Fast-neutron induced background in LaBr3:Ce detectors

The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce crystal to incident neutrons has been measured in the energy range En = 2-12 MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6 MeV with pulsed proton beams. Using the time-of-flight information between target and detector, energy spectra of the LaBr3:Ce detector resulting from fast neutron interactions have been obtained at 4 different neutron energies. Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured in a nearby Ge detector at the lowest proton beam energy. In addition, we obtained data for neutron irradiation of a large-volume high-purity Ge detector and of a NE-213 liquid scintillator detector, both serving as monitor detectors in the experiment. Monte-Carlo type simulations for neutron interactions in the liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and compared with measured data. Good agreement being obtained with the data, we present the results of simulations to predict the response of LaBr3:Ce detectors for a range of crystal sizes to neutron irradiation in the energy range En = 0.5-10 MeVComment: 28 pages, 10 figures, 4 Table

Development of a 3D-Imaging Calorimeter in Lanthanum Bromide for Gamma-Ray Space Astronomy

International audienceGamma-ray astronomy, in the energy range from 0.1 up to 100 MeV, holds many understudied questions connected with stellar nucleosynthesis, the Sun, neutron stars and black holes. To access the physics behind, a significant increase in instrumental sensitivity, compared to previous missions, e.g. NASA/CGRO and ESA/INTEGRAL, is needed. One of the promising concepts is an Advanced Compton telescope. It has good discovery potential and is able to avoid problems like high background in the MeV energy band. Under the project of creating a prototype of such instrument, we study cerium-doped lantanum(III) bromide (LaBr3:Ce) inorganic scintillator. Its internal qualities, especially good energy resolution and radiation tolerance, make it a smart choice for the calorimeter part of a future spaceborne telescope. At CSNSM Orsay, we have created a new detection module from 5x5 cm2 area and 1 cm thick LaBr3:Ce crystal scintillator coupled to 64 channel multi-anode photomultiplier and read out by the ASIC MAROC, used previously for the luminometer of the ATLAS detector (CERN). Characterization, thorough measurements with various radioactive sources, as well as, single photoelectron detection have been done. Furthermore, we made a comparison with the detailed GEANT4 based simulation including tracking of the optical photons. Finally, we have studied the 3D reconstruction of the first interaction point of incident gamma-ray, utilizing a neural network algorithm. This spatial position resolution plays a crucial part in the future implementations and together with the other measured properties makes our detector module very interesting for the next generation of space telescopes operating in the MeV range

Application of artificial neural network in 3D imaging with lanthanum bromide calorimeter

International audienceGamma-ray astronomy in the energy range from 0.1 up to 100 MeV holds many understudied questions connected with e.g. stellar nucleosynthesis, the active Sun, neutron stars and black holes. To access the physics behind, a significant improvement in detection sensitivity is needed compared to previous missions, e.g. CGRO and INTEGRAL. One of the promising concepts for a future gamma-ray mission is an Advanced Compton Telescope. Under the project of creating a prototype of such instrument, we study the perspectives of using a novel inorganic scintillator as a calorimeter part. Modern inorganic crystal or ceramics scintillators are constantly improving on qualities such as energy resolution and radiation hardness, and this makes them a smart choice for a new space-borne telescope. At CSNSM Orsay, we have assembled a detection module from a View the MathML source5×5cm2 area and 1 cm thick, cerium-doped lanthanum (III) bromide (LaBr3:Ce) inorganic scintillator coupled to a 64 channel multi-anode photomultiplier. The readout of the PMT signals is carried out with the ASIC MAROC, used previously for the luminometer of the ATLAS detector (CERN). Characterization, thorough measurements with various radioactive sources, as well as, single photoelectron detection have been done. Furthermore, we made a comparison of measurements with a detailed GEANT4-based simulation which includes tracking of the optical photons. Finally, we have studied the 3D reconstruction of the first interaction point of incident gamma rays, utilizing a neural network algorithm. This spatial position resolution plays a crucial part in the future implementations and, together with the other measured properties, it makes our detector module very interesting for the next generation of space telescopes operating in the MeV range

PACT: a sensitive 100 keV-10 MeV all sky Pairs and Compton Telescope

International audiencePACT is a Pair And Compton Telescope that aims to make a sensitive survey of the gamma-ray sky between 100 keV and 100 MeV. It will be devoted to the detection of radioactivity lines from present and past supernova explosions, the observation of thousands of new blazars, and the study of polarized radiations from gamma-ray bursts, pulsars and accreting black holes. It will reach a sensitivity of one to two orders of magnitude lower than COMPTEL/CGRO (e.g. about 50 times lower for the broad-band, survey sensitivity at 1 MeV after 5 years). The concept of PACT will be proposed for the AstroMeV mission in the framework of the M4 ESA Call. It is based upon three main components: a silicon-based gamma-ray tracker, a crystal-based calorimeter (e.g. CeBr3:Sr), and an anticoincidence detector made of plastic scintillator panels. Prototypes of these detector planes are currently tested in the laboratories

gamma ray emission in alpha particle interactions with C, Mg, Si, and Fe at Ealpa 50 90 MeV

Nuclear deexcitation lines are regularly observed in the amp; 947; ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and amp; 945; particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross section data for the amp; 947; ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the amp; 947; ray emission in interactions of amp; 945; particle beams of E amp; 945; 50 90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz Zentrum Berlin. Setups of three high purity Ge detectors and one LaBr3 Ce detector have been employed to detect the amp; 947; rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub ns wide pulses allowed the separation of beam induced prompt amp; 947; ray emission from the targets from other amp; 947; rays and neutron induced background. amp; 947; ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, 12C, 24Mg, 28Si, 56Fe, there are now measured cross section data from reaction threshold to E amp; 945; 90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross section compilation for strong amp; 947; ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross section determinations at accelerator laboratories for the establishment of an accurate cross section data base in a wide projectile energy rang

Gamma-ray emission in alpha-particle reactions with C, Mg, Si, Fe

International audienceCross sections for the strongest gamma-ray emission lines produced in alpha-particle reactions with C, Mg, Si, Fe have been measured in the range E_alpha = 50 - 90 MeV at the center for proton therapy at the Helmholtz-Zentrum Berlin. Data for more than 60 different gamma-ray lines were determined, with particular efforts for lines that are in cross section compilations/evaluations with astrophysical purpose, and where data exist at lower projectile energies. The data are compared with predictions of a modern nuclear reaction code and cross-section curves of the latest evaluation for gamma-ray line emission in accelerated-particle interactions in solar flares

γ\gamma-ray emission in α\alpha-particle interactions with C, Mg, Si, and Fe at Eα=50–90{E}_{\alpha}=50\text{--}90 MeV

International audienceNuclear deexcitation lines are regularly observed in the γ-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and α particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the γ-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the γ-ray emission in interactions of α-particle beams of Eα=50–90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one LaBr3:Ce detector have been employed to detect the γ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt γ-ray emission from the targets from other γ rays and neutron-induced background. γ-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, C12, Mg24, Si28, Fe56, there are now measured cross-section data from reaction threshold to Eα=90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong γ-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range

Characterization of LaBr3:Ce and CeBr3 calorimeter modules for 3D imaging in gamma-ray astronomy

International audienceFor the purpose of future space instrumentation for gamma-ray astronomy, we developed a small prototype of a Compton telescope and studied novel detector modules aimed for Compton imaging. We assembled and tested 2 modules, one with a cerium-doped lanthanum(111) bromide (LaBr3:Ce) crystal and the other with cerium(111) bromide (CeBr3). Both crystals measure 5 x 5 cm(2) in area and are 1 cm thick. They are coupled to and read out by 64-channel multi-anode PMTS. Our goals are to obtain the best possible energy resolution and position resolution in 3D on the first impact of an incident gamma-ray within the detector. Both information are vital for successful reconstruction of a Compton image with the telescope prototype. We developed a test bench to experimentally study both modules and have utilized a customized readout electronics and data acquisition system. Furthermore, we have written a detailed Geant4 simulation of the experiment, and utilize simulated data to train an Artificial Neural Network (ANN) algorithm to create a simplified 3D impact position reconstruction method. We give experimental test results obtained by both modules and present detailed parametrization and results from the Geant4 simulation and from the ANN. We compare and discuss the performance of the modules and conclude by giving a brief overview of the future prospects for using such modules in gamma-ray astronomy. (C) 2016 Elsevier B.V. All rights reserved