Detector Response Function Research Articles

Synthetic data for the study of the CUORE detector response function

CUORE (Cryogenic Underground Observatory for Rare Events) is a ton-scale experiment located at LNGS (Laboratori Nazionali del Gran Sasso) in Italy whose goal is to search for neutrino-less double beta decay (0υββ) in 130Te.CUORE exploits an array of 988 TeO2 crystals operated as Low-Temperature Detectors (LTDs) at 10 mK. These detectors show an excellent energy resolution, making the experiment one of the most competitive 0υββ searches in the world. In this scenario, the proposed research deals with the generation of synthetic (mock) data for the study of the CUORE detector response function. The production of synthetic data is a new tool we designed to consider all the missing information from a Montecarlo simulation: the detector non-idealities, as well as noise and pulse shape. The mock data are processed with the CUORE official analysis software, allowing us the evaluation of its impact on the final results.

Impact of new operational dosimetric quantities on individual monitoring services

The new operational dosimetric quantities framework, proposed in the ICRU95 report, has stimulated the scientific community to start investigations that aim to assess its impact on radiation protection practices. As part of this effort, the present study describes an inter-comparison exercise among individual monitoring services (IMSs) on passive whole-body dosimetry. The inter-comparison is performed in terms of both the existing operational dose quantity and its proposed replacement , to allow an evaluation of the actions that may be necessary to adapt dosimetry systems to the proposed quantity. For two of the tested IMSs, simple modifications to the detector response function, or the dose calculation algorithm, were sufficient to obtain results within acceptable limits. However, these approaches are not sufficient to give a level of performance comparable to that achieved in terms of . This may require a modification to dosemeter design.

Free-moving Quantitative Gamma-ray Imaging

The ability to map and estimate the activity of radiological source distributions in unknown three-dimensional environments has applications in the prevention and response to radiological accidents or threats as well as the enforcement and verification of international nuclear non-proliferation agreements. Such a capability requires well-characterized detector response functions, accurate time-dependent detector position and orientation data, a digitized representation of the surrounding 3D environment, and appropriate image reconstruction and uncertainty quantification methods. We have previously demonstrated 3D mapping of gamma-ray emitters with free-moving detector systems on a relative intensity scale using a technique called Scene Data Fusion (SDF). Here we characterize the detector response of a multi-element gamma-ray imaging system using experimentally benchmarked Monte Carlo simulations and perform 3D mapping on an absolute intensity scale. We present experimental reconstruction results from hand-carried and airborne measurements with point-like and distributed sources in known configurations, demonstrating quantitative SDF in complex 3D environments.

Inversion of statistics and thermalization in the Unruh effect

We derive a master equation for the reduced density matrix of a uniformly accelerating quantum detector in arbitrary dimensions, generically coupled to a field initially in its vacuum state, and analyze its late time regime. We find that such density matrix asymptotically reaches a Gibbs state. The particularities of its evolution towards this state are encoded in the response function, which depends on the dimension, the properties of the fields, and the specific coupling to them. We also compare this situation with the thermalization of a static detector immersed in a thermal field state, pinpointing the differences between both scenarios. In particular, we analyze the role of the response function and its effect on the evolution of the detector towards equilibrium. Furthermore, we explore the consequences of the well-known statistics inversion of the response function of an Unruh-DeWitt detector linearly coupled to a free scalar field in odd spacetime dimensions. This allows us to specify in which sense accelerated detectors in Minkowski vacuum behave as static detectors in a thermal bath and in which sense they do not.

Accelerated paths and Unruh effect. Part I. Scalars and fermions in Anti De Sitter spacetime

We have investigated the Unruh effect in Anti de-Sitter (AdS) spacetime by examining the response function of an Unruh-DeWitt particle detector with uniform constant acceleration. An exact expression of the detector response function for the scalar field has been obtained with different levels of non-linearity in even dimensional AdS spacetime. We also showed how the response of the accelerated Unruh detector coupled quadratically to massless Dirac field in D dimensional (D ≥ 2) AdS spacetime is proportional to that of a detector linearly coupled to a massless scalar field in 2D dimensional AdS spacetime. Here, the fermionic and scalar matter field is coupled minimally and conformally to the background AdS metric, respectively. Finally, we discuss about the extension of the results for more general stationary motion.

Invertibility of multi-energy X-ray transform.

PurposeThe goal is to provide a sufficient condition for the invertibility of a multi‐energy (ME) X‐ray transform. The energy‐dependent X‐ray attenuation profiles can be represented by a set of coefficients using the Alvarez–Macovski (AM) method. An ME X‐ray transform is a mapping from N AM coefficients to N noise‐free energy‐weighted measurements, where N≥2.MethodsWe apply a general invertibility theorem to prove the equivalence of global and local invertibility for an ME X‐ray transform. We explore the global invertibility through testing whether the Jacobian of the mapping J(A) has zero values over the support of the mapping. The Jacobian of an arbitrary ME X‐ray transform is an integration over all spectral measurements. A sufficient condition for J(A)≠0 for all A is that the integrand of J(A) is ≥0 (or ≤0) everywhere. Note that the trivial case of the integrand equals 0 everywhere is ignored. Using symmetry, we simplified the integrand of the Jacobian to three factors that are determined by the total attenuation, the basis functions, and the energy‐weighting functions, respectively. The factor related to the total attenuation is always positive; hence, the invertibility of the X‐ray transform can be determined by testing the signs of the other two factors. Furthermore, we use the Cramér–Rao lower bound (CRLB) to characterize the noise‐induced estimation uncertainty and provide a maximum‐likelihood (ML) estimator.ResultsThe factor related to the basis functions is always negative when the photoelectric/Compton/Rayleigh basis functions are used and K‐edge materials are not considered. The sign of the energy‐weighting factor depends on the system source spectra and the detector response functions. For four special types of X‐ray detectors, the sign of this factor stays the same over the integration range. Therefore, when these four types of detectors are used for imaging non‐K‐edge materials, the ME X‐ray transform is globally invertible. The same framework can be used to study an arbitrary ME X‐ray imaging system, for example, when K‐edge materials are present. Furthermore, the ML estimator we presented is an unbiased, efficient estimator and can be used for a wide range of scenes.ConclusionsWe have provided a framework to study the invertibility of an arbitrary ME X‐ray transform and proved the global invertibility for four types of systems.

Evaluation the nonlinear response function of a HPGe detector for 59 keV to 10.7 MeV gamma-rays using a Monte Carlo simulation and comparison with experimental data

Modeling of High Purity Germanium (HPGe) detector on a wide energy range is important in gamma-ray spectroscopy. The precisely modeled detector can be used for proton-induced prompt gamma-ray spectroscopy. In this work, we used both the gamma-rays of calibration sources and prompt gamma-rays emitted in proton capture reactions to model a coaxial p-type HPGe detector using Geant4 Monte Carlo simulation for the gamma-ray energy range of 59–10764 keV. The calibration sources were 137Cs, 241Am, 60Co, 152Eu, and 133Ba, while the prompt gamma-rays were due to the gamma-ray cascades following the 27Al(p,γ)28Si reaction capture at the resonant energies of 992, 1317 and 2483 keV, as well as the 23Na(p,γ)24Mg reaction capture at the resonant energies of 1417 and 1395 keV. According to the results obtained, the presented simulated and experimental spectra show a good agreement. In addition, the mean and maximum relative deviations between experimental and simulated efficiencies corresponding to 27 major peaks are smaller than 5% and 15%, respectively.

A compact stilbene crystal neutron spectrometer for NBI-heated plasma neutron diagnostics at EAST.

Stilbene crystal detectors are widely used as fast neutron measurement tools based on recoil proton detection, such as liquid scintillators. A compact stilbene crystal neutron spectrometer (CSCNS) has been installed at the Experimental Advanced Superconducting Tokamak (EAST) to obtain information on fuel ions produced in the plasma core because of its merits of good n/γ discrimination capability, high detection efficiency, and fast response. For the first time, CSCNS has been used for neutron emission spectroscopy measurements in EAST plasmas with neutral beam injection (NBI) heating. The CSCNS has the same horizontal line of sight as the time-of-flight enhanced diagnostics neutron spectrometer. Under NBI heating scenarios, the time trace of the neutron yield monitored by the CSCNS is similar to the one monitored by a standard 235U fission chamber. The experimental pulse height spectra are also similar to the simulated ones generated by folding the simulated neutron energy spectrum with the detector response functions. These results demonstrate the capability of the CSCNS for neutron diagnostics and the study of fast-ion physics in EAST.

Measurements of neutron fluxes from tokamak plasmas using a compact neutron spectrometer.

A compact neutron spectrometer based on the BC-501A liquid organic scintillator was applied to neutron measurements at the TUMAN-3M tokamak. The spectrometer was calibrated using measurements from the ion beam of the cyclotron accelerator. Neutron spectra were measured during discharges using a neutral deuterium beam injection into the TUMAN-3M D-plasma. An energy distribution of the neutrons from the plasma that hit the spectrometer was obtained from the measured BC-501A instrumental spectra by the DeGaSum code using detector response functions obtained in the course of the calibration. This allowed for the estimation of the 2.45MeV neutron yield and the evaluation of both the time evolution of the DD fusion rate and the characteristic time of the injected deuterium slowing down in discharges with neutral beam injection heating.

Verification and Validation of RAPID Formulations and Algorithms Based on Dosimetry Measurements at the JSI TRIGA Mark-II Reactor

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 Au(n,)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.

Physical approach to the marginalization of LIGO calibration uncertainties

The data from ground based gravitational-wave detectors such as Advanced LIGO and Virgo must be calibrated to convert the digital output of photodetectors into a relative displacement of the test masses in the detectors, producing the quantity of interest for inference of astrophysical gravitational wave sources. Both statistical uncertainties and systematic errors are associated with the calibration process, which would in turn affect the analysis of detected sources, if not accounted for. Currently, source characterization algorithms either entirely neglect the possibility of calibration uncertainties or account for them in a way that does not use knowledge of the calibration process itself. We present physiCal, a new approach to account for calibration errors during the source characterization step, which directly uses all the information available about the instrument calibration process. Rather than modeling the overall detector's response function, we consider the individual components that contribute to the response. We implement this method and apply it to the compact binaries detected by LIGO and Virgo during the second observation run, as well as to simulated binary neutron stars for which the sky position and distance are known exactly. We find that the physiCal model performs as well as the method currently used within the LIGO-Virgo collaboration, but additionally it enables improving the measurement of specific components of the instrument control through astrophysical calibration.

Modeling complex particles phase space with GAN for Monte Carlo SPECT simulations: a proof of concept

A method is proposed to model by a generative adversarial network the distribution of particles exiting a patient during Monte Carlo simulation of emission tomography imaging devices. The resulting compact neural network is then able to generate particles exiting the patient, going towards the detectors, avoiding costly particle tracking within the patient. As a proof of concept, the method is evaluated for single photon emission computed tomography (SPECT) imaging and combined with another neural network modeling the detector response function (ARF-nn). A complete rotating SPECT acquisition can be simulated with reduced computation time compared to conventional Monte Carlo simulation. It also allows the user to perform simulations with several imaging systems or parameters, which is useful for imaging system design.

Analytical modeling of the neutron response function of the NE213 organic liquid scintillator in the energy range of 0.2 MeV to 148 MeV

Determination of the neutron response function is essential for measuring the energy of neutrons emitted from natural and artificial neutron sources and nuclear reactions. This paper presents the calculation procedure of generating a neutron analytical response function for NE213 scintillation detectors in the energy range of 0.2–148 MeV. To obtain the analytical response function, the available neutron experimental response functions were grouped according to their behavior in different energy ranges. Different analytical functions were fitted to the experimental data of the detector response function for each neutron energy range. The function which best fits the experimental data was selected. Then a computer program was written for calculating the parameters of the analytical function by using the fitting functions and their parameters for each desired energy, and generating the analytical response functions. A comparison of the results shows that the analytical response functions are much faster and more consistent with the experimental response functions than the generated response functions of stand-alone codes and general-purpose Monte Carlo codes.

First application of large reactivity measurement through rod drop based on three-dimensional space–time dynamics

Reactivity measurement is an essential part of a zero-power physics test, which is critical to reactor design and development. The rod drop experimental technique is used to measure the control rod worth in a zero-power physics test. The conventional rod drop experimental technique is limited by the spatial effect and the difference between the calculated static reactivity and measured dynamic reactivity; thus, the method must be improved. In this study, a modified rod drop experimental technique that constrains the detector neutron flux shape function based on three-dimensional space-time dynamics to reduce the reactivity perturbation and a new method for calculating the detector neutron flux shape function are proposed. Correction factors were determined using Monte Carlo N-Particle transport code and transient analysis code for a pressurized water reactor at the Ulsan National Institute of Science and Technology and Xi'an Jiaotong University, and a large reactivity of over 2000 pcm was measured using the modified technique. This research evaluated the modified technique accuracy, studied the influence of the correction factors on the modification, and investigated the effect of constraining the shape function on the reactivity perturbation reduction caused by the difference between the calculated neutron flux and true value, using the new method to calculate the shape function of the detector neutron flux and avoiding the neutron detector response function (weighting factor) calculation.

Multiwavelength Photometry Derived from Monochromatic Kepler Data

Abstract The Kepler mission has provided a wealth of data, revealing new insights in time-domain astronomy. However, Kepler’s single bandpass has limited studies to a single wavelength. In this work we build a data-driven, pixel-level model for the pixel response function (PRF) of Kepler targets, modeling the image data from the spacecraft. Our model is sufficiently flexible to capture known detector effects, such as nonlinearity, intrapixel sensitivity variations, and focus change. In theory, the shape of the Kepler PRF should also be weakly wavelength-dependent, due to optical chromatic aberration and a wavelength-dependent detector response functions. We are able to identify these predicted changes in shape of the PRF using the residuals between Kepler data and our model. In this work, we show that these PRF changes correspond to wavelength variability in Kepler targets using a small sample of eclipsing binaries. Using our model, we demonstrate that pixel-level light curves of eclipsing binaries show variable eclipse depths, ellipsoidal modulation, and limb darkening. These changes at the pixel level are consistent with multiwavelength photometry. Our work suggests that each pixel in the Kepler data of a single target has a different effective wavelength, ranging from ≈550 to 750 nm. In this proof of concept, we demonstrate our model, and discuss possible uses for the wavelength-dependent PRF of Kepler. These uses include characterizing variable systems, and vetting exoplanet discoveries at the pixel level. The chromatic PRF of Kepler is due to weak wavelength dependence in the optical systems and detector of the telescope, and similar chromatic PRFs are expected in other similar telescopes, notably the NASA TESS telescope.

Detector Response to D-D Neutrons and Stability Measurements with 4H Silicon Carbide Detectors.

The use of wide-band-gap solid-state neutron detectors is expanding in environments where a compact size and high radiation hardness are needed, such as spallation neutron sources and next-generation fusion machines. Silicon carbide is a very promising material for use as a neutron detector in these fields because of its high resistance to radiation, fast response time, stability and good energy resolution. In this paper, measurements were performed with neutrons from the ISIS spallation source with two different silicon carbide detectors together with stability measurements performed in a laboratory under alpha-particle irradiation for one week. Some consideration to the impact of the casing of the detector on the detector’s counting rate is given. In addition, the detector response to Deuterium-Deuterium (D-D) fusion neutrons is described by comparing neutron measurements at the Frascati Neutron Generator with a GEANT4 simulation. The good stability measurements and the assessment of the detector response function indicate that such a detector can be used as both a neutron counter and spectrometer for 2–4 MeV neutrons. Furthermore, the absence of polarization effects during neutron and alpha irradiation makes silicon carbide an interesting alternative to diamond detectors for fast neutron detection.

Radioactive Source Localisation via Projective Linear Reconstruction.

Radiation mapping, through the detection of ionising gamma-ray emissions, is an important technique used across the nuclear industry to characterise environments over a range of length scales. In complex scenarios, the precise localisation and activity of radiological sources becomes difficult to determine due to the inability to directly image gamma photon emissions. This is a result of the potentially unknown number of sources combined with uncertainties associated with the source-detector separation—causing an apparent ‘blurring’ of the as-detected radiation field relative to the true distribution. Accurate delimitation of distinct sources is important for decommissioning, waste processing, and homeland security. Therefore, methods for estimating the precise, ‘true’ solution from radiation mapping measurements are required. Herein is presented a computational method of enhanced radiological source localisation from scanning survey measurements conducted with a robotic arm. The procedure uses an experimentally derived Detector Response Function (DRF) to perform a randomised-Kaczmarz deconvolution from robotically acquired radiation field measurements. The performance of the process is assessed on radiation maps obtained from a series of emulated waste processing scenarios. The results demonstrate a Projective Linear Reconstruction (PLR) algorithm can successfully locate a series of point sources to within 2 cm of the true locations, corresponding to resolution enhancements of between 5× and 10×.

Wide-range wavelength-tunable photon-pair source for characterizing single-photon detectors.

The temporal response of single-photon detectors is usually obtained by measuring their impulse response to short-pulsed laser sources. In this work, we present an alternative approach using time-correlated photon pairs generated in spontaneous parametric down-conversion (SPDC). By measuring the cross-correlation between the detection times recorded with an unknown and a reference photodetector, the temporal response function of the unknown detector can be extracted. Changing the critical phase-matching conditions of the SPDC process provides a wavelength-tunable source of photon pairs. We demonstrate a continuous wavelength-tunability from 526 nm to 661 nm for one photon of the pair, and 1050 nm to 1760 nm for the other photon. The source allows, in principle, to access an even wider wavelength range by simply changing the pump laser of the SPDC-based source. As an initial demonstration, we characterize single-photon avalance detectors sensitive to the two distinct wavelength bands, one based on Silicon, the other based on Indium Gallium Arsenide.

Monte-Carlo calculated detector response functions to unfold radiative neutron capture spectra

Results of geant4 Monte Carlo simulations carried out on the Budapest PGAA detector are presented in this paper. A complete set of detector response functions, i.e. the gamma spectra corresponding to incremental gamma-ray energies up to 12 MeV, were obtained by simulations and used to unfold the experimental gamma spectra of60Co and152Eu. The unfolding successfully removed the continuous Compton-background and the escape peaks related to a full-energy peak but preserved the shape and area of the peak itself. We finally demonstrated the applicability of this approach in determining the total radiative neutron capture cross-sections of the14N(n, γ) reaction, where an excellent agreement with literature data was found.

Assessing the Information Content of a Non-Destructive Testing CMOS Imaging Detector

The purpose of the present study was to assess the information content of a non-destructive testing (NDT) CMOS X-ray imaging detector in terms of the information capacity (IC), based on Shannon’s mathematical communication theory. IC was calculated after the experimental determination of the noise equivalent quanta (NEQ) under the IEC 62220-1-1:2015 standard’s RQA-5 beam quality. The detector response function was linear for the X-ray exposure range under investigation. At 70 kVp, under the RQA-5 irradiation, the IC value was 2119 bits/mm2. The information content of the particular detector was found comparable with other CMOS sensor / scintillating screens combinations, under similar X-ray exposure conditions.