Nuclear Radiation Detectors Research Articles

Cadmium Magnesium Telluride for Next-Generation X-Ray Free Electron Laser, Synchrotron, and Many Other Applications

We developed a picosecond photodetector based on our Bridgman-grown and specially engineered cadmium magnesium telluride (Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1-x}}$ </tex-math></inline-formula> MgxTe) single crystal that is sensitive to both optical and X-ray pulses for coarse timing in free-electron laser applications. Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1-x}}$ </tex-math></inline-formula> MgxTe is a widebandgap semiconductor with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma-ray radiation, thermal neutrons, and medical imaging. For femtosecond optical and X-ray cross-correlation, the material must have a very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have a very low bulk leakage current, in the 10–90 nA range for voltages to even 1000 V. Hence, the ability to tailor or engineer the material is very crucial. Picosecond response and the crystal growth of this specially engineered Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1-x}}$ </tex-math></inline-formula> MgxTe material are presented. Other characterization and transient measurements are discussed along with room-temperature semiconductor detector performance for other nuclear radiation detection applications.

Design of Experimental Circuit Board of Spectrometer Amplifier in Nuclear Electronics

The signal output by a nuclear radiation detector is small in amplitude and irregular in waveform, which needs to be amplified and shaped to measure accurately. Spectrometer amplifiers assume the role of signal amplification and shaping in nuclear radiation measurement instruments, strictly maintaining useful information from the detector output (such as energy information and time information of the rays) and minimizing their distortion during signal processing. According to the needs of undergraduate experimental teaching and nuclear instrument development and application of nuclear electronics courses in nuclear science and technology, this paper designs a flexibly switchable pole zero phase extinction circuit, linear pulse amplification circuit, integral filter forming circuit, and baseline restoration circuit in the experimental circuit board of spectrometer amplifier. The total magnification is about 0 ~ 2040 times adjustable, and the forming time is 0~20μs adjustable. It has the functions of limiting voltage amplitude and optional input and output polarity, which can be adapted to scintillator detectors, proportional counters, Si-PIN, SDD, HpGe and other semiconductor detectors.

An Economical Modification Method for MIL-101 to Capture Radioiodine Gaseous: Adsorption Properties and Enhancement Mechanism

Radioactive iodine is one of the inevitable by-products of nuclear energy application. However, it is a great threat to public health and the adsorbent needs to be adopted for removing the radioactive iodine. The iodine adsorbent needs to have some advantages, such as simple preparation method, low cost, high absorption capacity, and recyclable utilization. In order to meet the above requirements, the etched material of institute Lavoisier 101 (MIL-101) was prepared to absorb the gaseous iodine. After the MIL-101 is etched, the iodine adsorption performance has been greatly improved. The iodine adsorption experiment of etched MIL-101 with different etching time (1 h, 3 h, 4 h, and 6 h) was completed, the results show that the optimal etching time is 4 hours and the capture capacity of the etched MIL-101 is 371 wt%, which is about 22% higher than that of original MIL-101. The experiment results of XRD, FT-IR, and XPS prove that the components and structure of etched MIL-101 are accordable with those of MIL-101. The surface roughness is introduced in this work. The pore roughness is also an important factor to the adsorption capacity, and the related research also supports this conclusion. Furthermore, after iodine is absorbed, etched MIL-101 can be treated by ethanol for iodine release, and the etched MIL-101 has satisfied recyclability within three cycles. Compared with MIL-101, etched MIL-101 not only had good reversible adsorption of iodine but also can adsorb low-concentration iodine. The etched MIL-101 has a broad application prospect in nuclear emergency response and radiation detection.

Effects of Selenium Doping in Zinc Telluride from First Principles

Point defects and compensation in zinc telluride have been subjects of study for several decades due to the compound’s scientific/technological applications. Despite this, there remains some disagreement in the literature as to the fine details of its defect chemistry. Recently, it has also come under renewed interest due to the emerging Cd(1–x)ZnxTe(1–y)Sey material family, used in nuclear radiation detector applications. In this article, we use state-of-the-art computational tools to re-examine the native defect chemistry of ZnTe and explore how it changes upon addition of selenium using density functional theory with screened hybrid exchange–correlation functionals, thermochemical models of the equilibration environment, and statistical mechanics models of the point defect ensemble.

Electrical Properties of Cadmium Telluride Films and the Al/CdTe Based Schottky Barrier

It is shown that with an increase in the thickness of cadmium telluride films from 0.4 to 1 μm, the resistivity decreases from 8·108 to 8,1·107 Ohm·cm. It is equivalent to an increase in conductivity from 1,25·10-9 to 1,23·10-8 Ohm-1· cm-1. The resistivity and conductivity change only slightly at thicknesses above 1 μm.&#x0D; One broad maximum is observed on the X-ray diffraction pattern at film thicknesses D=0.4 μm. This indicates the imperfection of the crystallites. As the thickness increases to 1 μm, a number of clear reflections with increasing intensity appear on the X-ray diffraction pattern, which is associated with the improvement of the crystal structure of the films.&#x0D; The current-voltage characteristic of the Schottky diode is obtained. It is shown that with an increase in the forward displacement, a significant increase in the forward current is observed, as well as a noticeable increase in the reverse current with a reverse displacement. The initial section of the forward characteristic at voltages up to 10 V is linear, which is inherent in Schottky barriers. However, the characteristic becomes non-linear at high voltages.&#x0D; The nonlinearity of the current-voltage characteristic of the Schottky barrier in a fairly wide range of applied voltage is related to the grain boundary effect in polycrystalline films. Namely, as the applied voltage increases to a certain value, the density of trap states in the region of the crystallite boundary decreases; holes begin to fill, which is usually observed in semiconductors containing conductive particles in a non-conductive matrix. We used this effect when studying the possibility of manufacturing nuclear radiation detectors with a metal — semiconductor — metal structure.

Recent Trends in Elpasolite Single Crystal Scintillators for Radiation Detection

Scintillation detection has attracted great interest in nuclear medicine, nuclear radiation detection, high-energy physics, and non-destructive inspection. The elpasolite crystals with Ce3+ dopants are promising for these endeavors due to their modest light yield and extremely good proportionality when excited by the gamma ray. Moreover, the 6Li and 35Cl isotopes in elpasolite crystals endow them with excellent neutron detection capability. These features allow not only a high energy resolution but also a high detection sensitivity. The elpasolite scintillators also enable the precisely dual detection of gamma/neutron signals through pulse height discrimination (PHD) or pulse shape discrimination (PSD). In this work, we review recent investigations on using the typical elpasolite scintillators, including Ce3+-doped Cs2LiYCl6 (CLYC), Cs2LiLaCl6 (CLLC), and Cs2LiLaBr6 (CLLB), for the monitoring of gamma rays and neutrons. The scintillation properties, detection mechanism, and elpasolite crystal structure are also discussed with the aim of improving high-energy ray detection ability.

Finding Out and Exploration of Two New Equations for Calculating the Dead-time of Neutron Detectors and the Energy of Slow-downed Neutrons

One of the most important issues in nuclear science and technology is neutron detection and optimized usage of neutron detectors. The significance of this issue is to the extent that accurate neutron detection is the most desirable issue in nuclear energy engineering including in the area of nuclear reactors. To better design a neutron detector, many items should be taken into account. One of the items is neutron detector dead-time and its calculation. Nowadays, the dead-time of nuclear radiation detectors is among less-discussed objects and it may usually be neglected. In this research, a new equation for calculating the dead-time of neutron detectors has been found out in a way that applying this equation, the dead-time, which is a very significant issue in radiation detection, is calculated as accurately as possible. In addition, in this paper, the equation associated with the energy of a slow-downed incident neutron is specified. By this equation, the energy of an incident neutron that moves across a path undergoes slowing down and deposits its energy is obtained.

Study on the density of trap states between CdZnTe and passivation layer based on MIS structure

CdZnTe room temperature nuclear radiation detectors are widely used in the fields of homeland security, medical imaging and astrophysics. In the Cd1-xZnxTe radiation detector, the purpose of passivation is to reduce dark current and improve stability. In this study, CdZnTe etched by bromine-methanol (BM) was treated with standard H2O2 and NH4F passivation process. With the help of TEM and EDS measurement results, the thickness of the passivation layer ranges from 126 nm to 183 nm, and X-ray photoelectron spectroscopy (XPS) measurement results show that the TeO2 fraction can be increased on the passivated surface. The dispersion phenomenon on the capacitance-voltage and conductance-voltage curves indicates the existence of carrier trap states in the area near the interface. In order to determine the size of the trap state under this passivation method, an equivalent circuit model was constructed using the calculation method of electrical conductivity. Based on this model, when the voltage increases from 0 V to 1.4 V, the value of the trap state density obtained changes in between 1.07 × 1010 eV−1cm−2 and 5.85 × 1010 eV−1cm−2.

Ultrawide-range radiation detection based on dynamic identification and analysis of the response of a monolithic active pixel sensor.

In this paper, we present an ultrawide-range radiation detection method based on dynamic recognition and analysis of the response signal of a monolithic active pixel sensor (MAPS). Our analysis of the MAPS response mechanism determined that adaptive adjustment of the sensor's integral time is key to quantification of ionizing radiation in an ultrawide range. We also determined that different data processing methods are required for accurate quantification of high and low radiation dose rates. The results of experiments conducted after calibration demonstrate that our technique is capable of radiation detection across five orders of magnitude (ranging from milligrays per hour to hundreds of grays per hour), with errors of less than 5%. Chip-based nuclear radiation detection can be realized using our technique, enabling MAPS to be used as a supplement to traditional detectors in characterization of unknown and complex radiation environments.

Multi-robot collaborative radioactive source search based on particle fusion and adaptive step size

Multi-robot with nuclear radiation detectors plays a key role in nuclear safety and emergency disposal of radioactive contamination. However, the existing multi-robot radioactive source search process requires a large amount of computation, resulting in low search efficiency. This paper proposes a collaborative search method for unknown radioactive source through multi-robot information fusion and free energy strategy with adaptive step size. We use the cognitive difference principle to selectively fuse the measurement information of other robots to obtain a preliminary estimate of the probability distribution of radioactive source. Then, the multiple robots conduct particle fusion according to preset conditions to obtain accurate parameters of the radioactive source. Lastly, all of the robots cooperate to complete the search task of unknown radioactive source step by step through a free energy strategy with adaptive step size. Experimental results show that the search success rate of the proposed algorithm is improved to more than 95% with an efficient search.

Silicon Carbide Neutron Detectors for Harsh Nuclear Environments: A Review of the State of the Art

Silicon carbide (SiC) semiconductor is an ideal material for solid-state nuclear radiation detectors to be used in high-temperature, high-radiation environments. Such harsh environments are typically encountered in nuclear reactor measurement locations as well as high-level radioactive waste and/or “hot” dismantling–decommissioning operations. In the present fleet of commercial nuclear reactors, temperatures in excess of 300 °C are often encountered, and temperatures up to 800 °C are anticipated in advanced reactor designs. The wide bandgap for SiC (3.27 eV) compared to more widely used semiconductors such as silicon (1.12 eV at room temperature) has allowed low-noise measurements to be carried out at temperatures up to 700 °C. The concentration of thermally induced charge carriers in SiC at 700 °C is about four orders of magnitude less than that of silicon at room temperature. Furthermore, SiC radiation detectors have been demonstrated to be much more resistant to the effects of radiation-induced damage than more conventional semiconductors, such as silicon, germanium, or cadmium zinc telluride (CZT), and have been demonstrated to be operational after extremely high gamma-ray, neutron, and charged-particle doses. The purpose of the present review is to provide an updated state of the art for SiC neutron detectors and to explore their applications in harsh high-temperature, high-radiation nuclear reactor applications. Conclusions related to the current state-of-the-art of SiC neutron detectors will be presented, and specific ideal applications will be discussed.

Annealing Effect on a (0001)-Oriented ZnO Single-Crystal Bulk-Acoustic-Wave X-Ray Detector

This work demonstrates a ZnO single-crystal bulk-acoustic-wave (BAW) nuclear radiation detector based on piezoelectricity–photoconductivity interactions, which is suitable for developing a frequency-domain multiplexing system for cosmic X-ray and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\gamma } $ </tex-math></inline-formula> -ray observations. The nuclear radiation-generated photocarriers in ZnO crystals screen the piezoelectric charge and reduce the acoustic velocity, inducing a negative resonant frequency shift for the detector. (0001)-oriented ZnO single crystals are used to fabricate high-quality BAW detectors. Unannealed and annealed crystal detectors are compared, and the annealed detector is found to show a higher signal-to-noise ratio and faster response speed due to a higher quality factor and fewer defects. The annealed ZnO crystal shows a resistivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{11} {\Omega } \cdot $ </tex-math></inline-formula> cm, a high electromechanical coupling factor of 10.4%, and a high quality factor of ~500. The annealed detector also shows a linear X-ray response with a responsivity of 0.89 k/Gy for an X-ray tube voltage of 70 kV, indicating great potential for application of bulk single-crystal-based BAW detectors in the field of nuclear radiation detection.

Research Progress on Postgrowth Annealing of Cd1−xMnxTe Crystals

AbstractCadmium manganese telluride (Cd1−xMnxTe, abbreviated CMT) crystals have high resistivity, wide bandgap and good carrier transport properties, as well as being superior to traditional CdZnTe crystals in some respects. Therefore, CMT crystals are promising materials for room‐temperature nuclear radiation detectors. However, as‐grown CMT crystals usually include many defects dominated by Te inclusions. These defects greatly affect the device performance. In this paper, main defects such as point defects, dislocations, and inclusions in CMT materials are summarized and discussed. Postgrowth annealing is used to reduce and eliminate defects. It is a great method to improve the properties of as‐grown crystals. Annealing process includes annealing method, atmosphere, temperature, and time. The research progress of annealing process on crystal quality, photoelectric properties, and detector performance is reviewed.

Nuclear radiation detection based on the convolutional neural network under public surveillance scenarios

Abstract Nuclear energy is a clean and popular form of energy, but leakage and loss of nuclear material pose a threat to public safety. Radiation detection in public spaces is a key part of nuclear security. Common security cameras equipped with complementary metal oxide semiconductor (CMOS) sensors can help with radiation detection. Previous work with these cameras, however, required slow, complex frame-by-frame processing. Building on the previous work, we propose a nuclear radiation detection method using convolution neural networks (CNNs). This method detects nuclear radiation in changing images with much less computational complexity. Using actual video images captured in the presence of a common Tc-99m radioactive source, we construct training and testing sets. After training the CNN and processing our test set, the experimental results show the high performance and effectiveness of our method.

Deposition of CdZnTe Films with CSS Method on Different Substrates for Nuclear Radiation Detector Applications

CdZnTe (CZT) films were grown by closed space sublimation (CSS) method on (111)-oriented CZT wafers, non-oriented CZT wafers and FTO substrates. The compositional and morphological properties of CZT films on different substrates were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which indicated that CZT films grown on (111)-oriented CZT wafers had low dislocation density and high Zn composition. X-ray diffraction (XRD) measurements confirmed that CZT films grown on (111)-oriented CZT wafers had the best crystal quality. The I-V and DC photoconductivity measurements indicated that CZT films on (111)-oriented CZT wafer had good carrier transport performance. The energy spectra of CZT films grown on (111)-oriented CZT wafer presented that it had a good response to the nuclear radiation under 241Am.

Design and verification of a multi-layer single-sphere neutron spectrometer with water as the moderator

Measuring the neutron energy spectrum is important in nuclear radiation detection and protection. Common neutron spectrometers include the Bonner sphere spectrometer (BSS), time-of-flight neutron spectrometer, and plastic scintillation detector. Among them, the BSS is the most widely used for its wide measurement range and simple operation. A BSS usually occupies a large space because it contains several independent spheres working at the same time, leading to poor consistency. This paper proposes a multi-layer single-sphere spectrometer using water as the moderator. The spectrometer includes a multi-layered sphere that can be filled with water or air and a ^3He proportional counter placed in the center of the sphere. To verify the feasibility of this design, we use Geant4 to calculate the moderating ability of water and the response functions of the multi-layer single-sphere spectrometer. Additionally, several standard neutron energy spectra (from IAEA) are used to test the response characteristics of this spectrometer through simulation. The simulation results prove the feasibility of the design. This research provides a theoretical basis for a multi-layer single-sphere neutron spectrometer with water as the moderator.

Effect of deep level defects on CdZnTe detector internal electric field and device performance

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility (μe), electron transport time (TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

Lithium indium diselenide — An advanced material for neutron detection

This paper describes the synthesis, crystal growth, detector fabrication, radiation hardening studies, MCNP modeling, and characterization of lithium indium diselenide or LiInSe2. This newly-developed room-temperature thermal neutron detector has semiconducting and scintillating properties and it is suitable for neutron detection application. LiInSe2 was synthesized starting from elemental Li, In, Se in two steps due to high reactivity of Li. A single crystal of LiInSe2 was grown using the Vertical Bridgman method. The room temperature band gap was found to be 2.8eV using optical absorption measurements. Bulk resistivity was measured at ∼5 × 1011 Ωcm. Photoconductivity measurements of LiInSe 2 wafers identified a peak in the photocurrent around 445 nm. Nuclear radiation detectors were fabricated from single crystal wafer and the responses to alpha particles at various biases were measured. The mobility-lifetime product was estimated. Gamma irradiation studies were performed with calculated absorbed doses ranging from 0.2126 to 21,262 Gy. The characterization of the two wafers for their scintillator performance was conducted after each irradiation. The gamma irradiation produced a reduction of the light yield that translated to a lower channel number for the centroid of alpha detection spectra. It also showed a considerable reduction of the decay time after the first irradiation. These are the first studies on gamma radiation hardening with this material.

Considerations for Training an Artificial Neural Network for Particle Type Identification

In the nuclear sciences and radiation detection fields, the differentiation between gamma-ray and neutron interactions inside a detector volume continues to be an area of active research. Historically, the primary mechanism for conducting particle identification has been pulse shape discrimination (PSD). However, almost all variations of this technique rely on only two factors: the area of the tail and the total area of the pulse. In the last decade, the emergence of advanced machine learning techniques, most specifically artificial neural networks (ANNs), offers a unique opportunity to capitalize on the entirety of the waveform. But such techniques appear highly reliant on the quality of datasets used for training. Our research addresses this challenge to quantify the relative performances of networks trained on a variety of datasets and subjected to the same test. Furthermore, we offer an analysis of the portability of a network trained on one detector to a similar detector.

Recent Advances, Challenges, and Perspectives of Perovskite -Based Scintillators

Scintillators are currently widely used in high energy physics, nuclear physics, nuclear medical imaging, industrial exploration, security inspection and so on. The development of new applications puts forward the new requirements for scintillators, and it is becoming extremely urgent to discover the new scintillators. In recent years, perovskite materials present their advantages in the field of solar cell, light-emitting diode, laser, photodetector, memory and so on, owing to their high carrier mobility, long diffusion distance and continuously adjustable emission wavelength. Therefore, the perovskite-based scintillators have attracted great attention and interest due to their low detection threshold, high light yield, fast attenuation, and tunable emission wavelength. This review article summarizes the crystal structure and luminescence properties of organic-inorganic hybrid perovskite and inorganic perovskite scintillators. In addition, the fundamental application of perovskite scintillators for radiation detection has been discussed. The goal of this review article is to introduce the recent advances and development in perovskite scintillators, and a particular focus is given on the challenges and perspectives for their enormous potential application in nuclear medical imaging and radiation detection.