Detection Properties Research Articles

Monte Carlo characterization of high atomic number inorganic scintillators for in vivo dosimetry in 192 Ir brachytherapy.

There is increased interest in in vivo dosimetry for 192 Ir brachytherapy (BT) treatments using high atomic number (Z) inorganic scintillators. Their high light output enables construction of small detectors with negligible stem effect and simple readout electronics. Experimental determination of absorbed-dose energy dependence of detectors relative to water is prevalent, but it can be prone to high detector positioning uncertainties and does not allow for decoupling of absorbed-dose energy dependence from other factors affecting detector response. To investigate which measurement conditions and detector properties could affect their absorbed-dose energy dependence in BT in vivodosimetry. We used a general-purpose Monte Carlo (MC) code PENELOPE for the characterization of high-Z inorganic scintillators with the focus on ZnSe ( ) Z. Two other promising media CsI ( ) and Al2 O3 ( ) were included for comparison in selected scenarios. We determined absorbed-dose energy dependence of crystals relative to water under different scatter conditions (calibration phantom 12 × 12 × 30cm3 , characterization phantoms 20 × 20 × 20 cm3 , 30 × 30 × 30 cm3 , 40 × 40 × 40 cm3 , and patient-like elliptic phantom 40 × 30 × 25 cm3 ). To mimic irradiation conditions during prostate treatments, we evaluated whether the presence of pelvic bones and calcifications affect ZnSe response. ZnSe detector design influence was alsoinvestigated. In contrast to low-Z organic and medium-Z inorganic scintillators, ZnSe and CsI media have substantially greater absorbed-dose energy dependence relative to water. The response was phantom-size dependent and changed by 11% between limited- and full-scatter conditions for ZnSe, but not for Al2 O3 . For a given phantom size, a part of the absorbed-dose energy dependence of ZnSe is caused not due to in-phantom scatter but due to source anisotropy. Thus, the absorbed-dose energy dependence of high-Z scintillators is a function of not only the radial distance but also the polar angle. Pelvic bones did not affect ZnSe response, whereas large and intermediate size calcifications reduced it by 9% and 5%, respectively, when placed midway between the source and thedetector. Unlike currently prevalent low- and medium-Z scintillators, high-Z crystals are sensitive to characterization and in vivo measurement conditions. However, good agreement between MC data for ZnSe in the present study and experimental data for ZnSe:O by Jørgensenetal. (2021) suggests that detector signal is proportional to the average absorbed dose to the detector cavity. This enables an easy correction for non-TG43-like scenarios (e.g., patient sizes and calcifications) through MC simulations. Such information should be provided to the clinic by the detector vendors.

THE COMPTON NEUTRON HAFNIUM DETECTOR: ELECTRIC CHARGE GENERATION RATE

The properties of a Compton neutron detector with the emitter of metallic Hf were studying in this work. Using the previously calculated the emitter material nuclide composition during reactor irradiation, the dependence of the emitter signal value on the irradiation time was obtained with a step of 1 year for 5 years. It is shown that the composition modification due to nuclear transmutations changes the rate of an electric charge generation in the emitter.

Analytical investigation on the shape of the response functions of Superheated Drop Detectors using Evaluated Nuclear Data

In this paper, the response matrix of Superheated Drop Detector was analyzed and investigated using Evaluated Nuclear Data. Elastic, nonelastic and total neutron cross sections were extracted and used for calculating the probability of the production of charged particles as a result of neutron interaction with superheated liquid nuclei. The values of the response functions in each energy are proportional to the probability of the production of charged particles. It was proposed that the response function can be represented as the multiplication of the total neutron cross sections by a monotonic probability function. The parameters associated with this function change with changing the physical properties of the detector such as temperature or external pressure. The growth rate of this function decreases when the temperature decreases or the external pressure on detectors increases due to increase in threshold energy for the generated charged particles. So the growth rate and shape of this function are set by parameters which are dependent on the physical properties of Superheated Drop Detectors.

CLASS_GWB: robust modeling of the astrophysical gravitational wave background anisotropies

Gravitational radiation offers a unique possibility to study the large-scale structure of the Universe, gravitational wave sources and propagation in a completely novel way. Given that gravitational wave maps contain a wealth of astrophysical and cosmological information, interpreting this signal requires a non-trivial multidisciplinary approach. In this work we present the complete computation of the signal produced by compact object mergers accounting for a detailed modelling of the astrophysical sources and for cosmological perturbations. We develop the CLASS_GWB code, which allows for the computation of the anisotropies of the astrophysical gravitational wave background, accounting for source and detector properties, as well as effects of gravitational wave propagation. We apply our numerical tools to robustly compute the angular power spectrum of the anisotropies of the gravitational wave background generated by astrophysical sources in the LIGO-Virgo frequency band. The end-to-end theoretical framework we present can be easily applied to different sources and detectors in other frequency bands. Moreover, the same numerical tools can be used to compute the anisotropies of gravitational wave maps of the sky made using resolved events.

Scintillation properties of Yb-doped Bi4Ge3O12 single crystals emitting near-infrared luminescence

Yb-doped Bi4Ge3O12 (BGO) single crystals with different dopant concentrations were synthesized by the floating zone method, and the photoluminescence (PL) and scintillation properties in visible to near-infrared (NIR) wavelength ranges were evaluated. In PL and scintillation, a broad emission band was observed at 400–600 nm, which was ascribed to the electronic transitions of Bi3+. Furthermore, NIR emission bands due to Yb3+ were observed at 1000 nm. To evaluate scintillation detector properties, the relationship between emission intensity in the NIR range and X-ray exposure dose rate was investigated. Among the present samples, 0.5 and 1% Yb-doped BGO showed good linearity in the dynamic range from 0.006 to 60 Gy h−1.

Enhancement of the EGSnrc code egs_chamber for fast fluence calculations of charged particles

PurposeSimulation of absorbed dose deposition in a detector is one of the key tasks of Monte Carlo (MC) dosimetry methodology. Recent publications (Hartmann and Zink, 2018; Hartmann and Zink, 2019; Hartmann et al., 2021) have shown that knowledge of the charged particle fluence differential in energy contributing to absorbed dose is useful to provide enhanced insight on how response depends on detector properties. While some EGSnrc MC codes provide output of charged particle spectra, they are often restricted in setup options or limited in calculation efficiency. For detector simulations, a promising approach is to upgrade the EGSnrc code egs_chamber which so far does not offer charged particle calculations. MethodsSince the user code cavity offers charged particle fluence calculation, the underlying algorithm was embedded in egs_chamber. The modified code was tested against two EGSnrc applications and DOSXYZnrc which was modified accordingly by one of the authors. Furthermore, the gain in efficiency achieved by photon cross section enhancement was determined quantitatively. ResultsElectron and positron fluence spectra and restricted cema calculated by egs_chamber agreed well with the compared applications thus demonstrating the feasibility of the new code. Additionally, variance reduction techniques are now applicable also for fluence calculations. Depending on the simulation setup, considerable gains in efficiency were obtained by photon cross section enhancement. ConclusionThe enhanced egs_chamber code represents a valuable tool to investigate the response of detectors with respect to absorbed dose and fluence distribution and the perturbation caused by the detector in a reasonable computation time. By using intermediate phase space scoring, egs_chamber offers parallel calculation of charged particle fluence spectra for different detector configurations in one single run.

POLYHARMONIC DETECTOR OF WEAK SPHIGMOMETRIC SIGNALS

The application of chaotic modes of nonlinear dynamics is valid within the process of description and study of circulatory processes in the human body. Such an approach can potentially ensure the most plausible reproduction and reliability of the detection of weak biological images of signals in conditions of powerful interference arising from other systems of the human body and through external influences. The essence of the method of detecting polyharmonic signals by a chaotic detector is to use sharp transitions between chaotic and periodic modes of operation during the action of the detected signal. The weak signal processing circuit is actually a nonlinear filter with a certain frequency resource. The simulation of the nonlinear Duffing system allowed us to conclude that the frequency resource of such a chaotic detector is sufficient to detect not only weak harmonic but also polyharmonic signals against the background of powerful fluctuation noise. In this case, the operating frequency range of the chaotic detector is up to a decade, and the reaction of the nonlinear system in the phase plane with respect to the action of the harmonic signal generally does not change. A simulation model (Simulink) and a reconstruction of sphygmometric sensor signals for modeling in conditions of powerful interference were developed. The possibility of detecting a polyharmonic signal with a high level of reliability under the condition of signal-to-noise ratio up to -20 dB, and with a permissible level of reliability – up to -37 dB in real time, is shown. The possibility of detecting polyharmonic signals by a chaotic detector in the conditions of fluctuating non-Gaussian noise according to different criteria of discrimination of chaotic generator operating modes is also confirmed. The confirmed properties of the chaotic detector allow the analysis and diagnosis of the human condition according to the main first harmonics of the spectrum of the weak sphygmometric signal, which determine the nature of the disease of the cardiovascular system. The proposed method of detecting sphygmometric signals by the chaotic detector can be used for non-contact study of pulse wave signals by remote non-contact sensors, the work of which is associated with the appearance of a high level of interference

Scintillator surface modification by glancing angle deposition of thin ZrO2 films

In this research, we evaluated the properties of ZrO2 films produced with the glancing angle deposition technique and evaluated its effect on the detector properties. With using ZrO2, we created films with a refraction index in the range of 1.3 to 2.0, and produced a four layer graded-index (GRIN) antireflection coating. A BGO scintillator sample with an applied GRIN coating demonstrated up to ∼ 53% light output enhancement in comparison with the reference ones. For LYSO scintillators, the observed magnitude of the effect was less, ∼ 11%. Thus, this method is a technologically applicable way to improve the characteristics of existing and projected detector systems.

Calibration-free retrieval of density information from computed tomography data

In many research areas, particularly in materials science, retrieving a 3D distribution of the material density in a sample is of key interest. Although standard lab-based X-ray μCT imaging is capable of retrieving the 3D distribution of local attenuation coefficients, the local density cannot be determined unambiguously without the use of calibration standards due to the polychromaticity of the used X-ray tubes. In this paper, two methods are presented to retrieve this information based on accurate knowledge of the polychromatic properties of source and detector in the used μCT system. The methods use a very different approach, one being a polychromatic pre-processing method and one relying on a novel polychromatic iterative reconstruction method, yet produce equivalent results. They are limited to objects with a homogeneous composition, but are extremely powerful in a broad range of applications in materials characterization where the density distribution is of interest. Moreover, the method relying on iterative reconstruction has the potential to be applied for multi-material objects as well. A number of application examples illustrate the potential of the methods to not only retrieve quantitative estimates of density and sub-voxel porosity, but also to greatly reduce or eliminate the spectral artifacts that often hinder conventional calibration schemes.

Prospects for the Detection of the Diffuse Supernova Neutrino Background with the Experiments SK-Gd and JUNO

The advent of gadolinium-loaded Super-Kamiokande (SK-Gd) and of the soon-to-start JUNO liquid scintillator detector marks a substantial improvement in global sensitivity for the Diffuse Supernova Neutrino Background (DSNB). The present article reviews the detector properties most relevant for the DSNB searches in both experiments and estimates the expected signal and background levels. Based on these inputs, we evaluate the sensitivity of both experiments individually and combined. Using a simplified statistical approach, we find that both SK-Gd and JUNO have the potential to reach >3σ evidence of the DSNB signal within 10 years of measurement. Combination of their results is likely to enable a 5σ discovery of the DSNB signal within the next decade.

Analysis of a JWST NIRSpec Lab Time Series: Characterizing Systematics, Recovering Exoplanet Transit Spectroscopy, and Constraining a Noise Floor

Abstract The James Webb Space Telescope’s (JWST) NIRSpec instrument will unveil the nature of exoplanet atmospheres across the wealth of planet types, from temperate terrestrial worlds to ultrahot Jupiters. In particular, the 0.6–5.3 μm PRISM mode is especially well suited for efficient spectroscopic exoplanet observations spanning a number of important spectral features. We analyze a lab-measured NIRSpec PRISM mode Bright Object Time Series observation from the perspective of a JWST user to understand the instrument performance and detector properties. We create two realistic transiting exoplanet time-series observations by performing injection-recovery tests on the lab-measured data to quantify the effects of real instrument jitter, drift, intrapixel sensitivity variations, and 1/f noise on measured transmission spectra. By fitting the time-series systematics simultaneously with the injected transit, we can obtain more realistic transit-depth uncertainties that take into account noise sources that are currently not modeled by traditional exposure time calculators. We find that sources of systematic noise related to intrapixel sensitivity variations and point-spread function motions are apparent in the data at the level of a few hundred ppm but can be effectively detrended using a low-order polynomial with detector position. We recover the injected spectral features of GJ 436 b and TRAPPIST-1 d and place a 3σ upper limit on the detector noise floor of 14 ppm. We find that the noise floor is consistent with <10 ppm at the 1.7σ level, which bodes well for future observations of challenging targets with faint atmospheric signatures.

Incomplete Charge Collection at Inter-Pixel Gap in Low- and High-Flux Cadmium Zinc Telluride Pixel Detectors.

The success of cadmium zinc telluride (CZT) detectors in room-temperature spectroscopic X-ray imaging is now widely accepted. The most common CZT detectors are characterized by enhanced-charge transport properties of electrons, with mobility-lifetime products μeτe > 10−2 cm2/V and μhτh > 10−5 cm2/V. These materials, typically termed low-flux LF-CZT, are successfully used for thick electron-sensing detectors and in low-flux conditions. Recently, new CZT materials with hole mobility-lifetime product enhancements (μhτh > 10−4 cm2/V and μeτe > 10−3 cm2/V) have been fabricated for high-flux measurements (high-flux HF-CZT detectors). In this work, we will present the performance and charge-sharing properties of sub-millimeter CZT pixel detectors based on LF-CZT and HF-CZT crystals. Experimental results from the measurement of energy spectra after charge-sharing addition (CSA) and from 2D X-ray mapping highlight the better charge-collection properties of HF-CZT detectors near the inter-pixel gaps. The successful mitigation of the effects of incomplete charge collection after CSA was also performed through original charge-sharing correction techniques. These activities exist in the framework of international collaboration on the development of energy-resolved X-ray scanners for medical applications and non-destructive testing in the food industry.

Advanced plastic scintillation detectors for low-background experiments

Many international low-background experiments are showing increasing interest in the use of different plastic scintillation detectors. Based on our experience in the field of quality improvement of the polystyrene (PS) based plastic scintillation detectors, this work is focusing on a further enhancement of the scintillator light output and the associated energy resolution crucial for the detection of a very rare nuclear processes. To produce PS scintillators from liquid styrene various stabilization additives and conditions of polymerization process are commonly used. These factors, i.e. stabilization additives and atmospheric oxygen, have a negative impact on above mentioned optical properties of the scintillation detectors. Within this study, several samples under different conditions, e.g. concentrations of luminescent additives; presence of stabilization additives; air and inert atmosphere, were prepared and tested using a unique tunable electron spectrometer providing a monoenergetic electron beam ranging from 200 keV to 1.5 MeV.

TCAD simulations of non-irradiated and irradiated low-gain avalanche diodes and comparison with measurements

In this work, the results of Technology-CAD (TCAD) device-level simulations of non-irradiated and irradiated Low-Gain Avalanche Diode (LGAD) detectors and their validation against experimental data will be presented. Thanks to the intrinsic multiplication of the charge within these silicon sensors, it is possible to improve the signal to noise ratio thus limiting its drastic reduction with fluence, as it happens instead for standard silicon detectors. Therefore, special attention has been devoted to the choice of the avalanche model, which allows the simulation findings to better fit with experimental data. Moreover, a radiation damage model (called “New University of Perugia TCAD model”) has been fully implemented within the simulation environment, to have a predictive insight into the electrical behavior and the charge collection properties of the LGAD detectors, up to the highest particle fluences expected in the future High Energy Physics (HEP) experiments. This numerical model allows to consider the comprehensive bulk and surface damage effects induced by radiation on silicon sensors. By coupling the “New University of Perugia TCAD model” with an analytical model that describes the mechanism of acceptor removal in the multiplication layer, it has been possible to reproduce experimental data with high accuracy, demonstrating the reliability of the simulation framework.

Influence of impurities and structural defects on the properties of CdTe- and CdZnTe-based detectors

The most researched materials for uncooled semiconductor detectors of ionizing radiation are CdTe:Cl and Cd0.9Zn0.1Te, which allow to obtain detectors with high values of resistivity ρ and electron mobility. In the process of producing detector materials, the background impurities and defects can be introduced into their matrix, and as a result the deep levels appear in the bandgap, acting as centers of capture and recombination of nonequilibrium charge carriers and reducing the registration ability of detectors. The aim of this study was to determine by computer simulation method the nature of the effect of background impurities and structural defects on the electrophysical and detector properties of CdTe and CdZnTe. Quantitative studies were conducted using reliability-tested models. The authors used the examples of Cl, Fe, Pb, Cr, Co, Ti, V, Ni, Ge, Sn to study the effect of doping and background impurities on the resistivity ρ, lifetime of nonequilibrium electrons and holes, the charge collection efficiency η of detectors based on CdTe and Cd0.9Zn0.1Te. The influence of cadmium vacancies on the degradation of the ρ and η of the detectors based on the materials under study was clarified. Impurities were found that reduce ρ and η in detectors based on CdTe:Cl and Cd0.9Zn0.1Te:Al. The ultimate concentration of donor impurities and defects with their uniform distribution over the crystal volume without the formation of clusters was determined. The effect of the Fermi level and defect levels on the change and degradation of the properties of the materials under study was found. The ratios of the concentrations of background impurities and defects were established, making it possible to obtain semiconductors CdTe:Cl and Cd0.9Zn0.1Te of an acceptable detector quality.

Atmospheric neutrinos in next-generation xenon and argon dark matter experiments

We study the sensitivity of future xenon- and argon-based dark matter and neutrino detection experiments to low-energy atmospheric neutrinos. Not accounting for experimental backgrounds, the primary obstacle for identifying nuclear recoils induced by atmospheric neutrinos is the tail of the electron recoil distribution due to $pp$ solar neutrinos. We use the NEST code to model the solar and atmospheric neutrino signals in a xenon detector and find that an exposure of 700 tonne-years will produce a $5\sigma$ detection of atmospheric neutrinos. We explore the effect of different detector properties and find that a sufficiently long electron lifetime is essential to the success of such a measurement.

Fabrication and First Full Characterisation of Timing Properties of 3D Diamond Detectors

Tracking detectors at future high luminosity hadron colliders are expected to be able to stand unprecedented levels of radiation as well as to efficiently reconstruct a huge number of tracks and primary vertices. To face the challenges posed by the radiation damage, new extremely radiation hard materials and sensor designs will be needed, while the track and vertex reconstruction problem can be significantly mitigated by the introduction of detectors with excellent timing capabilities. Indeed, the time coordinate provides extremely powerful information to disentangle overlapping tracks and hits in the harsh hadronic collision environment. Diamond 3D pixel sensors optimised for timing applications provide an appealing solution to the above problems as the 3D geometry enhances the already outstanding radiation hardness and allows to exploit the excellent timing properties of diamond. We report here the first full timing characterisation of 3D diamond sensors fabricated by electrode laser graphitisation in Florence. Results from a 270MeV pion beam test of a first prototype and from tests with a β source on a recently fabricated 55×55μm2 pitch sensor are discussed. First results on sensor simulation are also presented.

Radiation hardness of PantherPix hybrid pixel detector

Hybrid pixel detectors (HPD) are nowadays well known and widely used in fundamental research, e.g. in high energy physics experiments. Over the last decade, segmented semiconductor detectors have also found use in medicine. The total doses received by medical radiation detectors often reach a significant level (up to several hundreds of kGy per decade), especially in applications such as transmission portal in-vivo dosimetry. Such doses might affect detector properties. Therefore, it is necessary to evaluate their performance after absorbing a significant radiation dose. PantherPix is a novel 2D hybrid pixel detector which is designed specifically for use in radiation therapy. As was concluded in earlier studies, it is suitable for radiotherapy quality assurance (QA) and portal dosimetry. In this paper, the PantherPix radiation hardness is investigated using a 60Co source. The dependence on dose of the full depletion voltage, leakage current, detector power consumption and detector response are provided. The PantherPix radiation tolerance has been shown to be adequate for common cumulative doses delivered to radiation detectors in radiotherapy over several decades and its performance has been verified for doses up to 3000 kGy.

Single-photon microwave photonics

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultra-weak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of single-photon microwave photonics (SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector (SNSPD) and a successive time-correlated single photon counting (TCSPC) module. Experimental results show that an ultrahigh optical sensitivity down to −100 dBm has been achieved, and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Radiation Hardness Property of Ultra-Fast 3D-Trench Electrode Silicon Detector on N-Type Substrate.

The radiation fluence of high luminosity LHC (HL-LHC) is predicted up to 1 × 1016 1 MeV neq/cm2 in the ATLAS and CMS experiments for the pixel detectors at the innermost layers. The increased radiation leads to the degradation of the detector properties, such as increased leakage current and full depletion voltage, and reduced signals and charge collection efficiency, which means it is necessary to develop the radiation hard semiconductor devices for very high luminosity colliders. In our previous study about ultra-fast 3D-trench electrode silicon detectors, through induced transient current simulation with different minimum ionizing particle (MIP) hitting positions, the ultra-fast response times ranging from 30 ps to 140 ps were verified. In this work, the full depletion voltage, breakdown voltage, leakage current, capacitance, weighting field and MIP induced transient current (signal) of the detector after radiation at different fluences will be simulated and calculated with professional software, namely the finite-element Technology Computer-Aided Design (TCAD) software frameworks. From analysis of the simulation results, one can predict the performance of the detector in heavy radiation environment. The fabrication of pixel detectors will be carried out in CMOS process platform of IMECAS based on ultra-pure high resistivity (up to 104 ohm·cm) silicon material.