MODES SNM is a collaborative project (funded under the FP7 - Security program), aimed at developing a
prototype for a mobile, modular detection system for radioactive and Special Nuclear Materials (SNM). To
maximize the detection capability for SNM, the prototype will combine detectors for fast and thermal neutrons, as well as for gamma-rays. The key detector technology in the development is high pressure scintillation cells filled with noble gases, as recently developed by ARKTIS. The project started officially at the beginning of 2012, for a duration of 30 months. The goal of the project is to deliver a fully integrated and field tested prototype of a modular mobile system capable of passively detecting weak or shielded radioactive sources with accuracy higher than currently available systems. We will present the status of the project, preliminary results and future prospects.
Elena Aprile, Alessandro Curioni, Karl-Ludwig Giboni, Masanori Kobayashi, Uwe Oberlack, Edward Chupp, Philip Dunphy, Tadayoshi Doke, Jun Kikuchi, Sandro Ventura
LXeGRIT is the first prototype of a novel concept of Compton telescope, based on the complete 3D reconstruction of the sequence of interactions of individual γ-rays in one position sensitive detector. This balloon-borne telescope consists of an unshielded time projection chamber with an active volume of 400 cm2 × 7 cm filled with high purity liquid xenon. Four VUV PMTs detect the fast xenon scintillation light signal, providing the event trigger. 124 wires and 4 anodes detect the ionization signals, providing the event spatial coordinates and total energy. In the period 1999-2001, LXeGRIT has been extensively tested both in the laboratory and at balloon altitude, and its response in the MeV region has been thoroughly characterized. Here we summarize some of the results on pre-flight calibration, even reconstruction techniques, and performance during a 27 hour balloon flight on October 4-5. We further present briefly the on-going efforts directed to improve the performance of this prototype towards the requirements for a base module of a next-generation Compton telescope.
Alessandro Curioni, Elena Aprile, Karl-Ludwig Giboni, Masanori Kobayashi, Uwe Oberlack, Edward Chupp, Philip Dunphy, Tadayoshi Doke, Jun Kikuchi, Sandro Ventura
KEYWORDS: Data acquisition, Monte Carlo methods, Atmospheric particles, Sensors, Particles, Atmospheric modeling, Telescopes, Energy efficiency, Space telescopes, Liquids
LXeGRIT is the first prototype of a novel Compton telescope for MeV γ-ray astrophysics based on a Liquid Xenon Time Projection Chamber (LXeTPC), sensitive in the energy band of 0.15-10 MeV. In this homogeneous, 3D position sensitive detector, γ-rays with at least two interactions in the sensitive volume of 2800 cm3, are imaged as in a standard Compton telescope. γ-rays with a single interaction cannot be imaged and constitute a background which can be easily identified and rejected. Charged particles and localized β-particles background is also easily suppressed based on the TPC localization capability with millimeter resolution. A measurement of the total γ-ray background rate in near space conditions and the background rejection power of the LXeTPC was a primary goal of the LXeGRIT balloon flight program. We present here a preliminary analysis addressing this question, based on balloon flight data acquired during the Oct 4-5, 2000 LXeGRIT balloon flight from Ft. Sumner, NM. In this long duration balloon experiment, the LXeGRIT TPC was not surrounded by any γ-ray or charged particle shield. Single site events and charged particles were mostly rejcted on-line at the first and second trigger level. The remaining count rate of single-site γ-ray events, at an average atmospheric depth of 3.2 g cm-2, is consistent with that expected from atmospheric and diffuse γ-ray background, taking into account the instrument mass model and response.
LXeGRIT is a balloon-borne Compton telescope employing a large volume liquid xenon time projection chamber (LXe-TPC) as the central (gamma) -ray detector. It is designed to image (gamma) - rays in the energy range of approximately 200 keV to 20 MeV, with an angular resolution of about 3 degrees (1 sigma) at 2 MeV, within a field-of-view (FOV) of about 1 sr. The detector's energy and three-dimensional spatial resolution as measured during pre-flight calibration experiments, are (Delta) E1xe/E equals 8.8% (root)1MeV/E and < 1 mm RMS, respectively. The detection efficiency for Compton events varies between 1.5% and 4% depending on energy and event selection. We describe the instrument as flown on May 7, 1999 and review its overall performance at balloon altitude. The launch occurred at 13:26:54 UT from Ft. Sumner, New Mexico and the flight was terminated about 9 hours later. The Crab was in the instrument FOV for a few hours. Analysis of these data is in progress.
LXeGRIT is a balloon-borne Compton telescope based on a liquid xenon time projection chamber (LXeTPC) for imaging cosmic (gamma) -rays in the energy band of 0.2 - 20 MeV. The detector, with 400 cm2 area and 7 cm drift gap, is filled with high purity LXe. Both ionization and scintillation light signal are detected to measure the energy deposits and the three spatial coordinates of individual (gamma) -ray interactions within the sensitive volume. The TPC has been characterized with repeated measurements of its spectral and Compton imaging response to (gamma) -rays from radioactive sources such as 22Na, 137Cs, 88Y and Am-Be. The detector shows a linear response to g-rays in the energy range 511 keV - 4.4 MeV, with an energy resolution (FWHM) of (Delta) E/E equals 8.8% (root)1MeV/E. Compton imaging of 88Y (gamma) -ray events with two detected interactions is consistent with an angular resolution of approximately 3 degrees (RMS) at 1.8 MeV.
KEYWORDS: Sensors, Monte Carlo methods, Reconstruction algorithms, Xenon, Telescopes, Compton scattering, Liquids, Gamma ray imaging, Detection and tracking algorithms, Kinematics
The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon born experiment sensitive to (gamma) -rays in the energy band of 0.2 - 20 MeV. The main detector is a time projection chamber filled with high purity liquid xenon (LXeTPC), in which the three-dimensional location and energy deposit of individual (gamma) -ray interactions are accurately measured in one homogeneous volume. To determine the (gamma) - ray initial direction (Compton imaging), as well as to reject background, the correct sequence of interactions has to be determined. Here we report the development and optimization of an algorithm to reconstruct the Compton scattering sequence and show its performance on Monte Carlo events and LXeGRIT data.
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