Detector Response Function Research Articles

Study of the PWR ex-core detector response simulation based on the 3D SN method

Simulation of the ex-core detector response function (DRF) is of great importance for reactor power monitoring, control and protection systems. However, the 3D DRF calculation requires vast majorities of computational resources due to its characteristics such as deep penetration, strong anisotropic scattering, large computational geometry, etc. In this paper, the step characteristics (SC) spatial differencing scheme and GMRES algorithm have been implemented in the 3D SN code to ensure the simulation efficient. The adjoint first-collision (FC) source method is developed to mitigate the ray effect in the DRF simulation. The Kobayashi benchmarks are calculated to verify the correctness of the FC module. Numerical results based on the Kori-1 reactor ex-core detector indicate that the SN-FC method has the comparable accuracy with multi-group Monte-Carlo method but achieves much higher efficiency.

Velocity-space sensitivity of the neutron camera on MAST

The Neutron Camera installed at the Mega Ampere Spherical Tokamak (MAST) provided fundamental information regarding the neutron emission and the behavior of fast ions. The signal measured by the Neutron Camera depended on its observation direction relative to the plasma region. Furthermore, only a certain part of the energy-pitch region contributed to the measured signal. This region is determined by the fast ion Weight Functions. In this paper, the Weight Functions of the Neutron Camera are calculated using DRESS. The results show that the instrument is most sensitive to neutrons created in fusion reactions involving a thermal ion and an ion in the beam energy region. Synthetic spectra are also calculated and, after folding with the detector's response function, compared with experimental pulse height spectra for three selected plasma discharges. Also, Weight Functions for the Neutron Camera Upgrade on MAST-U are calculated and discussed. The results can be applied for future fast ion studies at MAST-U, combining Neutron Camera Upgrade data with those of other fast ion diagnostics, such as Fast Ion Deuterium Alpha and the Neutral Particle Analyzer diagnostics.

First neutron spectroscopy measurements with a compact C7LYC based detector at EAST

The paper describes a new compact neutron spectrometer optimized for the detection of 2.5 MeV neutrons for fusion plasma applications. The first neutron spectroscopy measurements on a nuclear fusion plasma experiment (EAST) with this detector are also reported together with the data interpretation. The detector allowed separating the different neutron emission components from the plasma and to validate the effectiveness of the Neutral Beam Injection (NBI) heating. A possible improvement of the diagnostic has been also identified in order to increase the detector sensitivity to weak components of the neutron spectrum, such as those due to the Ion Cyclotron Resonace Heating (ICRH). The relatively simple response function of the C7LYC detector to 2.5 MeV neutrons together with its good capability in the n/γ discrimination, makes this detector an interesting spectrometer for deuterium (D) plasma diagnostics. In particular, its compactness allows for integration in a multi-line of sight camera where space constraints are present.

Second-order adjoint sensitivity analysis of a general ratio of functionals of the forward and adjoint fluxes in a multiplying nuclear system with source

In the present work, the Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) is applied to a generic multiplying subcritical nuclear system comprising a non-fission neutron source in order to compute efficiently and exactly all of the 1st- and 2nd-order functional derivatives (“sensitivities”) of a system response with respect to the system’s many parameters. The system response is defined to be a ratio of two general nonlinear functionals of the forward and adjoint particle fluxes, while the system parameters include isotopic number densities, microscopic cross sections, fission spectrum parameters, neutron sources, and detector response functions. Such ratios of functionals represent the most general models for quantities of fundamental importance in reactor physics, including eigenvalues, ratios of reaction rates and forward/adjoint flux-weighted multi-group cross sections. The exact expressions obtained in this work will be used in subsequent works to perform a large-scale sensitivity analysis of a polyethylene-reflected plutonium metal sphere experimental benchmark to the nuclear data characterizing this benchmark, comprising 21,976 first-order sensitivities and 482,944,576 second-order sensitivities.

Experimental and synthetic measurements of polarized synchrotron emission from runaway electrons in Alcator C-Mod

This paper presents the first experimental analysis of polarized synchrotron emission from relativistic runaway electrons (REs) in a tokamak plasma. Importantly, we show that the polarization information of synchrotron radiation can be used to diagnose spatially-localized RE pitch angle distributions. Synchrotron-producing REs were generated during low density, Ohmic, diverted plasma discharges in the Alcator C-Mod tokamak. The ten-channel motional Stark effect diagnostic was used to measure spatial profiles of the polarization angle and the fraction of detected light that was linearly-polarized. Spatial transitions in of —from horizontal to vertical polarization and vice versa—are observed in experimental data and are well-explained by the gyro-motion of REs and high directionality of synchrotron radiation. Polarized synchrotron emission is modeled with the synthetic diagnostic Soft; its output Green’s (or detector response) functions reveal a critical RE pitch angle at which flips by 90° and is minimal. Using Soft, we determine the dominant RE pitch angle which reproduces measured and values. The spatiotemporal evolutions of and are explored in detail for one C-Mod discharge. For channels viewing REs near the magnetic axis and flux surfaces q = 1 and 4/3, disagreements between synthetic and experimental signals suggest that the sawtooth instability may be influencing RE dynamics. Furthermore, other sources of pitch angle scattering, not considered in this analysis, could help explain discrepancies between simulation and experiment.

A Directional Detector Response Function for Anisotropic Detectors

For a radiation detector that is not isotropic, a directional detector response is needed to accurately account for the variation in a detector’s behavior depending on the incoming particle direction. The concept of the detector response function has been extended to include particle direction using a set of pregenerated detector responses based on the orientation of the incoming radiation and the detector. This directional detector response function (DDRF) then can be applied to the flux and current tallies computed by a Monte Carlo simulation. Validation of the new approach has been done by comparing simulated count rates processed with the DDRF to measured count rates taken with a 5.08 × 10.16 × 40.64-cm NaI(Tl) detector. The comparisons show that the applied method produces good agreement with both background and source measurements with a 137Cs source. Furthermore, separation of the detector response generation from Monte Carlo particle transport calculations provides greater flexibility in locating single or multiple detectors without any interference in the model and also enables simulation of various models using the same detector response without the need for generating additional detector responses if the same detector is being used.

Resolution modeling in projection space using a factorized multi-block detector response function for PET image reconstruction

Positron emission tomography (PET) images usually suffer from limited resolution and statistical uncertainties. However, a technique known as resolution modeling (RM) can be used to improve image quality by accurately modeling the system’s detection process within the iterative reconstruction. In this study, we present an accurate RM method in projection space based on a simulated multi-block detector response function (DRF) and evaluate it on the Siemens hybrid MR-BrainPET system. The DRF is obtained using GATE simulations that consider nearly all the possible annihilation photons from the field-of-view (FOV). Intrinsically, the multi-block DRF allows the block crosstalk to be modeled. The RM blurring kernel is further generated by factorizing the blurring matrix of one line-of-response (LOR) into two independent detector responses, which can then be addressed with the DRF. Such a kernel is shift-variant in 4D projection space without any distance or angle compression, and is integrated into the image reconstruction for the BrainPET insert with single instruction multiple data (SIMD) and multi-thread support. Evaluation of simulations and measured data demonstrate that the reconstruction with RM yields significantly improved resolutions and reduced mean squared error (MSE) values at different locations of the FOV, compared with reconstruction without RM. Furthermore, the shift-variant RM kernel models the varying blurring intensity for different LORs due to the depth-of-interaction (DOI) dependencies, thus avoiding severe edge artifacts in the images. Additionally, compared to RM in single-block mode, the multi-block mode shows significantly improved resolution and edge recovery at locations beyond 10 cm from the center of BrainPET insert in the transverse plane. However, the differences have been observed to be low for patient data between single-block and multi-block mode RM, due to the brain size and location as well as the geometry of the BrainPET insert. In conclusion, the RM method proposed in this study can yield better reconstructed images in terms of resolution and MSE value, compared to conventional reconstruction without RM.

Neutron spectrum unfolding for the development of a novel neutron detector for fusion

In future fusion power plants, such as DEMO, the D-T neutron emission rate is predicted to exceed 1 × 1021 n s−1. Accurately monitoring neutron energies and intensities will be the primary method for estimating fusion power, and calculating key nuclear parameters, including the tritium breeding ratio and nuclear heating. The noVel nEutRon Detector for fusIon (VERDI) project, implemented under the EUROFusion Enabling Research 2017 program, aims to develop a detector capable of withstanding the harsh environment of a future fusion power plant. The VERDI detector is based on the foil activation technique, which relies on neutron spectrum unfolding methods to process the convolution of gamma-ray measurement and detector response function to infer the neutron energy spectrum. This paper details the experimental method and results collected using six prototype VERDI detectors during an initial experiment performed in July 2017 at the ENEA Frascati Neutron Generator (FNG) under D-T neutrons (14 MeV). The measured activities of product isotopes are compared with equivalent data calculated using the FISPACT-II code to provide an average C/Eact agreement of 1.05±0.13. Experimental results from the FNG have been applied to neutron spectrum unfolding techniques using established unfolding codes, MAXED and GRAVEL.

Contribution of random noise in the ITER RNC diamond neutron detectors pulses to the counting rate uncertainty

The main goal of the ITER Radial Neutron Camera (RNC) is to provide the plasma neutron emission profile (neutron emissivity) through measurement of the uncollided 14 MeV and 2.5 MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions. The system is based on an array of detectors (diamonds are among the candidate detectors) located in collimated lines of sight (LOS) viewing the plasma through the ITER Equatorial Port Plug #1. Tomographic reconstruction techniques are used to calculate the neutron emissivity.The contribution of random noise on diamond detector pulses to the count rate uncertainty is investigated in this paper. The energy spectrum of the neutrons impinging on the detector has been calculated by means of MCNP calculations for one line of sight of the RNC In-Port system. The spectrum has been convoluted with the diamond detector response functions and the Pulse Height Spectrum (PHS) has been obtained. Experiments have been carried out with the CAEN™ 5810D detector emulator, that is able to produce arbitrary pulse height distributions as those expected in the ITER RNC. Random noise has been added on each detector pulse of the distribution using the detector emulator. The resulting uncertainty produced on the count rate has been evaluated as a function of the random noise level.

Application of the Second-Order Comprehensive Adjoint Sensitivity Analysis Methodology to Compute First- and Second-Order Sensitivities of Flux Functionals in a Multiplying System with Source

This work presents an application of the Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) to the neutron transport Boltzmann equation that models a multiplying subcritical system comprising a nonfission neutron source to compute efficiently and exactly all of the first- and second-order functional derivatives (sensitivities) of a detector’s response to all of the model’s parameters, including isotopic number densities, microscopic cross sections, fission spectrum, sources, and detector response function. As indicated by the general theoretical considerations underlying the 2nd-ASAM, the number of computations required to obtain the first and second orders increases linearly in augmented Hilbert spaces as opposed to increasing exponentially in the original Hilbert space. The results presented in this work are currently being implemented in several production-oriented three-dimensional neutron transport code systems for analyzing specific subcritical systems.

CYSP-BEAM: A multi-detector directional spectrometer for in-beam neutron spectrometry

CYSP-BEAM is a directional neutron spectrometer formed by a thick polyethylene cylindrical collimator followed by a sensitive capsule that contains several active thermal neutron detectors located at different depths along the cylindrical axis. Due to a thick lateral shield made of polyethylene and borated rubber, only neutrons from the direction identified by the collimating aperture can reach the internal detectors. As the response function of the internal detectors tend to peak at increasing energies as the detector depth increases, the device has spectrometric properties. This type of moderated spectrometer, whose prototype was the CYSP (CYlindrical SPectrometer), is capable to combine the functionalities of Bonner Spheres in a single device, thus requiring only one exposure to measure all the energy components of the incident beam, from thermal up to GeV neutrons. The neutron spectrum is obtained via few-channel unfolding methods. With respect to the original CYSP, the new CYSP-BEAM device is optimized to operate in the direct intense beam of neutron producing installations, such as large scale neutron science facilities. Compared with CYSP, CYSP-BEAM has narrower collimating aperture and the internal detectors have sensibility a factor 100 lower. Its response matrix was simulated using MCNPX. This paper describes the new device focusing on the internal detectors, the response matrix and the test measurement performed using the 14 MeV beam produced at the ENEA Frascati Neutron Generator (FNG).

Experimental determination of the “collimator monitoring fill factor” and its relation to the error detection capabilities of various 2D‐arrays

The collimator monitoring fill factor (CM-FF) introduced by Stelljes etal. (2017) and the FWHM fill factor (FWHM-FF) introduced by Gago-Arias etal. (2012) were determined using the measured photon fluence response functions of various 2D-arrays. The error detection capabilities of 2D-arrays were studied by comparing detector signal changes and local gamma index passing rates in different field setups with introduced collimation errors. The fill factor is defined as the ratio of the sensitive detector area and the cell area of a detector, defined by the detector arrangement on a 2D-array. Gago-Arias etal. calculated the FWHM-FF, using the FWHM² of a detector's fluence response function KM (x) as the sensitive detector area. For the CM-FF a sensitive detector width w(Δ mm, d%) is calculated. The sensitive detector width is the lateral extent of KM (x), lying inside the detector cell area, along which a collimator error of Δ mm yields a signal change exceeding a detection threshold of d%. The sensitive area for a single detector is calculated using w(Δ mm, d%)². The CM-FF is then calculated as the ratio of the sensitive area of a detector within its cell area and the detector cell area. The fluence response functions of the central detector of the OCTAVIUS 729, 1500, and 1000 SRS array (all PTW-Freiburg, Freiburg, Germany) and the MapCHECK 2 array (Sun Nuclear, Melbourne, US) were measured using a photon slit beam. The FWHM-FF and the CM-FF were calculated and compared for all 2D-arrays under investigation. The error detection capabilities of 2D-arrays in quadratic fields were studied by investigating the signal changes in the detectors adjacent to the collimator edge when changing the collimator position. The change in local gamma index passing rate with respect to the introduced collimator error was investigated for an ionization chamber and a diode array in quadratic and two intensity modulated fields. Values for the CM-FF and FWHM-FF were 1.0 and 0.35, respectively for the area of the liquid-filled 1000 SRS ionization chamber array with a detector to detector distance of 5mm and 0.32 and 0.04, respectively, for the MapCHECK 2 diode array. For the vented ionization chamber array OCTAVIUS 729 fill factors were calculated as CM-FF=0.59 and FWHM-FF=0.53, while the OCTAVIUS 1500 array yielded fill factors of CM-FF=0.77 and FWHM-FF=0.72. Signal changes in vented ionization chambers for collimator errors of 1mm surpassed those of diodes by a factor of 2 in quadratic fields. The gamma index passing rates in quadratic fields reflect those findings. In intensity modulated fields, the decline of the gamma index passing rate is bigger for the ionization chamber array compared to the diode array when introducing collimator errors. The calculated values of the CM-FF correlate with the signal changes in quadratic field setups with introduced collimator position errors of 1mm, while the FWHM-FF underestimates the error detection capabilities of 2D-arrays. An increased error detection capability of the ionization chamber array compared to diode array was observed in quadratic and intensity modulated fields.

Second-order sensitivities of a general functional of the forward and adjoint fluxes in a multiplying nuclear system with source

This work presents an application of the Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) to compute efficiently and exactly all of the 1st- and 2nd-order functional derivatives (“sensitivities”) of a generic scalar-valued response to parameters for a multiplying subcritical system comprising a non-fission neutron source. The response is defined to be a nonlinear functional of the forward and adjoint particle fluxes while the system parameters include isotopic number densities, microscopic cross sections, fission spectrum, sources, and detector response functions. As indicated by the general theoretical considerations underlying the 2nd-ASAM, the number of computations required to obtain the 1st- and 2nd-order increases linearly in augmented Hilbert spaces as opposed to increasing exponentially in the original Hilbert space. This unique feature provides the fundamental reason for the unmatched efficiency of the 2nd-ASAM for computing exactly all of the 1st- and 2nd-order responses sensitivities to model parameters. The results presented in this work are currently being implemented in several production-oriented three dimensional neutron transport code systems for analyzing specific subcritical systems.

Filter-based energy-resolved X-ray computed tomography with a clinical imager

ABSTRACT Filter-based energy-resolved X-ray computed tomography (CT) is an approach for implementing energy-resolved CT imaging using a flat-panel-detector-based cone-beam system. In this study, we performed experiments with a 20-cm-diameter phantom on a clinical X-ray imager. The material density results showed good agreement with the ideal values. We also propose an improved method for obtaining the detector response function and the X-ray spectrum, which requires fewer measurements and will be practical for future clinical use. Issues such as scatter and image noise remain to be addressed.

268. Free beta-software for testing of digital mammographic equipment according to EUREF publication “Supplement to European Guidelines”, version 1.0, 2013

Purpose The recent publication “Supplement to European Guidelines”, version 1.0, 2013, (S1), has reviewed the tests for quality assurance of digital mammographic equipment. The majority of the tests considered as essential or desirable regard the detector and the resulting quality of the images. The analyses are very demanding if no suitable tools for the automatic analysis of the images are available. The authors developed a free prototype of such a tool to be improved with the practise and the feedbacks of the possible users. Methods MaMMoS1 is a homemade software for analyzing mammographic digital images. It was written in MATLAB® but it does not require Matlab installed on the computer. It was developed at our facilities for helping us in our routine quality controls. In the intention of the authors it would be a starting platform that should be improved by feedback and suggestions from the users. Currently it performs the following test-items described in S1: (Essential) 2b.2.2.1.1 Response function/2b.2.2.1.2 Noise evaluation. 2b.2.1.3.5 AEC Breast thickness and composition compensation. 2b.2.2.3.1 Image receptor homogeneity. 2b.2.4.5 Ghost image/erasure thoroughness. (Desirable) 2b.2.1.3.6 Local dense area. It can be downloaded at: https://www.fisicamedica.it/gruppi/gruppo-regionale/toscana . Instructions for the installation and use of the software are given in a readme file. Results The software has been routinely applied proving useful for the calculation of the requested parameters. Each test requires no more than a few seconds. It is possible to process images on site and so it is possible to identify defective performance soon after the measurements, possibly apply corrective procedures and repeat the test. Conclusions The introduction of MaMMoS1 in our quality assurance program has allowed economic and human resources savings as a considerable amount of time during each check can be saved. It can be updated to include additional analysis and tools to make the quality checks faster and easier for the user. The detector performances, homogeneity, response function, ghost, and noise, can be fully explored so the software can be used for digital detector of other modalities with respect to mammography an in the future include additional more specific features. Download : Download high-res image (208KB) Download : Download full-size image

Scalar and fermionic Unruh Otto engines

We investigate the behaviour of quantum heat engines, in which a qubit is put through the quantum equivalent of the Otto cycle and the heat reservoirs are due to the Unruh effect. The qubit is described by an Unruh-DeWitt detector model coupled quadratically to a scalar field and alternately to a fermion field. In the cycle, the qubit undergoes two stages of differing constant acceleration corresponding to thermal contact with a hot and cold reservoir. Explicit conditions are derived on the accelerations required for this cycle to have positive work output. By analytically calculating the detector response functions, we show that the dimensionality of the quadratic and fermionic coupling constants introduces qualitatively different behaviour of the work output from this cycle as compared to the case in which the qubit linearly couples to a scalar field.

Methodology for a fast determination of EDX Si(Li) detector response function in the 5 keV to 15 keV range

Standard methods used for establishing EDX Si(Li) detectors response functions (DRF) are tedious and require a significant amount of work and beam time, which is not always available. That fact frequently leads to the disregard of the specific DRF at the time of the measurement, and to the fit of spectra using “general” response functions, which were determined on detectors with different characteristics. The accurate description of the low energy side asymmetry of the peaks is necessary to quantify trace elements accurately and to determine fundamental parameters like X-ray intensity ratios and ionization cross sections. In the present work, a simple method to monitor the energy dependence of EDX detectors response function in the 5 keV to 15 keV range is presented. Four PIXE generated X-ray spectra of thin mono-elemental (Ti, Fe, Ni, and Au) films are shown to be enough for this purpose. The methodology can be used as a laboratory-based protocol to establish the DRF and to monitor it over time.

Advanced detector signal acquisition and electron beam scanning for high resolution SEM imaging

The advancement of materials science at the mesoscale requires improvements in both sampling volumes/areas and spatial resolution in order to make statistically significant measurements of microstructures that influence higher-order material properties, such as fatigue and fracture. Therefore, SEM-based techniques have become desirable due to improvements in imaging resolution, large sample handling capability, and flexibility for in-situ instrumentation. By using fast sampling of SEM electron detector signals, intrinsic beam scanning defects have been identified that are related to the response time of the SEM electron beam deflectors and electron detectors. Mitigation of these beam scanning defects using detector sampling approaches and an adaptive model for settling time is shown to produce higher resolution SEM images, at faster image acquisition times, with a means to quantify the different response functions for various beam deflectors and detectors including those for electrons and ions.

On the improved stability of the version 7 MIPAS ozone record

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared limb emission spectrometer on the Envisat platform. From 2002 to 2012, it performed pole-to-pole measurements during day and night, producing more than 1000 profiles per day. The European Space Agency (ESA) recently released the new version 7 of Level 1B MIPAS spectra, in which a new set of time-dependent correction coefficients for the nonlinearity in the detector response functions was implemented. This change is expected to reduce the long-term drift of the MIPAS Level 2 data. We evaluate the long-term stability of ozone Level 2 data retrieved from MIPAS v7 Level 1B spectra with the IMK/IAA scientific level 2 processor. For this, we compare MIPAS data with ozone measurements from the Microwave Limb Sounder (MLS) instrument on NASA's Aura satellite, ozonesondes and ground-based lidar instruments. The ozonesondes and lidars alone do not allow us to conclude with enough significance that the new version is more stable than the previous one, but a clear improvement in long-term stability is observed in the satellite-data-based drift analysis. The results of ozonesondes, lidars and satellite drift analysis are consistent: all indicate that the drifts of the new version are less negative/more positive nearly everywhere above 15 km. The 10-year MIPAS ozone trends calculated from the old and the new data versions are compared. The new trends are closer to old drift-corrected trends than the old uncorrected trends were. From this, we conclude that the nonlinearity correction performed on Level 1B data is an improvement. These results indicate that MIPAS data are now even more suited for trend studies, alone or as part of a merged data record.

Characterization of a CLYC detector for underground experiments

Large size detectors based on Cs2LiYCl6:Ce (CLYC) are capable of performing a combined γ-ray and neutron spectrometry and constitute a promising technology for a wide range of applications in nuclear and high energy physics. Due to their novelty, the comprehensive characterization of the performance of individual CLYC detectors is of great importance for determining their range of applicability. In this work we report on a wide series of measurements performed with a commercial 2”×2” CLYC crystal. Good energy and timing resolution values, of 4.7% (@ 662 keV) and 1340 ps (FWHM) respectively, were achieved, and a neutron/γ separation figure of merit value of 4.2 was obtained. A dedicated measurement for investigating the intrinsic background of the detector was performed at the Laboratorio Subterráneo de Canfranc (Spain). It evidenced a sizeable contamination in the detector materials which poses limits in the use of CLYC in low background experiments. In addition, detailed Monte Carlo simulations with the GEANT4 toolkit were performed for modelling the response function of the CLYC detector to γ-rays. An excellent agreement with the experimental data has been achieved.