Detector Response Function Research Articles

Study of CdTe detector response functions using different MCNPX computational modeling detailing

The spectra measured with cadmium telluride (CdTe) detectors show high spectral distortions that must be corrected by applying a mathematical algorithm along with the detector's response functions. Simplified computational modeling of the CdTe detector is generally used to obtain its response functions. In this work, the Monte Carlo code MCNPX was used to study the response functions of a CdTe detector using more complex detector modeling and compared it with those obtained by simplified modeling. Raw spectra were corrected using the response matrices obtained for the simplified and detailed modeling of the CdTe and compared with those obtained with reference-validated software.

An X-ray fluorescence experimental method for photon-counting detector in computed tomography system

The X-ray fluorescence (XRF) spectrum of specific elements can be utilized in energy calibration, energy resolution measurement, and analysis of energy response functions for photon-counting detectors (PCDs). The applications can be beneficial for PCD threshold accuracy, performance verification, and optimizing image quality. In previous literature, the experimental configuration for the XRF spectrum typically employed a vertical configuration to avoid the influence of the primary X-ray beam. However, such an experimental configuration is constrained by the fixed position of the X-ray source and detector in the computed tomography (CT) system. Hence, the purpose of this study is to investigate a horizontal configuration for XRF measurements and compare the differences in XRF spectrum with vertical configuration. The results indicate that the spectral characteristics of the horizontal and vertical configurations are similar, suggesting that the horizontal configuration could be applied for energy calibration and spectral analysis in PCD-CT systems.

Determination of neutron spectrum based on artificial neural network using liquid scintillation detector EJ-301.

This paper focuses on the neutron spectrum measurement using a liquid scintillation detector, where the neutron spectrum could be identified and unfolded from the light output distribution of the EJ-301 liquid scintillation detector through a linear artificial neural network (ANN). The response functions of the EJ-301 detector for monoenergetic neutron sources, as well as the light outputs, have been simulated and calculated by Monte Carlo procedure FLUKA. The linear ANN was trained and tested through the simulated data, where response functions were set as the input of ANN and the corresponding neutron spectra were output. Therefore, the neutron spectrum-unfolding model was created. This spectrum-unfolding model was tested through the light outputs induced by monoenergetic neutrons and the random superposition of them. Unfolding results show that this model could identify the information of the neutron spectrum accurately from the light outputs of a liquid scintillation detector. Moreover, the EJ-301 detector was used to measure the radioactivity of 252Cf, and the pulse height distribution induced by neutrons was derived through the charge-comparison method to remove the influence of gamma rays. The measured pulse height distribution was unfolded by the trained model, and measured results show that the unfolded neutron spectrum of 252Cf was consistent with the reference one. This paper presents the feasibility that the unknown neutron spectrum could be identified and confirmed through a linear neural network trained by simulated monoenergetic neutron response functions, which could be a candidate of choice for the determination of the neutron spectrum.

Characterization of neutron spectrum of polyethylene-moderated AmBe neutron source using a passive single-cylindrical neutron spectrometer

The changes in the neutron spectrum produced by the AmBe neutron source moderated in the polyethylene sphere need to be characterized. A passive single-moderator neutron spectrometer with indium foil activation neutron detector has been developed to characterize the neutron spectrum of an AmBe source inside a polyethylene sphere. The detector response function was calculated using the MCNPX 2.7 program with IRDFF-II nuclear data library. Measurements were conducted by placing the Single-Cylindrical Neutron Spectrometer (SCNS) on the outer surface of the sphere for 5 h. The 116mIn activity due to neutron activation in each indium foil was measured using a gamma spectrometer with an HPGe detector. By identifying the count value at the peak energy of 1294 KeV and considering an HPGe detector efficiency of 3.2% at the foil position 1 mm above the detector surface, the activity of 116mIn was obtained. The activity value of 116mIn from each indium foil was compared with the MCNPX simulation results. The neutron spectrum was unfolded using the UMG 3.3 program with activity data input of 116mIn for each foil and detector response. A neutron spectrum was obtained with a total neutron flux of 634 ± 60 n/cm2·s, consisting of 25% thermal neutrons, 16% epithermal neutrons, and 61% fast neutrons. When compared with the simulation results, the total neutron flux in the spectrum produced by SCNS-In showed only a small difference of 1%. Based on these neutron spectrum measurements, it was determined that placing the AmBe neutron source inside a 15″ diameter PE-sphere will reduce the fast neutron flux by 78%.

Validation of the FLUKA code to simulate response functions of organic liquid scintillator for high‐energy neutrons

In this research, the FLUKA code was employed to calculate the response functions of the BC501A organic scintillation detector for energies ranging from 25 to 800 MeV. Using the AUXSCORE, EVENTBIN and TCQUENCH cards, the response function of the BC501A organic scintillation detector to mono-energetic neutrons in the energy range of 25–800 MeV was computed. The comparison confirms that the simulation results obtained from the FLUKA code show a promising agreement with the results obtained from experiments, other codes, and the analytical method.

COSMONAUT: A COmpact spectrometer for measurements of neutrons at the ASDEX upgrade tokamak.

A COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak (COSMONAUT) has been developed for spectroscopy measurements of the 2.45MeV neutron emission from deuterium plasmas at the ASDEX Upgrade. The instrument is based on a CLYC-7 inorganic scintillator, whereby the detection of fusion neutrons occurs via their interaction with 35Cl nuclei in the detector crystal, leading to a peak in the detector response function and providing excellent neutron/gamma-ray discrimination capabilities. The diagnostics is installed along a radial line of sight and makes use of a digital system to record time resolved data for the whole duration of the discharge. Measurements in ASDEX Upgrade plasmas with neutral beam injection have been carried out and are successfully interpreted using state-of-the-art modeling codes. Next step applications of the diagnostics are in experiments aimed at generating energetic particles by ion cyclotron resonance heating schemes. In these scenarios, COSMONAUT will provide unique information on the acceleration of deuterons beyond the beam injection energy and on their confinement, for comparison with modeling.

Balancing Performance and Portability: A Study on CsI(Tl) Crystal Sizes for Real-Time Gamma-Ray Spectrum and Dose Monitoring

Current radiation dosimeters sometimes face accuracy limitations or provide only cumulative doses over long periods. To contribute to this area, we developed a portable monitor that measures the energy spectrum and dose of gamma rays in real time. To achieve this, we used an improved sequential Bayesian estimation algorithm. The dose rate was then derived from the energy spectrum by applying a flux-to-dose conversion coefficient. The monitor consists mainly of a CsI(Tl) scintillator and a multi-pixel photon counter (MPPC). In developing this device, we focused on striking a balance between measurement accuracy, ease of use, and portability. As an essential aspect of the research, we investigated the influence of the CsI(Tl) crystal size on the performance of the monitor to determine an optimal size. This was accomplished by calculating the detection efficiency and energy resolution through experimental measurements using standard gamma-ray sources and simulations using MCNP5. Within the scope of the research, detector response functions were created for each crystal size for an energy range of 10 keV to 3 MeV. Considering an optimal balance of detection efficiency and energy resolution alongside a compact size suitable for portable applications, the crystal measuring 2.6 × 2.6 × 1.3 cm3 was deemed preferable.

DRiFT current mode, trigger settings and flexible detector specifications applied to scintillator arrays

MCNP radiation transport output is post-processed by DRiFT, a Detector Response Function Toolkit to simulate detailed nuclear instrumentation response. DRiFT can be used to assess the performance and potential limitations of scintillator, gas, and semiconductor detectors under a variety of simulated conditions not easily achievable in a laboratory setting. This work describes new updates in DRiFT for scintillator simulations which focus on the capability to simulate scintillators in current mode, an expansion of trigger options, and the ability to customize individual detector properties in a simulation. These improvements are designed to facilitate the ability to model large arrays of scintillator detectors with higher fidelity than was previously possible and are demonstrated in three examples. The first shows the difference between operating DRiFT in current and pulse mode. In the second example, which is intended to demonstrate deviations in individual detector performance, each detector has properties (PMT gain, optical transport, scintillation yield, etc.) that vary between detectors and are specified in DRiFT. A final example examines how DRiFT could be used to optimize digitizer settings in high rate measurements with split signals using the new common trigger option.

A comparative evaluation of sample preparation techniques for the therapeutic monitoring of carbamazepine in human plasma by RPLC/DAD

Four sample preparation techniques, namely direct protein precipitation through a) trichloroacetic acid addition (PPA) or b) acetonitrile addition (PPO), c) liquid-liquid extraction in n-octanol followed by the direct injection of the organic layer, and d) supramolecular solvent extraction in a tetrahydrofuran/n-octanol/water coacervate (SUPRAS) were evaluated to be used for the RPLC/DAD assay of carbamazepine in human plasma samples, targeting therapeutic monitoring (TM) purposes. The chromatographic approach to separating carbamazepine from human plasma matrices was designed to be a simple gradient elution with an octadecyl chemically modified silica gel stationary phase, and a mobile phase composed of acetonitrile (organic) and HPLC grade water (aqueous), both with 0.1% formic acid. Monitoring at 290 nm allowed for the detection of carbamazepine. After optimizing both sample preparation procedures and chromatographic separation parameters, LOQ values of 3 µg/mL (PPA), 0.6 µg/mL (PPO), 12 ng/mL (LLE) and 50 ng/mL (SUPRAS) were determined. Detector response functions were studied over an interval up to 20 µg/mL (ULOQ).

High-purity germanium semiconductor modeling in the detector response function toolkit

We have extended the detector response function toolkit (DRiFT) to provide modeling capabilities of semiconductor sensors. DRiFT provides realistic nuclear instrumentation response by post-processing Monte-Carlo N-particle (MCNP®) radiation transport outputs. MCNP® is capable of modeling radiation transport in complex environments, but has limited detector physics and readout electronics modeling capabilities. Semiconductor detector response can be calculated with a high-fidelity for a flexible range of environments by utilizing MCNP® to simulate radiation interactions inside of detector volumes, and then using DRiFT to model charge transport and signal formation in the semiconductor, as well as the readout electronics. DRiFT models charge transport in the semiconductor, the preamplifier, shaping amplifier, pulse pile-up, and electronic noise to generate detector response. The semiconductor application in DRiFT can model a range of semiconductor materials, shapes, and sizes; and is demonstrated here for a large volume coaxial high-purity germanium (HPGe) detector. Here, we compare detector response functions of a coaxial HPGe detector with measurement of 60Co, 133Ba, and 137Cs at varying count rates, and we conduct a parameter study to demonstrate the effect of changing parameters in the DRiFT simulation. The HPGe detector response function shows excellent agreement with measurements of difference sources with varying dead times and count rates.

Dose Measurements at Provision Proton Therapy Center.

Proton therapy is an advanced method for treating cancerous tumors, and its adoption has expanded significantly in recent years. The production of high-energy protons, however, may result in the creation of secondary neutrons and gamma rays. Hence, ensuring radiation safety at proton therapy centers is crucial, with shielding playing a vital role. This study aimed to evaluate the efficacy of the shielding implemented at the Provision Proton Therapy center in Knoxville, TN, USA. For this purpose, we measured and compared gamma ray radiation levels within the treatment room and the facility's roof. These measurements were conducted using a NaI(Tl) scintillator detector. The PHITS Monte Carlo code was used to deconvolute the incident spectrum using detector response functions. Findings reveal that the facility's shielding effectively protects the general public from gamma ray radiation, with the effective dose within the treatment room being minimal and dose on the roof was comparable to background radiation levels. However, it is important to note that this study did not address the issue of secondary neutron radiation field, which is an important aspect of dose and radiation safety in proton therapy centers.

A compact scintillator-based detector for high energy neutron spectrometry

A compact neutron spectrometer consisting of a 6 mm × 6 mm × 120 mm prism of EJ-276 plastic scintillator capable of pulse shape discrimination coupled to a single silicon photomultiplier is described. In principle this device will be capable of spectroscopic measurements exceeding 100 MeV using unfolding analyses with detector response functions measured at neutron time-of-flight facilities. A characterisation of the device is described and illustrated with measurements of the detector response made at three fast neutron facilities with energies between 5.0 MeV and 63.5 MeV. Nearly mono-energetic detector response functions were used to produce neutron energy spectra by unfolding light output distributions measured with the detector in the energy range of interest.

Quartz as an accurate high-field low-cost THz helicity detector

Emerging concepts employing angular momentum of THz light for ultrafast material control rely on the measurement of undistorted intense THz fields and on the precise knowledge about sophisticated THz helicity states. Here, we establish z-cut α-quartz as a precise electro-optic THz detector for full amplitude, phase, and polarization measurement of highly intense THz fields, all at a fraction of costs of conventional THz detectors. We experimentally determine its detector response function, in excellent agreement with our modeling. Thereupon, we develop a swift and reliable protocol to precisely measure arbitrary THz polarization and helicity states. This two-dimensional electro-optic sampling in α-quartz fosters rapid and cost-efficient THz time-domain ellipsometry and enables the characterization of polarization-tailored fields for driving chiral or other helicity-sensitive quasi-particles and topologies.

Prospects for combined analyses of hadronic emission from γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray sources in the Milky Way with CTA and KM3NeT

The Cherenkov Telescope Array and the KM3NeT neutrino telescopes are major upcoming facilities in the fields of γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray and neutrino astronomy, respectively. Possible simultaneous production of γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} rays and neutrinos in astrophysical accelerators of cosmic-ray nuclei motivates a combination of their data. We assess the potential of a combined analysis of CTA and KM3NeT data to determine the contribution of hadronic emission processes in known Galactic γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray emitters, comparing this result to the cases of two separate analyses. In doing so, we demonstrate the capability of Gammapy, an open-source software package for the analysis of γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray data, to also process data from neutrino telescopes. For a selection of prototypical γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray sources within our Galaxy, we obtain models for primary proton and electron spectra in the hadronic and leptonic emission scenario, respectively, by fitting published γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray spectra. Using these models and instrument response functions for both detectors, we employ the Gammapy package to generate pseudo data sets, where we assume 200 h of CTA observations and 10 years of KM3NeT detector operation. We then apply a three-dimensional binned likelihood analysis to these data sets, separately for each instrument and jointly for both. We find that the largest benefit of the combined analysis lies in the possibility of a consistent modelling of the γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray and neutrino emission. Assuming a purely leptonic scenario as input, we obtain, for the most favourable source, an average expected 68% credible interval that constrains the contribution of hadronic processes to the observed γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray emission to below 15%.

Influence of dead layer on the response function of planar and coaxial Ge detector using Monte Carlo method

Germanium crystals have a dead layer that causes a decrease in efficiency since the layer is not useful for detection but strongly attenuates photons. The thickness of this inactive layer is not well known due to the existence of a transition zone where photons are increasingly absorbed. Therefore, using data provided by manufacturers in the detector simulation model, some strong discrepancies appear by changing the dead layer. Investigations into the Ge detector response functions for gamma rays have been conducted using straightforward physical mechanisms implemented by Monte Carlo simulations. The detector response function feature's most probable interaction mechanisms are described. The Monte Carlo method is applied to simulate the calibration of a HPGe detector in order to determine the total inactive germanium layer thickness and the active volume that is needed in order to study the response function for both types of detectors. Results indicated a strong impact of dead layer variations on the response function of the simulated detectors.

Pre-Launch Spectral Calibration of the Absorbed Aerosol Sensor.

Spectral calibration consists of the calibration of wavelengths and the measurement of the instrument's spectral response function (SRF). Unlike conventional slits, the absorbed aerosol sensors (AAS) are used as a slit homogenizer, in which the SRF is not a conventional Gaussian curve. To be more precise, the SRF is the convolution of the slit function of the spectrometer, the line spread function of the optical system, and the detector response function. The SRF of the slit homogenizer is a flat-topped multi-Gaussian function. Considering the convenience of fitting, a super-Gaussian function, which has a distribution similar to the flat-topped multi-Gaussian function, is employed to fit the measured data in a spectral calibration. According to the results, the SRF's shapes resembling a Gaussian curve with a flat top could be derived, which contains a full width at half maximum (FWHM) of 1.78-1.82 nm for the AAS. The results show that the correlation is about 0.99, which indicates the usefulness of the fitting function that could better characterize the SRF of the instrument.

Measuring response functions for a new compact neutron spectrometer

A compact neutron spectrometer consisting of a (0.6 x 0.6 x 12.0 cm3) EJ-276 plastic scintillator coupled to a silicon photomultiplier has been designed. An essential aspect of the characterisation of the spectrometer is the measurement of detector response functions for neutron energies above 20 MeV. The process of producing response functions for neutron energies between 10 MeV and 60 MeV for the compact detector using neutron time-of-flight measurements at iThemba LABS is presented.

First Measurement of the Nuclear-Recoil Ionization Yield in Silicon at 100eV.

We measured the nuclear-recoil ionization yield in silicon with a cryogenic phonon-sensitive gram-scale detector. Neutrons from a monoenergetic beam scatter off of the silicon nuclei at angles corresponding to energy depositions from 4keV down to 100eV, the lowest energy probed so far. The results show no sign of an ionization production threshold above 100eV. These results call for further investigation of the ionization yield theory and a comprehensive determination of the detector response function at energies below the keV scale.

Research of dynamic rod worth measurement technique based on the pin-by-pin response function

The dynamic rod worth measurement (DRWM) technique is widely applied in PWR engineering. In DRWM, the response function of the ex-core detector is very significant to calculate the spatial-correction factors which are introduced to eliminate the spatial effects due to the rapid movement of control rods. Theoretically, the peripheral pins of the peripheral fuel assemblies close to the ex-core detector have large contributions to the ex-core detector signal. However, the conventional DRWM technique only uses the nodal response function, which can’t consider the pin-level contribution. Therefore, the DRWM technique based on the pin-by-pin response function has been proposed in this study. This proposed technique has been applied and verified with the measurement data of commercial PWRs operated in China. The engineering verification showed that this technique could provide accurate spatial-correction factors, and the measured control-rod worth satisfies the engineering acceptance criteria.

Reconstruction algorithm for the runaway electron energy distribution function of the ITER hard x-ray monitor

Hard x-ray (HXR) spectrometry in ITER can provide information about Runaway Electrons (REs) in tokamak plasmas. Non-trivial reconstruction techniques must be applied to study the Energy distribution of REs in tokamaks since the diagnostic signals are convoluted with the emission of bremsstrahlung radiation from REs reaching the detector and the detector response function. A developed tool, coupled with the PREDICT code, has been described in this report for reconstructing the Runaway Electron energy distribution function (REDF) from HXR spectrum. Bremsstrahlung emission spectra and the detector response function are utilized in a forward modelling process to generate synthetic HXR spectra for different test REDF to which artificial noise is added. These HXR spectra are utilized to reconstruct the REDFs that can provide information about the REs in the plasma. The reconstruction process has been applied to the ITER HXR Monitor configuration for the first time. The effect of reduced optical transmission efficiency is studied on the reconstruction process and the accuracy of the extracted RE parameters. The performance of the reconstruction process is also tested for different amount of photon counts to identify the minimum number of photon counts required for optimal reconstruction. Preliminary results of RE-current estimation using the reconstruction process are also presented.