Deep Learning reconstruction with uncertainty estimation for γ\gamma photon interaction in fast scintillator detectors

This article presents a physics-informed deep learning method for the quantitative estimation of the spatial coordinates of gamma interactions within a monolithic scintillator, with a focus on Positron Emission Tomography (PET) imaging. A Density Neural Network approach is designed to estimate the 2-dimensional gamma photon interaction coordinates in a fast lead tungstate (PbWO4) monolithic scintillator detector. We introduce a custom loss function to estimate the inherent uncertainties associated with the reconstruction process and to incorporate the physical constraints of the detector. This unique combination allows for more robust and reliable position estimations and the obtained results demonstrate the effectiveness of the proposed approach and highlights the significant benefits of the uncertainties estimation. We discuss its potential impact on improving PET imaging quality and show how the results can be used to improve the exploitation of the model, to bring benefits to the application and how to evaluate the validity of the given prediction and the associated uncertainties. Importantly, our proposed methodology extends beyond this specific use case, as it can be generalized to other applications beyond PET imaging.Comment: Submitted to Artificial Intelligenc

Detector energy calibration in the STEREO neutrino experiment

International audienceThe STEREO experiment was developed to investigate the hypothesis of a light sterile neutrino arising from the observed discrepancy between measured reactor antineutrino fluxes and revised flux predictions, known as the Reactor Antineutrino Anomaly. The detector is located at 10 m from the compact nuclear reactor core of the Institut Laue- Langevin. The segmentation of the detector target in 6 cells allows measuring the neutrino energy spectrum at different baselines. Antineutrino interactions are detected by the inverse b-decay reaction in Gd-loaded liquid scintillator. STEREO started taking data in November 2016. About 70 days of data have been recorded during reactor operation and 25 days during reactor shut down. STEREO plans to record 150 days more in 2018. To perform a correct energy reconstruction of neutrino events, the detector energy response must be determined accurately. Different radioactive gamma-ray sources, from 0:5 to 4:4 MeV, are used to constrain the non-linearity of the scintillator response. Calibration data analysis provides the relation between the charge detected by the photomultipliers and the true deposited gamma energy obtained by simulations. The main goal is to reconstruct the energy scale within a 2% uncertainty

Detection of 1 keV - 1 MeV energy neutrons by means of new technique applied to neutron reactor dosimetry

La dosimétrie neutronique en réacteur se base sur l'analyse de l'activité de dosimètres irradiés, dont certains isotopes-cibles sont l'objet de réactions d'activation ou de fission sous l'effet des neutrons. Les différentes cibles sont sensibles aux neutrons d’énergie particulière. La caractérisation des spectres neutroniques est bien établie dans les domaines thermique, epithermique (Eneutron 1 MeV), mais il y a une absence de détecteur dans le domaine énergétique entre 1 keV et 1 MeV. Le travail de thèse a abouti sur un choix final: la capture (n, γ) sur les isotopes 92Zr et 94Zr, présents dans le zirconium naturel, pour former les isotopes 93Zr (stable) et 95Zr (radioactif). L'expérience ZIMA a été réalisée sur le réacteur OSIRIS pour démontrer la faisabilité de la méthode de détection proposée. Les analyses post-irradiation sont la spectrométrie γ et la spectrométrie de masse par accélérateur. Pour analyser les résultats expérimentaux, ZIMA a été simulée avec le code neutronique TRIPOLI-4 basé sur la méthode de Monte Carlo. Les rapports Calcul/Expérience présentés dans la thèse permettent de conclure que la détection neutronique (1 keV – 1 MeV) par capture de 94Zr et 92Zr donne des résultats probants. Les mesures obtenues sont exploitables.Reactor dosimetry goal is to reconstruct neutron spectrum in a particular reactor location. Today we can reconstruct with precision thermal (MeV) parts of neutron spectrum by using dosimeters with an adequate sensitivity. Nowadays there is no dosimeter for the intermediate energy region 1 keV - 1 MeV. Thus, the PhD goal is to select the 1 keV - 1 MeV sensible target-isotope and nuclear reaction and verify our solution by experimental irradiation. PhD final choice is for neutron capture reaction (n, γ) on 92Zr and 94Zr. Neutron irradiation produces 2 isotopes: 93Zr and 95Zr, stable and radioactive. Irradiation experiment was performed in OSIRIS reactor. Post-irradiation analyses of irradiated Zr samples are γ spectrometry and Accelerator Mass Spectrometry. In order to simulate irradiation experiment we performed calculation with neutron transport code TRIPOLI-4, based on Monte Carlo method. The goal of ZIMA (Zirconium Irradiation for Mass and Activity analysis) experiment was to prove the feasibility of 1 keV - 1 MeV neutron detection by (n,γ) capture on 92Zr and 94Zr under boron nitride filter. C/E ratios presented in this PhD allow us to conclude that activation of 94Zr and 92Zr gives us acceptable results

Deep Learning reconstruction with uncertainty estimation for γ photon interaction in fast scintillator detectors

International audienceThis article presents a physics-informed deep learning method for the quantitative estimationof the spatial coordinates of gamma interactions within a monolithic scintillator, with a focuson Positron Emission Tomography (PET) imaging. The authors propose a density neuralnetwork approach to estimate the 2-dimensional gamma photon interaction coordinates fora fast lead tungstate (PbWO$_4$) monolithic scintillator detector. This approach considersuncertainties on the estimated coordinates and accounts for physical constraints on thedetector. The results demonstrate the effectiveness of the proposed approach for accurateposition estimation and the benefits of the uncertainties estimation. The authors discuss itspotential impact on improving PET imaging quality and highlight the generalization of theproposed methodology for other applications

Deep Learning reconstruction with uncertainty estimation for γ\gamma photon interaction in fast scintillator detectors

International audienceThis article presents a physics-informed deep learning method for the quantitative estimation of the spatial coordinates of gamma interactions within a monolithic scintillator, with a focus on Positron Emission Tomography (PET) imaging. A Density Neural Network approach is designed to estimate the 2-dimensional gamma photon interaction coordinates in a fast lead tungstate (PbWO4) monolithic scintillator detector. We introduce a custom loss function to estimate the inherent uncertainties associated with the reconstruction process and to incorporate the physical constraints of the detector. This unique combination allows for more robust and reliable position estimations and the obtained results demonstrate the effectiveness of the proposed approach and highlights the significant benefits of the uncertainties estimation. We discuss its potential impact on improving PET imaging quality and show how the results can be used to improve the exploitation of the model, to bring benefits to the application and how to evaluate the validity of the given prediction and the associated uncertainties. Importantly, our proposed methodology extends beyond this specific use case, as it can be generalized to other applications beyond PET imaging

Search for light sterile neutrinos with the STEREO experiment

The stereo experiment is searching for a non-standard oscillation in the propagation of anti-neutrinos produced by a nuclear reactor which could be the sign for the existence of a sterile state of eV mass and the origin of the reactor anti-neutrino anomaly. In this paper, results from 66 days of reactor turned on and 138 days of reactor turned off are reported excluding large amplitude oscillations. A special focus is put on the data analysis and studies of correlated backgrounds. In particular the origin of the correlated background measured in reactor turned off periods is discussed. This background mainly originates from neutrons produced by cosmic radiation

Search for light sterile neutrinos with the STEREO experiment

International audienceThe stereo experiment is searching for a non-standard oscillation in the propagation of anti-neutrinos produced by a nuclear reactor which could be the sign for the existence of a sterile state of eV mass and the origin of the reactor anti-neutrino anomaly. In this paper, results from 66 days of reactor turned on and 138 days of reactor turned off are reported excluding large amplitude oscillations. A special focus is put on the data analysis and studies of correlated backgrounds. In particular the origin of the correlated background measured in reactor turned off periods is discussed. This background mainly originates from neutrons produced by cosmic radiation

Improved STEREO simulation with a new gamma ray spectrum of excited gadolinium isotopes using FIFRELIN

International audienceThe STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes,$^{155}$Gd and$^{157}$Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8MeV. The complex level schemes of$^{156}$Gd and$^{158}$Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd (n, $\gamma$ ) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user

First antineutrino energy spectrum from 235^{235}U fissions with the STEREO detector at ILL

International audienceThis article reports the measurement of the 235U-induced antineutrino spectrum shape by the Stereo experiment. 43 000 antineutrinos have been detected at about 10 m from the highly enriched core of the ILL reactor during 118 full days equivalent at nominal power. The measured inverse beta decay spectrum is unfolded to provide a pure 235U spectrum in antineutrino energy. A careful study of the unfolding procedure, including a cross-validation by an independent framework, has shown that no major biases are introduced by the method. A significant local distortion is found with respect to predictions around E ν ≃ 5.3 MeV. A Gaussian fit of this local excess leads to an amplitude of A = 12.1 ± 3.4% (3.5σ)

Improved Sterile Neutrino Constraints from the STEREO Experiment with 179 Days of Reactor-On Data

The STEREO experiment is a very short baseline reactor antineutrino experiment. It is designed to test the hypothesis of light sterile neutrinos being the cause of a deficit of the observed antineutrino interaction rate at short baselines with respect to the predicted rate, known as the Reactor Antineutrino Anomaly. The STEREO experiment measures the antineutrino energy spectrum in six identical detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this article, results from 179 days of reactor turned on and 235 days of reactor turned off are reported in unprecedented detail. The current results include improvements in the description of the optical model of the detector, the gamma-cascade after neutron captures by gadolinium, the treatment of backgrounds, and the statistical method of the oscillation analysis. Using a direct comparison between antineutrino interaction rates of all cells, independent of any flux prediction, we find the data compatible with the null oscillation hypothesis. The best-fit point of the Reactor Antineutrino Anomaly is rejected at more than 99.9% C.L