Development Of Radiation Detectors Research Articles

Effect of Sintering Time and Cl Doping Concentrations on Structural, Optical, and Luminescence Properties of ZnO Nanoparticles

Zinc oxide (ZnO) nanoparticles were synthesized hydrothermally using zinc acetate dihydrate and sodium thiosulfate pentahydrate precursors. The synthesized powders were sintered in air at 600 °C for different durations with a Cl-doping concentration of 25 mg/g. The optimal sintering time was found to be 5 h, resulting in the successful formation of the ZnO phase with small particle sizes of around 90 nm, nominal atomic fractions of Zn and O (~50%, ~50%), and increased luminescence intensity. The ideal concentration of Cl was discovered to be 25 mg/g of ZnO, which resulted in the highest luminescence intensity. The ZnO luminescence characteristics were observed in emission bands peaking at approximately 503 nm attributed to the transition from oxygen vacancies. A considerable improvement in the emission intensity was observed with increased Cl doping concentration, up to eight orders of magnitude, compared to pristine ZnO nanoparticles. However, the luminescence intensity decreased in samples with higher concentrations of Cl doping due to concentration quenching. These preliminary outcomes suggest that Cl-doped ZnO nanoparticles could be used for radiation detector development for radon monitoring and other related applications.

(Invited) Photo Induced Effects in OTFTs: Mechanisms and Applications

The technology based on organic devices and sensors is becoming attractive for a wide range of applications. Indeed, the intrinsic characteristics of the organic materials, as the low-temperature process, flexibility, lightweight, biocompatibility, and even biodegradability, make them the basis for devices for the emerging flexible plastic electronics. Among the different possible applications, the electro-optical properties of organic semiconductors can be exploited for the development of devices for photosensing [1], imaging array [2], and optical memory [3]. The wide number of organic materials with different absorption spectra allows the development of photosensors with large spectral sensitivity or tuned to specific wavelengths. In particular, organic phototransistors (OPTs) are particularly promising since they combine light detection, typical of the photodiodes (OPD), with the intrinsic signal amplification that increases the device sensitivity. The response of the OPTs to light irradiation was widely studied in the last years. The photons with energy above the optical gap generate excitons that can dissociate into free holes and electrons and, in p-type devices, the photo-generated electrons are trapped. Negative trapped charges induce the shift of the flat band voltage as well as the threshold voltage of the OPT resulting in the increase of the drain current [4]. The location and the nature of the defect states are still under investigation. Depending on the organic semiconductor, gate dielectric and device structure, the defects have been identified as interface states between semiconductor and insulators [2], defects into the semiconductors [3], defects induced by the diffusion of oxygen or moisture into the OSC [5]. Trapped charge near the source/drain electrodes can also reduce the injection contact barrier, increasing the drain current [6]. In any case, photo-induced effects appear to be a quite general effect since they are observed in devices with different semiconductor molecules and different gate dielectric (both organic and inorganic). In this presentation, the different mechanisms will be reviewed and the photo-induced effects will be discussed for OTFTs with evaporated and solution-processed semiconductors and different device structures. The high stability of these devices under gate bias stress, allows to investigate in detail the effects induced by the light.Furthermore, this presentation will show the application of the electro-optical properties of the OTFTs to the development of radiation detectors based on Organic Photo Transistors (OPTs), made on flexible substrate, and coupled with plastic scintillators. The OPTs are based on organic semiconductor dinaphtho [2,3-b:2′,3′-f] thieno[3,2-b] thiophene (DNTT) and have Bottom Gate/Top contact multi-finger device structure in order to simplify the device coupling with scintillator and increase the device area. The channel length, L, and channel width, W, are 100 µm and 2 cm, respectively. The gate, source and drain, and the semiconductor layer (DNTT, 30 nm thick) are thermally evaporated through metal masks. Spin coated layers of Cytop are used as gate dielectric and passivation layer. Thanks to the high quality of the semiconductor and of the dielectric/semiconductor interface, the devices show good electrical characteristics, with field effect mobility of about 1 cm2/Vs, a threshold voltage of the order of -10 V and subthreshold voltage of about 1V/dec. Furthermore, the devices do not show hysteresis of the transfer characteristics and are quite stable under bias stress. The OPTs have been characterized by electrical and optical measurement in order to evaluate the figures of merit parameters of the photodetectors, such as the photo-switching speed, the responsivity, and the photocurrent on/off ratio (also indicated as photosensitivity). The measurements have been carried out under monochromatic light with λ= 450 nm (above the optical gap of the DNTT). At this wavelength, these OPTs are able to detect very low light intensity (of the order of few nW/cm2), with a responsivity of 0.25 A/W and sensitivity of 2x10-2. The OPTs are successfully coupled with siloxane based scintillator.This work is supported by INFN-CNS5 project "FIRE".[1] J. Huang et al., Adv. Mater. 2020, 32, 1906027 [2] Y. Chu et al., Adv. Sci. 2016, 3, 1500435 [3] K. Pei et al., Adv. Mater. 2018, 30, 1706647 [4] A. Pierre and A.C. Arias, Flex. Print. Electron 1 (2016) 043001 [5] R. Jia and e. al., Adv. Funct. Mater., vol. 29, p. 1905657, 2019.[6] X. Wang et al., J. Appl. Phys. 107, 024509 (2010).

Studies on DC transport and terahertz conductivity of granular molybdenum thin films for microwave radiation detector applications

The morphological, transport, and terahertz optical properties of DC magnetron-sputtered granular molybdenum thin films with nano-grains embedded in an amorphous molybdenum/molybdenum oxide matrix have been studied in their normal and superconducting states. The superconducting transition temperatures of these films are much higher than that of bulk molybdenum. The optical properties of these thin films have been studied using terahertz time-domain spectroscopy. Their properties have been compared with those of the existing materials used for the development of radiation detectors. The films' resistivity lies in the >100 μΩ cm range, ideal for making highly sensitive radiation detectors. Hall measurements indicate holes as the dominant carriers with very small mean free path and mobility. In the normal state, the films are disordered bad metals. However, they have a large superfluid density and stiffness in their superconducting state. The properties of the films in the normal and superconducting states are promising for their use in cryogenic radiation detectors for microwave, terahertz, and far-infrared frequency ranges.

Performance evaluation of YAlO3 scintillator plates with different Ce concentrations

Since Ce-doped YAlO3 (YAP(Ce)) scintillators have small non-proportionality, it is useful to develop a radiation imaging detector for low-energy gamma photons or X-rays. However, the YAP(Ce) performance with different Ce concentrations remains unclear. Consequently, we measured the basic performance of YAP(Ce) plates with different Ce concentrations. We used three types of YAP(Ce) scintillator plates with different Ce concentrations: 0.05% Ce, 1% Ce, and 2% Ce. The YAP(Ce) plates were 10 mm × 10 mm x 0.5 mm. We measured and compared the energy spectra, the decay times, the α-γ ratio, and the non-proportionality. We also evaluated the relation between these performances and the Ce concentrations. The light output of a YAP(Ce) showed positive correlation with the Ce concentrations, and the decay time of the YAP(Ce) showed a negative correlation with them. The energy resolution slightly improved for a YAP(Ce) with higher Ce concentrations. We found the α-γ ratio were slightly larger for higher Ce concentrations. The YAP(Ce) plate with a 2% Ce had the highest light output and the best energy resolution as well as the shortest decay time. Based on these results, the YAP(Ce) plate with a concentration of 2% Ce is a better selection for the development of radiation detectors or radiation imaging detectors for low-energy gamma photons or X-rays as well as alpha particles.

Differences in the Impurity Ionization in Quasi-Classically Strong Constant and Alternating Electric Fields in a Two-Dimensional Superlattice Based on Graphene

The coefficient of the absorption of an electromagnetic wave in a two-dimensional superlattice based on graphene, in the presence of a constant electric field for the case of quasi-classically strong electric fields is investigated. The anisotropy of the absorption coefficient is revealed at different orientations of the vector of the constant electric field and the vector of polarization of the alternating electric field. It is demonstrated that the slow increase in the absorption coefficient at low frequencies is caused by impurity absorption, and its faster increase at higher frequencies is determined by miniband-to-miniband transitions. These peculiar properties can be used for the development of radiation detectors.

Development of a stable and sensitive semiconductor detector by using a mixture of lead(II) iodide and lead monoxide for NDT radiation dose detection

Recently, high-energy radiation has been widely used in various industrial fields, including the medical industry, and increasing research efforts have been devoted to the development of radiation detectors to be used with high-energy radiation. In particular, nondestructive industrial applications use high-energy radiation for ships and multilayered objects for accurate inspection. Therefore, it is crucial to verify the accuracy of radiation dose measurements and evaluate the precision and reproducibility of the radiation output dose. Representative detectors currently used for detecting the dose in high-energy regions include Si diodes, diamond diodes, and ionization chambers. However, the process of preparing these detectors is complex in addition to the processes of conducting dosimetric measurements, analysis, and evaluation. Furthermore, the minimum size that can be prepared for a detector is limited. In the present study, the disadvantages of original detectors are compensated by the development of a detector made of a mixture of polycrystalline PbI2 and PbO powder, which are both excellent semiconducting materials suitable for detecting high-energy gamma rays and X-rays. The proposed detector shows characteristics of excellent reproducibility and stable signal detection in response to the changes in energy, and was analyzed for its applicability. Moreover, the detector was prepared through a simple process of particle-in-binder to gain control over the thickness and meet the specific value designated by the user. A mixture mass ratio with the highest reproducibility was determined through reproducibility testing with respect to changes in the photon energy. The proposed detector was evaluated for its detection response characteristics with respect to high-energy photon beam, in terms of dose-rate dependence, sensitivity, and linearity evaluation. In the reproducibility assessment, the detector made with 15 wt% PbO powder showed the best characteristics of 0.59% and 0.25% at 6 and 15 MV, respectively. Based on its selection in the reproducibility assessment, the 15 wt% PbO detector showed no dependence on the dose-rate changes, with R-SD < 1%. Finally, a coefficient of determination of 1 in the linearity assessment demonstrated very good linearity with regards to changes in dose. These results demonstrate the applicability and usefulness of the proposed detector made from a mixture of PbI2 and PbO semiconductors.

Current tendencies in the development of neutron and X-ray detectors for common use

The paper is a brief review of activities of Federal State Unitary Enterprise “VNIIA” and National Research Nuclear University “MEPhI” in the development of radiation detectors for various applications.

Spectroscopic investigation of gamma radiation-induced coloration in silicate glass for nuclear applications

Silicate glass irradiated by γ-rays was investigated in this study using spectroscopic analyses which included ultraviolet–visible (UV–Vis) absorption, electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR). The phenomenon of coloration on γ-ray-irradiated silicate glass was analyzed and the effect of annealing on the silicate coloration was also investigated. The results revealed that the coloration originates from the creation of hole-centers (HC) caused by radiation. The shade of the coloration highly correlates to the amount of these HC-related defects but can be reversed by thermal annealing. The variation in coloration is an effective predictive factor in understanding radiation damage on silicate glass. Therefore, this study is relevant in the development of radiation detectors using silicate material as well as in the permanent disposal of high-level nuclear waste in glass form.

Pulse height distribution of signals produced by exposing a thin GEM chamber to beta rays from an Sr-90 source

Researchers at Changwon National University’s Radiation Detector Development Laboratory(RDD) fabricated a single-channel double-GEM(gas electron multiplier) chamber and measured the pulse height distribution of signals produced by exposing the chamber to an Sr-90 source provided by the Korea Research Institute of Standards and Science(KRISS). A beta-ray electron incident on the GEM chamber ionizes gaseous molecules in the drift region of the chamber by means of electromagnetic interactions. After the leased electrons are amplified by electron avalanches in the GEM stages, the multiplied electrons go from the lowest GEM foil toward the anode of the chamber and induce one signal pulse, corresponding to the incident electron, on the readout pad. The charge signal distribution measured during Sr-90 radioactive source irradiation was compared with the simulation done by using a Landau probability distribution. The energy loss distribution of beta-ray electrons, which deposited part of their energy in a thin GEM chamber while traversing gases within the drift region of that chamber, was in good agreement with the calculation of the Landau probability distribution. The pulse height distributions for energy losses of beta-ray electrons incident on the chamber due to Sr-90 disintegrations were observed in order to select a suitable gas mixture for the chamber. The ratios of the Ar/CO2 gas were 75/25, 80/20, 85/15, and 90/10.

MOVPE Growth of Thick Single Crystal CdZnTe Epitaxial Layers on Si Substrates for Nuclear Radiation Detector Development

Details about the MOVPE growth of thick single crystal CdZnTe layers on (211)Si substrates are presented. The growth was carried out at a substrate temperature of 650°C, using dimethylcadmium, dimethylzinc, and diethyltellurium precursors. Control of Zn-concentration in the range from 0 to 0.2 was performed by controlling the precursors' flow-rates and ratio. Results from the XRD showed grown layers were single crystalline with no phase separation observed. The 4.2 K PL results show high intensity bound-exciton peaks which shifted to higher energies with increasing Zn-concentrations. A p-CdZnTe/p-CdTe/n-CdTe/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si hetero-junction diode was fabricated and evaluated for its possible application in nuclear radiation detector development, which exhibited good rectification property.

Advances in TlBr detector development

Thallium bromide (TlBr) is a promising compound semiconductor for fabrication of gamma-ray detectors. The attractive physical properties of TlBr lie in its high photon stopping power, high resistivity and good charge transport properties. Gamma-ray detectors fabricated from TlBr crystals have exhibited excellent spectroscopic performance. In this paper, advances in TlBr radiation detector development are reviewed with emphasis on crystal growth, detector fabrication, physical properties and detector performance.

Nanotechnology: A new era for photodetection?

Nowadays we live in the so-called “Silicon Era”, in which devices based on the silicon technology permeate all aspects of our daily life. One can simply think how much silicon is in the everyday household objects, gadgets and appliances. The impact of silicon technology has been very relevant in photodetection as well. It enables designing large or very large-scale integration devices, in particular microchips and pixelled detectors like the Silicon Photo Multiplier made of micrometric channels grouped in mm 2 pixels. However, on the horizon, the recent development of nanotechnologies is opening a new direction in the design of sub-micron photodevices, owing to the capability to deal with individual molecules of compounds or to chemically grow various kinds of materials. Among them, carbon compounds appear to be the most promising materials being chemically very similar to silicon, abundant and easy to handle. In particular, carbon nanotubes (CNT) are a very intriguing new form of material, whose properties are being studied worldwide providing important results. The photoelectric effects observed on carbon nanotubes indicate the possibility to build photodetectors based on CNTs inducing many people to claim that we are at the beginning of a Post Silicon Era or of the Carbon Era. In this paper, we report on the most important achievements obtained on the application of nanotechnologies to photodetection and medical imaging, as well as to the development of radiation detectors for astro-particle physics experiments.

The study on optically stimulated luminescence dosimeter based on the SrS:Eu, Sm and CaS:Eu, Sm

With the increasing use of nuclear energy, there is a need for a wider range of effcient dosimeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulfides (AES) have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono-, binary and ternary sulfides of alkaline earths (IIa-VIb) have been prepared and their TL properties have been studied with respect to exposure (x-ray) response and fading. In this paper, some results on SrS:Eu, Sm and CaS:Eu, Sm phosphors are presented. A type of novel OSL dosimeter is described. The dosimeter takes advantage of the characteristics of charge trapping materials SrS:Eu, Sm and CaS:Eu, Sm that exhibit optically stimulated luminescence (OSL). The measuring range of the dosimeter is from 0.01 to 1000 Gy. The OSL dosimeters provide capability for remote monitoring radiation locations which are difficult to access and hazardous. This equipment is relatively simple, small in size and has low power consumption. The device is suitable for space radiation dose exploration. In addition, it also can be used in IC and other radiation occasions and has good prospects.

First Observation of Signals Due to KAERI's 10 MeV Electron Beam by Using GEM Detectors

Department of Physics, University of Texas, Arlington, TX 76019, U.S.A.(Received 12 September 2006)Performance tests of a single channel double Gas Electron multiplier (GEM) detector constructedby the Radiation Detector Development Group of Changwon National University (CNU) and amulti-channel double GEM chamber constructed by the High Energy Physics Group of the Univer-sity of Texas at Arlington was carried out at the Korea Atomic Energy Research Institute (KAERI’s)RF accelerator by using 10-MeV electron beams during May 20 - 26, 2006. In this experiment, weobserved signals by both 10-MeV beam electrons and X-ray photons in the CNU single-channeldouble GEM chamber and in the UTA chamber by using an oscilloscope and photographed wave-forms. By analyzing the chamber output signals on the oscilloscope, computing the number ofX-rays photons produced by bremsstrahlung of the beam electrons in a 2-mm lead plate, calculat-ing the angular distribution of beam electrons caused by multiple scatterings in the lead plate, andestimating the interaction probabilities of X-ray photons in the lead plate, the Ar/CO

Systematic study of pre-irradiation effects in high efficiency CVD diamond nuclear particle detectors

Many outstanding properties of diamond can, in principle, lead to the development of radiation detectors with interesting capabilities. In particular, diamond-based nuclear particle detectors are good candidates to replace silicon-based detectors in several fields, e.g. in high-flux applications such as next generation particle-accelerator experiments or beam monitoring. However, the high concentration of defects (grain boundaries, impurities) in synthetic diamond films can strongly limit the detector's performance. A significant increase in the efficiency of CVD diamond detectors is achieved by means of pre-irradiation (pumping) with β particles. We report here on a systematic study of the effects of pumping in high-quality microwave CVD diamond films. The efficiency ( η) and charge collection distance (CCD) of nuclear particle detectors based on these films depend on the methane content in the growth gas mixture and on the film thickness. Both efficiency and CCD behave in a markedly different way in the as-grown and pumped states. Experimental data are found to agree with a recently proposed model (Appl. Phys. Lett. 75 (1999) 3216) discussing how in-grain defects and grain boundaries affect the charge collection spectra of CVD diamond detectors, before and after pumping. The dependence of pumping effects at different operating temperatures of the detector is also reported.

Plasma sprayed alumina coatings for radiation detector development

Conventional design of radiation detectors uses sintered ceramic insulating modules. The major drawback of these ceramic components is their inherent brittleness. Ion chambers, in which these ceramic spacers are replaced by metallic components with plasma spray coated alumina, have been developed in our Research Centre. These components act as thin spacers that have good mechanical strength as well as high electrical insulation and replace alumina insulators with the same dimensions. As a result, the design of the beam loss monitor ion chamber for CAT could be simplified by coating the outer surface of the HT electrode with alumina. One of the chambers developed for isotope calibrator for brachytherapy gamma sources has its outer aluminium electrode (60 mm dia × 220 mm long) coated with 250 µ thick alumina (97%) + titania (3%). In view of potential applications in neutron-sensitive ion chambers used in reactor control instrumentation, studies were carried out on alumina 100 µ to 500 µ thick coatings on copper, aluminium and SS components. The electrical insulation varied from 108 ohms to 1012 ohms for coating thicknesses above 200 µ. The porosity in the coating resulted in some fall in electrical insulation due to moisture absorption. An improvement could be achieved by providing the ceramic surface with moisture-repellent silicone oil coating. Irradiation at Apsara reactor core location showed that the coating on aluminium was found to be unaffected after exposure to 1017 nvt fluence.

Detection of charged particles in amorphous silicon layers

The succesful development of radiation detectors made from amorphous silicon coul offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particle. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics.

Geology and Radwaste

"Geology and Radwaste." Nuclear Technology, 75(2), p. 233 Additional informationNotes on contributorsGeoffrey G. EichholzGeoffrey G. Eichholz is Regents’ Professor of Nuclear Engineering at the Georgia Institute of Technology, which he joined in 1963. He obtained his PhD in physics at the University of Leeds, England, and was awarded the DSc degree in 1979. He edited the book Radioisotopes Engineering and is the author of Environmental Aspects of Nuclear Power and Principles of Nuclear Radiation Detection, both published by Ann Arbor Science Publishers. His research interests include the migration of radioactive wastes, environmental surveillance problems, radiation detector development, industrial radiation applications, nuclear materials technology, and the health physics of nonionizing radiations.

Detection of Charged Particles in Amorphous Silicon Layers

The successful development of radiation detectors made from amorphous silicon could offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particles. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics.

Iodine-129: Evaluation of Releases from Nuclear Power Generation

"Iodine-129: Evaluation of Releases from Nuclear Power Generation." Nuclear Technology, 69(1), p. 120 Additional informationNotes on contributorsGeoffrey G. EichholzGeoffrey G. Eichholz is Regents’ Professor of Nuclear Engineering at the Georgia Institute of Technology, which he joined in 1963. He obtained his PhD in physics at the University of Leeds, England, and was awarded the DSc degree in 1979. He has edited the book Radioisotopes Engineering and is the author of Environmental Aspects of Nuclear Power and Principles of Nuclear Radiation Detection, both published by Ann Arbor Science Publishers. His research interests include the migration of radioactive wastes, environmental surveillance problems, radiation detector development, industrial radiation applications, nuclear materials technology, and the health physics of nonionizing radiations.