Abstract
The present work is focused on the characterization of a
Timepix3 (TPX3) based test system for the identification of
particles produced by the complex decay chain of
222
Rn. The
detector ...used is composed of a pixelated Cadmium Telluride (CdTe)
semiconductor (500 μm thick) bump-bonded on an ASIC TPX3
chip. Measurements were carried out at the NIXT Laboratory (ENEA
Frascati) using radioactive sources and exploiting the presence of
natural radon gas by collecting its decay products on the sensor
surface. Estimation of the radon gas risk is one of the most
important problems in radiation protection and has stimulated
further development of new advanced methods suitable for detecting
this gas in confined environments. A study of the spatial uniformity
and high energy calibration is also presented and an improved
cluster analysis is introduced. The performance highlighted in this
study will allow a detailed and faster analysis of the radon
products and may have an important impact on the environmental
radioprotection applications. This paper describes the application
and use of this test system to identify the different decay
signatures and follow the temporal evolution of the Radon decay
chain.
A pixelated 2-D detector combining chemical-vapor-deposited diamond and the Timepix3 chip ("Diamondpix") is presented. Its conceptual design with a brief description of the Timepix3 chip acquisition ...modes is outlined. The performance has been tested with fluorescence X-rays, fast neutrons, and electron beam. A first energy calibration has been obtained with X-rays and compared with an equivalent silicon Timepix3 detector. Measurements on fast neutrons and other radioactive source demonstrated a good gamma/neutron rejection capability. Moreover, Diamondpix has been exposed to a beam of ultrarelativistic electrons showing that it can act as a very powerful monitor of beam position, measuring simultaneously the charge released inside the detector and the time of arrival (ToA) of the particles by reconstructing the time profile of the beam bunches. Finally, high-intensity measurements show some delayed signals probably related to the trap defects inside the diamond. The first study of their spatial distribution correlated with the measurements of the charge released inside the diamond and ToA is also discussed.
The particular physics of Laser Produced Plasmas (LPP) needs some diagnostic requirements. Specifically, the X-ray monitoring of the plasma is known to be difficult since typically X-ray emissions ...are concentrated in bursts from a few tens of ps to few ns, based on the power and pulse time width of the laser. Therefore, the energy measurement of the radiation coming from a single experimental run is basically unfeasible using conventional techniques. Additional particles can be produced from LPP experiments, especially high energy gamma photons and electrons. As a case study in recent experiments, carried out on VEGA-2 laser facility (CLPU, Salamanca, Spain), the aim was to produce neutrons through photonuclear reactions on different types of solid targets. We have used the Timepix3 chip, in a “side-on” configuration, in order to produce a quick estimate of the gamma photons energy involved in the reactions. This detector, based on silicon, is realized with a single chip of 256 × 256 pixels bump-bonded with a 14 mm × 14 mm × 300 μm silicon layer. Interaction of gammas with the detector in this configuration produces some characteristic clusters of pixels and, for each cluster, a variety of physical and morphological parameters can be defined. Based on some of these parameters, we have characterized the detector response using some known laboratory gamma sources and the related Geant4 simulations. This allows quick energy discrimination for the gamma photons coming from different experimental runs.
This paper introduces a novel architecture for optimizing radiation shielding using a genetic algorithm with dynamic penalties and a custom parallel computing architecture. A practical example ...focuses on minimizing the Total Ionizing Dose for a silicon slab, considering only the layer number and the total thickness (additional constraints, e.g., cost and density, can be easily added). Genetic algorithm coupled with Geant4 simulations in a custom parallel computing architecture demonstrates convergence for the Total Ionizing Dose values. To address genetic algorithm issues (premature convergence, not perfectly fitted search parameters), a Total Ionizing Dose Database Vault object was introduced to enhance search speed (data persistence) and to preserve all solutions’ details independently. The Total Ionizing Dose Database Vault analysis highlights boron carbide as the best material for the first layer for neutron shielding and high-Z material (e.g., Tungsten) for the last layers to stop secondary gammas. A validation point between Geant4 and MCNP was conducted for specific simulation conditions. The advantages of the custom parallel computing architecture introduced here, are discussed in terms of resilience, scalability, autonomy, flexibility, and efficiency, with the benefit of saving computational time. The proposed genetic algorithm-based approach optimizes radiation shielding materials and configurations efficiently benefiting space exploration, medical devices, nuclear facilities, radioactive sources, and radiogenic devices.
The resistance of melanoma to current treatment modalities represents a major obstacle for durable therapeutic response, and thus the elucidation of mechanisms of resistance is urgently needed. The ...crucial functions of activating transcription factor-2 (ATF2) in the development and therapeutic resistance of melanoma have been previously reported, although the precise underlying mechanisms remain unclear. Here, we report a protein kinase C-ɛ (PKCɛ)- and ATF2-mediated mechanism that facilitates resistance by transcriptionally repressing the expression of interferon-β1 (IFNβ1) and downstream type-I IFN signaling that is otherwise induced upon exposure to chemotherapy. Treatment of early-stage melanomas expressing low levels of PKCɛ with chemotherapies relieves ATF2-mediated transcriptional repression of IFNβ1, resulting in impaired S-phase progression, a senescence-like phenotype and increased cell death. This response is lost in late-stage metastatic melanomas expressing high levels of PKCɛ. Notably, nuclear ATF2 and low expression of IFNβ1 in melanoma tumor samples correlates with poor patient responsiveness to biochemotherapy or neoadjuvant IFN-α2a. Conversely, cytosolic ATF2 and induction of IFNβ1 coincides with therapeutic responsiveness. Collectively, we identify an IFNβ1-dependent, cell-autonomous mechanism that contributes to the therapeutic resistance of melanoma via the PKCɛ-ATF2 regulatory axis.
GEM-based thermal neutron beam monitors for spallation sources Croci, G.; Claps, G.; Caniello, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2013, Letnik:
732
Journal Article
Recenzirano
The development of new large area and high flux thermal neutron detectors for future neutron spallation sources, like the European Spallation Source (ESS) is motivated by the problem of 3He shortage. ...In the framework of the development of ESS, GEM (Gas Electron Multiplier) is one of the detector technologies that are being explored as thermal neutron sensors. A first prototype of GEM-based thermal neutron beam monitor (bGEM) has been built during 2012. The bGEM is a triple GEM gaseous detector equipped with an aluminum cathode coated by 1μm thick B4C layer used to convert thermal neutrons to charged particles through the 10B(n,7Li)α nuclear reaction. This paper describes the results obtained by testing a bGEM detector at the ISIS spallation source on the VESUVIO beamline. Beam profiles (FWHMx=31mm and FWHMy=36mm), bGEM thermal neutron counting efficiency (≈1%), detector stability (3.45%) and the time-of-flight spectrum of the beam were successfully measured. This prototype represents the first step towards the development of thermal neutrons detectors with efficiency larger than 50% as alternatives to 3He-based gaseous detectors.
Thermal neutron detection plays a crucial role in numerous scientific and technical applications such as nuclear reactor physics, particle accelerators, radiotherapy, materials analysis and space ...exploration. There are several challenges associated with the accurate identification and quantification of thermal neutrons. The present work proposes a detailed characterization of a Timepix3 (TPX3) detector equipped with a Lithium Fluoride (
6
LiF) converter in order to study its response to thermal neutrons that are identified through the
6
Li(n,
α
)
3
H reaction. The TPX3-based test system has been installed at the HOTNES facility in ENEA and the analysis highlighted its excellent performance showing high effectiveness in the identification of neutrons through morphological analysis of tracks produced by alpha and triton particles, after accurate discrimination from the gamma background. With the use of Monte Carlo simulations, it has been demonstrated that the main contribution is due to tritons and its signal can be used effectively in the identification of thermal neutrons obtaining an efficiency of 0.9 % for 25 meV neutrons. This allows the TPX3 to have important applications as an environmental monitor for thermal neutrons. This monitoring system can be simply realized and is easy to manage because of its compact size and its digital acquisition that allows a real-time analysis.
nGEM fast neutron detectors for beam diagnostics Croci, G.; Claps, G.; Cavenago, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2013, Letnik:
720
Journal Article
Recenzirano
Fast neutron detectors with a sub-millimetric space resolution are required in order to qualify neutron beams in applications related to magnetically-controlled nuclear fusion plasmas and to ...spallation sources. A nGEM detector has been developed for the CNESM diagnostic system of the SPIDER NBI prototype for ITER and as beam monitor for fast neutrons lines at spallation sources. The nGEM is a triple GEM gaseous detector equipped with polypropylene and polyethylene layers used to convert fast neutrons into recoil protons through the elastic scattering process. This paper describes the results obtained by testing a nGEM detector at the ISIS spallation source on the VESUVIO beam line. Beam profiles (σx=14.35mm, σy=15.75mm), nGEM counting efficiency (around 10-4 for 3MeV<En<15MeV), detector stability (≈4.5%) and the effect of filtering the beam with different type of materials were successfully measured. The x beam profile was compared to the one measured by a single crystal diamond detector. Finally, the efficiency of the detector was simulated exploiting the GEANT4 tool.
A study of crystal assisted collimation has been continued at the CERN SPS for different energies of stored beams using 120 GeV/c and 270 GeV/c protons and Pb ions with 270 GeV/c per charge. A bent ...silicon crystal used as a primary collimator deflected halo particles using channeling and directing them into the tungsten absorber. A strong correlation of the beam losses in the crystal and off-momentum halo intensity measured in the first high dispersion (HD) area downstream was observed. In channeling conditions, the beam loss rate induced by inelastic interactions of particles with nuclei is significantly reduced in comparison with the non-oriented crystal. A maximal reduction of beam losses in the crystal larger than 20 was observed with 270 GeV/c protons. The off-momentum halo intensity measured in the HD area was also strongly reduced in channeling conditions. The reduction coefficient was larger than 7 for the case of Pb ions. A strong loss reduction was also detected in regions of the SPS ring far from the collimation area. It was shown by simulations that the miscut angle between the crystal surface and its crystallographic planes doubled the beam losses in the aligned crystal.
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