High Energy Radiation Detection Research Articles

Analysis of the spectrum of electromagnetic radiation generated by electrical discharges

The stidy presents research results considering measurement and detection of electromagnetic radiation (EMR) generated by partial discharges (PDs) in the air and during breakdown. The key objective of the works was to develop a methodology of detection of ionising radiation generated by electrical discharges. This includes design of experimental setup for simulation of discharges under laboratory conditions and selection of appropriate measuring devices. For measurements of visible light and UV radiation, a HR-4000 spectrophotometer was chosen. The high energy ionising radiation was detected by means of a scintillation counter by own production. The experimental studies involved registration of EMR emitted by both PD and electrical breakdowns of the measuring system for various point-point electrodes arrangements. Then, characteristic spectra were defined in bands from visible light, through UV to the X-ray radiation frequencies. The use of high-energy radiation detection for determining basic forms of discharges and the potential possibility of the detailed specification of their power balance are curtail achievements of the presented article. The other contributions lie in the simultaneously application of two independent discharge detection methods.

Data-enabled structure–property mappings for lanthanide-activated inorganic scintillators

The use of machine learning (ML) models toward development of validated structure–property relationships for two fundamental properties of activated inorganic scintillators for high energy radiation detection, namely the light yield (LY) and the decay time constant, is explored. The ML models are built on easily accessible proxies of materials—interchangeably referred to as features, descriptors or fingerprints—that are carefully selected on the basis of a physical understanding of the scintillation mechanism. Our study indicates that the developed physics-based ML models employing kernel ridge regression (KRR) and AdaBoost algorithm applied on top of a decision tree-based regression are able to “learn” the underlying design rules in a multi-dimensional feature space and thereby enable reasonably accurate predictions of the two target properties on unseen compounds (i.e., on a held-out test set). For instance, within a set of twenty-five cerium- or europium-doped scintillator materials, our analysis reveals a strong correlation between the average ionic part of the dielectric constant and the LY, irrespective of the specific chemistry of the compounds, indicating that the average ionic part of the dielectric constant is a particularly relevant descriptor toward prediction of the LY. Our results also demonstrate that, despite the use of small training datasets, the developed models are able to quickly distinguish high performing chemistries from those with relatively poor performance and therefore can play a crucial role in screening of new compounds with an attractive combination of targeted properties. The present study provides necessary motivation for future efforts involving ML models with relatively large training datasets, vast feature space explorations, and experimental design in search of promising novel scintillator chemistries.

Coherent spin dynamics of electrons and holes in CsPbBr3 perovskite crystals

The lead halide perovskites demonstrate huge potential for optoelectronic applications, high energy radiation detectors, light emitting devices and solar energy harvesting. Those materials exhibit strong spin-orbit coupling enabling efficient optical orientation of carrier spins in perovskite-based devices with performance controlled by a magnetic field. Here we show that elaborated time-resolved spectroscopy involving strong magnetic fields can be successfully used for perovskites. We perform a comprehensive study of high-quality lead halide perovskite CsPbBr3 crystals by measuring the exciton and charge carrier g-factors, spin relaxation times and hyperfine interaction of carrier and nuclear spins by means of coherent spin dynamics. Owing to their ‘inverted’ band structure, perovskites represent appealing model systems for semiconductor spintronics exploiting the valence band hole spins, while in conventional semiconductors the conduction band electrons are considered for spin functionality.

Sm3+ and Gd3+ Co-doped lead phosphate glasses for γ-rays shielding and sensing

Six samples of rare earth (Sm3+ and Gd3+) co-doped lead alumino phosphate glasses of composition (58.2–2 x)PbO-40P2O5 − 1.8Al2O3-xSm2O3-xGd2O3 (where x = 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4 mol%) were synthesized and explored for its scintillation properties. Prepared samples are found to have high density and better radiation shielding properties than halide scintillator and some conventional concretes and alloys. Optical characterization of samples confirms strong sensitivity for absorbing UV–visible radiation and enhanced luminescent properties due to energy transfer/energy down conversion process from Pb2+ to Gd3+ and then to Sm3+. Prepared samples when stimulated with high energy radiations under proper design suggest their possible use as high energy radiation detection and phosphors in scintillation counters for gamma-rays and X-rays detection. The synthesized glass systems are promising materials for developing optoelectronic devices like lasers and optical amplifiers, and gamma rays shielding material for radioactive waste encapsulation and detection of radiations.

Optical characteristics of single crystal Gd3Al2Ga3O12 : Ce

New emerging high-energy radiation detection techniques are based on the use of rare-earth ion doped materials. There is a great demand for new inorganic scintillators for medical applications, including X-ray and g radiation detection. In these applications, the new scintillating materials must comply with the main requirements such as high optical quality, high light yield, short response time etc. Materials satisfying these requirements include Gd3Al2Ga3O12: Ce (GAGG : Ce) scintillating single crystals. By now the optical characteristics of GAGG : Ce have been studied insufficiently. We have therefore measured the spectral reflectance and transmittance characteristics of these crystals using optical spectroscopy in the 200–750 nm range. We have also measured the absorbance and refractive indices and the extinction coefficients, and assessed the optical band gap for GAGG : Ce crystals. For measuring the refractive indices, we have used two spectrophotometric methods, i.e. by the measured Brewster angle and by the reflectance for low incidence angles, i.e., close to the normal. Based on the results we have drawn up the dispersion functions of the refractive indices.

Studies on Cr electrode of CdZnTe detector for high energy radiation detection

Electrode with proper contact properties is of vital importance to CdZnTe detector for high energy radiation detection. In this work, Au and Cr electrodes are prepared on CdZnTe surface using magnetron sputtering method. The surface morphology and the interface structure are analyzed using atomic force microscopy and X-ray photoelectron spectroscopy (XPS). No reaction is found at Au/CZT interface. But for Cr/CdZnTe, interface layers of CrO and Te were found, which forms a structure of Cr/Cr–O/Te/CdZnTe with a metal-insulator-metal tunnel junction. Due to this interface structure, Schottky Barrier height was tuned, which enhanced the collection efficiency and energy resolution for high energy irradiation. The energy resolution of CdZnTe detector with Cr electrode for 137Cs isotope with the energy of 662 keV reaches about 1.3%. The adhesive force of Cr is also enhanced because of the interface reaction. The results prove Cr to be a proper electrode material for CdZnTe detectors.

Luminescence characteristics of rare-earth-doped barium hexafluorogermanate BaGeF6 nanowires: fast subnanosecond decay time and high sensitivity in H2O2 detection.

Fluorides are promising host materials for optical applications. This paper reports the photoluminescent (PL) and cathodoluminescent (CL) characteristics of barium hexafluorogermanate BaGeF6 nanowires codoped with Ce3+, Tb3+ and Sm3+ rare earth ions, produced by a solvothermal route. The synthesized BaGeF6 nanowires exhibit uniform morphology and size distribution. X-ray diffraction divulges the one-dimensional growth of crystalline BaGeF6 structure, with the absence of any impurity phases. Visible luminescence is recorded from the nanowires in green and red regions, when the nanowires are codoped with Ce3+/Tb3+, and Ce3+/Tb3+/Sm3+, respectively, under a UV excitation source. The PL emission from the codoped BaGeF6 nanowires, when excited by a 254 nm source, originates from the efficient energy transfer bridges between Ce3+, Tb3+ and Sm3+ ions. The decay time of the visible luminescent emission from the nanowires is in the order of subnanoseconds, being one of the shortest decay time records from inorganic scintillators. The CL emission from the BaGeF6 nanowires in the tunable visible range reveals their potential use for the detection of high-energy radiation. The PL emissions are sensitive to H2O2 at low concentrations, enabling their high-sensitivity detection of H2O2 using BaGeF6 nanowires. A comparison with BaSiF6 nanowires is made in terms of decay time and its sensitivity towards H2O2.

Sintering of GGAG:Ce3+, xY3+ transparent ceramics in oxygen atmosphere

Abstract Cerium doped gadolinium gallium aluminum garnet ceramics (GGAG:Ce) have promising applications such as medical imaging, high power WLEDs and other high energy radiation detection due to their excellent and unique combination of chemical and physical properties. Partial substitution of gadolinium with yttrium can improve some of the optical and scintillation properties even further. The goal of this work is to research the effect of Y 3+ to the sintering of GGAG ceramics. The optical transmittance, micro-structure and grain growth kinetics have been investigated. This research indicates that the doping of Y 3+ ion would transfer the main sintering mechanism for grain growth from solid state mass transport to liquid phase mass transport, thereby reducing the activation energy of the sample.

CdTe Timepix detectors for single-photon spectroscopy and linear polarimetry of high-flux hard x-ray radiation.

Single-photon spectroscopy of pulsed, high-intensity sources of hard X-rays - such as laser-generated plasmas - is often hampered by the pileup of several photons absorbed by the unsegmented, large-volume sensors routinely used for the detection of high-energy radiation. Detectors based on the Timepix chip, with a segmentation pitch of 55 μm and the possibility to be equipped with high-Z sensor chips, constitute an attractive alternative to commonly used passive solutions such as image plates. In this report, we present energy calibration and characterization measurements of such devices. The achievable energy resolution is comparable to that of scintillators for γ spectroscopy. Moreover, we also introduce a simple two-detector Compton polarimeter setup with a polarimeter quality of (98 ± 1)%. Finally, a proof-of-principle polarimetry experiment is discussed, where we studied the linear polarization of bremsstrahlung emitted by a laser-driven plasma and found an indication of the X-ray polarization direction depending on the polarization state of the incident laser pulse.

Luminescent Properties of Polycrystalline Cerium-Doped Lutetium Pyrosilicate Powders

Single phase LPS powders with nanosize particles were synthesized by a sol-gel process. Temperature and calcination temperature dependence of luminescence of the synthetic LPS:Ce powders were investigated under vacuum ultraviolet (VUV)-UV excitation. Luminescence intensity of LPS:Ce powders increase with calcination temperature, but it reaches the maximum at 1250 °C. Decay time of the LPS:Ce powders also slightly increasing from 27.1 to 30.5 ns as calcining temperature elevating. Both of them attribute to improved crystallization of LPS:Ce powders. Total luminescence intensity of LPS:Ce powder calcined at 1350 °C for 2 h has no noteworthy variation as the temperature rising in temperature 30-260 K range, this luminescence stability suggests that LPS:Ce would also be a good scintillator for high energy radiation detection in low temperature condition with temperature variation.

Synthesis and thermoluminescence properties of SrAl 2 O 4 (EU) phosphor irradiated with cobalt-60, 6 MV and 16 MV photon beams

Abstract Powder samples of SrAl 2 O 4 (Eu) were synthesized by the combustion method using urea as a fuel. The combustion products were calcined at 700 °C for 1 h. X-ray diffraction (XRD) patterns of the prepared sample exhibit sharp diffraction peaks and absence of any amorphous phase. The average crystalline size was found to be ~33.04 nm, calculated by using Debye Scherer's formula. The scanning electron microscope (SEM) images reveal that the crystallites have no uniform shape and the presence of several micro- and nano-particles within the grain. This may be due to the non-uniform distribution of temperature and mass flow in the combustion flame which results in the non-uniform shape of crystallites. The thermogravimetric analysis (TGA) indicates that the prepared sample is thermally stable up to 900 °C. Thermoluminescence (TL) behavior of prepared samples was studied after irradiation with Co-60gamma rays, 6 mega voltage (MV) and 16 MV photon beams at various doses. Glow curve of the prepared SrAl 2 O 4 (Eu:1%) sample was similar in shape irrespective of incident energy and radiation type. The dominant peak in each glow curve appeared around at 312 °C. No shifts in peak positions have been observed. All the glow curves of sample doped with Eu(3%) have relatively higher intensity as compared to the sample doped with Eu(1%). Energy dependence has been observed in the present phosphor. This could be because of increase in the probability of Compton's interaction at this energy range due to transmission of primary as well as scattered radiation and decrease in mass attenuation coefficient with the increase in energy. The trapping parameters namely activation energy ( E ), order of kinetics ( b ) and frequency factor ( s ) have been determined using the glow curve shape (Chen's) method. These phosphors could be utilized for display applications, dating, temperature sensor, low as well as high energy radiation detection and dosimetry especially where tissue equivalency is not much desirable like gamma irradiator, environmental and retrospective dose assessment.

Waveguide inscription in Bismuth Germanate crystals using high repetition rate femtosecond lasers pulses

We report on the inscription of optical waveguides into crystalline bismuth germanate (Bi4Ge3O12, BGO) via the femtosecond laser direct-write (FLDW) technique. We found that by utilizing femtosecond laser pulses at Megahertz (MHz) repetition rates, a uniquely different fabrication regime can be exploited. In this paper, we show that cumulative heating effects can initiate a local transformation of the crystalline structure into an amorphous (glass-like) state that is characterized by an increased refractive index. We compare and contrast this novel, type-I modification based waveguide inscription regime with the previously reported fabrication of type-II damage/stress field structures in BGO and present measurements that indicate that the femtosecond laser writing process unavoidably causes a reduction in the electro-optic coefficient in the waveguides as compared to the bulk material. We discuss the potential of this technique for the fabrication of advanced sensor arrays for high-energy radiation detection and voltage sensing applications.

Ionic conduction in TlBr — Impact of Te acceptor dopant exsolution

Thallium bromide (TlBr) is an attractive material for high-energy radiation detection applications due to its high molecular weight and relatively large band gap. Previous studies on acceptor doping with Se and S revealed limited solubility of the acceptor dopant in the TlBr crystal, leading to long term changes in dark ionic conductivity, and, presumably, detector sensitivity and performance. Here, the ionic conductivity of TlBr acceptor doped with the larger ionic radius Te2 − (2.21 Å versus 1.98 Å for Se2 −) is studied using impedance spectroscopy. Due to the low concentration of Te, in contrast to Se or S doping, acceptor dopant–defect association was not observed. Acceptor exsolution was confirmed at temperatures below 100 °C by following changes in ionic conductivity with time. The time constant and activation energy (0.27 ± 0.14 eV) for exsolution of Te are considerably lower than that of Se, with the mechanistic origin of the activation energy related to Br migration, in marked contrast to that of Se exsolution, which is controlled instead by Tl migration, as discussed here. This long term, time-dependent change in dark resistance could negatively impact radiation detector sensitivity and therefore acceptor doping should be avoided.

Point defects in Cd(Zn)Te and TlBr: Theory

The effects of various crystal defects on the performances of CdTe, Cd1−xZnxTe (CZT), and TlBr for room-temperature high-energy radiation detection are examined using first-principles theoretical methods. The predictive, parameter-free, atomistic approaches used provide fundamental understanding of defect properties that are difficult to measure and also allow rapid screening of possibilities for material engineering, such as optimal doping and annealing conditions. Several recent examples from the author's work are reviewed, including: (i) accurate calculations of the thermodynamic and electronic properties of native point defects and point defect complexes in CdTe and CZT; (ii) the effects of Zn alloying on the native point defect properties in CZT; (iii) point defect diffusion and binding leading to Te clustering in Cd(Zn)Te; (iv) the profound effect of native point defects—principally vacancies—on the intrinsic material properties of TlBr, particularly its electronic and ionic conductivity; and (v) a study on doping TlBr to independently control the electronic and ionic conductivity.

Transient photocurrent measurements in alkali chalcogenide ternary compound semiconductors

The charge transport properties of two alkali metal chalcogenide, semiconductor ternary compounds Cs2Cd3Te4 and Cs2Hg6S7, having potential as efficient high-energy radiation detectors, were investigated. A key property that determines the detector performance is the minority carrier lifetime, which was determined by measurement of photocurrent transients using pulsed laser excitation. The alkali metal chalcogenide semiconductor crystals were grown by a modified Bridgman method. The Cs2Cd3Te4 compound has a minority lifetime of 2.45 µs at 295 K, which is comparable to that of cadmium zinc telluride (CZT). The Cs2Hg6S7 showed charge trapping with decay times of 120 µs. The excellent charge transport properties of Cs2Cd3Te4 indicate that this ternary compound semiconductor should be well suited for gamma radiation detector devices that operate at room temperature.

Ionic Conductivity of TlBr$_{1 - {\rm x}}$I$_{\rm x}$$({\rm x} = 0, 0.2, 1)$: Candidate Gamma Ray Detector

The ionic conductivity of TlBr, TlI and their solid solutions, candidates for high energy radiation detection, was examined using impedance spectroscopy. The orthorhombic to cubic phase change in TlI was observed via a steep change in conductivity with increasing temperature, whereas the TlBr-TlI solid solution was cubic throughout the measured temperature range, in agreement with the literature. The intrinsic conductivity of the cubic phase of each material showed nearly identical behavior, indicating that I substitution for Br has little to no effect on the combined defect formation and transport parameters in the studied range. Additionally, optical transmission was correlated with I concentration.

Ultrahigh gain AlGaN/GaN high energy radiation detectors

AbstractDue to its remarkable tolerance to high energy ionizing radiation, GaN has recently attracted attention as a promising material for dosimetry applications. However, materials issues that lead to persistent photoconductivity, poor sensitivity, and requirements for large operational voltages have been hurdles to realization of the full potential of this material. Here we demonstrate that the introduction of a two‐dimensional electron gas channel, through the addition of AlGaN/GaN heterointerfaces, can be used to create intrinsic amplification of the number of electrons that can be collected from single ionization events, yielding exceptionally large sensitivities in ultralow dose rate regimes. Furthermore, anomalous photo‐responses, which severely limit response times of GaN‐based devices, can be eliminated using these heterostructures. Measurements using focused monochromatic synchrotron radiation at 1–20 keV, as well as focused 20 MeV protons, reveal that these devices provide the capability for high sensitivity and resolution real time monitoring, which is competitive with and complementary to state‐of‐the‐art detectors. Therefore, AlGaN/GaN heterostructure devices are extremely promising for future applications in fields ranging from high energy physics to medical imaging.

Thallium Bromide Deposited Using Spray Coating

Spray coating was used to produce thallium bromide samples on glass substrates. The influence of several fabrication parameters on the final structural properties of the samples was investigated. Substrate position, substrate temperature, solution concentration, carrying gas, and solution flow were varied systematically, the physical deposition mechanism involved in each case being discussed. Total deposition time of about 3.5 h can lead to 62-μm-thick films, comprising completely packed micrometer-sized crystalline grains. X-ray diffraction and scanning electron microscopy were used to characterize the samples. On the basis of the experimental data, the optimum fabrication conditions were identified. The technique offers an alternative method for fast, cheap fabrication of large-area devices for the detection of high-energy radiation, i.e., X-rays and γ-rays, in medical imaging.

The Defect and Transport Properties of Donor Doped Single Crystal TlBr

Thallium bromide (TlBr) is attractive for high energy radiation detection, given its large molecular weight and wide energy bandgap. However, TlBr exhibits levels of ionic conductivity that can lead to an undesirable leakage, or dark current, thereby reducing sensor performance. To investigate the role of dopants in controlling the ionic conductivity, single crystals of TlBr were grown using zone refining and/or vertical Bridgman methods with controlled levels of donor (Pb) dopants. Their electrical properties were examined as a function of temperature with frequency dependent impedance spectroscopy. A Schottky-based defect equilibria model was fitted to the resulting conductivity data, and enthalpies of Schottky defect formation , cation migration , and anion migration were extracted. Br vacancies were found to posses about 5 orders of magnitude higher mobility than that of Tl vacancies at .

Characterization of Conductivity in Single Crystal TlBr

TlBr is an ionic material with good potential for use in high energy radiation detectors because of its relatively large band gap and heavy elements. In these sensors, incident radiation excites electron hole pairs that are collected as the response, and the mobility-lifetime product for electrons and holes, as well as low dark current are common figures of merit. TlBr reportedly displays ionic conductivity that leads to undesirable leakage, or dark current thereby reducing sensor response. This work focuses on the development of a defect and transport model appropriate to TlBr. The derived enthalpies of migration and Schottky defect formation are compared with literature values.