Detectable Flux Research Articles

Measurements of Low Optical Power with Cryostat-Based Predictable Quantum Efficient Detector at Liquid Nitrogen Temperature

Abstract We have validated optical power measurements with a Predictable Quantum Efficient Detector (PQED) at liquid nitrogen temperature (77 K) at low optical power from 130 fW to 3.3 pW. Two laser wavelengths at 514 nm and 785 nm were used. The lowest measured optical power corresponds to a photon flux of 0.5·106 photons per second (785 nm). The PQED’s responsivity is linear within the relative measurement uncertainties of 8% at 0.5·106 ph/s and 1.4% at 10·106 ph/s (95% confidence level), which enables the calibration of other low photon flux detectors directly against a primary standard of optical power.

Design and application of portable eddy current inspection device for thimble tubes of nuclear power plant

Abstract The Thimble tube is an important piece of equipment in the nuclear power plant; its role is to provide a neutron flux detector with a channel for the reactor fuel assembly. Eddy current detection is the main way to evaluate and track the wear of the thimble tube. In order to conduct more efficient detection of the thimble tube, this paper has carried out a series of studies on the mechanical device of the eddy current detection of the thimble tube and the software control system. The inspection system is compact, portable, and does not require an external power supply or gas source, making it easy to carry and operate. It is well-suited for promotion in various nuclear power plants.

Radiation Damage on Silicon Photomultipliers from Ionizing and Non-Ionizing Radiation of Low-Earth Orbit Operations.

Silicon Photomultipliers (SiPMs) are single photon detectors that gained increasing interest in many applications as an alternative to photomultiplier tubes. In the field of space experiments, where volume, weight and power consumption are a major constraint, their advantages like compactness, ruggedness, and their potential to achieve high quantum efficiency from UV to NIR makes them ideal candidates for spaceborne, low photon flux detectors. During space missions however, SiPMs are usually exposed to high levels of radiation, both ionizing and non-ionizing, which can deteriorate the performance of these detectors over time. The goal of this work is to compare process and layout variation of SiPMs in terms of their radiation damage effects to identify the features that helps reduce the deterioration of the performance and develop the next generation of more radiation-tolerant detectors. To do this, we used protons and X-rays to irradiate several Near Ultraviolet High-Density (NUV-HD) SiPMs with small areas (single microcell, 0.2 × 0.2 mm2 and 1 × 1 mm2) produced at Fondazione Bruno Kessler (FBK), Italy. We performed online current-voltage measurements right after each irradiation step, and a complete functional characterization before and after irradiation. We observed that the main contribution to performance degradation in space applications comes from proton damage in the form of an increase in primary dark count rate (DCR) proportional to the proton fluence and a reduction in activation energy. In this context, small active area devices show a lower DCR before and after irradiation, and we propose light or charge-focusing mechanisms as future developments for high-sensitivity radiation-tolerant detectors.

Критичність паливовмісних матеріалів в об'єкті "Укриття"

The article presents the results of the analysis of the validity of simplifications and assumptions accepted by researchers in the models of neutron-physical characteristics of fuel-containing materials (FCM) in the "Shelter" object (SO). The analysis and substantiation of the FCM nuclear safety will be one of the important issues during the SO operation for a long time, until the moment of retrieval and disposal of nuclear materials from the ChNPP Unit 4 destroyed in 1986. A significant number of nuclear materials in the SO are uncontrolled, and the geometry of their location is also little known. Therefore, the use of traditional methods of nuclear safety analysis to determine the conditions for reaching criticality in the volume of FCM can lead to significant uncertainties, depending on the assumptions and simplifications made in FCM models. In contrast to traditional nuclear facilities with design characteristics and control systems, there is no possibility to deterministically influence the FCM, and accordingly to determine their dynamic characteristics in the SO. In such conditions, it is necessary to take a responsible approach to obtain and interpret the values of FCM parameters by control systems of the SO. For example, in 1990, one of the neutron flux detectors recorded an abnormal change in the neutron pulse count rate for about 100 hours. This event is often called a “neutron incident”, and it formed the basis of some models, in which the possibility of reaching criticality in one of the FCM clusters is assumed. The article presents the results of the study on the physical possibility of the anomalous event in 1990, as well as the results of the analysis of simplifications and assumptions made in models of FCM criticality. An important result of the conducted research is the justification of the need to include in the FCM criticality model the effects of reactivity on fuel and water temperature, as well as to take into account delayed neutrons.

Performance evaluation of a 71Ga(n,γ)72Ga reaction-based epithermal neutron flux detector at an AB-BNCT device

The 71Ga(n,γ)72Ga reaction-based epithermal neutron flux detectors are novel instruments developed to measure the epithermal neutron flux of boron neutron capture therapy (BNCT) treatment beams. In this study, a spherical epithermal neutron flux detector using 71Ga(n,γ)72Ga reaction was prototyped. The performance of the detector was experimentally evaluated at an accelerator-based BNCT (AB-BNCT) device developed by Lanzhou University, China. Based on the experimental results and related analysis, we demonstrated that the detector is a reliable tool for the quality assurance of BNCT treatment beams.

Investigating magnetization of permanent magnets by magnetic flux viewing film

Permanent magnets are used in many current industrial as well as home appliances today. Frequently, kitchen plastic magnets could be found at the refrigerators at home. However, the magnetic domain structure of such permanent plastic foils is not known and understood to the users at all. The purpose of this paper is to explain the magnetic domain structure of plastic magnets with Halbach array and ferrite or neodymium magnet polarization orientation. Principles of magnetic field visualization foils (magnetic flux detector and colour changing viewing film) is explained and demonstrated on multipole magnetic structures. Experiments with magnetic polarization reversal by the strong neodymium magnet in weaker ferrite magnetic material is demonstrated. All presented principles are collected in the simple magnetic set and suggested for education of school children of different ages. Elementary school children below 10 years age are mostly interested only in making hidden pictures in magnetic paper and ferrite magnet. Older school children of 11–12 years are able to absorb more knowledge about behaviour and properties of magnets.

Experimental validation of a BNCT epithermal neutron flux detector using 55Mn(n,γ)56Mn reaction at an accelerator-based BNCT facility

The epithermal neutron flux is one of the key beam quality factors for boron neutron capture therapy (BNCT), its accurate measurement is extremely important as it is directly related to the beam quality assurance (QA) and radiation dose evaluation in BNCT. In this work, a spherical BNCT epithermal neutron flux detector using 55Mn(n,γ)56Mn reaction was redesigned and prototyped. The detector prototype was experimentally validated at the accelerator-based BNCT (AB-BNCT) facility developed by Lanzhou University. The experimental results and related analysis indicate that the detector can be a reliable tool for the QA of BNCT treatment beam.

Recoil Proton Telescopes and Parallel Plate Avalanche Counters for the 235U(n,f) cross section measurement relative to H(n,n)H between 10 and 450 MeV neutron energy

With the aim of measuring the 235U(n,f) cross section at the n_TOF facility at CERN over a wide neutron energy range, a detection system consisting of two fission detectors and three detectors for neutron flux determination was realized. The neutron flux detectors are Recoil Proton Telescopes (RPTs), based on scintillators and solid state detectors, conceived to detect recoil protons from the neutron-proton elastic scattering reaction. This system, along with a fission chamber and an array of parallel plate avalanche counters for fission event detection, was installed for the measurement at the n_TOF facility in 2018, at CERN.An overview of the performances of two RPTs — especially developed for this measurement — and of theparallel plate avalanche counters are described in this article. In particular, the characterizationin terms of detection efficiency by Monte Carlo simulations and response to neutron beam, the studyof the background, dead time correction and characterization of the samples, are reported. Theresults of the present investigation show that the performances of these detectors are suitable foraccurate measurements of fission reaction cross sections in the range from 10 to 450 MeV.

Nuclear design of a shielded cabinet for electronics: The ITER radial neutron camera case study

The Radial Neutron Camera (RNC) is a diagnostic system located in ITER Equatorial Port #1 providing several spatial and time-resolved parameters for the fusion power estimation, plasma control and physics studies. The RNC measures the uncollided 14 MeV and 2.5 MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions through an array of neutron flux detectors located in collimated Lines of Sight. Signals from RNC detectors (fission chambers, single Crystal Diamonds and scintillators) need preamplification because of their low amplitude. These preamplifiers have to be as close as possible to the detectors in order to minimize signal degradation and must be protected against fast and thermal neutrons, gamma radiation and electromagnetic fields. The solution adopted is to host the preamplifiers in a shielded cabinet located in a dedicated area of the Port Cell, behind the Bioshield Plug. The overall design of the cabinet must ensure the necessary magnetic, thermal and nuclear shielding and, at the same, satisfy weight and allocated volume constraints and maintain its structural integrity. The present paper describes the nuclear design of the shielded cabinet, performed by means of 3D particle transport calculations (MCNP), taking into account the radiation streaming through the Bioshield penetrations and the cross-talk effect from the neighboring Lower and Upper Ports. We present the assessment of its nuclear shielding performances and analyze the compliancy with the alert thresholds for commercial electronics in terms of neutron flux and cumulated ionizing dose.

Validation and optimization of the epithermal neutron flux detector using the 71Ga(n,γ)72Ga reaction

An intense epithermal neutron flux is necessary for boron neutron capture therapy (BNCT), a promising technique for the treatment of malignant tumors. The epithermal neutron flux is an essential characteristic of the BNCT neutron beam and its measurement is directly related to the reliability of the treatment planning system. Such a tool could be a cylindrical activation detector using 71Ga(n,γ)72Ga reaction. This paper describes a detector made in the likeness of the previously proposed one and presents the results of numerical simulation of the detector sensitivity and its experimental use. The paper notes the difference between the simulated sensitivity of the detector and the sensitivity of the previously proposed one and makes assumptions about the reason for this difference. The work also proposes an improvement of the detector, which allows not only to reduce the contribution of fast neutrons to the detector sensitivity, but also to provide a new opportunity to refine the spectrum of neutrons that are most effective for the treatment of deep-seated tumors.

Detector requirements for model-independent measurements of ultrahigh energy neutrino cross sections

The ultrahigh energy range of neutrino physics (above $\ensuremath{\sim}{10}^{7}\text{ }\text{ }\mathrm{GeV}$), as yet devoid of detections, is an open landscape with challenges to be met and discoveries to be made. Neutrino-nucleon cross sections in that range---with center-of-momentum energies $\sqrt{s}\ensuremath{\gtrsim}4\text{ }\text{ }\mathrm{TeV}$---are powerful probes of unexplored phenomena. We present a simple and accurate model-independent framework to evaluate how well these cross sections can be measured for an unknown flux and generic detectors. We also demonstrate how to characterize and compare detector sensitivity. We show that cross sections can be measured to ${\ensuremath{\simeq}}_{\ensuremath{-}30}^{+65}%$ precision over $\sqrt{s}\ensuremath{\simeq}4--140\text{ }\text{ }\mathrm{TeV}$ (${E}_{\ensuremath{\nu}}={10}^{7}\ensuremath{-}{10}^{10}\text{ }\text{ }\mathrm{GeV}$) with modest energy and angular resolution and $\ensuremath{\simeq}10$ events per energy decade. Many allowed novel-physics models (extra dimensions, leptoquarks, etc.) produce much larger effects. In the distant future, with $\ensuremath{\simeq}100$ events at the highest energies, the precision would be $\ensuremath{\simeq}15%$, probing even QCD saturation effects.

Reactor space-dependent transfer function at low frequency approximated by neutron diffusion theory perturbation

The space-dependent transfer function defines the response of the neutron flux in reactor core to a periodic perturbation at a point in the core. To compute it at low excitation frequency for the ZED-2 zero power reactor, we introduce a perturbation method. The ZED-2 reactor is used to investigate the properties of CANDU® lattices. In CANDU®, the low frequency noise (0.1–5 Hz) allows one to study mechanical oscillations of structures in the core, the reactor control systems, as well as delayed neutron effects. The method for computing the ZED-2 transfer function was inspired by the results of measurements in the ZED-2 reactor. They showed that, at low excitation frequency, the imaginary part of the space-dependent transfer function is, up to normalization by the steady-state neutron flux, the same over all the core, while the real part varies significantly with the position of the flux detectors or the perturber in the core. This method was then found useful to compute the response of the ZED-2 reactor core to low frequency perturbations where other methods were found hard to apply. This opens the path to generalization of this method to CANDU® reactors. A rough calculation shows for which types of thermal reactors this perturbation theory is not worth applying. Also, the perturbation theory introduced here can be applied to other problems described by linear operators having a second smallest eigenvalue larger in absolute value compared to the perturbation. A further development, using the perturber induced reactivity, was found to make the core response normalization unnecessary. The theoretical basis of that method is outlined.

MENUS—Materials engineering by neutron scattering

Materials engineering by neutron scattering (MENUS) at the second target station will be a transformational high-flux, versatile, multiscale materials engineering diffraction beamline with unprecedented new capabilities for the study of complex materials and structures. It will support both fundamental and applied materials research in a broad range of fields. MENUS will combine unprecedented long-wavelength neutron flux and unique detector coverage to enable real-time studies of complex structural and functional materials under external stimuli. The incorporated small angle neutron scattering and transmission/imaging capabilities will extend its sensitivity to larger length scales and higher spatial resolution. Multimodal MENUS will provide crystallographic and microstructure data to the materials science and engineering community to understand lattice strain/phase transition/microstructure/texture evolution in three orthogonal directions in complex material systems under combined extreme applied conditions. The capabilities of MENUS will open new scientific opportunities and meet the research needs for science challenges to enable studies of a range of phenomena and answer the key questions in material design/exploration, advanced material processing, transformative manufacturing, and material operations of national impacts in our daily life.

Algorithms for processing self-powered neutron detector signals important for determination of local parameters in each part of the VVER core

These investigation findings prove the possibility of a engineering solution for VVER core automatic protection during operation in both nominal and transient conditions within ICIS using local parameters (i.e. linear heat power of the most stressed fuel rod, departure from nucleate boiling ratio). Such engineering solution will be implemented by safety system software-hardware (PTK-Z) on the basis of signals coming from in-core neutron flux detectors, temperature sensors, primary coolant flow and coolant pressure transducers. The article presents the following: a list of in-core neutron flux detectors, a list of transducers of primary coolant monitoring for thermal engineering conditions (temperature, flow rate, pressure), whose signals are delivered to the terminals of instrumentation gauges (PTK-Z) for the purpose of actuating safety actions in accordance with local parameters. The paper shows arrangement of in-core neutron flux detector equipment, above view of self-powered neutron detector (SPND) location in safety channels, axial arrangement of SPND along the core, algorithms for processing SPND signals important for determination of local parameters in each part of the core in both normal and abnormal operation conditions.

Дослідження спектральних образів нейтронного шуму реакторів типу ВВЕР у нерегламентних теплогідравлічних режимах активних зон

The information on the peculiarities of the manifestations of potentially dangerous thermohydraulic anomalies, that occur unpredictably during the operation of the WWER reactor core, is generalized. Considerable attention is paid to the threat of uncontrolled occurrence of latent pre-emergency and emergency operating states in fuel assemblies during the generation of the vapor phase on the surface of fuel elements, including the heat transfer crisis with subsequent boiling of the coolant. It is noted that under these conditions, heat transfer, which should occur exclusively in the convective mode, is also characterized by the uncontrolled occurrence of the boiling process, from the activation of the first centers of vaporization to the formation of a developed bubble structure of the coolant. The limited possibilities of modern technical means of monitoring the technical condition of WWER, which do not provide detection of these anomalies and preemergency heat transfer regimes, are considered. Given the data on neutron flux fluctuations, it is shown that the noise components at the output of standard electron emission neutron flux meters carry important diagnostic information on thermohydraulic processes in the volume of the core, which is currently lost. With this in mind, it is concluded that it is necessary to immediately develop a methodology for the operational identification of random spectral realizations of neutron noise, which is registered at the outputs of neutron detectors of existing in-reactor control systems. The nature of the necessary reliable data on the spectral structure of the main types of diagnostic images (signatures or patterns) of neutron noise, which is registered at the output of standard neutron flux detectors in accordance with the main types of thermohydraulic anomalies, is determined. The analysis of known data and performed with the participation of authors of reactor experiments on the basis of which it is proved that the spectral structure of auto- and coherent signal density at the output of standard neutron flux detectors contains comprehensive diagnostic information on the type and location of vapor-liquid structures of WWER reactor core. With this in mind, the information characteristics of individual spectral ranges of neutron noise are analyzed and conclusions are made about their direct correspondence to the characteristic thermohydraulic processes as objects of diagnostics.

An adjoint sensitivity analysis of the Telegrapher’s neutron kinetic equations

The work presented herein is an approach to the kinetic uncertainty analysis of the Telegrapher’s neutron kinetic equations. The adjoint sensitivity analysis framework has been resorted to meet this end. Burnup induced uncertainty in the value of the delayed neutron fraction is addressed and its impact on the neutron population (as an observable quantity by the way of flux detectors) is investigated. Results compared against those obtained through an exact forward analysis approach confirm quite satisfactory accuracy of the proposed variational method. The effect of relaxation time on the adjoint system dynamics is moreover explored.

Uncertainty analysis for CCD-augmented CASI® BRDF measurement system

This work presents a measurement uncertainty analysis for a system designed to simultaneously capture specular in-plane and out-of-plane bidirectional reflectance distribution function (BRDF) data with high spatial resolution by augmenting the Complete Angle Scatter Instrument (CASI®) with a charge-coupled device (CCD) camera. Various scatter flux, incident flux, scatter angle, and detector solid angle uncertainty contributions are considered and evaluated based on imperfectly known system parameters. In particular, incident flux temporal fluctuation, detector noise and non-linearity, and out-of-plane aperture misalignment considerations each require significant adjustment from original CASI® uncertainty analysis, and expressions for neutral density (ND) filter, scatter angle, and solid angle uncertainties each require new formulations. Ultimately, ND filter uncertainty produces the largest contribution for the augmented system—at least when using unrefined worst-case tolerances—followed by solid angle uncertainty and pixel non-linearity. Total BRDF uncertainty and its contributing terms are compiled for several measurement scenarios, and compared with those from original analyses for single-pixel detectors. In particular, when ND filter uncertainty can be ignored or mitigated, total BRDF uncertainty values are comparable to those for the original system.

ANALYSIS OF RELIABILITY OF AUTOMATIC CORE PROTECTION FUNCTION OF THE REACTOR V-412 IN RESPONSE TO LOCAL PARAMETERS: MAXIMUM LINEAR POWER, DEPARTURE FROM NUCLEATE BOILING RATIO

The research subject is finding an engineering solution for V-412 core automatic protection during operation in both steady-state and transient conditions within ICIS using local parameters (i.e. maximum linear power, departure from nucleate boiling ratio). Such engineering solution will be implemented by safety system software-hardware (PTK-Z) on the basis of signals coming from in-core neutron flux detectors, temperature sensors, primary coolant flow and coolant pressure transducers. Calculated survey of possibility to use Kalman filters or corrective filter to eliminate time delay in SPND signals was carried out. The inaccuracy in the method of maximum linear power monitoring was determined. This work shows that the solution was found using the practice of in-core instrumentation, and ICIS designing and operation with improved metrology, reliability and time parameters and using advanced data communication technologies intended for important challenges of the world market, and as a response to standards.

Two-dimensional time- and space-resolved diagnostic method for an integrated implosion process.

To precisely measure and evaluate X-ray generation and evolution in a hohlraum during an implosion process, we present a two-dimensional (2D) time- and space-resolved diagnostic method by combining a compressed ultrafast photography (CUP) system and a simplified version of space-resolving flux detector (SSRFD). Numerical experiment results showed that the reconstruction quality of the conventional CUP significantly improved owing to the addition of the external SSRFD, especially when a coded mask with a large pixel size was used in the CUP. Further, the performance of the CUP cooperation with the SSRFD was better than that of adding an external charge-coupled device or streak camera. Compared with existing ultrafast imaging techniques in laser fusion, the proposed method has a prominent advantage of measuring the 2D evolution of implosion by combining high temporal resolution of streak camera and high spatial resolution of SSRFD; moreover, it can provide guidance for designing diagnostic experiments in laser fusion research.

Design and performance of an epithermal neutron flux detector using 55Mn(n,γ)56Mn reaction for BNCT

The measurement of the epithermal neutron (0.5 eV – 10 keV) flux of a boron neutron capture therapy (BNCT) treatment beam is a critical issue to its quality assessment and evaluation of the radiation dose to the treated patients. In this work, an activation detector using 55Mn(n,γ)56Mn reaction is designed by Monte Carlo simulations to measure the epithermal neutron flux of BNCT treatment beam. The detector is spherical and it has an absorber/moderator/absorber/manganese (Mn) foil arrangement from outside to inside. The activation material, i.e., Mn foil, is located at the geometrical center of the detector. After the design, the performance of the detector is evaluated by Monte Carlo simulations using the treatment neutron beams of operating reactor-based BNCT facilities. The results and related analysis indicate that the proposed detector will be efficiently applicable in the quality assessment of BNCT treatment beam and evaluation of the radiation dose to the treated patients.