31 research outputs found

    Adaptation of PTB’s analytical modelling for TDCR–Cherenkov activity measurements at LNHB

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    Proceedings of the 23rd International Conference on Advances in Liquid Scintillation Spectrometry (LSC), Copenhagen, DENMARK, APR 30-MAY 05, 2017. Organizer: Tech Univ DenmarkInternational audienceDesigned for triple to double coincidence ratio measurements based on liquid scintillation, the three-photomultipliers detection system can also be applied for Cherenkov counting using aqueous solutions. For activity determination, a specific modelling of Cherenkov light emission has to be constructed. For that purpose, the analytical modelling first developed at PTB was adapted to account for the physical features of the detection system used at LNHB. The first results are presented in the case of activity measurements of two high-energy β−-emitters (90Y and 89Sr). The analytical modelling was also tested for the standardization of 68Ge in a solution of 68Ge/68Ga in equilibrium in the framework of a BIPM international comparison in 2014

    Standardization of 68^{68}Ge/68^{68}Ga using the 4πβ−γ\pi \beta-\gamma coincidence method based on Cherenkov counting

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    Proceeding of the 21st International Conference on Radionuclide Metrology and its Applications (ICRM), Argentinian Comis Nacl Energia Atomica, Buenos Aires, ARGENTINA, MAY 15-19, 2017. Organizer: Argentinian Comis Nacl Energia Atomica.International audienceIn the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of 68^{68}Ge in a solution of 68^{68}Ge/68^{68}Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in 68^{68}Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of 18^{18}F for PET imaging). Due to the volatility of germanium, the activity standardization of 68^{68}Ge was investigated at LNHB by means of 4πβ−γ\pi \beta -\gamma coincidence counting based on Cherenkov measurements. This technique was applied to take advantage of the Cherenkov threshold (similar to 260 keV in aqueous solutions) in order to prevent counting from electron-capture events associated with 68^{68}Ge disintegrations. Cherenkov counting was performed using glass and polyethylene vials and the resulting activity concentrations were compared with 4πβ−γ\pi \beta -\gamma coincidence measurements based on liquid scintillation. The efficiency-extrapolation curve obtained with Cherenkov measurements in glass vials was compared to Monte Carlo simulations based on the Geant4 code

    Calculation of extrapolation curves in the 4π(LS)β-γ coincidence technique with the Monte Carlo code Geant4

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    International audienceAt LNE-LNHB, a liquid scintillation (LS) detection setup designed for Triple to Double Coincidence Ratio (TDCR) measurements is also used in the β-channel of a 4π(LS)β–γ coincidence system. This LS counter based on 3 photomultipliers was first modeled using the Monte Carlo code Geant4 to enable the simulation of optical photons produced by scintillation and Cerenkov effects. This stochastic modeling was especially designed for the calculation of double and triple coincidences between photomultipliers in TDCR measurements. In the present paper, this TDCR-Geant4 model is extended to 4π(LS)β–γ coincidence counting to enable the simulation of the efficiency–extrapolation technique by the addition of a γ-channel. This simulation tool aims at the prediction of systematic biases in activity determination due to eventual non-linearity of efficiency–extrapolation curves. First results are described in the case of the standardization 59Fe. The variation of the γ-efficiency in the β-channel due to the Cerenkov emission is investigated in the case of the activity measurements of 54Mn. The problem of the non-linearity between β-efficiencies is featured in the case of the efficiency tracing technique for the activity measurements of 14C using 60Co as a tracer

    Subsequent comparison of measurements of neutron source emission rate (2016-17) - CCRI(III)-K9.AmBe.2

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    International audienceSection III (neutron measurements) of the Comité Consultatif des Rayonnements Ionisants, CCRI, conducted a subsequent comparison of primary measurements of the neutron emission rate of an 241^{241}Am-Be(α\alpha,n) radionuclide source. The aim of this comparison was to compare primary measurements of the neutron emission rate of an 241^{241}Am-Be(α\alpha,n) radionuclide source for laboratories who were outliers in the previous comparison (K9.AmBe) or who were unable to participate. Three laboratories participated – LNHB (France), ENEA-INMRI (Italy) and NPL (UK) – with NPL as the pilot institute and the link to the K9.AmBe comparison. Measurements were made in 2016-17. Each laboratory reported the neutron emission rate into 4π\pi sr together with a detailed uncertainty budget.All participants used the manganese bath technique

    Approche stochastique du modèle RCTD pour la mesure de l’activité en Cherenkov et par scintillation liquide

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    International audienceIn the field of radionuclide metrology, the TDCR method is a primary technique based on liquid scintillation using a threephotomultiplier instrumentation. The application of the TDCR model classically implemented in laboratories is investigated in the case of low-energy deposition in the liquid scintillator. For that purpose, the condition of stochastic independence between photomultipliers is introduced in order to express the classical probabilistic relations used for the detection efficiencies of coincidences. Experimentally observed in the case of 3^3H standardization, the time dependence arises when the coincidence resolving time is shorter than the time distribution of scintillation photons. The geometric dependence is also investigated because of the sensitivity of coincidence counting with the position of light emission inside the volume of the liquid scintillator. For that purpose, a new TDCR modeling using the Monte Carlo code Geant4 has been implemented in order to simulate the propagation of photons from their creation in the optical chamber to the production of photoelectrons in liquid scintillation counter. In both cases of stochastic dependence, the influence on the calculation of detection efficiencies and thus on the activity determination is presented. The new TDCR-Geant4 model was also developed to take into account Cherenkov emission; it has been applied to confirm the emission of Cherenkov photons subsequently created by Compton scattering in the photomultiplier windows. Using the TDCR-Geant4 model, a new primary technique is also presented by implementing the TDCR method using the Cherenkov emission. This new technique has been applied to the standardization of the short-lived radiopharmaceutical 11^{11}C (T1/2_{T1/2} about 20 min).En métrologie de l’activité, la méthode RCTD (Rapport des Coïncidences Triples à Doubles) est une technique primaire fondée sur la scintillation liquide, utilisant une instrumentation spécifique à trois photomultiplicateurs. Le modèle RCTD statistique de l’émission lumineuse permettant le calcul des rendements de détection des coïncidences est étudié dans le cas de dépôts de basses énergies dans le liquide scintillant. Pour cela, l’indépendance stochastique entre les photomultiplicateurs est introduite comme condition préalable à l’écriture des relations classiques du modèle statistique. Deux phénomènes pouvant conduire à la non-validité de cette condition sont décrits. Mise en évidence expérimentalement avec la mesure d’activité du tritium (3^3H), la dépendance stochastique de type temporel se manifeste par une perte systématique de coïncidences lorsque le temps de résolution est trop court comparé à la distribution temporelle des photons de scintillation. La dépendance stochastique de type géométrique est également étudiée en raison de la sensibilité du comptage des coïncidences selon le point d’origine de l’émission lumineuse dans le volume du liquide scintillant. Cette étude a été possible grâce au développement d’une nouvelle modélisation avec le code Monte-Carlo Geant4 intégrant la simulation de la propagation des photons optiques jusqu’à la production des photoélectrons dans le détecteur. Dans les deux cas de dépendance stochastique, l’influence sur le calcul des rendements de détection des coïncidences et par suite sur la détermination de l’activité est exposée. Le nouveau modèle RCTD-Geant4 intègre aussi l’émission de photons Cherenkov ; il a permis la confirmation de l’émission de lumière « parasite » sous forme de photons Cherenkov suite à la diffusion Compton dans les faces d’entrée des photomultiplicateurs. Une nouvelle technique primaire RCTD-Cherenkov a également été développée grâce au modèle RCTD-Geant4 ; elle a été notamment appliquée à la mesure d’activité du carbone-11 (radiopharmaceutique à durée de vie courte, T1/2T_{1/2} de l’ordre de 20 min)

    Simulation of the response of an ionization chamber to 214^{214}Bi emission.Application to the measurement of 222^{222}Rn.

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    International audiencePENELOPE simulations of a Vinten ionization chamber (IC) were performed to investigate the influence of the thickness of glass-ampoules used in 222^{222}Rn standardization. The simulation reveals a non-negligible variation of the energy deposited in the chamber gas region (which may induce a proportional variation of the measured current) when considering the β\beta transition emissions of the daughters of 222^{222}Rn. This reinforces the idea of using a specialist container (made of metal to preserve the integrity of the container) that would circulate between the metrology laboratories in the context of international comparison exercises using the BIPM international reference system (SIR)

    Custom radioactive standards to assess detector performance

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    International audienceThe field of CBRNE measurements presents many challenges and requires the development of advanced instrumentation.The Laboratoire National Henri Becquerel (http://www.lnhb.fr/) has the capabilities to manufacture custom radioactive standards, traceable according to ISO 17025. Our calibration certificates are recognized by our homologues [1] (NIST, NPL, etc.) and the laboratory has a comprehensive authorization for radionuclide use. If needed, we can recommend surrogate elements to match the emissions of rare or short-lived radionuclides. In addition to providing custom standards, we can help with their use to evaluate the performance of the RN prototypes being developed in terms of detection limits and linearity of the detector response. In addition, discrimination capabilities can be checked (emission interferences or even cross-talk between channels) via the measurement of radionuclide mixture. The standards manufactured can also be used to test the performance of signal processing algorithms in conditions close to field constraints.Our sources have been successfully used to test an original signal processing strategy based on artificial spiking neural networks to enable fast radionuclide identification at low count rate for radiological threats [2], or to test imaging systems for nuclear medicine needs [3].The LNHB is ready to study what standards can be manufactured to enable a reliable performance assessment of advanced devices developed, or even to test them in our premises

    Nuclide++: A C++ module to include DDEP recommended radioactive decay Data in Geant4

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    International audienceThis article describes the Nuclide++++ module developed at LNE-LNHB to simulate the decay schemes related to single or multiple radionuclides, by randomly selecting decay pathways. Written in C++++, with respect of the Geant4 coding style, this module can be used transparently in Geant4-based simulation applications as an alternative to the existing Radioactive Decay Module (RDM). Nuclide++++ takes advantage of the DDEP recommended data, accurate β\beta-emitting spectra calculation and detailed description of the atomic rearrangement. This module can be useful in many applications, especially those involving radioactive sources. The reliability of the module was verified through comparisons with a while chosen radionuclides

    Determination of X- and gamma-ray emission intensities in the decay of 131 I

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    20th International Conference on Radionuclide Metrology and its Applications (ICRM), organized by TU Wien, 8-12 June 2015 ,Vienna, Austria.International audienceThe activity per unit mass of an iodine-131 solution was absolutely standardized by both the 4 pi beta-gamma coincidence method and the 4 pi gamma counting technique. The calibrated solution was used to prepare point sources after a preliminary deposit of AgNO3 to prevent the loss of volatile iodine. Relative and absolute photon emission intensities of 15 sgamma-rays and those of the two K X-rays of xenon were determined by gamma-ray spectrometry, with relative uncertainties of 0.8% for the three main emissions
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