64 research outputs found
QUENCH: A software package for the determination of quenching curves in Liquid Scintillation counting
Proceedings of the 20th International Conference on Radionuclide Metrology and its Applications (ICRM), 8-11 June 2015, Vienna, Austria. Organizer TU Wien. Editors Franz-Josef Maringer, Dirk Arnold, Uwe WätjenInternational audienceIn Liquid Scintillation Counting (LSC), the scintillating source is part of the measurement system and its detection efficiency varies with the scintillator used, the vial and the volume and the chemistry of the sample. The detection efficiency is generally determined using a quenching curve, describing, for a specific radionuclide, the relationship between a quenching index given by the counter and the detection efficiency. A quenched set of LS standard sources are prepared by adding a quenching agent and the quenching index and detection efficiency are determined for each source. Then a simple formula is fitted to the experimental points to define the quenching curve function. The paper describes a software package specifically devoted to the determination of quenching curves with uncertainties. The experimental measurements are described by their quenching index and detection efficiency with uncertainties on both quantities. Random Gaussian fluctuations of these experimental measurements are sampled and a polynomial or logarithmic function is fitted on each fluctuation by chi(2) minimization. This Monte Carlo procedure is repeated many times and eventually the arithmetic mean and the experimental standard deviation of each parameter are calculated, together with the covariances between these parameters. Using these parameters, the detection efficiency, corresponding to an arbitrary quenching index within the measured range, can be calculated. The associated uncertainty is calculated with the law of propagation of variances, including the covariance terms
Développement d'un système de mesure directe du débit d'émission de sources neutroniques
La méthode de mesure de référence du débit d émission de sources neutroniques se fonde sur la technique du bain de manganèse. Elle est destinée à étalonner des sources de neutrons utilisant des radionucléides (241AmBe, 239PuBe, 252Cf, ) en termes de débit d émission neutronique sous 4p sr. Ce dispositif est complété par un banc de mesure de l anisotropie d émission utilisant un support rotatif et un compteur long de type BF3. La source à mesurer est immergée dans une solution de sulfate de manganèse et les neutrons émis sont capturés par les constituants du bain. Dans une configuration classique (sphère de bain de manganèse de 1 m de diamètre et solution concentrée), environ la moitié de ces neutrons conduisent à la création de 56Mn par réaction (n, g) sur 55Mn. Le radionucléide 56Mn a une période radioactive d environ 2,6 heures et le bain de manganèse atteint son activité de saturation en 56Mn quand le nombre d atomes radioactifs créés par unité de temps devient égal au nombre d atomes se désintégrant pendant ce même temps. Le débit d émission de la source peut alors être déduit de l activité en 56Mn de la solution à saturation, via une modélisation ad hoc des réactions nucléaires se produisant dans le bain. Cette installation a été récemment rénovée au LNE-LNHB afin de respecter les règles de sécurité et de radioprotection en vigueur. Cette rénovation a été l occasion de moderniser et de remettre à niveau les méthodes de mesure et de modélisation du bain et d entreprendre une étude sur le développement d un détecteur original pour la mesure directe en ligne de l activité du manganèse. Ce détecteur est fondé sur la méthode de mesure par coïncidences b-g. La voie bêta est constituée de deux photomultiplicateurs permettant de détecter l émission de lumière due à l effet Cerenkov et la voie gamma utilise un détecteur à scintillateur solide. L intérêt de cette méthode de mesure est qu elle permet d avoir accès à l activité du bain sans nécessiter d étalonnage préalable, contrairement à la méthode classique qui utilise un compteur gamma et nécessite la fabrication d une source de haute activité. Le principe de mesure a été validé à l'aide d'un prototype de détecteur et d'une modélisation effectuée à l'aide du code de calcul stochastique GEANT4. Le détecteur définitif a été réalisé et les mesures obtenues ont été comparées à celles données par une méthode primaire présente au laboratoire. Par ailleurs, des modélisations du bain de manganèse effectuées sous GEANT4, MCNPX et FLUKA, ont été comparées afin de choisir le code le plus fiable. Cette comparaison a permis d'identifier des lacunes notamment dans le code GEANT4 ainsi que des facteurs d'incertitude nécessitant une attention particulière, tels que la modélisation de l'émission neutronique et le choix des sections efficaces. Enfin, un étalonnage de source neutronique a été réalisé grâce à la méthode Cerenkov-gamma et aux facteurs correctifs donnés par la nouvelle modélisation du bain sous MCNPX. Ces mesures ont été complétées dans le cadre d'une comparaison comprenant également des mesures par l'ancienne méthode après étalonnage du couple bain/détecteur par irradiation d'une cible de manganèse en réacteur. Au terme de cette étude, plusieurs voies d'améliorations ont été proposées, dont certaines font déjà l'objet de travaux au LNHB.The manganese bath technique is the reference method for neutron source emission rates calibration. It is used to calibrate neutron sources using radionuclides (AmBe, PuBe, 252Cf, ) in terms of neutron emission rate under 4p sr. As a complement to this technique, the anisotropy of the source is measured using a rotating source holder and a neutron long counter. The neutron source to be measured is immersed in a manganese sulphate solution whereby the emitted neutrons are captured within the bath contents. In a typical configuration (a 1m diameter sphere and a concentrated solution), approximately half of the neutrons lead to the creation of 56Mn via the 55Mn(n, g) capture reaction. The 56Mn radionuclide has a half-life of approximately 2.6 hours and the bath reaches saturation when the number of nuclei decaying is equal to the number of nuclei created per unit time. The neutron emission rate from the source can then be deduced from the 56Mn activity at saturation, assuming proper modelling of the nuclear reactions occuring in the bath. The manganese bath facility at LNE-LNHB has been recently refurbished in order to comply with appropriate safety and radioprotection regulations. This has lead to the upgrading of both the measurement methodology and the modelling of the bath, and a study on the development of a new detector for the on-line measurement of the manganese activity was started. This new detector uses the b-g coincidence measurement method. The bêta channel consists of two photomultipliers tubes which allow the detection of Cerenkov light, and the gamma channel uses a solid scintillation detector. The advantage of this measurement method is that it allows the determination of the bath activity without any prior calibration, unlike the former method which uses a gamma-ray detector calibrated using a high activity manganese source. The principle of the Cerenkov-gamma coincidence measurement has been validated by a prototype of the detector and via modelling of the system using the stochastic transport code GEANT4. The final detector has also been made and the results obtained have been compared to those from a primary measurement method already in use at LNE-LNHB. Furthermore, a comparison of the results from modelling the manganese bath with GEANT4, MCNPX and FLUKA have been undertaken to find the most reliable code. This comparison lead to the identification of various weaknesses, particularly in GEANT4, and several uncertainty factors, such as the modeling of the neutron emission and the choice of the cross-section library. Finally, neutron source calibration has been carried out with the Cerenkov-gamma method and the correction factors given by the new modeling of the bath using MCNPX. These results have been complemented with a comparison with the former method simultaneously undertaken, after calibration of the detector in the bath using a 56Mn source irradiated in a nuclear reactor. At the end of this study, several improvements have been proposed, from which a number are currently under development at LNE-LNHB.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF
Développement de Calorimètres Métalliques Magnétiques pour le Spectrométrie Bêta
L'objectif de ce travail de thèse est de démontrer le potentiel des calorimètres métalliques magnétiques pour la spectrométrie bêta via une mesure du spectre du 63-Ni. Ce nucléide fait partie des émetteurs bêta pour lesquels la théorie est connue et les calculs crédibles. Nous proposons une méthode d'observation expérimentale du spectre, à basse énergie surtout, permettant de valider les calculs théoriques.Un traitement des données spécifique à l'établissement d'un spectre continu a été établi et optimisé, prenant en compte les paramètres d'une mesure cryogénique avec un calorimètre métallique magnétique et les exigences de la spectrométrie bêta.Deux types de sources ont été réalisés, un dépôt sous forme de sel de nickel à partir d'une goutte séchée de solution de NiCl2 et un dépôt métallique de nickel issu d'une électrodéposition. Les sources électrodéposées se sont révélées être le type de source adéquate pour la spectrométrie du 63-Ni.Les performances des calorimètres métalliques magnétiques, parmi lesquelles le fort rendement de détection ou le faible seuil en énergie, permettent d'obtenir des résultats suffisamment précis pour la validation expérimentale des calculs théoriques.The aim of this thesis is to demonstrate the potential of metallic magnetic calorimeters for beta spectrometry by measuring the spectrum of 63-Ni. This nuclide is one of the beta emitters for which theory is well-known and calculation reliable. We propose a method for experimental observation, especially at low energies, which allows to validate the theoretical calculation.A dedicated data analysis has been established and optimized. It takes into account the parameters of a cryogenic measurement and also the specific requirements of beta spectrometryTwo types of sources have been realized, a deposit of nickel salt from a dried drop of a solution of NiCl2 and a metallic electroplated source of Ni. The electroplated sources turn out to be the appropriate type of source for 63-Ni spectrometry.The performances of metallic magnetic calorimeters, such as high detection efficiency and low energy threshold, lead to results precise enough to validate experimentally the theory.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF
A new compact TDCR-Cherenkov counter for the online measurement of Mn-56 activity
Best poster presentation in LSC2017 conferenceInternational audienc
Parcours de formation des étudiants de master
International audienceCet ouvrage issu des recherches du groupe de travail sur l'enseignement supérieur du céreq est consacré à la question des parcours étudiants dans l’enseignement supérieur et plus particulièrement, au segment Master, en centrant l’analyse sur les parcours de formation des étudiants
New determination of the 3He mixing ratio in the Earth's lower atmosphere from an international tritium intercomparison exercise
International audienceThe light isotope of helium, 3He, is essentially a primordial substance entrapped within the Earth's interior during the formation of the planet. It is released into the atmosphere by volcanic/magmatic activity, and eventually escapes to outer space. 3He is also produced by the radioactive beta-decay of tritium. Hence, measurements of 3He can be used to derive the concentration of tritium. The so-called “3He ingrowth” method uses a mass spectrometer to detect the amount of 3He that accumulates in a sample during a given period of storage. The 3He measurements are classically calibrated against an air standard. The method thus relies on the accurate knowledge of the atmospheric mixing ratio of 3He. This value is based on mass spectrometric measurements with gravimetrically or volumetrically prepared 3He standard mixtures. Here, we apply the 3He ingrowth method in reverse, using a solution of tritiated water prepared for an international comparison of tritium activity measurements to precisely determine the 3He mixing ratio of our air standard. The measured atmospheric mixing ratio of 3He, based on a series of ten measurements, is [3He] = 7.12 ± 0.06 ppt. This value is between 1% and 2% lower than previous determinations reported in the literature. However, all results remain statistically consistent
On-site measurement of C and F half-life by TDCR counting
International audienceThe 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. 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 such as calibrating solutions with short-lived radionuclides, preventing radioactive source transportation, and performing on-site comparisons to promote radionuclide metrology harmonization. The standardization of 11C and 18F measurement devices, such as a dose calibrator, is necessary in radiopharmaceutical production sites. Due to their short half-life, a primary on-site calibration is more interesting for the laboratory. However, impurities in the radiopharmaceutical solution must be checked in such a context. While this is easily done in the case of gamma emitters, it is much more complicated for pure beta emitters, for example. One solution is then to follow the radioactive decay of the solution in order to quantify possible impurities. In this work, we present new half-life measurements of 11C and 18F decays performed at the Orsay Hospital in the CEA/SHFJ laboratory (France). These measurements were carried out by liquid scintillation using two custom portable micro-TDCR and mini-TDCR devices. The measured data were analysed to evaluate the half-life of these two radionuclides as accurately as possible, and those for count rates above 400,000 s-1 until almost complete decay of the radionuclide. The measured half-lives were determined to be 20,333 (7) min for 11C and 1,8287 (2) h for 18F. The former result is more precise by a factor of three compared to DDEP recommendation of 20,361 (23) min. The latter falls in the most precise available measurements as the DDEP recommended value is 1,82890 (23) h. In this paper, the results and corresponding uncertainty budgets will be described precisely. Accidental coincidence correction and background influence will be discussed in detail. Indeed, these two parameters were identified as the major contribution for such on-site measurements. A review of the half-life data and the impact of its measures will also be discussed. Finally, an evaluation of the sensitivity to impurities will be carried out in order to define the detection capabilities of such an on-site measurement technique
In quest of the optimal coincidence resolving time in TDCR LSC
International audienceThis paper presents studies of the influence of the coincidence resolving time on the activity calculated by the Triple-to-Double Coincidences Ratio (TDCR) method in Liquid Scintillation (LS) counting. Recently, published methods for the correction for accidental coincidences in TDCR counting open the possibility to use resolving times up to several µs, long enough not to miss true coincidences and to study the effects of delayed fluorescence.3H, 14C, 55Fe and 63Ni LS-sources in UltimaGold (UG), UG LLT and Toluene+PPO cocktails were measured using a TDCR counter connected to a digitizer working in list-mode. The necessary resolving time to include 99.9% of the logical sum of double (D) coincidences was found to be 1.2 µs for 3H, 1 µs for 55Fe and 500 ns for 63Ni in UG. The activity of all LS-sources was calculated using the TDCR method for resolving times from 10 ns to 2 µs and a significant dependence between the calculated activity and resolving time was observed. A dedicated Monte Carlo (MC) code was used to simulate list-mode data from TDCR measurements. The simulation results suggest that the 3H activity calculated by the TDCR method is overestimated regardless of the used resolving time if delayed fluorescence is present which is not described by the used ionization quenching function.Efficiency variation measurements of 3H in UG LLT show a strong dependence of the optimal kB parameter on the used resolving time: 85 µm/MeV at 40 ns and 110 µm/MeV at 200 ns, leading to 2.5% difference in calculated activity. In the framework of this study the efficiency variation methods by chemical quenching and gray filters were compared and a difference of 60 µm/MeV between the two was observed. The results from this article demonstrate that regardless of the available corrections for accidental coincidences, it is not advisable to increase the resolving time beyond what is necessary to register all prompt fluorescence events. Moreover, even for short coincidence resolving times, delayed fluorescence could have a significant influence on the activities calculated by the TDCR method
3 H activity comparison between FTMC, VNIIM and LNE-LNHB
Proceedings of the 20th International Conference on Radionuclide Metrology and its Applications (ICRM), 6-11 June 2015, Vienna, Austria. Organizer TU Wien. Editors Franz-Josef Maringer, Dirk Arnold, Uwe Wätjen.International audienceAn activity comparison of tritiated water was organized in 2013 between 3 laboratories: FTMC (Lithuania), LNE-LNHB (France) and VNIIM (Russia). The solution was prepared by LNHB and ampoules were sent to the others laboratories. This solution was standardized in terms of activity per unit mass by participant laboratories using the Triple to Double Coincidence Ratio (TDCR) method in liquid scintillation counting (LSC). The tritiated water solution is traceable to the solution prepared by LNHB for the CCRI(II)-K2.H-3 2009 H-3 international comparison
Investigation of the possible effect of the accidental coincidences correction on the determination of optimal kB value by efficiency variation with gray filters
International audienceRecently, analytical and experimental methods for evaluating accidental coincidences in TDCR measurements were proposed. It was shown that the correction for accidental coincidences depends on the experimental counting rates and that it is significant not only for measurements of high-activity sources but also in low-level LSC measurements. The efficiency variation by optical grey filters, on the other hand, is widely used for determining the optimal value of the Birks’ ionization quenching parameter kB, which has the major contribution to the uncertainty in the TDCR standardization of low-energy β-emitters like 3H.Since there is a change in the counting rates between measurements of a sample with different grey filters, it is interesting to investigate the effect of accidental coincidences on the choice of the proper kB value. This question is of practical relevance because it is interesting to assess the correctness of the estimates of kB applied in the past when no accidental coincidence corrections have been applied.To achieve this goal, we have re-analyzed a large set of experimental data of kB determinations by applying and not applying analytical accidental coincidence corrections. Examples of the obtained results are shown in Fig. 1. Overall, at this point, we do not see a statistically significant effect of the accidental coincidence correction on the optimal kB value. These results verify the choices of kB by efficiency variation by grey filters made in the past. More results for different nuclides and TDCR systems will be presented
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