Detection Of Ionizing Radiation Research Articles

Ce doped garnet structure crystalline scintillation materials for HEP instrumentation

To date, more than 200 scintillation materials have been developed, however only a few of them are widely used for detectors design and construction. A general trend is to use for detectors the elements produced from the selected top-quality grade scintillation materials instead of expensive novel chemically not stable halides. Another trend, which came in the last few years, is to apply new achievements from the theory of scintillation materials to engineer the properties of the materials for a particular application. From that point of view, the complex oxides with garnet structure is a family of materials, for which properties can be tuned for the best performance for a particular application at the ionizing radiation detection.

Quantifying DNA damage induced by ionizing radiation and hyperthermia using single DNA molecule imaging.

Ionizing radiation (IR) is a common mode of cancer therapy, where DNA damage is the major reason of cell death. Here, we use an assay based on fluorescence imaging of single damaged DNA molecules isolated from radiated lymphocytes, to quantify IR induced DNA damage. The assay uses a cocktail of DNA-repair enzymes that recognizes and excises DNA lesions and then a polymerase and a ligase incorporate fluorescent nucleotides at the damage sites, resulting in a fluorescent “spot” at each site. The individual fluorescent spots can then be counted along single stretched DNA molecules and the global level of DNA damage can be quantified. Our results demonstrate that inclusion of the human apurinic/apyrimidinic endonuclease 1 (APE1) in the enzyme cocktail increases the sensitivity of the assay for detection of IR induced damage significantly. This optimized assay also allowed detection of a cooperative increase in DNA damage when IR was combined with mild hyperthermia, which is sometimes used as an adjuvant in IR therapy. Finally, we discuss how the method may be used to identify patients that are sensitive to IR and other types of DNA damaging agents.

Bright Blue Emitting Cu-Doped Cs2ZnCl4 Colloidal Nanocrystals.

We report here the synthesis of undoped and Cu-doped Cs2ZnCl4 nanocrystals (NCs) in which we could tune the concentration of Cu from 0.7 to 7.5%. Cs2ZnCl4 has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl4 tetrahedra surrounded by Cs+ cations. According to our electron paramagnetic resonance analysis, in 0.7 and 2.1% Cu-doped NCs the Cu ions were present in the +1 oxidation state only, while in NCs at higher Cu concentrations we could detect Cu(II) ions (isovalently substituting the Zn(II) ions). The undoped Cs2ZnCl4 NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at ∼2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (∼55%) for the samples with a low Cu concentration ([Cu] ≤ 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (∼2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped Cs2ZnCl4 NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.

X-ray detection based on crushed perovskite crystal/polymer composites

Organic-inorganic hybrid perovskite materials have attracted increasing attention in recent years for ionizing radiation detection due to their large cross-section for high energy X-ray or gamma ray, defect-tolerance, large mobility lifetime product, tunable bandgap and facile preparation of single crystals. However, the thickness of solution processed perovskite polycrystalline films are normally limited, and single crystals are fragile and hard to be utilized as a device. In this article, we successfully realized the preparation of the perovskite crystal/polymer composites, through a novel process involving mechanically grinding and sieving. X-ray detectors were fabricated based on the relatively thick composite films via solution process. The device performance under the irradiation of X-rays were also investigated, in terms of stability, dark current, noise and temporal response. Our devices exhibited remarkable performance metrics, which proved that the perovskite composite films can be used to fabricate highly efficient and low-cost X-ray detectors.

Perovskite Quantum-Dot-in-Host for Detection of Ionizing Radiation.

The concept of quantum-dot-in-perovskite solids pioneered by Ning and co-workers introduces a useful class of solution-processed type I heterostructures for optoelectronics applications. Concurrent searches for solution-processable detectors of ionizing radiation have focused on lead-halide perovskites. As described in this issue of ACS Nano, Cao et al. examined CsPbBr3 nanocrystals imbedded in Cs4PbBr6 as a wider gap host and determined its performance and possibilities as a scintillator for X-ray imaging. In this Perspective, we describe issues and research opportunities on ionizing radiation imaging and spectroscopy based on the CsPbBr3@Cs4PbBr6 composite and other perovskite-dot-in-host combinations in which the dot may be of lower dimensionality than 3, and we explore ionizing radiation detectors using halide perovskites.

Modeling a Thick Hydrogenated Amorphous Silicon Substrate for Ionizing Radiation Detectors

There is currently a renewed interest in hydrogenated amorphous silicon (a-Si:H) for use in particle detection applications. Whilst this material has been comprehensively investigated from a numerical perspective within the context of photovoltaic and imaging applications, the majority of work related to its application in particle detection has been limited to experimental studies. In this study, a material model to mimic the electrical and charge collection behaviour of a-Si:H is developed using the SYNOPSYSc Technology Computer Aided Design (TCAD) simulation tool Sentaurus. The key focus of the model is concerned with the quasi-continuous defect distribution of acceptor and donor defects near the valence and conduction bands (tails states) and a Gaussian distribution of acceptor and donor defects within the mid-gap with the main parameters being the defect energy level, capture cross-section and trap density. Currently, Sentaurus TCAD offers Poole-Frenkel mobility and trap models, however, these were deemed to be incompatible with thick a-Si:H substrates. With the addition of a fitting function, the model was able to provide acceptable agreement (within 10nA.cm-2) between simulated and experimental leakage current density for a-Si:H substrates with thicknesses of 12 and 30μm. Additional transient simulations performed to mimic the response of the 12μm thick device demonstrated excellent agreement (1%) with experimental data found in the literature in terms of the operating voltage required to deplete thick a-Si:H devices. The a-Si:H model developed in this work provides a method of optimising a-Si:H based devices for particle detection applications.

Microwave-Assisted Growth of Silver Nanoparticle Films with Tunable Plasmon Properties and Asymmetrical Particle Geometry for Applications as Radiation Sensors

We report a simple and fast microwave-assisted method to grow silver nanoparticle films with tunable plasmon resonance band. Microwaving time controls nucleation and growth as well as particle agglomeration, cluster formation, particle morphology, and the plasmonic properties. Films produced with times shorter than 30 s presented a single well-defined plasmon resonance band (~ 400 nm), whereas films produced with times longer than 40 s presented higher wavelength resonances modes (> 500 nm). Plasmon band position and intensity can be easily tuned by controlling microwaving time and power. SEM and AFM images suggested the growth of asymmetrical silver nanoparticles. Simulated extinction spectra considering particles as spheres, hemispheres, and spherical caps were performed. The films were employed to enhance the sensitivity of ionizing radiation detectors assessed by optically stimulated luminescence (OSL) via plasmon-enhanced luminescence. By tuning the plasmon resonance band to overlap with the OSL stimulation (530 nm), luminescence enhancements of greater than 100-fold were obtained, demonstrating the importance of tuning the plasmon resonance band to maximize the OSL intensity and detector sensitivity. This versatile method to produce silver nanoparticle films with tunable plasmonic properties is a promising platform for developing small-sized radiation detectors and advanced sensing technologies.

Investigation on the characteristics of ZnO and ZnO-Pb structure for gamma radiation detection

Zinc oxide (ZnO) thin films of multilayers structure were fabricated by chemical bath deposition (CBD) method on a glass substrate. After growing, the optical, structural and morphological characterizations of the samples were studied. Moreover, the crystallite size and energy band gap were calculated by using X-ray diffractometer (XRD) and UV-visible spectrometer, respectively. XRD showed that the crystalline size of the samples decreased with increasing the layers up to four layers, while the energy band gap increased with increasing the layers. Field emission scanning electron microscope (FESEM) used to study the morphological properties of the samples. Based on the effective atomic number, electron density and light yield properties of the samples make it suitable to be used as an ionizing radiation detector. Eventually, the samples will be used as a scintillator material to detect ionizing radiation.

Morphology and mobility as tools to control and unprecedentedly enhance X-ray sensitivity in organic thin-films

Organic semiconductor materials exhibit a great potential for the realization of large-area solution-processed devices able to directly detect high-energy radiation. However, only few works investigated on the mechanism of ionizing radiation detection in this class of materials, so far. In this work we investigate the physical processes behind X-ray photoconversion employing bis-(triisopropylsilylethynyl)-pentacene thin-films deposited by bar-assisted meniscus shearing. The thin film coating speed and the use of bis-(triisopropylsilylethynyl)-pentacene:polystyrene blends are explored as tools to control and enhance the detection capability of the devices, by tuning the thin-film morphology and the carrier mobility. The so-obtained detectors reach a record sensitivity of 1.3 · 104 µC/Gy·cm2, the highest value reported for organic-based direct X-ray detectors and a very low minimum detectable dose rate of 35 µGy/s. Thus, the employment of organic large-area direct detectors for X-ray radiation in real-life applications can be foreseen.

Remote Detection of Uranium Using Self-Focusing Intense Femtosecond Laser Pulses

Optical measurement techniques can address certain important challenges associated with nuclear safety and security. Detection of uranium over long distances presents one such challenge that is difficult to realize with traditional ionizing radiation detection, but may benefit from the use of techniques based on intense femtosecond laser pulses. When a high-power laser pulse propagates in air, it experiences collapse and confinement into filaments over an extended distance even without external focusing. In our experiments, we varied the initial pulse chirp to optimize the emission signal from the laser-produced uranium plasma at an extended distance. While the ablation efficiency of filaments formed by self-focusing is known to be significantly lower when compared to filaments produced by external focusing, we show that filaments formed by self-focusing can still generate luminous spectroscopic signatures of uranium detectable within seconds over a 10-m range. The intensity of uranium emission varies periodically with laser chirp, which is attributed to the interplay among self-focusing, defocusing, and multi-filament fragmentation along the beam propagation axis. Grouping of multi-filaments incident on target is found to be correlated with the uranium emission intensity. The results show promise towards long-range detection, advancing the diagnostics and analytical capabilities in ultrafast laser-based spectroscopy of high-Z elements.

On MAPS-On-Diamond sensors and their potential as innovative devices

Synthetic diamond is a very attractive material to build sensors and devices due to its properties as radiation resistance, very low noise, human tissue equivalence. Aside from costs and dimensions, one important drawback is the creation of highly segmented devices. Recently, a new technique, the silicon-on-diamond bonding via laser pulses, has been developed to instrument diamond substrates with pixellated CMOS imagers acting as readout chips to obtain ionizing radiation detectors. This new class of devices could be polarized at the same voltage levels of a standard diamond detector, i.e. 1 V/μm to reach the depletion region. The bias is applied between the diamond side and the silicon side, and it drops almost entirely through the diamond thickness leaving undisturbed the working of the CMOS circuitry. When an e-h pair is created in the diamond, the charges of one type will drift towards the diamond-silicon interface according to the sign of the polarization applied and then collected by the metal electrode on the silicon surface. The collected signal is due both to the charge created in the silicon and to the charge created in the diamond bulk. As CMOS silicon layer, we have used a custom Monolithic Active Pixel Sensors (MAPS) where are implemented both small pixels and low noise electronic circuits. A proof of principle of the bonding of a thinned MAPS and a diamond substrate producing a MAPS-On-Diamond device has been fabricated (no damage to the CMOS circuitry) and is capable of collecting both contributions. We will discuss the present limitation of the produced devices and the possibility of using a commercial CMOS Image Sensor (CIS) as the instrumented layer for the diamond substrate and asses the expected performances in detecting ionizing radiation.

Bismuth chalcohalide-based nanocomposite for application in ionising radiation detectors

Bismuth sulpho iodide (BiSI) belongs to the family of chalcohalides, which present several attractive electro-optic properties. In particular, BiSI is a semiconductor which could be used in X and gamma ray detection due to a band gap of 1.6 eV, density of 6.4 g cm−3, and absorption coefficient for 60 keV radiation of 5.6 cm2 g−1. This work presents a facile synthesis under solvothermal conditions of a nanocomposite consisting of BiSI nanorods and amorphous carbon structures. Furthermore, it studies its ionising radiation detection properties at room temperature, when prototype detectors were built from pellets. The construction conditions of pellets were also studied, varying the applied pressure and heat treatment to the nanocomposite. Dark current density and response to different exposure rates of a 241Am source were measured for the prototype detectors built. It was found that heat treatment of pellets considerably improves detectors performance. Dark current density was one order of magnitude lower than for the pellets without heat treatment, and its response to the 241Am source, linear, with a signal to noise ratio of 7 for 20 V. Finally, the resistivity for the heat treated detector was in the order of 1011 Ω cm, comparable to other materials studied for this application.

Photodetectors based on solution-processable semiconductors: Recent advances and perspectives

The detection of light, one of the most important technologies, has widespread applications in industry and our daily life, e.g., environmental monitoring, communications, surveillance, image sensors, and advanced diagnosis. Along with the remarkable progress in the field of organics, those based on quantum dots, and recently emerged perovskite optoelectronics, photodetectors based on these solution-processable semiconductors have shown unprecedented success. In this review, we present the basic operation mechanism and the characterization of the performance metrics based on these novel materials systems. Then, we focus on the current research status and recent advances with the following five aspects: (i) spectral tunability, (ii) cavity enhanced photodetectors, (iii) photomultiplication type photodetectors, (iv) sensitized phototransistors, and (v) ionizing radiation detection. At the end, we discuss the key challenges facing these novel photodetectors toward manufacture and viable applications. We also point out the opportunities, which are promising to explore and may require more research activities.

Luminescence of alumina ceramic doped with lanthanum under medium- and high-dose irradiation

The synthesis of La-doped alumina ceramics results in a formation of new pulsed cathodoluminescence bands and thermoluminescence peaks which associated with phases of lanthanum aluminate (LaAlO3) and lanthanum aluminium oxide (LaAl11O18). Annealing at high temperatures (up to 1600 °C) with maximum lanthanum concentration allows to create ceramics with high intensity of 510 pulsed cathodoluminescence band and 370 K thermoluminescence peak. The high intensity of new peaks thermoluminescence demonstrates the material sensitivity to ionizing radiation and the possibility of its use as ionizing radiation detectors in the case of expanding the sublinear dose recording range.

ДОСЛІДЖЕННЯ ПРОЦЕСІВ ДЕТЕКТОРА ГАММА-ВИПРОМІНЮВАННЯ ДЛЯ РОЗРОБКИ ПОРТАТИВНОГО ЦИФРОВОГО СПЕКТРОМЕТРА

When considering methods of combating the illicit circulation of nuclear materials, it is necessary to detect trace amounts of materials, and in many cases not to seize them immediately, but to establish the place of storage, processing, routes of movement, etc. As a result, there is a new demand for isotope identification measurements to meet a wide range of different requirements. Measurements should be carried out in the field in a short time, when results need to be obtained within tens of seconds. The devices with which the personnel work should be small and low-background. Such requirements appear when working to identify cases of illegal trade in nuclear materials and radioactive sources, as well as when solving radiation protection problems and when handling radioactive devices and waste. In this work, new generation radiation sensors and measuring systems based on them have been created, which open up previously unknown possibilities in solving problems of nuclear fuel analysis, increasing the accuracy and efficiency of monitoring technological parameters and the state of protective barriers in nuclear power plants, and creating means for IAEA inspections. For the first time a portable digital gamma-ray spectrometer for radiation reconnaissance in the field was developed and created. Distinctive features of such devices are: The analysis showed that the required value of error due to energy dependence of the sensitivity can be achieved using, for example, Analog Devices 10-bit AD9411 ADCs with a sampling rate of 170 MHz. The number of quantization levels is determined by the requirement to measure the dose rate of gamma radiation with an energy of at least 10 keV. This minimum energy corresponds to the use of 10-bit ADCs. On the basis of the developed model, an ionizing radiation detector for dosimetry was created. Its fundamental difference from known devices is the use of CdZnTe crystals as a primary gamma-ray converter (sensor). The advantages of such a solution, proved by previous studies, made it possible to create a detector with: high resolution, no more than 40 keV; a wider dynamic range of values of the recorded radiation dose rate - from background to emergency operating modes of the reactor; lower value of the energy equivalent of noise.

Optimizing CdZnTeSe Frisch-Grid Nuclear Detector for Gamma-Ray Spectroscopy

Wide bandgap semiconductor materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Additional major applications include medical imaging, spectroscopy, and astrophysics. Most current room-temperature ionizing radiation detector devices are fabricated from cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). Cadmium zinc telluride selenide (CdZnTeSe or CZTS) can be grown with high crystal yield compared to CdTe and CdZnTe. Thus, CZTS has the advantage of lowering the cost of room-temperature nuclear detectors. Thick CdTe-based detectors are prone to the trapping of charge carriers, thus limiting energy resolution and efficiency. A Frisch-Grid configuration helps to solve this problem. This research is focused on optimizing the Frisch-grid configuration for a CZTS detector. The CZTS was grown by traveling heater method. Infrared images of the CZTS matrix largely showed the absence of tellurium inclusions. The resistivity of the CZTS obtained from a current-voltage plot is of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Ω.cm. The charge-transport characterized by measuring the electron mobility-lifetime product is 4.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V. Detector resolution was measured for various Frisch-ring widths. For a 4.8 × 4.9 × 9.7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> detector, the best Frisch-ring widths were found to be 3-4 mm. A detector resolution of 1.35% full-width-at-half-maximum was obtained for the 3-mm width at -2300 V bias voltage for the 662-keV gamma peak of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs. A resolution of 1.36% was obtained for the 4-mm width at -1800 V applied bias.

Multi-elemental analysis of high-purity molybdenum by electrothermal vaporization inductively coupled plasma mass spectrometry

High purity molybdenum and its compounds are used for the synthesis of ionizing radiation detectors for search for dark matter and double beta decay. Properties of these detectors largely depend on their trace composition. The new mass-spectrometry with inductively coupled plasma (ICP-MS) and electrothermal vaporization (ETV) method was developed for the analysis of high-purity molybdenum. The samples were introduced into the ICP using the ETV device. The vaporization curves of matrix element (molybdenum) and trace elements were studied in detail. The dependence of analytical signal and limits of detection (LODs) of analytes versus ETV-ICP-MS instrumental parameters (ICP power, transport flow, ion optics settings) was established. The proposed method of ETV-ICP-MS analysis allowed us to control the content of 28 trace elements in high-purity molybdenum with a purity of 6N (99.9999% wt.) and provided LODs from 0.3 to 200 ng g-1. Using of ETV for ICP-MS analysis of molybdenum led to decreasing of the LODs of trace elements from 3 to 200 times comparing with ICP-MS analysis with standard sample introduction system. The validation of proposed ETV-ICP-MS method was performed by spike experiment and by comparing the results of ETV-ICP-MS, ICP-MS, and atomic absorption spectrometry with electrothermal vaporization (GFAAS) analysis.

Degradation Under Influence of Radiation Defects of Detector Properties of CdTe and Cd0.9Zn0.1Te Irradiated by Neutrons

This work is devoted to the study by computer simulation of the mechanisms of the influence of radiation defects, arising under the influence of neutron irradiation, on the changes in electrical properties: resistivity ρ, electron mobility μn, lifetime of nonequilibrium electrons τn and holes τp in Cd0.9Zn0.1Te and charge collection efficiency η of uncooled ionizing radiation detectors based on this material. Radiation defects, which are corresponded by deep energy levels in the band gap, act as trapping centers of nonequilibrium charge carriers, noticeably affect the degree of compensation by changing ρ of the detector material, the recombination processes, decreasing τn and τp, and also the scattering of conduction electrons, decreasing μn, that ultimately can cause degradation of the charges collection efficiency η. The specific reasons for the deterioration of the electrophysical and detector properties of this semiconductor under the influence of neutron irradiation were identified, and the main factors affecting the increase in the resistivity of Cd0.9Zn0.1Te during its bombardment by low-energy and high-energy neutrons, leading to complete degradation of the recording ability of detectors based on this materials, were found. The recombination of nonequilibrium charge carriers is noticeably stronger than the decrease in μn affects the degradation of detector properties, therefore, the effect of recombination processes at deep levels of radiation defects on the degradation of τn, τp, and η of detectors based on Cd0.9Zn0.1Te was studied. A comparative analysis of the properties of Cd0.9Zn0.1Te with the previously studied CdTe:Cl was made. An attempt was made to explain the higher radiation resistance of Cd0.9Zn0.1Te compared to CdTe:Cl under neutron irradiation by the influence of the radiation self-compensation mechanism with participation of deep donor energy levels: interstitial tellurium and tellurium at the site of cadmium. In addition, the rate of recombination at defect levels in Cd0.9Zn0.1Te is, ceteris paribus, lower than in CdTe:Cl due to the smaller difference between the Fermi level and the levels of radiation defects in cadmium telluride. The relationship between the band gaps of Cd0.9Zn0.1Te and CdTe:Cl, the concentration of radiation defects, the Fermi level drift during irradiation, and the radiation resistance of the detectors were also noted. The important role of purity and dopant shallow donor concentration in initial state of the detector material is indicated.

Optical Investigations of In&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;2.7&lt;/sub&gt;Sb&lt;sub&gt;0.3&lt;/sub&gt; Thin Films Prepared by Thermal Evaporation Technique

The III-VI compound semiconductors are important for the fabrication of ionizing radiation detectors, solid-state electrodes, and photosensitive heterostructures, solar cell as well as ionic batteries. In this paper, In2Se2.7Sb0.3 thin films have been grown by thermal evaporation technique onto a with chemically clean glass substrate. Amorphous nature of the films has been discovered by UV-VIS spectrophotometer. The analysis by absorption spectra within the spectral range 200nm -900 nm has been used for the optical characterization of thin films. From these data the optical constants (absorption coefficient (α), refractive index (η), extinction coefficient (k)) and optical band gap (Eg) are studied. The results were discussed, and reported in detail.

Performance of four CVD diamond radiation sensors at high temperature

Ionising radiation detectors based on wide band-gap materials have the potential to operate at temperatures higher than 200°C. Such detectors are important in applications such as monitoring near nuclear reactors and in deep oil and gas well borehole logging. We discuss the development of alpha particle detectors, based on CVD diamond, which operate with high charge collection efficiency and energy resolution at temperatures up to 225°C. Four nominally identical commercial, electronic grade, CVD diamonds have been coated with a thin metal conductive layer in our laboratory and then attached to ceramic PCB. We present the I–V characteristics, the charge collection efficiency and the energy resolution for alpha particles from a mixed 239Pu,241Am,244Cm source, for the four sensors operating at temperatures from 20 to 250°C. Monte Carlo simulations of the energy spectra and charge collection efficiency and experimental measurements of these are presented. Energy resolutions between 1.6% and 4.0% at elevated temperatures with charge collection efficiency exceeding 96% were measured. The potential for thermal neutron detection is discussed.