 mol L −1 nitric acid solution, has a density of (1.028±0.002) g mL −1 at 20 °C, has carrier ion concentrations of about 11 μg Pb 2+ and 21 μg Bi 3+ per gram of solution, and is certified to contain a massic activity (9.037±0.22) kBq g −1 as of the reference time 1200 EST, 15 June 2006. All of the uncertainties cited above correspond to standard uncertainties multiplied by a coverage factor k=2. The standardization for the 210Pb content of the solution was based on 4 παβ liquid scintillation (LS) measurements using CIEMAT/NIST 3H-standard efficiency tracing (CNET). Confirmatory determinations were also performed by high-resolution HPGe γ-ray spectrometry, by 2 πα spectrometry with a Si surface barrier detector of separated 210Po, and by 4 πβ(LS)– γ(NaI) anticoincidence counting.

239Np as a tracer of 237Np in effluent samples and low level nuclear waste

In this paper a technique to separate and measure both isotopes (237Np and 239Np) together is presented. A combined shape pulse discrimination liquid scintillation measurement with gamma-spectrometry, permits a precise measurement after the radiochemical separation. This technique was carried out by using an Eichrom chromatographic column (TEVA) as the first step of a more complete method, applied in the Nuclear Regulatory Authority, to separate actinides in nuclear waste and liquid effluents. The MCA is 0.08 Bq/l by alpha-spectrometry and 0.22 Bq/l (2σ) by liquid scintillation counting (LSC) for 93.7% of measurement efficiency and 98.4% of chemical recovery.

Radon and tritium measurements in drinking water in a region of central Italy (Umbria)

In the last years the interest in drinking and mineral water radioactivity has grown. Recently national and EU regulations replaced the previous drinking water norms with the aim to strengthen consumers security concerning drinking water quality. Perugia and Urbino Universities carried out a joint study on the radiological characterization of the water destined for human consumption in the Umbria region. The aim of this work was to produce a map of the radon and tritium concentrations in the water of this area as a basis for the implementation of hydrogeological knowledge and to determine a possible related radiological risk for the local population.222Rn measurements were performed by liquid scintillation and gamma-spectrometry and3H measurements by liquid scintillation. Up to now, the222Rn concentrations ranged 5.9-65.79 Bq/l and3H concentrations are always lower than the detection limit (8.6 Bq/l).

The monitoring of tap waters in Milano: planning, methods and results

The radiometric monitoring of tap waters has been carried out, in Northern Italy, since late the 1980s as part of the activities headed by the National Surveillance Network on environmental radioactivity. Measurements were accomplished by gamma spectrometry over large samples of water that were drained in a single place and concentrated by ion exchange resin treatment. More recently a regular, periodical monitoring was started using liquid scintillation measurements. In this manner, gross alpha and beta activities, uranium, (226)Ra and (222)Rn concentrations are determined at present. Nevertheless, a single-point sampling may be not fully representative of the whole Milano aqueduct, significantly extended and fed by a number of wells. As a control, an extended monitoring of the aqueduct was planned and variations of water radioactivity in different Milano areas have been assessed.

Metabolic measurement techniques to assess bone fracture healing: a preliminary study.

The purpose of this study was to project the effectiveness of using positron emission tomography for evaluation of fracture healing using the analogous method of liquid scintillation. A reproducible comminuted fracture model in rabbit femurs was stabilized with external fixation. Thirty-nine rabbits were divided into four groups: Group A had slight distraction, Group B had shortening, Group C had a bone defect, and Group D was the sham control group. At 2 and 4 weeks after fracture, the femurs had liquid scintillation measurements using 2-[14C]-deoxyglucose (2DG C-14). Glucose uptake was significantly elevated in the experimental limb relative to the contralateral control femurs at both times. The distraction group showed a significant decrease in uptake from 2-4 weeks. There was a high correlation between the liquid scintillation measurements and the radiographic fracture healing scores, with higher levels of 2DG C-14 uptake corresponding to lower levels of fracture healing calcification. The high correlation found between 2DG C-14 uptake and radiographic scores suggests that positron emission tomography used in conjunction with a glucose-based radiopharmaceutical such as 2-[18F]fluoro-2-deoxyglucose can monitor the fracture healing process effectively.

Effects of Lactic Acid Bacteria on the Uptake and Distribution of the Food Mutagen Trp-P-2 in Mice

Background : Lactic acid bacteria have been reported to have antimutagenic and anticarcinogenic properties in vivo and in vitro. Lactobacillus acidophilus and Bifidobacterium longum have earlier been shown to bind the food mutagen Trp-P-2 in vitro. Methods : The influence of oral supplementation with L. acidophilus NCFB 1748 and B. longum BB 536 on the uptake and distribution of 14 C-labelled Trp-P-2 in several mouse tissues was quantified by liquid scintillation measurements and examined by tape section autoradiography (gives an unbiased qualitative registration of differences in overall tissue distribution) in the present investigation. Furthermore, the effect of β -naphthoflavone (BNF), a cytochrome P4501A (CYP1A)-inducing agent, on the distribution of 14 C-labelled Trp-P-2 was examined. Results : After oral (6 mg/kg; 5 μCi) or iv (1.2 mg/kg; 1 μCi) administration of 14 C-labelled Trp-P-2, high levels of radioactivity were observed in the bile, urine and contents of the gastrointestinal tract. Lower levels were present in the liver, lung, kidney, intestines, brown fat, submaxillary salivary gland and thymus. In mice supplemented with lactic acid bacteria there was a significantly decreased level (29%-73%) of radioactivity in the lung, thymus, liver, kidney, submaxillary salivary gland and small intestine as compared with controls. In mice pretreated with BNF, a low but distinct localization of radioactivity in the lung was observed, whereas no similar localization occurred in controls. Conclusions : The results suggest that (i) there is a decreased bioavailability of the Trp-P-2 in the majority of the tissues examined in bacteria supplemented mice and (ii) there is a low but distinct CYP1A-dependent activation of Trp-P-2 in the lung of BNF-treated mice.

Technetium-99 in Fucus and seawater samples in the Finnish coastal area of the Baltic Sea, 1999

Liquid discharges of 99Tc from the Sellafield nuclear facilities increased largely in the mid 90"""s. These releases are transported to the Nordic sea areas by the ocean currents. Results of the 99Tc activities along the Norwegian coastal areas and in the North Sea have been reported but then again, the spreading of 99Tc into Baltic Sea has not been studied thoroughly. Fucus vesiculosus and seawater samples were collected in the summer 1999 from the Finnish coastal areas for measuring 99Tc in the Baltic Sea area. A modified analytical method for measuring 99Tc in the environmental samples was developed at that time. The method based on extraction chromatography and liquid scintillation measurement of 99Tc. The 99Tc concentration in the Fucus vesiculosus in the Finnish coast of the Baltic Sea varied from 1.6 to 11.6 Bq/kg (dry weight) being highest at the most northern sampling sites. These values were considerable lower than those in the Danish and Norwegian coasts. The variation in the concentrations observed are probably due to biological factors. The 99Tc concentration in the Baltic Sea water studied was below 0.2 Bq/m3.

Standardisation of 89Sr using three different methods

Three independent methods were used to standardise a 89Sr solution within the frame of an international comparison organised by BIPM/CCRI(II): 4 π liquid scintillation (LS) spectrometry, based on the CIEMAT/NIST efficiency tracing method, and direct activity measurements with a windowless 4 π CsI(Tl)-sandwich spectrometer and a 4 π pressurised gas proportional counter. Quantitative solid point-like sources were prepared paying special attention during the source drying phase. The impurities in the original solution were measured and corrected for in the results of all three methods. The activity concentration of 89Sr was found to be 26.21±0.08 kBq g −1. A new half-life value for 89Sr of 50.61±0.05 days was determined from the LS measurements. The measurement methods, including the impurity measurements, are described and the results compared, considering the advantages and disadvantages of each method.

Study of the stability problems of 110mAg samples in several commercial liquid scintillators

The stability of 110mAg samples for liquid scintillation measurements has been studied in four commercial scintillators: Insta-Gel® Plus, Ultima-Gold™, HiSafe™ II and HiSafe™ III. Samples using 15 ml of cocktail with four different levels of carrier, 0.0, 1.5, 3.0 and 6.0 μg of AgNO 3, were prepared and their total count rate and spectral behaviour monitored for two months. Only samples in HiSafe™ III were completely stable for the full term studied.

Measurement of 241 Pu in environmental samples

Concentrations of 241Pu in the air and deposition samples in Finland after the 1986 Chernobyl accident were estimated with the aid of ingrowth of 241Am. Plutonium-241 was clearly shown to be present in the Chernobyl fallout in Finland. Pu was unevenly distributed and the mean radioactivity ratio of 241/239,240Pu was 70 for air and 71 for deposition samples. Here, a radiochemical method for determination of 241Pu in the environmental samples was also developed. The method was based on the liquid scintillation measurement of 241Pu with a pulse shape analyser after Pu separation. Efficiency calibration was performed with the aid of 3H standard instead of the 241Pu standard. The method was tested by comparing the results with the method of 241Am ingrowth and some reference samples. The detection limit for 241Pu was 0.007 Bq per sample. The 241Pu concentrations in the sediment samples taken from the Baltic Sea varied between <0.5 and 27 Bq·kg-1. The effect of the Chernobyl accident could be seen both from the 241Pu concentrations and from the Pu isotope ratios in vertical distributions of sliced samples.