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A mm <sup>3</sup> Fiber-Coupled Scintillator for In-Core Thermal Neutron Detection in CROCUS
摘要： The article presents the development, characterization and in-core testing of a miniature neutron detector for the investigation of highly localized in-core neutronics effects in the zero-power reactor CROCUS, operated at école Polytechnique fédérale de Lausanne (EPFL), Switzerland. A ZnS:6LiF screen, mixing inorganic scintillator and neutron converter, with a surface of 1 mm2 and a thickness of 0.2 mm was coupled with a silicon photomultiplier (SiPM) via a 10-m optical fiber. Analog read-out electronics were adopted in this prototype version to process the SiPM output signal. A first campaign was carried out to assess the detection system capabilities in terms of neutron detection and counting in mixed neutron-gamma radiation fields. The miniature detector was thoroughly characterized with a Pu-Be source installed in the CARROUSEL facility, and subsequently tested inside a control rod guide tube of the CROCUS reactor in different reactor conditions, i.e. at shutdown, startup and critical. The detector shows a linear response with the reactor power increase up to 6.5 W (i.e. around 108 cm-2·s-1 total neutron flux) and excellent neutron counting capabilities when compared to other localized detection systems available in CROCUS, such as miniature fission chambers and sCVD diamond detectors. In addition, the exposure of the miniature detector to a 60Co source with an activity of ～250 GBq, combined with the computation of the gamma flux in CROCUS with the Serpent 2 Monte Carlo code, confirmed the gamma insensitivity of the system in a mixed neutron-gamma field.
关键词： miniature neutron detector,CROCUS zero-power reactor,optical fiber devices,in-core neutron detectors,miniature scintillator devices
更新于2025-09-23 15:21:01
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Temperature dependence of scintillation responses in rare-earth-ions-doped LiCaAlF6 single crystals
摘要： We have tested high-temperature responses of prototype neutron detectors equipping Ce-doped lithium silicate glass (GS20), LiCaAlF6:Ce, LiCaAlF6:Eu, LiCaAlF6:Ce, Na, and LiCaAlF6:Eu, Na. These detectors were prepared by coupling of the scintillators to a photomultiplier tube (PMT) for high-temperature environments (R1288, Hamamatsu). In the pulse height spectra under thermal neutron irradiation in the temperature range from 25°C to 150°C, peak heights of all the samples decreased with increasing temperatures. The decreasing rates for the peak heights of LiCaAlF6 scintillators were lower than that of GS20. The LiCaAlF6 scintillators can be used in the temperature range from 25°C to 150°C.
关键词： fluoride,scintillator,neutron,single crystal
更新于2025-09-23 15:21:01
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Tests under irradiation of optical fibers and cables devoted to corium monitoring in case of severe accident in a Nuclear Power Plant
摘要： The DISCOMS project, which stands for “DIstributed Sensing for COrium Monitoring and Safety”, considers the potential of distributed sensing technologies, based on remote instrumentations and Optical Fiber Sensing cables embedded into the concrete floor under the reactor vessel, to monitor the status of this third barrier of confinement. This paper focuses on the selection and testing of singlemode (SM) optical fibers with limited RIA (Radiation Induced Attenuation) to be compliant with remote distributed instruments optical budgets, the ionizing radiation doses to sustain, and their reduction provided by the concrete basemat shielding. The tests aimed at exposing these fibers and the corresponding sensitive optical cables, to the irradiation doses expected during the normal operation of the reactor (up to 60 years for the European Pressurized Reactor), followed by a severe accident. Several gamma and mixed (neutron-gamma) irradiations were performed at CEA Saclay facilities: POSé?DON irradiator and ISIS reactor, up to a gamma cumulated dose of about 2 MGy and fast neutron fluence (E > 1 MeV) of 6 x 1015 n/cm2. The first gamma test permitted to assess the RIA at various optical wavelengths, and to select three radiation tolerant singlemode fibers (RIA < 5 dB/100 m, at 1550 nm operating wavelength). The second one was performed on voluminous strands of sensitive cables encapsulating selected optical fibers, up to approximately the same accumulated dose, at two temperatures: 30°C and 80°C. A significant increase of the RIA, without any saturation tendency, appeared for fibers inserted into cables, correlated with the increase of the hydroxyl attenuation peak at 1380 nm. Molecular hydrogen generated by the radiolysis of compounds of the cable is at the origin of this phenomenon. A third gamma irradiation run permitted to measure the radiolytic hydrogen production yield of some compounds of a dedicated temperature cable sample. The efficiency of a carbon coating layer over the silica cladding, acting as a barrier against hydrogen diffusion, was also successfully confirmed. Finally, the efficiency of this carbon coating layer has also been tested under neutron irradiation, then qualified as a protection barrier against hydrogen diffusion in the optical fiber cores.
关键词： carbon coating layer,radiation effects,optical fibers,hydrogen diffusion,gamma,radiolysis,rad-hard optical fiber,neutron,distributed measurement
更新于2025-09-23 15:21:01
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Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide
摘要： Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.
关键词： solar cells,inelastic neutron spectroscopy,lattice dynamics,hybrid perovskite,thermal conductivity
更新于2025-09-23 15:21:01
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Growth and characterization of Cs2LiLaCl6:Ce single crystals
摘要： Cs2LiLaCl6:Ce (CLLC) is a promising scintillator material for dual gamma/neutron detection. The vertical Bridgman technique, with a LiCl-rich melt and high axial temperature gradient, was used to grow transparent CLLC crystals for the first time. The stoichiometric CLLC powder melted incongruently with a melting range of 343-442 oC. Additional LiCl suppressed the formation of Cs3LaCl6 second phase, which was identified in crystals grown from stoichiometric melts. CLLC was found to have a Stokes shift of about 1358 cm-1 and a photoluminescence decay time of 34.6 ns. Direct electron-hole capture by Ce3+ ions and core-valence luminescence were the main contributors to the X-ray induced luminescence spectrum. A 9×8 mm3 cylinder of the CLLC crystal with 0.5at% Ce had an energy resolution of 7.1% at 662 keV. The scintillation decay times of the CLLC crystal excited with 662 keV gammas were 79 ns and 1491 ns.
关键词： A1. Absorption spectra,B2. Scintillator materials,B1. Cs2LiLaCl6:Ce,B3. Neutron detection,A2. Bridgman technique
更新于2025-09-23 15:21:01
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Crystal structure and ferroelectric polarization of tetragonal (Bi <sub/>1/2</sub> Na <sub/>1/2</sub> )TiO <sub/>3</sub> –12BaTiO <sub/>3</sub>
摘要： We have investigated the crystal structure and ferroelectric polarization of (Bi1/2Na1/2)TiO3–12%BaTiO3 by high-resolution neutron powder di?raction Rietveld analysis and density-functional theory calculations. It is revealed that the sample has a ferroelectric distortion in tetragonal P4mm symmetry along with a large tetragonality c/a of 1.022. The A- and B-site atoms exhibit a cooperative o?-center displacement along the polar c-axis, which results in a large spontaneous polarization of 54 μC/cm2.
关键词： crystal structure,neutron powder diffraction,tetragonal (Bi1/2Na1/2)TiO3–12BaTiO3,density-functional theory,ferroelectric polarization
更新于2025-09-23 15:21:01
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LiF based scintillation neutron detector at high counting rates
摘要： In this work we revisit the problem of the restricted count rate capability of thermal neutron detectors utilizing the ZnS scintillator. The effect of the long afterglow of the scintillator on the detector performance at high counting rates is studied. A count rate capability substantially above values currently regarded as feasible is demonstrated.
关键词： thermal neutron detector,SiPM,ZnS:6LiF scintillator,count rate capability
更新于2025-09-23 15:21:01
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Efficiency enhancement of thermonuclear DD reaction in femtosecond laser plasma with the use of structured low-average-density targets
摘要： An increase in the yield of fast neutrons is experimentally demonstrated by exciting a nuclear DD reaction in the interaction of a relativistically intense (over 1018 W cm–2) ultrashort laser pulse with a deuterated low-average-density target volume-structured at the wavelength scale. It is shown that decreasing the average target density from 0.78 to 0.35 g cm–3 doubles the neutron flux, which reaches 7 ′ 104 particles per 1 J of input energy. The effect may be associated with an increase in the number of accelerated deuterium ions due to the three dimensional expansion of individual elements of the target structure.
关键词： structured target,relativistic laser plasma,thermonuclear DD reaction,neutron source
更新于2025-09-23 15:19:57
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LIGO and Gravitational Waves, III: Nobel Lecture, December 8, 2017
摘要： The ?rst observation of gravitational waves, by LIGO on September 14, 2015, was the culmination of a near half century e?ort by (cid:2)1200 scientists and engineers of the LIGO/Virgo Collaboration. It was also the remarkable beginning of a whole new way to observe the universe: gravitational astronomy.
关键词： neutron stars,LIGO,black holes,gravitational astronomy,gravitational waves
更新于2025-09-23 15:19:57
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Polarization analysis for magnetic field imaging at RADEN in J-PARC/MLF
摘要： Polarized neutron imaging is an attractive method for visualizing magnetic fields in a bulk object or in free space. In this technique polarization of neutrons transmitted through a sample is analyzed position by position to produce an image of the polarization distribution. In particular, the combination of three-dimensional spin analysis and the use of a pulsed neutron beam is very effective for the quantitative evaluation of both field strength and direction by means of the analysis of the wavelength dependent polarization vector. Recently a new imaging instrument “RADEN” has been constructed at the beam line of BL22 of the Materials and Life Science Experimental Facility (MLF) at J-PARC, which is dedicated to energy-resolved neutron imaging experiments. We have designed a polarization analysis apparatus for magnetic field imaging at the RADEN instrument and have evaluated its performance.
关键词： polarization analysis,Polarized neutron imaging,RADEN,J-PARC/MLF,magnetic field imaging
更新于2025-09-23 15:19:57