Simulation Of Detector Response Research Articles

Sub-pixel electron detection using a convolutional neural network

Modern direct electron detectors (DEDs) provided a giant leap in the use of cryogenic electron microscopy (cryo-EM) to study the structures of macromolecules and complexes thereof. However, the currently available commercial DEDs, all based on the monolithic active pixel sensor, still require relative long exposure times and their best results have only been obtained at 300 keV. There is a need for pixelated electron counting detectors that can be operated at a broader range of energies, at higher throughput and higher dynamic range. Hybrid Pixel Detectors (HPDs) of the Medipix family were reported to be unsuitable for cryo-EM at energies above 80 keV as those electrons would affect too many pixels. Here we show that the Timepix3, part of the Medipix family, can be used for cryo-EM applications at higher energies. We tested Timepix3 detectors on a 200 keV FEI Tecnai Arctica microscope and a 300 keV FEI Tecnai G2 Polara microscope. A correction method was developed to correct for per-pixel differences in output. Timepix3 data were simulated for individual electron events using the package Geant4Medipix. Global statistical characteristics of the simulated detector response were in good agreement with experimental results. A convolutional neural network (CNN) was trained using the simulated data to predict the incident position of the electron within a pixel cluster. After training, the CNN predicted, on average, 0.50 pixel and 0.68 pixel from the incident electron position for 200 keV and 300 keV electrons respectively. The CNN improved the MTF of experimental data at half Nyquist from 0.39 to 0.70 at 200 keV, and from 0.06 to 0.65 at 300 keV respectively. We illustrate that the useful dose-lifetime of a protein can be measured within a 1 second exposure using Timepix3.

Generation of Synthetic Data for a Radiation Detection Algorithm Competition

This work details the generation of synthetic radiation data using large-scale Monte Carlo transport models to evaluate radiation search detection algorithms. Modular 3-D Monte Carlo models spanning multiple city blocks were constructed, loosely based on downtown Knoxville, TN, containing buildings composed of multiple materials (brick, granite, and concrete), sidewalks, a four-lane road, side streets, parking lots, and grassy fields. Background and simulated source detector response calculations from these models were used to create synthetic list mode data sets for a 2" × 4" × 16" NaI(Tl) detector moving through a city street at a constant speed. For the background simulations, major isotopes were computed individually so that background composition and variability could be computed efficiently outside Monte Carlo. The source detector response included six simulated sources placed at 15 source locations. Detector response was developed to be periodic through the city street so that a detector path could begin at one end of the model and wrap around to the other. This framework allowed for the creation of diverse data sets, each with its own unique background and simulated source detector response. Synthetic data allows for high-quality labels, which are useful in developing data-driven radiation detection algorithms. This methodology was used to create synthetic data sets which were released as part of a public data competition to spur the development of new radiation detection algorithms for radiological search applications.

Maximum likelihood reconstructions for rotating scatter mask imaging

The rotating scatter mask system is capable of determining the direction of a single point gamma or neutron source. However, the point source approximation does not hold for many realistic applications, requiring more detailed reconstructions with this system. This study is the first to characterize the rotating scatter mask as a gamma imager, or camera, through a detailed analysis of the relative error, precision, noise, and convergence time as a measure of reconstruction performance. Simulated 137Cs sources and detector responses were generated in MCNP v6.1.4 and v6.2 with high fidelity and low statistical uncertainty. An analysis of variance was applied to maximum-likelihood expectation–maximization algorithms to determine the most significant factors in reconstructing the image, focusing on the source’s shape, size, and direction relative to the detector. Parameters for a Median Root Prior smoothing function were optimized to balance performance over a variety of source distributions. The algorithm performed reasonably well for point sources and for sources that spanned less than 30° in size and were located near the equatorial region of the rotating system. In most other scenarios, the algorithm either oversmoothed the image, resulting in blurry images, or completely failed to reconstruct the image. Increasing the resolution improved the reconstruction quality, while increasing the neighborhood size for the Median Root Prior reduced the image’s noise, but at a significant cost to computational efficiency. These results demonstrate that rotating scatter mask imaging is possible and introduces a potential alternative to other imagers. However, they also demonstrate that new techniques must be developed to increase the system’s performance and robustness for gamma imaging applications.

Monte Carlo Simulation of the TAIGA Hybrid Gamma-Ray Experiment

The TAIGA experiment (Tunka Advanced Instrument for cosmic ray physics and Gamma-ray Astronomy) combines heterogeneous arrays of imaging and non-imaging Cherenkov light detectors for registration of extensive air showers. Monte Carlo simulation of the whole detector response was carried out and is described in this article.

Gamma detector response simulation inside the pedestal of Fukushima Daiichi Nuclear Power Station

Gamma detector response simulation inside the pedestal of Fukushima Daiichi Nuclear Power Station

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.

Design studies using MCNP6® for an oil well logging prototype tool and a test facility

Many oil well logging tools carry on board highly radioactive C137s and/or A241m-Be sources. These dangerous radionuclides are often unsecured and used in remote locations. There is some risk of the material being stolen to create dirty bombs. To address this problem, our research group has designed and constructed an oil well logging prototype tool and a testing facility to attempt to demonstrate that a neutron machine source can replace the use of C137s and 241Am-Be sources. A Deuterium-Tritium (DT) neutron generator was chosen for the study. Various tool and testing facility designs were studied using the MCNP6® code. The final tool and test facility are described. The design process and MCNP6® tools used to model the well-logging prototype tool and facility are described. Simulated and experimental detector responses comparison are presented.

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.

Measurement of Charge Cloud Size in X-Ray SOI Pixel Sensors

We report on a measurement of the size of charge clouds produced by X-ray photons in X-ray SOI (Silicon-On-Insulator) pixel sensor named XRPIX. We carry out a beam scanning experiment of XRPIX using a monochromatic X-ray beam at 5.0 keV collimated to $\sim 10$ $\mu$m with a 4-$\mu$m$\phi$ pinhole, and obtain the spatial distribution of single-pixel events at a sub-pixel scale. The standard deviation of charge clouds of 5.0 keV X-ray is estimated to be $\sigma_{\rm cloud} = 4.30 \pm 0.07$ $\mu$m. Compared to the detector response simulation, the estimated charge cloud size is well explained by a combination of photoelectron range, thermal diffusion, and Coulomb repulsion. Moreover, by analyzing the fraction of multi-pixel events in various energies, we find that the energy dependence of the charge cloud size is also consistent with the simulation.

Spatial and temporal structure of EAS reflected Cherenkov light signal

A compact device lifted over the ground surface might be used to observe optical radiation of extensive air showers (EAS). Here we consider spatial and temporal characteristics of Vavilov-Cherenkov radiation (“Cherenkov light”) reflected from the snow surface of Lake Baikal, as registered by the SPHERE-2 detector. We perform detailed full direct Monte Carlo simulations of EAS development and present a dedicated highly modular code intended for detector response simulations. Detector response properties are illustrated by example of several model EAS events. The instrumental acceptance of the SPHERE-2 detector was calculated for a range of observation conditions. We introduce the concept of “composite model quantities”, calculated for detector responses averaged over photoelectron count fluctuations, but retaining EAS development fluctuations. The distortions of EAS Cherenkov light lateral distribution function (LDF) introduced by the SPHERE-2 telescope are understood by comparing composite model LDF with the corresponding function as would be recorded by an ideal detector situated at the ground surface. We show that the uncertainty of snow optical properties does not change our conclusions, and, moreover, that the expected performance of the SPHERE experiment in the task of cosmic ray mass composition study in the energy region ∼ 10 PeV is comparable with other contemporary experiments. Finally, we compare the reflected Cherenkov light method with other experimental techniques and briefly discuss its prospects.

3D convolutional GAN for fast simulation

Machine Learning techniques have been used in different applications by the HEP community: in this talk, we discuss the case of detector simulation. The need for simulated events, expected in the future for LHC experiments and their High Luminosity upgrades, is increasing dramatically and requires new fast simulation solutions. We describe an R&D activity aimed at providing a configurable tool capable of training a neural network to reproduce the detector response and speed-up standard Monte Carlo simulation. This represents a generic approach in the sense that such a network could be designed and trained to simulate any kind of detector and, eventually, the whole data processing chain in order to get, directly in one step, the final reconstructed quantities, in just a small fraction of time. We present the first application of three-dimensional convolutional Generative Adversarial Networks to the simulation of high granularity electromagnetic calorimeters. We describe detailed validation studies comparing our results to Geant4 Monte Carlo simulation. Finally we show how this tool could be generalized to describe a whole class of calorimeters, opening the way to a generic machine learning based fast simulation approach.

Scattered neutron background in thermal neutron detectors

Inelastic neutron scattering instruments require very low background; therefore the proper shielding for suppressing the scattered neutron background, both from elastic and inelastic scattering is essential. The detailed understanding of the background scattering sources is required for effective suppression. The Multi-Grid thermal neutron detector is an Ar/CO2 gas filled detector with a 10B4C neutron converter coated on aluminium substrates. It is a large-area detector design that will equip inelastic neutron spectrometers at the European Spallation Source (ESS). To this end a parameterised Geant4 model is built for the Multi-Grid detector. This is the first time thermal neutron scattering background sources have been modelled in a detailed simulation of detector response. The model is validated via comparison with measured data of prototypes installed on the IN6 instrument at ILL and on the CNCS instrument at SNS. The effect of scattering originating in detector components is smaller than effects originating elsewhere.

Supernova neutrino detection in LZ

In the first 10 seconds of a core-collapse supernova, almost all of its progenitor's gravitational potential, O(1053 ergs), is carried away in the form of neutrinos. These neutrinos, with O(10 MeV) kinetic energy, can interact via coherent elastic neutrino-nucleus scattering (CEνNS) depositing O(1 keV) in detectors. In this work we describe the performances of low-background dark matter detectors, such as LUX-ZEPLIN (LZ), optimized for detecting low-energy depositions, in detecting these neutrino interactions. For instance, a 27 M⊙ supernova at 10 kpc is expected to produce ∼350 neutrino interactions in the 7-tonne liquid xenon active volume of LZ. Based on the LS220 EoS neutrino flux model for a SN, the Noble Element Simulation Technique (NEST), and predicted CEνNS cross-sections for xenon, to study energy deposition and detection of SN neutrinos in LZ. We simulate the response of the LZ data acquisition system (DAQ) and demonstrate its capability and limitations in handling this interaction rate. We present an overview of the LZ detector, focusing on the benefits of liquid xenon for supernova neutrino detection. We discuss energy deposition and detector response simulations and their results. We present an analysis technique to reconstruct the total number of neutrinos and the time of the supernova core bounce.

Time-resolved diode dosimetry calibration through Monte Carlo modeling for invivo passive scattered proton therapy range verification.

PurposeOur group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water‐equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam‐specific response to WEPL fit for the selected ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water‐equivalent plastic. This necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time‐resolved diode dosimetry technique.MethodsMeasurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The ‘scout’ beams were then applied in the simulation environment to simulated water‐equivalent plastic, a CT of water‐equivalent plastic, and a patient CT data set to assess uncertainty.ResultsSimulated detector response in water‐equivalent plastic was validated against measurements for ‘scout’ spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie.ConclusionFeasibility has been shown for performing the calibration of the detector response for three ‘scout’ beams through simulation for the time‐resolved diode dosimetry technique in passive scattered proton delivery.

A precision device needs precise simulation: Software description of the CBM Silicon Tracking System

Precise modelling of detectors in simulations is the key to the understanding of their performance, which, in turn, is a prerequisite for the proper design choice and, later, for the achievement of valid physics results. In this report, we describe the implementation of the Silicon Tracking System (STS), the main tracking device of the CBM experiment, in the CBM software environment. The STS makes uses of double-sided silicon micro-strip sensors with double metal layers. We present a description of transport and detector response simulation, including all relevant physical effects like charge creation and drift, charge collection, cross-talk and digitization. Of particular importance and novelty is the description of the time behaviour of the detector, since its readout will not be externally triggered but continuous. We also cover some aspects of local reconstruction, which in the CBM case has to be performed in real-time and thus requires high-speed algorithms.

Initial performance studies of a general-purpose detector for multi-TeV physics at a 100 TeV pp collider

This paper describes simulations of detector response to multi-TeV particles and jets at the Future Circular Collider (FCC-hh) or Super proton-proton Collider (SppC) which aim to collide proton beams with a centre-of-mass energy of 100 TeV. The unprecedented energy regime of these future experiments imposes new requirements on detector technologies which can be studied using the detailed GEANT4 simulations presented in this paper. The initial performance of a detector designed for physics studies at the FCC-hh or SppC experiments is described with an emphasis on measurements of single particles up to 33 TeV in transverse momentum. The reconstruction of hadronic jets has also been studied in the transverse momentum range from 50 GeV to 26 TeV. The granularity requirements for calorimetry are investigated using the two-particle spatial resolution achieved for hadron showers.

Comparisons of SN and Monte-Carlo methods in PWR ex-core detector response simulation

The ex-core detector response calculation is an important part in reactor design. However, the response function cannot be measured by experiments quantitatively. Ex-core detector response simulation is therefore required. For decades, the SN code has been used as the dedicated tool. Nowadays, more and more engineers are expressing an interest in using the Monte-Carlo method instead of the SN method in simulations, as it is expected that the Monte-Carlo method will give higher accuracy. In this paper, the modeling and simulation of ex-core detector responses is briefly reviewed based on the Korean Kori Unit 1 reactor. Then, the differences between the SN simulation and Monte-Carlo simulation are compared. The sensitivity of computational conditions is also discussed. It is shown that the problem dependence of cross sections and meshing dependence of spatial discretization in the ex-core detector response calculations are not as strong as expected. However, the ray effect is the main shortcoming for the SN calculation. Based on the analysis, two benefits are shown by using MCNP for the direct 3D calculation. Firstly, the impact of ray effect is eliminated without using the SN angular discretization. Secondly, the direct 3D calculation is easier to perform based on the powerful ability of 3D modeling and parallel computing of the Monte-Carlo code. The new DRF values are adopted in the dynamic control rod reactivity measurement of Kori Unit 1 reactor. The results show that the new DRF values improve the error of measured control rod worth by a percentage of 3.

On the connection of gamma-ray bursts and X-ray flashes in the BATSE and RHESSI databases

Classification of gamma-ray bursts (GRBs) into groups has been intensively studied by various statistical tests in previous years. It has been suggested that there was a distinct group of GRBs, beyond the long and short ones, with intermediate durations. However, such a group is not securely confirmed yet. Strangely, concerning the spectral hardness, the observations from the Swift and RHESSI satellites give different results. For the Swift/BAT database it is found that the intermediate-duration bursts might well be related to so-called X-ray flashes (XRFs). On the other hand, for the RHESSI dataset the intermediate-duration bursts seem to be spectrally too hard to be given by XRFs. The connection of the intermediate-duration bursts and XRFs for the BATSE database is not clear as well. The purpose of this article is to check the relation between XRFs and GRBs for the BATSE and RHESSI databases, respectively. We use an empirical definition of XRFs introduced by other authors earlier. For the RHESSI database we also use a transformation between the detected counts and the fluences based on the simulated detector response function. The purpose is to compare the hardnesses of GRBs with the definition of XRFs. There is a 1.3-4.2 % fraction of XRFs in the whole BATSE database. The vast majority of the BATSE short bursts are not XRFs because only 0.7-5.7 % of the short bursts can be given by XRFs. However, there is a large uncertainty in the fraction of XRFs among the intermediate-duration bursts. The fraction of 1-85 % of the BATSE intermediate-duration bursts can be related to XRFs. For the long bursts this fraction is between 1.0 % and 3.4 %. The uncertainties in these fractions are large, however it can be claimed that all BATSE intermediate-duration bursts cannot be given by XRFs. At least 79 % of RHESSI short bursts, at least 53 % of RHESSI intermediate-duration bursts, and at least...

Evaluation of neutron light output response functions in EJ-309 organic scintillators

An accurate model of the nonlinear detector response of organic scintillators to neutrons is required to correctly simulate fast neutron detection, as well as interpret measured pulse height data. Several empirical and semi-empirical models are available to fit measured scintillator light output data. In this work, EJ-309 light output data from neutrons depositing 1.15–5.15MeV on hydrogen were analyzed using empirical models as well as semi-empirical models based on the work of Birks and Voltz. Although all tested models fit the experimental light output data well in the measured range, the models were observed to diverge in low-energy extrapolation. The models were then tested by comparing a measurement and MCNPX-PoliMi simulation of an EJ-309 detector response to fast neutrons from a 252Cf spontaneous fission source. The agreement between the measured and simulated pulse height distributions varied significantly depending on the light output model used. The best agreement between simulated and measured neutron pulse height distributions was achieved by using the Birks model. The bin-by-bin agreement was better than 5% over the range 0.08–2.18MeVee, and better than 10% from 2.18 to 3.13MeVee. The integral count rate over the range 0.08–3.14MeVee differed by less than 1% in absolute units.

A scintillator-based approach to monitor secondary neutron production during proton therapy.

The primary objective of this work is to measure the secondary neutron field produced by an uncollimated proton pencil beam impinging on different tissue-equivalent phantom materials using organic scintillation detectors. Additionally, the Monte Carlo code mcnpx-PoliMi was used to simulate the detector response for comparison to the measured data. Comparison of the measured and simulated data will validate this approach for monitoring secondary neutron dose during proton therapy. Proton beams of 155- and 200-MeV were used to irradiate a variety of phantom materials and secondary particles were detected using organic liquid scintillators. These detectors are sensitive to fast neutrons and gamma rays: pulse shape discrimination was used to classify each detected pulse as either a neutron or a gamma ray. The mcnpx-PoliMi code was used to simulate the secondary neutron field produced during proton irradiation of the same tissue-equivalent phantom materials. An experiment was performed at the Loma Linda University Medical Center proton therapy research beam line and corresponding models were created using the mcnpx-PoliMi code. The authors' analysis showed agreement between the simulations and the measurements. The simulated detector response can be used to validate the simulations of neutron and gamma doses on a particular beam line with or without a phantom. The authors have demonstrated a method of monitoring the neutron component of the secondary radiation field produced by therapeutic protons. The method relies on direct detection of secondary neutrons and gamma rays using organic scintillation detectors. These detectors are sensitive over the full range of biologically relevant neutron energies above 0.5 MeV and allow effective discrimination between neutron and photon dose. Because the detector system is portable, the described system could be used in the future to evaluate secondary neutron and gamma doses on various clinical beam lines for commissioning and prospective data collection in pediatric patients treated with proton therapy.