Counting Detector Research Articles

Energy and electron drift time measurements in a pixel CCI TlBr detector with 1.3 MeV prompt-gammas

Assessing the position of the Bragg peak (BP) in hadron radiotherapy utilizing prompt-gamma imaging (PGI) presents many challenges in terms of detector physics. Gamma detectors with the capability of extracting the best energy, timing, and spatial information from each gamma interaction, as well as with high detection efficiency and count rate performance, are needed for this application. In this work we present the characterization of a pixel Čerenkov charge induction (CCI) thallium bromide (TlBr) detector in terms of energy and and electron drift time for its potential use in PGI. The CCI TlBr detector had dimensions of 4 × 4 × 5 mm3 and one of its electrodes was segmented in pixels with 1.7 mm pitch. A silicon photomultiplier (SiPM) was optically coupled to one of the faces of the TlBr slab to read out the Čerenkov light promptly emitted after the interaction of a gamma ray. The detector was operated stand-alone and the 1.275 prompt gammas from a 22Na radioactive source were used for the study. The electron drift time was obtained by combining the Čerenkov and charge induction signals and then used as a measure of the depth of interaction. The electron mobility in TlBr was estimated as ∼27 cm2 V−1 s−1. Energy resolutions between 3.4% and 4.0% at 1.275 MeV were obtained after depth-correction. These values improved to 3.0%–3.3% when events with drift times of 3–6 μs were selected. These results show the potential of pixel CCI TlBr detectors to resolve gamma interactions in the detector with mm-like accuracy in 3D and with excellent energy resolution. Previous studies with CCI TlBr devices have shown a timing resolution of <400 ps full width at half maximum when detecting 511 keV gamma rays, therefore, the timing accuracy is expected to improve with the increased energy of the gamma rays in PGI. While other important detector characteristics such as count rate capability remain to be studied, results from this work combined with other preliminary data show pixel CCI detectors can simultaneously provide excellent energy, timing, and spatial resolution performance and are a very promising option for PGI in hadron therapy.

Traceability of the Sentinel-3 SLSTR Level-1 Infrared Radiometric Processing

Providing uncertainties in satellite datasets used for Earth observation can be a daunting prospect because of the many processing stages and input data required to convert raw detector counts to calibrated radiances. The Sea and Land Surface Temperature Radiometer (SLSTR) was designed to provide measurements of the Earth’s surface for operational and climate applications. In this paper the authors describe the traceability chain and derivation of uncertainty estimates for the thermal infrared channel radiometry. Starting from the instrument model, the contributing input quantities are identified to build up an uncertainty effects tree. The characterisation of each input effect is described, and uncertainty estimates provided which are used to derive the combined uncertainties as a function of scene temperature. The SLSTR Level-1 data products provide uncertainty estimates for fully random effects (noise) and systematic effects that can be mapped for each image pixel, examples of which are shown.

Experimental study of photon-counting CT neural network material decomposition under conditions of pulse pileup.

.Purpose: We investigated the performance of a neural network (NN) material decomposition method under varying pileup conditions.Approach: Experiments were performed at tube current settings that provided count rates incident on the detector through air equal to 9%, 14%, 27%, 40%, and 54% of the maximum detector count rate. An NN was trained for each count-rate level using transmission measurements through known thicknesses of basis materials (PMMA and aluminum). The NN trained for each count-rate level was applied to x-ray transmission measurements through test materials and to CT data of a rod phantom. Material decomposition error was evaluated as the distance in basis material space between the estimated thicknesses and ground truth.Results: There was no clear trend between count-rate level and material decomposition error for all test materials except neoprene. As an example result, Teflon error was 0.33 cm at the 9% count-rate level and 0.12 cm at the 54% count-rate level for the x-ray transmission experiments. Decomposition error increased with count-rate level for the neoprene test case, with 0.65-cm error at 9% count-rate level and 1.14-cm error at the 54% count-rate level. In the CT study, material decomposition error decreased with increasing incident count rate. For example, the material decomposition error for Teflon was 0.089, 0.066, 0.054 at count-rate levels of 14%, 27%, and 40%, respectively.Conclusions: Results demonstrate over a range of incident count-rate levels that an NN trained at a specific count-rate level can learn the relationship between photon-counting spectral measurements and basis material thicknesses.

EXTENDED MSM METHOD TO ESTIMATE THE REACTIVITY OF A SUB-CRITICAL CORE DRIVEN BY AN ACCELERATOR BASED NEUTRON SOURCE

The Modified Source Multiplication method is used to determine an unknown reactivity level of a reactor from a known one if one has access to the detector counting for both levels when the reactor is fed by a constant neutron source like an Am-Be source. When available, an accelerator driven source, in continuous mode, can be useful as its intensity can be tunable and then adapted to the experimental conditions. However, in that case, the MSM technique must be extended to account for an external source whose intensity, energy and angular distributions can vary from one measurement to another. In this paper, this Modified Multi-Source Multiplication (MMSM) method is applied to measurements done during the FREYA project in the GUINEVERE facility, operated with the GENEPI-3C accelerator providing a mixture of (D,T) and (D,D) neutrons. The monitoring of these sources through the detection of the associated charged particles allows the calculation of the MMSM factors and the estimate of the reactivity values. The results are compared in different configurations with the reactivity obtained with an Am-Be source or in dynamic measurements performed with GENEPI-3C. Their excellent agreement shows the possibility of using such accelerator-based neutron sources for MSM measurements when they are correctly monitored. This is of great interest for deep sub-critical level characterization for which detector count rates per source neutrons might be low.

SUBCRITICALITY ESTIMATION BY VIRTUAL NEUTRON CAPTURE METHOD

The criticality safety control technique is required for the fuel debris removal from the Fukushima Dai-Ichi Nuclear Power Station which experienced a severe accident. The subcriticality estimation is expected to be done with only limited information about the fuel debris while the primary containment vessel internal survey work is ongoing. The purpose of this study is to develop the subcriticality estimation method called the virtual neutron capture method. The neutrons from the surface of the fuel debris represent a major portion of detector counts. The method consists of two evaluations: the evaluation at the surface of the fuel debris for which the isotope compositions are known by fuel debris sampling and the evaluation at the region of the fuel debris for which these compositions are unknown. For the unknown composition region, the average isotope composition with arbitrary water content is given. The method surveys the relationship with the detector count and the neutron multiplication factor with any size of the unknown composition region and any ratio of the water content before the on-site evaluation. The method is verified by experiments done in the Kyoto University Critical Assembly. The method shows that the maximum difference from the reference neutron multiplication factor is 4.5 %dk. As a result, the virtual neutron capture method can be adopted to the subcriticality monitoring if the method includes the estimation margin of 4.5 %dk within the neutron multiplication factor range from 0.70 to 0.95.

Реконструкция пространственного распределения источников излучения в пропорциональной рассеивающей среде

A new method of image reconstruction for single-photon emission computed tomography in a proportional scattering medium is investigated. The detector counts were obtained using Monte Carlo simulation with the Geant4 nuclear physics software system, which eliminates the need for a real tomograph, radiopharmaceuticals and a phantom under study. In this case, the detector counts obtained with the Geant4 do not practically differ from those that would have been obtained in a full-scale experiment for the real scattering medium. The influence of the absorbing and scattering properties of thirteen different substances as a medium, in which the spatial distribution of radiation sources is immersed, on the accuracy of the tomogram reconstruction is investigated. The significant advantage of the proposed algorithm for reconstruction of emission tomograms in comparison with the traditional one is shown.

THE SOURCE JERK INTEGRALMETHOD FOR SUB-CRITICALITY MEASUREMENTS IN ADS

Three sub-critical (SC) core configurations were investigated in the VENUS-F zero power reactor coupled with the GENEPI-3C accelerator. The SC10 and SC12 were a mock-up of a MYRRHA start-up core and SC11 represented a more complex MYRRHA core loaded with various types of in-pile-sections. The sub-criticality of 11 variants of these VENUS-F cores was changed in several steps from -6$ down to -30$ using the safety and control rods. Their sub-criticalities were determined with the Source Jerk Integral (SJI) method using 11 fission chambers located all over the reactor. For the data analysis, the 8-group delayed neutron parameters from the JEFF-3.1.2 evaluated nuclear data library were used. Reliability and reproducibility of the experimental results were tested by repeating the measurements, swapping the detectors and varying the accelerator beam intensity, thus changing the detector count rates and verifying the validity of the dead time corrections. The obtained results are compared with MCNP calculations.

Short-term prediction of freeway travel times by fusing input-output vehicle counts and GPS tracking data

ABSTRACT Short-term travel time prediction on freeways is the most valuable information for drivers when selecting their routes and departure times. Furthermore, this information is also essential at traffic management centers in order to monitor the network performance and anticipate the activation of traffic management strategies. The importance of reliable short-term travel time predictions will even increase with the advent of autonomous vehicles, when vehicle routing will strongly rely on this information. In this context, it is important to develop a real-time method to accurately predict travel times. The present paper uses vehicle accumulation, obtained from input-output diagrams constructed from loop detector data, to predict travel times on freeway sections. Loop detector count drift, which typically invalidates vehicle accumulation measurements, is corrected by means of a data fusion algorithm using GPS measurements. The goodness of the methodology has been proven under different boundary conditions using simulated data.

Determination of the Affected Steam Generator during Primary-to-Secondary Leakage in WWER-1000 Using a Geiger-Muller Counter

The main indicator of a primary-to-secondary leakage in WWER-1000 is the increased secondary side activity. Activity can be detected by radiation devices. Accordingly, the online monitoring of the secondary side activity allows the reactor operator to successfully determine the affected steam generator and implement appropriate actions to transfer the reactor in a safe state. The detectors are supposed to be installed behind the steam generator pipelines outside of the containment.&#x0D; The scattered photon spectrum, formed from N-16 decay in the detection area, is analyzed. The possibility of using a detection unit with a Geiger-Muller counter to register particles with energies that exceed the device energy range, which is indicated in the technical specifications, is confirmed.&#x0D; The paper indicates that the detector response is determined by two different approaches. In the first case, the absorbed dose rate is calculated by the energy deposition method (KERMA factor), and in the second case, the detector count rate is calculated by taking into account the secondary ionization processes. The calculation results of the detector response taking into account the dead time are presented. The dead time effect on the absorbed dose rate registered by the counter is analyzed. The calculated response coefficients of the detector for the main reference radionuclides of the primary side, which could be potentially transported into the detector’s registration volume, is obtained. Additionally, the paper provides for the maximum limit of the detected absorbed dose rate of BDMG-04-02B.&#x0D; The calculations were carried out using MCNP6 neutronic code focused on the analysis of the elementary particle interaction with surrounding materials.

Response matrix validation of a [formula omitted]-based multi-shell neutron spectrometer

A new type of compact multi-shell neutron spectrometer (MuNS) was developed at PNRI. It consists of a series of concentric polyethylene shells that can be combined to form Bonner spheres with different diameters ranging from 5 cm to 30 cm. With respect to conventional Bonner spheres, this system is more flexible and portable. MuNS can accommodate either passive or active neutron detectors. The response matrix of the MuNS with a cylindrical 3He proportional counter (He-MuNS) was calculated using Monte Carlo simulations for incident neutrons with energies ranging from 1 meV to 100 MeV. Anisotropy effect was investigated through simulations and is found to be at most 90% for the smallest configuration, indicating that He-MuNS should have a specific orientation during deployment. Validation of the calculated response matrix and calibration of the He-MuNS system were performed using a 252Cf reference source and the shadow cone method. The quotient of the measured and calculated neutron counts in the 3He detector was computed for every sphere and the value was found to be constant within 5.1%. Results confirm the validity of the He-MuNS model and the simulated response matrix.

A Passive, Fully Staring THz Video Camera Based on Kinetic Inductance Bolometer Arrays

Current state-of-the-art security video cameras operating in the THz regime employ up to a few hundred detectors together with optomechanical scanning to cover an adequate fieldof-view for practical concealed object detection. As a downside, the scanning reduces the integration time per pixel compromising sensitivity, increases the complexity, and reduces the reliability of the system. In contrast to this, we demonstrate a video camera, for the first time, basing its operation on the concept of a fully staring 2-D detector array with a single detector element responsible for a single imaged pixel. The imaging system is built around the detector technology of kinetic inductance bolometers, allowing the operation in the intermediate temperature range >5K and the scale-up of the detector count into multikilo-pixel arrays and beyond. The system is designed for a field-of-view of 2 × 1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and an imaging distance of 2.5 m. We describe the main components of the system and show images from concealed object experiments performed at a near-video rate of 9 Hz.

Determination the concentration of heavy elements and gross alpha, beta, and gamma activities in soil samples from Tworeach district at Karbala governorate

In this study, the radiological efficacy of selected samples of a hole produced by a rocket dropped during military operations in the second Gulf battle was measured. Since the fall of the rocket in 1991 on district of Tuwayrej, Karbala at central Iraq until this moment, there have been many miscarriages in women as well as cases of congenital malformation in children. For these reasons and in response to the appeals of the residents of the region, we conducted this study. Twelve different samples of soil were collected for the study area from different distances (0, 25, 50 and 100 m) and with different directions (North, South, East and West) from the edge of the hole. chemical method to calculate the percentage elements (Na, Cr, Ni, Ca, Fe, K, and Mg), in this samples, and using physical method to calculate the concentration of the natural radioactivity in the same samples the instrumentations used to count the gross alpha, beta, activities was alpha/beta proportional counter and High purity Germanium detector to calculate the gross gamma activity to count the radiation from these samples. The obtained results show that the gross alpha, beta and gamma activities ranged from (2.15 to 36.23Bq/Kg), (37.37 to 217.17Bq/Kg) and (2.26 to 50.92 Bq/Kg) respectively. In comparing the practical results with the global calculated results, the radiation levels of the studied models were found to be within permissible limits.

Stopping muon effect and estimation of intracloud electric field

Employing large thunderstorm ground enhancements (TGEs) as a manifestation of the strong electric field in thundercloud we measure fluxes of almost all species of secondary cosmic rays to estimate the strength of the intracloud electric field. The modulation that electric field poses on charged particle flux gives a sizable change in count rate of detectors measuring high energy muon flux and inclined muon flux in the presence of a TGE. The muon stopping effect, observed by the particle detectors located at 3200 m altitude at Aragats Space Environmental Center (ASEC) implicates the abrupt decline of count rate of high energy muons (at vertical incidence with energies above 250 MeV and at inclined incidence with azimuth angle θ> 22° for lower energies). For the large TGE events (relative enhancement > 10% in SEVAN detector upper layer, registering low energy charged particles and electrons) muon count rate decreases down to 2-5% from the mean count rate measured before the TGE event. A simple model of shifting of the energy spectrum of particles entering the electric field was applied for the analysis of several events where the muon stopping (deceleration) effect has been observed. For the large TGE events that occurred during last decade the maximal potential drop of 350 MV was estimated. The most probable electric field strength for this event was found to be ∼2 kV/cm.

Thermal kinetic inductance detectors for millimeter-wave detection

Thermal Kinetic-Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. In this paper, we first discuss the expected noise sources in TKIDs and derive the limits where the phonon noise contribution dominates over the other detector noise terms: generation–recombination, amplifier, and two-level system noise. Second, we characterize aluminum TKIDs in a dark environment. We present measurements of TKID resonators with quality factors of about 105 at 80 mK. We also discuss the bolometer thermal conductance, heat capacity, and time constants. These were measured by the use of a resistor on the thermal island to excite the bolometers. These dark aluminum TKIDs demonstrate a noise equivalent power, NEP = 2×10−17W/Hz, with a 1/f knee at 0.1 Hz, which provides background noise limited performance for ground-based telescopes observing at 150 GHz.

Advanced algorithms for signal processing scintillation gamma ray detectors at high counting rates

Gamma ray spectrometry measurements at high detector counting rates (on the order of 107 s−1 and higher) are relevant for high-temperature plasma diagnostics for existing tokamaks and during the development of gamma ray diagnostic systems for the ITER tokamak under construction. At high loads, to obtain spectra without distortion and with a small amount of dead time, it is necessary to use advanced scintillation detector signal processing methods, which can resolve superimposed pulses. Two algorithms that can be used for digital signal processing of scintillation gamma ray detectors with many piled-up pulses are considered in this article, the fitting and deconvolution methods. These algorithms are compared with both one another and two less sophisticated pulse-height analysis algorithms (maximum height and total sum under the peak) in applications that process model and measured signals. Baseline detection algorithms are also considered, which are necessary when processing signals from detectors. The algorithms are applied to LaBr3(Ce) detector signal processing. For the modeled signals, the best results in terms of the number of resolved events and energy resolution at counting rates up to 2 × 107 s−1 of the LaBr3(Ce) detector are demonstrated by the fitting method. In the real gamma ray measurements at a loading of 5.1 106 s−1, the deconvolution method demonstrated the best energy resolution.

Sensitive neutron transverse polarization analysis using a 3He spin filter.

We report an experimental implementation for neutron transverse polarization analysis that is capable of detecting a small angular change (≪10-3 rad) in neutron spin orientation. This approach is demonstrated for monochromatic beams, and we show that it could be extended to polychromatic neutron beams. Our approach employs a 3He spin filter inside a solenoid with an analyzing direction perpendicular to the incident neutron polarization direction. The method was tested with polarized neutron beams and a spin rotator placed inside a μ-metal shield just upstream of the analyzer. No cryogenic superconducting shields or additional neutron spin manipulations are needed. With a counting detector, we experimentally show that the angular resolution δθ=1/(PnAN) rad is only determined by the counting statistics for the total counts N and the product of the neutron polarization Pn and the analyzing power A. With a high-flux neutron beam, 10-6 rad angular sensitivity is feasible within a day. This simple, classical-quantum-limited transverse polarization analysis scheme may reduce the overall complexity of experimental implementation for applications requiring sensitive neutron polarimetry and improve the precision in fundamental science studies and polarized neutron imaging.

The background model of the medium energy X-ray telescope of Insight-HXMT

The Medium Energy X-ray Telescope (ME) is one of the main payloads of the Hard X-ray Modulation Telescope (dubbed as Insight-HXMT). The background of Insight-HXMT/ME is mainly caused by the environmental charged particles and the background intensity is modulated remarkably by the geomagnetic field, as well as the geographical location. At the same geographical location, the background spectral shape is stable but the intensity varies with the level of the environmental charged particles. In this paper, we develop a model to estimate the ME background based on the ME database that is established with the two-year blank sky observations of the high Galactic latitude. In this model, the entire geographical area covered by Insight-HXMT is divided into grids of 5°×5° in geographical coordinate system. For each grid, the background spectral shape can be obtained from the background database and the intensity can be corrected by the contemporary count rate of the blind FOV detectors. Thus the background spectrum can be obtained by accumulating the background of all the grids passed by Insight-HXMT during the effective observational time. The model test with the blank sky observations shows that the systematic error of the background estimation in 8.9−44.0 keV is ∼1.3% for a pointing observation with an average exposure ∼5.5 ks. We also find that the systematic error is anti-correlated with the exposure, which indicates the systematic error is partly contributed by the statistical error of count rate measured by the blind FOV detectors.

Advanced characterization of an optical fibre sensor system based on an MPPC detector for measurement of X-ray radiation in clinical linacs

A reliable, accurate and in-vivo dosimetry system for measuring the radiation dose and profiling the X-ray beam during radiotherapy is reported. Its dynamic range is investigated using an accurately controlled pulsed light emitting diode (LED) system. Highly resolved temporal analog and digital signals were captured from the analog and digital outputs of a multi-pixel photon counter (MPPC) detector when exposed to the LED system. The photon distribution of a low intensity pulsed LED light source was observed and is found to obey a Poisson distribution with changing light intensity. The average number of photons was obtained using the digital MPPC output signals which in turn allowed the appropriate intensity of the light source to be determined for the correct light exposure conditions for the detector. The average analog output voltage over a single 3 μs pulse is determined to indicate the intensity of the detected light. The MPPC detector output analog signal is limited to a narrow range (0.6 V–1.4 V) to ensure adequate signal detection level (the lower limit) and prevention of entry into saturation (the upper limit) which also corresponds to a digital output signal range (in counts). An average photon number range of 3–7 for the digital output signal is established, which leads to the establishment of a unique and constant photon number to average output voltage ratio of 4.64 ± 0.10. Experimental results show that the establishment of this ratio is significant as adherence to it ensures the correct exposure conditions of the MPPC and speeds up the measurement cycle in the clinical setting.

Radiation Source Localization Using Surrogate Models Constructed from 3-D Monte Carlo Transport Physics Simulations

Recent research has focused on the development of surrogate models for radiation source localization in a simulated urban domain. We employ the Monte Carlo N-Particle (MCNP) code to provide high-fidelity simulations of radiation transport within an urban domain. The model is constructed to employ a source location () as input and return the estimated count rate for a set of specified detector locations. Because MCNP simulations are computationally expensive, we develop efficient and accurate surrogate models of the detector responses. We construct surrogate models using Gaussian processes and neural networks that we train and verify using the MCNP simulations. The trained surrogate models provide an efficient framework for Bayesian inference and experimental design. We employ Delayed Rejection Adaptive Metropolis (DRAM), a Markov Chain Monte Carlo algorithm, to infer the location and intensity of an unknown source. The DRAM results yield a posterior probability distribution for the source’s location conditioned on the observed detector count rates. The posterior distribution exhibits regions of high and low probability within the simulated environment identifying potential source locations. In this manner, we can quantify the source location to within at least one of these regions of high probability in the considered cases. Employing these methods, we are able to reduce the space of potential source locations by at least 60%.

Accelerating quantum optics experiments with statistical learning

Quantum optics experiments, involving the measurement of low-probability photon events, are known to be extremely time-consuming. We present a methodology for accelerating such experiments using physically motivated ansatzes together with simple statistical learning techniques such as Bayesian maximum a posteriori estimation based on few-shot data. We show that it is possible to reconstruct time-dependent data using a small number of detected photons, allowing for fast estimates in under a minute and providing a one-to-two order of magnitude speed-up in data acquisition time. We test our approach using real experimental data to retrieve the second order intensity correlation function, G(2)(τ), as a function of time delay τ between detector counts, for thermal light as well as anti-bunched light emitted by a quantum dot driven by periodic laser pulses. The proposed methodology has a wide range of applicability and has the potential to impact the scientific discovery process across a multitude of domains.