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In this paper, detailed verification and experimental validation of the formulations and algorithms of the Multi-stage Response-function Transport (MRT)–based Real-time Analysis for Particle-transport and In-situ Detection (RAPID) code system is presented. In particular, RAPID's fission matrix formulation for eigenvalue calculations and its detector response function for reaction rate calculations have been examined in this study. As part of a collaboration between Virginia Tech and the Jožef Stefan Institute (JSI), RAPID is used to simulate dosimetry experiments performed at the JSI TRIGA Mark II reactor. In these measurements, wire dosimeters are irradiated at different axial and radial locations in the reactor, and their signature activity is measured. The RAPID calculations require the determination of the fission neutron source distribution and the 197 Au(n, γ) 198 Au reaction rates in the wires. In addition, the Monte Carlo code Serpent is used for comparison of the RAPID-calculated criticality eigenvalue, three-dimensional fission neutron source distribution. The validation results show excellent agreement of RAPID with both the experiments and the reference Serpent calculation, with an average relative difference of about 3% with respect to the measurements. [ABSTRACT FROM AUTHOR]

An experimental system for detection of back-scattered electrons (BSE) in the scanning electron microscope (SEM) for three-dimensional (3D) visualization of the microstructure topography is described. The 3D surface topography reconstruction is carried out according to the algorithm of profile reconstruction from the preliminarily determined angular dependencies of BSE with the use of a calibration specimen. It is shown that the instrument function of the detector system, i.e., the detector response function, as well as the geometric factor, that takes the transformation of the angle distribution for single and multiple scattering of BSEs into consideration, cause a significant impact on the detected signal. [ABSTRACT FROM AUTHOR]

• Singular Value Decomposition a new method to the continuous internal bremsstrahlung spectrum for deconvolution procedure. • Internal bremsstrahlung spectrum of 90Sr/90Y isotope obtained using 5.08 × 5.08 cm NaI(Tl) detector. • Detector response functions of NaI (Tl) detector are determined using peak to total ratio and detector efficiencies. • The result of stripping procedure shows a very good agreement between theory and experiment. We have tried to obtain the spectrum of internal bremsstrahlung photons which are released simultaneously with beta particles and neutrinos from the 90Sr-90Y source in secular equilibrium. Detector parameters of the 5.08 cm × 5.08 cm NaI(Tl) detector are determined using standard calibration sources. A detector response function is generated for a single-energy gamma photon using detector parameters and Monte Carlo method. The Singular Value Decomposition (SVD) method is used for stripping of the detector response function effects from the raw experimental spectrum. The stripped experimental data are compared with KUB theory and a different stripping method that we used our former work on the same isotope. There is a much better agreement between experimental and theoretical findings comparing the former experimental data. [ABSTRACT FROM AUTHOR]

Purpose: The authors have previously shown the feasibility of using an artificial neural network (ANN) to eliminate the volume average effect (VAE) of scanning ionization chambers (ICs). The purpose of this work was to evaluate the method when applied to beams of different energies (6 and 10 MV) and modalities [flattened (FF) vs unflattened (FFF)], measured with ICs of various sizes. Methods: The three‐layer ANN extracted data from transverse photon beam profiles using a sliding window, and output deconvolved value corresponding to the location at the center of the window. Beam profiles of seven fields ranging from 2 × 2 to 10 × 10 cm2 at four depths (1.5, 5, 10 and 20 cm) were measured with three ICs (CC04, CC13, and FC65‐P) and an EDGE diode detector for 6 MV FF and FFF. Similar data for the 10 MV FF beam was also collected with CC13 and EDGE. The EDGE‐measured profiles were used as reference data to train and test the ANNs. Separate ANNs were trained by using the data of each beam energy and modality. Combined ANNs were also trained by combining data of different beam energies and/or modalities. The ANN's performance was quantified and compared by evaluating the penumbra width difference (PWD) between the deconvolved and reference profiles. Results: Excellent agreement between the deconvolved and reference profiles was achieved with both separate and combined ANNs for all studied ICs, beam energies, beam modalities, and geometries. After deconvolution, the average PWD decreased from 1–3 mm to under 0.15 mm with separate ANNs and to under 0.20 mm with combined ANN. Conclusions: The ANN‐based deconvolution method can be effectively applied to beams of different energies and modalities measured with ICs of various sizes. Separate ANNs yielded marginally better results than combined ANNs. An IC‐specific, combined ANN can provide clinically acceptable results as long as the training data includes data of each beam energy and modality. [ABSTRACT FROM AUTHOR]

The correct determination of the X-ray peak areas in PIXE spectra by fitting with a computer program depends crucially on accurate parameterization of the detector peak response function. In the Guelph PIXE software package, GUPIXWin, one of the most used PIXE spectra analysis code, the response of a semiconductor detector to monochromatic X-ray radiation is described by a linear combination of several analytical functions: a Gaussian profile for the X-ray line itself, and additional tail contributions (exponential tails and step functions) on the low-energy side of the X-ray line to describe incomplete charge collection effects. The literature on the spectral response of silicon X-ray detectors for PIXE applications is rather scarce, in particular data for Silicon Drift Detectors (SDD) and for a large range of X-ray energies are missing. Using a set of analytical functions, the SDD response functions were satisfactorily reproduced for the X-ray energy range 1–15 keV. The behaviour of the parameters involved in the SDD tailing functions with X-ray energy is described by simple polynomial functions, which permit an easy implementation in PIXE spectra fitting codes. [ABSTRACT FROM AUTHOR]

This work presents the organic scintillation simulation capabilities of DRiFT, a post-processing D etector R esponse F unction T oolkit for MCNP ® output. DRiFT is used to create realistic scintillation detector response functions to incident neutron and gamma mixed-field radiation. As a post-processing tool, DRiFT leverages the extensively validated radiation transport capabilities of MCNP ® 6 , which also provides the ability to simulate complex sources and geometries. DRiFT is designed to be flexible, it allows the user to specify scintillator material, PMT type, applied PMT voltage, and quenching data used in simulations. The toolkit's capabilities, which include the generation of pulse shape discrimination plots and full-energy detector spectra, are demonstrated in a comparison of measured and simulated neutron contributions from 252 Cf and PuBe, and photon spectra from 22 Na and 228 Th sources. DRiFT reproduced energy resolution effects observed in EJ-301 measurements through the inclusion of scintillation yield variances, photon transport noise, and PMT photocathode and multiplication noise. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the geometry dependence of the detector response function (DRF) of three commonly used scanning ionization chambers and its impact on a convolution-based method to address the volume averaging effect (VAE). Methods: A convolution-based approach has been proposed recently to address the ionization chamber VAE. It simulates the VAE in the treatment planning system (TPS) by iteratively convolving the calculated beam profiles with the DRF while optimizing the beam model. Since the convolved and the measured profiles are subject to the same VAE, the calculated profiles match the implicit "real" ones when the optimization converges. Three DRFs (Gaussian, Lorentzian, and parabolic function) were used for three ionization chambers (CC04, CC13, and SNC125c) in this study. Geometry dependent/independent DRFs were obtained by minimizing the difference between the ionization chamber-measured profiles and the diode-measured profiles convolved with the DRFs. These DRFs were used to obtain eighteen beam models for a commercial TPS. Accuracy of the beam models were evaluated by assessing the 20%-80% penumbra width difference (PWD) between the computed and diode-measured beam profiles. Results: The convolution-based approach was found to be effective for all three ionization chambers with significant improvement for all beam models. Up to 17% geometry dependence of the three DRFs was observed for the studied ionization chambers. With geometry dependent DRFs, the PWD was within 0.80 mm for the parabolic function and CC04 combination and within 0.50 mm for other combinations; with geometry independent DRFs, the PWD was within 1.00 mm for all cases. When using the Gaussian function as the DRF, accounting for geometry dependence led to marginal improvement (PWD < 0.20 mm) for CC04; the improvement ranged from 0.38 to 0.65 mm for CC13; for SNC125c, the improvement was slightly above 0.50 mm. Conclusions: Although all three DRFs were found adequate to represent the response of the studied ionization chambers, the Gaussian function was favored due to its superior overall performance. The geometry dependence of the DRFs can be significant for clinical applications involving small fields such as stereotactic radiotherapy. [ABSTRACT FROM AUTHOR]

Striping noise is a well-known phenomenon that arises in most multi-detector optical imaging instruments. Such noise affects both visual interpretation and quantitative analysis. Therefore, destriping is an essential step before absolute calibration and image interpretation. Histogram matching is one of the most popular algorithms used to reduce striping. The assumption underlying histogram matching is that each detector has the same gray level distribution. This assumption is easily satisfied when the image is sufficiently large, but it often cannot be satisfied for small images. An improved histogram matching algorithm based on sliding windows is proposed in this paper. The algorithm presupposes that the gray level distribution of each column (taking the vertical striping noise as an example) is similar to the gray level distribution of the column-centered local area. The size of the local area is determined by a histogram growing algorithm. Compact High Resolution Imaging Spectrometer (CHRIS), Moderate Resolution Imaging Spectroradiometer (MODIS) and Hyperspectral Imager (HSI) images were used to test the new and traditional algorithms. These destriping results were compared using improvement factors, inverse coefficients of variation and mean profiles. The results of the comparison indicate that the improved histogram matching algorithm has obvious advantages over traditional method. [ABSTRACT FROM AUTHOR]

In every X-ray spectroscopy measurement the influence of the detection system causes loss of information. Different mechanisms contribute to form the so-called detector response function (DRF): the detector efficiency, the escape of photons as a consequence of photoelectric or scattering interactions, the spectrum smearing due to the energy resolution, and, in solid states detectors (SSD), the charge collection artifacts. To recover the original spectrum, it is necessary to remove the detector influence by solving the so-called inverse problem. The maximum entropy unfolding technique solves this problem by imposing a set of constraints, taking advantage of the known a priori information and preserving the positive-defined character of the X-ray spectrum. This method has been included in the tool UMESTRAT (Unfolding Maximum Entropy STRATegy), which adopts a semi-automatic strategy to solve the unfolding problem based on a suitable combination of the codes MAXED and GRAVEL, developed at PTB. In the past UMESTRAT proved the capability to resolve characteristic peaks which were revealed as overlapped by a Si SSD, giving good qualitative results. In order to obtain quantitative results, UMESTRAT has been modified to include the additional constraint of the total number of photons of the spectrum, which can be easily determined by inverting the diagonal efficiency matrix. The features of the improved code are illustrated with some examples of unfolding from three commonly used SSD like Si, Ge, and CdTe. The quantitative unfolding can be considered as a software improvement of the detector resolution. [ABSTRACT FROM AUTHOR]

Internal bremsstrahlung (IB) accompanying the β − decay of 204 Tl was measured using a 5.08×5.08 cm 2 NaI(Tl) detector employing a magnetic deflection method in the range of 10–760 keV. A novel approach, the Singular Value Decomposition (SVD), is applied to unfold the raw detector spectrum of 204 Tl. Unfolded IB spectrum is compared with the KUB theory. The measured spectrum is found to show fairly good agreement with the KUB theory in the energy range of 100–600 keV. The distribution beyond the 600 keV takes a positive deviation from the theory. [ABSTRACT FROM AUTHOR]

BACKGROUND: While spectral CT using single photon counting detector has shown a number of advantages in diagnostic imaging, knowledge of the detector response function of an energy-resolved detector is needed to correct the signal bias and reconstruct the image more accurately. OBJECTIVE: The objective of this paper is to study the photo counting detector response function using laboratory sources, and investigate the signal bias correction method. METHODS: Our approach is to model the detector response function over the entire diagnostic energy range (20 keV

Two coaxial and a low-energy HPGe detector were characterized with Monte Carlo simulations, using the geant4 toolkit. The geometry of the detectors, including the dimensions of the crystal and the internal structural parts, were initially taken from the factory specifications and from X-ray radiographies, and were later fine-tuned. The detector response functions, with special emphasis on the absolute full-energy peak efficiencies and peak-to-total ratios, were calculated and compared to experimental data taken at different measurement geometries. Between 150 keV and 11 MeV an agreement within 1-2 standard deviation has been achieved, whereas systematic deviations were experienced at lower energies. [ABSTRACT FROM AUTHOR]

Abstract: The solution of the unfolding problem is an ever-present issue in X-ray spectrometry. The maximum entropy technique solves this problem by taking advantage of some known a priori physical information and by ensuring an outcome with only positive values. This method is implemented in MAXED (MAXimum Entropy Deconvolution), a software code contained in the package UMG (Unfolding with MAXED and GRAVEL) developed at PTB and distributed by NEA Data Bank. This package contains also the code GRAVEL (used to estimate the precision of the solution). This article introduces the new code UMESTRAT (Unfolding Maximum Entropy STRATegy) which applies a semi-automatic strategy to solve the unfolding problem by using a suitable combination of MAXED and GRAVEL for applications in X-ray spectrometry. Some examples of the use of UMESTRAT are shown, demonstrating its capability to remove detector artifacts from the measured spectrum consistently with the model used for the detector response function (DRF). [Copyright &y& Elsevier]

The absorbed energy distribution (AED) in X-ray imaging detectors is an important factor that affects both energy resolution and image quality through the Swank factor and detective quantum efficiency. In the diagnostic energy range (20–140 keV), escape of characteristic photons following photoelectric absorption and Compton scatter photons are primary sources of absorbed-energy dispersion in X-ray detectors. In this paper, we describe the development of an analytic model of the AED in compound X-ray detector materials, based on the cascaded-systems approach, that includes the effects of escape and reabsorption of characteristic and Compton-scatter photons. We derive analytic expressions for both semi-infinite slab and pixel geometries and validate our approach by Monte Carlo simulations. The analytic model provides the energy-dependent X-ray response function of arbitrary compound materials without time-consuming Monte Carlo simulations. We believe this model will be useful for correcting spectral distortion artifacts commonly observed in photon-counting applications and optimal design and development of novel X-ray detectors. [ABSTRACT FROM AUTHOR]

Abstract: A Monte Carlo simulation study has been conducted of 60Co photons Compton scattered in concrete, illustrating the degraded energy spectra of gamma-ray radiation. Results are produced representing a NaI(Tl) detector model. We were able to analyse energy distributions of photons that reach the detector system after suffering several successive Compton scatterings in the target. The predicted decrease in intensity of single- and multiple-scattering peaks with increase in thickness of the target medium are in good agreement with experimental observations and findings reported by others. [Copyright &y& Elsevier]

We have written a Monte Carlo code to simulate the experimental results of a previously reported study. We were able to analyse the energy distributions of photons that reached the detector system after suffering several successive Compton scatterings in the target. We have also investigated how the number of multiply backscattered events depends on the target thickness and the energy of the primary photons. [ABSTRACT FROM AUTHOR]

Abstract: The Monte Carlo-based Energy Dispersive X-ray Fluorescence (MCXRF) elemental analyzer approach can be used to accurately calculate elemental weight fractions in rock formations or metal alloys, by least-squares regression of the measured X-ray spectrum with computer-generated elemental library spectra. The analog sampling scheme in a Monte Carlo simulation cannot generate satisfactory results for trace elements due to their low sampling probability. A stratified sampling variance-reduction technique is proposed and implemented to enable each element in the measured sample to have equal opportunity of being sampled with adjusted weights. Essentially, all computed elemental libraries have good statistical precision and improve the accuracy of the elemental analysis results. [Copyright &y& Elsevier]

Abstract: A simple Monte Carlo program named CEARDRFs has been developed to generate very accurate detector response functions (DRFs) for scintillation detectors. It utilizes relatively rigorous gamma-ray transport with simple electron transport, and accounts for two phenomena that have rarely been treated: scintillator non-linearity and the variable flat continuum part of the DRF. It has been proven that these physics and treatments work well for 3×3″ and 6×6″ cylindrical NaI detector in CEAR''s previous work. Now this approach has been expanded to cover more scintillation detectors with various common shapes and sizes. Benchmark experiments of 2×2″ cylindrical BGO detector and 2×4×16″ rectangular NaI detector have been carried out at CEAR with various radiactive sources. The simulation results of CEARDRFs have also been compared with MCNP5 calculations. The benchmark and comparison show that CEARDRFs can generate very accurate DRFs (more accurate than MCNP5) at a very fast speed (hundred times faster than MCNP5). The use of this program can significantly increase the accuracy of applications relying on detector spectroscopy like prompt gamma-ray neutron activation analysis, X-ray fluorescence analysis, oil well logging and homeland security. [Copyright &y& Elsevier]

In this study, a Monte Carlo program has been developed to simulate the response function of the NaI(Tl) detector with all features for Co and Cs and to investigate the effects of detector housing material on response function. The pulse height spectra in a 2″ × 2″ NaI(Tl) detector due to these gamma ray sources have been measured. Comparison of the experimentally obtained and simulated spectra shows that there is good agreement between both spectra. Energy distributions of gamma photons that generate the backscattering peak in the response function were obtained and the contribution of single, double and multiple Compton scattering events to these distributions was investigated. [ABSTRACT FROM AUTHOR]

The energy spectra of beta rays emitted fromSr and Tl radioisotopes were obtained by using a silicon surface barrier detector with a 1000 μm depleted layer and 50 mm effective area. The detector response function is interpreted by making use of range distributions of mono-energetic electrons in matter and by assuming a linear energy loss along the range in the depleted layer of the detector. An analytical expression is given for pulse height distribution obtained in the surface barrier detector. A good agreement is observed between the experimental results and theoretical interpretation. [ABSTRACT FROM AUTHOR]

Abstract: X-ray fluorescence data bases have significant contradictions, and inconsistencies. We have identified that the main source of the contradictions, after the human factors, is rooted in the signal processing approaches. We have developed signal processors to overcome many of the problems by maximizing the information available to the analyst. These non-paralyzable, fully digital signal processors have yielded improved resolution, line shape, tailing and pile up recognition. The signal processors account for and register all events, sorting them into two spectra, one spectrum for the desirable or accepted events, and one spectrum for the rejected events. The information contained in the rejected spectrum is mandatory to have control over the measurement and to make a proper accounting and allocation of the events. It has established the basis for the application of the fundamental parameter method approach. A fundamental parameter program was also developed. The primary X-ray line shape (Lorentzian) is convoluted with a system line shape (Gaussian) and corrected for the sample material absorption, X-ray absorbers and detector efficiency. The peaks also can have, a lower and upper energy side tailing, including the physical interaction based long range functions. It also employs a peak and continuum pile up and can handle layered samples of up to five layers. The application of a fundamental parameter method demands the proper equipment characterization. We have also developed an inverse fundamental parameter method software package for equipment characterisation. The program calculates the excitation function at the sample position and the detector efficiency, supplying an internally consistent system. [Copyright &y& Elsevier]

Abstract: A gamma-ray beam produced by Compton scattering of a laser beam with a relativistic electron beam has been used for nuclear physics research at the high intensity -ray source () facility at Duke University. The success of many experiments using the gamma-ray beam critically depends on the accurate knowledge of the gamma-ray beam energy distribution which is typically obtained by unfolding a measured energy spectrum. Conventionally, the detector response function used in the spectrum unfolding is simulated by a simple Monte Carlo code in which an isotropic gamma-ray event generator is used. However, for a Compton scattered gamma-ray beam, this simulation method could lead to an inaccurate detector response function, since it neglects the spatial and energy distributions of the gamma-ray beam. In this paper, we will present a novel end-to-end gamma-ray spectrum reconstruction method by completely modeling the process of the Compton gamma-ray beam production, collimation, transportation and detection. Using this method, we have successfully reconstructed the energy distribution of beams for nuclear physics research with a high degree of accuracy. [Copyright &y& Elsevier]

Abstract: In Computed Tomography (CT) X-ray intensities are measured by large-scale solid-state detectors. The standard set-up comprises a scintillator pixel array attached to a matrix of photo sensors, which in turn is read out by analog-to-digital conversion electronics. We have developed and validated a three-dimensional system model describing the cascaded system process. The first step comprises a Monte-Carlo (MC) tracking of the primary X-ray quanta energy deposition, taking into account the relevant fluorescence and scattering processes. The second step models the transport of optical photons in the scintillator pixels formed by a solid-state bulk with surrounding back-scattering TiO2 walls. In a third step the individual events are integrated to a read-out signal and analyzed for their statistical properties. The system model is verified by a comparison to optical measurements. A scintillator array is excited by a needle beam X-ray source. The emitted light field is read out by a high-resolution CCD sensor. A good agreement between simulation and experiments is found, with a typical deviation in the range of 5%. The detector response function D(E, E′) is used to quantify the spectral behavior. It yields the probability to measure an energy E′ for an incoming quantum energy E. We calculate the expected energy 〈E′(E)〉 and link the deviations from proportionality in E to properties of the signal transport. Finally the impact of the signal transport statistics on the output signal-to-noise ratio is analyzed. [Copyright &y& Elsevier]

Abstract: Micro-pocket fission detectors (MPFDs) have recently been fabricated and successfully tested as in-core flux monitoring devices in the nuclear reactor in Kansas State University. These detectors are sufficiently small to be inserted between fuel elements. Data from an MPFD array can be converted into a 3D power-density map of the reactor core for real-time flux monitoring. In the present study, the necessary mathematical models are developed that relate the power-density profiles in fuel rods to the MPFDs'' response. The applicability of an inversion algorithm proposed for obtaining power-density profiles is also verified in this study. [Copyright &y& Elsevier]

A new approach to generating detector response functions (DRFs) for NaI detectors is developed and demonstrated. It consists of using Monte Carlo simulation with a specific purpose code (named g03) that utilizes relatively rigorous gamma-ray transport with very simple electron transport. The approach accounts for two phenomena that have not been previously treated in this way: NaI non-linearity and the variable flat continua part of the DRF. The first is accounted for by utilizing the known non-linear relationship between NaI scintillation efficiency and deposited electron energy within the Monte Carlo code. The second is accounted for by using a semi-empirical relationship between electron range and incident gamma-ray energy within the Monte Carlo code. The resulting DRFs for 3″ × 3″ and 6″ × 6″ NaI detectors are benchmarked with the extensive existing data of Heath [AEC Research and Development Report, Physics, TID-4500] for the 3″ × 3″ detectors and with new data for the 6″ × 6″ detectors. Results indicate that the approach is accurate and the use of this approach should increase the accuracy of prompt gamma-ray neutron activation analysis significantly. [Copyright &y& Elsevier]

For fitting PIXE spectra with a computer program the detector response function should be known with good enough precision to guarantee accurate determination of the elemental yields. The response of a semiconductor detector to monochromatic X-ray radiation does not have a simple dependence on energy. Normally, it can be described by a linear combination of several analytical functions: Gaussian or Voigt for the line itself, and additional tail contributions simulating the incomplete charge collection (ICC) – exponential tails and step functions – on the low-energy side of the line. In this work thin MicroMatter monoelemental targets were irradiated with 1–3 MeV protons and corresponding X-ray spectra were measured. It was found that the response functions can be satisfactorily reproduced for the X-ray energy range 4–10 keV. The precision of the response function determination is slightly hampered for soft X-rays (below 4 keV) due to bremsstrahlung background from the Nuclepore backing. Our procedure has been applied for the two Si(Li) detectors used for routine PIXE analysis in the laboratory. [Copyright &y& Elsevier]

• A realistic response function is modeled for the CdTe detectors used in a hard X-ray diagnostic of the TCV tokamak. • The characteristics of the detector observed in the measurement of multiple radioactive. sources are considered in the modeling. • The measured energy spectra of radioactive sources can be correctly reconstructed using the new response function. • The response function is applied to a hard X-ray synthetic diagnostic for the study of energetic electrons. The response function of CdTe detectors used in a hard X-ray spectrometer system (HXRS) on the TCV tokamak fusion experiment is modeled based on the measured energy spectra from multiple gamma-ray sources. The response function consists of an asymmetric Gaussian photopeak, an exponentially inclined shelf structure below the photopeak, and CdTe escape peaks. It is demonstrated that the measured energy spectra of radioactive sources can be correctly reconstructed using this response function. This model is applied to a hard X-ray synthetic diagnostic used to convert a modeled electron distribution function to a measured hard X-ray signal, for the study of energetic electrons in the TCV tokamak. [ABSTRACT FROM AUTHOR]