The Yakutsk Extensive Air Shower Array has been continuously operating for more than 50 years (since 1970) and up until recently it has been one of world’s largest ground-based instruments aimed at ...studying the properties of cosmic rays in the ultra-high energy domain. In this report we discuss results recently obtained at the array—on cosmic rays’ energy spectrum, mass composition and directional anisotropy—and how they fit into the world data. Special attention is paid to the measurements of muonic component of extensive air showers. Theoretical results of particle acceleration at shocks are also briefly reviewed. Future scientific and engineering plans on the array modernization are discussed.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•CdZnTe large-volume radiation detector.•Crystalline defects in generated during and after growth process.•Characterization of the different crystalline defects.•Nature, size and concentration of the ...secondary phase defects.•Effect of various defects on the performance of the radiation detectors.
Commercial detector-grade cadmium zinc telluride (CZT) crystals still suffer from various types of extended defects, e.g., dislocations, micro-grains, grain boundaries, and Te-rich secondary phases. Most of these defects cannot readily be identified and characterized using conventional techniques, though they are believed to be the dominant factor causing non-uniformity in the detector response. In this work, we revealed and characterized these secondary-phase defects in CZT crystals by employing multiple advanced techniques, e.g. X-ray diffraction topography, micro-scale X-ray response mapping, chemical etching and infrared microscopy. We then evaluate the detector performance of the crystals by recording high spatial-resolution raster scans of the charge collection and spectral response. We directly correlated the influence of the secondary-phase defects on the performance of the detector responses. The experimental results exhibit clear evidence of the undesirable effects of extended defects on the performance of commercial CZT radiation detectors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We grew CdTexSe1−x (CTS) crystals from a Te-rich solution by using the traveling heater method (THM). The average size distribution and concentration of Te inclusions/precipitates in these as-grown ...samples were measured to be ~7×104cm−3, which is much lower than values typical for the present state-of-the-art commercial CdZnTe (CZT) material. Their low-temperature photoluminescence measurement indicates high quality of the material; however the resistivity obtained via I–V curve measurements was ~5×108Ω-cm, which is low in comparison to that required for gamma detectors. A well-resolved alpha response peak can be detected for both planar- and hemispherical detector geometry. The (μτ)e value for our as-grown sample at room temperature was found to be ~4×10−3cm2/V.
•CdTeSe grown by the traveling heater method.•Concentrations of the secondary phase found to be ~7×104cm−3, which is 5–8 times lower than standard commercial CZT.•The (μτ)e value for our as-grown sample at room temperature was found to be ~4×10−3cm2/V.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We characterized the structural quality of CdTexSe1−x crystals grown by the Traveling Heater Method (THM) from a Te-rich solution using Synchrotron White Beam X-ray Diffraction Topography in the ...reflection mode. Structural defects were also studied by chemical etching of the crystal surfaces. The crystals were found to be fairly free from strains, and they had very few sub-grain boundaries and dislocation/sub-grain boundary networks.
•CdTeSe grown by the Traveling Heater Method.•Low concentration of sub-grain boundaries.•Absence of sub-grain boundary network.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The concentration and size distribution of Te inclusions/precipitates in CZT are key factors in a device's performance. High concentrations can degrade the performance drastically, especially for ...long drift-length devices (more than about 10-mm thick). Here, we extend our previous findings on the concentration and size distribution of Te inclusions/precipitates in CZT wafers grown by the THM technique, by considering the rate of cooling of the ingots. We measured their distribution along the diameter of the wafers in a conventional slow-cooled and a fast-cooled ingot. The overall average concentration of Te inclusions/precipitates for the slow-cooled sample was less than 1×10
5
cm
−3, attesting to their suitability for fabricating thick radiation-detection devices.
► THM growth of CdZnTe and Te inclusion/precipitates mapping was carried out. ► Mapping of Te inclusions/precipitates of as-grown CZT by THM, for the first time. ► The size, distribution, and concentrations were less/comparable to the commercial CZT. ► Effect of the rate of cooling on concentration of Te inclusions/precipitates was studied.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, ...so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beam-line recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices' performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.
Core SiO2 quartz fibers of the Large Hadron Collider (LHC) ATLAS Zero-degree Calorimeter (ZDC) are expected to experience integrated doses of a few giga-Rad (Grad) at their closest position to the ...LHC beam. An array of fibers was irradiated with 200 MeV protons and spallation-generated mixed spectra (primarily fast neutrons) at the Brookhaven National Laboratory (BNL) Linac. Specifically, 1 mm- and 2 mm-diameter quartz (GE 124) rods of 50 mm length were exposed to direct 200 MeV protons leading to peak integrated dose of ~ 28 Grad ( ~ 0.28 GGy). Exposure of 1 mm-diameter SiO2 fibers to a neutron flux was also achieved in the spallation field generated by 128 MeV protons. In the post-irradiation analysis, the quartz fiber transmittance was evaluated as a function of the absorbed dose. Significant degradation of the transmittance and increased radiation damage of the material were observed. Microscopic evaluation of the fibers revealed extensive micro-structural damage and irradiation-induced defects. The measurements revealed that a threshold fluence ( ~ 2.6 1016 p/cm2) or dose of ~ 10 Grad (0.1 GGy) appears to exist beyond which light transmittance drops below 10%. Also observed is that fiber transmittance loss increased drastically with SiO2 fiber diameter (1 mm vs. 2 mm diameter). This is attributed, in part, to the earlier lateral leakage from the 1 mm fiber of knock-on electrons and primary protons implying that more damage-inducing protons travel within the bulk of the 50 mm long 2-mm fibers. While Monte Carlo simulations performed tend to support such assumption, future experiments and sensitivity studies are envisioned to address the fiber diameter influence on degradation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Surface passivation reportedly is an effective technique for controlling surface leakage current and its related electronic noise. Several chemical agents have been effectively used for passivating ...cadmium zinc telluride (CdZnTe or CZT) surfaces; however, the long-term stability and the adverse effect on the metal contacts remain questionable. In this study, we reviewed two popular passivating agents, viz. hydrogen peroxide (H
2
O
2
) and a mixture of ammonium fluoride and hydrogen peroxide (NH
4
F + H
2
O
2
). Our aim was to identify an ideal one that can effectively and permanently lower surface leakage currents without adversely affecting the metal contacts. We characterized their topographic features and their long-term effectiveness in terms of detector performance, and compared the results to understand their nature. We determined which chemical species were formed, and recorded the peaks of elemental Cd and Te via x-ray photoelectron spectroscopy (XPS) and micron-scale spatial resolution x-ray fluorescence (
μ
-XRF). We describe in detail the formation of new chemical species and the material nonuniformity of differently treated surfaces. Their effectiveness was assessed from experimental findings of their electrical properties and the spectral response. Our results imply that both passivating agents lowered the surface leakage current, and improved the detection efficiency of the CZT detectors, but their effectiveness was unstable over time.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
The nEXO neutrinoless double beta (0νββ) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in 136Xe. ...Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of 1028 years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of 1.35 × 1028 yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model.
Cadmium Zinc Telluride (CZT) is among the most promising materials for room-temperature X- and gamma-ray detectors. However, crystal defects such as Te inclusions and subgrain boundaries ...significantly hamper their performances. In this work, we evaluated CZT crystals grown by the modified low-pressure Bridgman technique at the IMEM Institute, Parma. We characterized the crystals by IR microscopy to identify the sizes and concentrations of the Te inclusions, along with high spatial resolution X-ray response mapping to measure the uniformity of their charge-transport properties. In addition, we employed white X-ray beam diffraction topography to analyze their crystalline structure.
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