Search for: All records

Active learning engages students in activities that could enhance their ability to analyze, synthesize, and evaluate the material being learned. Evidence-based studies have shown that active learning increases student performance in Science, Technology, Engineering, and Mathematics (STEM) courses. This paper presents the design of active learning units in nuclear engineering. The goal is to enhance students learning and technical skills, thereby improving their preparation for success in pursuing STEM graduate programs and careers in nuclear engineering. Three modes of active learning that are of interest are problem-solving, lab-based hands-on activities, and simulation. The active learning units are aimed at using interactive mode to provide students with the mastering of fundamental principles and concepts, and better understanding of how equations translate and apply to real-life engineering situations. The introductory nuclear engineering topics to be covered include radioactivity and half-life, binding energy, atom density, radiation interactions, radiation dose, radiation shielding, stopping power, and fission. An assessment plan for the effectiveness of the active-learnings units is also presented. 

Cadmium zinc telluride selenide (CdZnTeSe) has shown great promise in reducing the cost of semiconductor nuclear detectors that can operate at room temperature without cryogenic cooling. This is due to the high yield of detector-grade materials in the CdZnTeSe crystal growth process, which can be attributed to the much smaller numbers of Te inclusions and grain boundary network in CdZnTeSe compared to other CdTe-based semiconductors such as CdZnTe. In the present work, we study the effects of surface passivation on CdZnTe detectors using a mixture of ammonium fluoride and hydrogen peroxide solution (NH4F + H2O2 + H2O). Detectors fabricated from CdZnTeSe crystals showed very good energy resolutions: 1.1% for the 662-keV gamma peak of Cs-137 by Frisch-grid detectors, and 5.9% for the 59.6-keV gamma peak of Am-241 by planar detectors. Experimental results show that the leakage current is increased immediately after passivation and then decreases as the surfaces stabilizes. The resistivity of the CdZnTeSe is of the order of 10**10 Ω-cm. The surface passivation improved the energy resolution of planar detector by 18% for the 59.6-keV gamma peak of Am-241. 

Multilayered thermoelectric Sn/Sn+SnO2 thin films were prepared using KJL DC/RF magnetron sputtering system under Ar gas plasma on the SiO2 substrates. The thicknesses of the fabricated thin films were found using Filmetrics UV thickness measurement system. The fabricated thin films were annealed at different temperatures for one hour to tailor the thermoelectric properties. In this study, unannealed, annealed at 150 and 300 °C samples were characterized using Thermo Fisher XPS system brought to the Alabama A&M University by the NSF-MRI support. X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA) is a type of analysis used for characterization of various surface materials. XPS is mostly known for the characterization of thin films - which are coatings that have been deposited onto a substrate and may be comprised of many different materials to alter or enhance the substrate’s performance. XPS analysis provides information for composition, chemical states, depth profile, imaging and thickness of thin film. This paper focuses on the application of XPS techniques in thin film research for Sn/Sn+SnO2 multilayered thermoelectric system and SiO2 substrates annealed at different temperatures. Since SiO2 substrates were used during the deposition of the multilayer thin films, we would like to perform detailed XPS studies on the SiO2 substrates. SiO2 substrates is being used with many researchers, this manuscript will be good reference for the researchers using SiO2 substrates. Thermal treatment of the substrates and the multilayered thin films has caused some changes of the XPS characterization including binding energy, depth profile, peak value and FWHM. The treatment effects were discussed and compared to each other. 

Cadmium telluride (CdTe) and its ternary and quaternary compounds have found applications in the development of X-ray and gamma-ray detectors used in nuclear detection and medical imaging applications. Example of these detectors include CdZnTe (CZT), CdMnTe (CMT), and CdZnTeSe (CZTS). These nuclear detectors can operate at room temperature without cryogenic cooling. This paper presents comparative studies of these semiconductor material. The properties studied include detector resistivity, Te inclusions, grain boundary networks, mobility/lifetime of the charge carriers, and energy resolution. The effects of passivation with chemicals such as KOH and NH4F, are also presented. X-ray photoelectron spectroscopy (XPS) studies showed increase in the quantity of TeO2 on surfaces of these materials after passivation in KOH and NH4F. While CZT detector has wide commercial availability, it has more Te inclusions and grain boundary network compared to CZTS. CMT and CZTS have better crystal uniformity than CZT. The comparatively low presence of Te inclusions and grain boundary network in CZTS gives it a higher crystal growth yield for detector-grade material. 

High-resistivity zinc cadmium telluride (CdZnTe) semiconductor is a very popular material for room-temperature nuclear detection applications. It is used for the detection of X-rays and gamma rays in many areas: nuclear and radiological threat detection, medical imaging, gamma spectroscopy, and astrophysics. Mechanical stability at the interface of electrical contacts and the detector material is an important factor in terms of durability and shelf life of detector devices. Other engineering factors where that interface plays an important role include thermal expansion due to temperature changes and vibrations that may result from certain applications. The surface composition of the material play an important role in the surface stability of the material. The stoichiometric composition of the detector surfaces also affects its surface current, which, in turn, contributes to electronic noise. High electronic noise is detrimental to the energy resolution of the detector device. X-ray photoelectron spectroscopy (XPS) is a good technique for determining dominant surface composition of materials. In this current study, the authors used an XPS to look at the dominant composition materials on the surface of a CdZnTe wafer. The experiments involved loading CdZnTe wafers into the XPS machine and recording the peaks of the binding energies of elements and compounds present on the surfaces. The XPS results showed the presence of Zn, Te, O, Cd, C, Cl, Si, and TeO2. These results are important in the engineering of CdZnTe radiation detection devices. 

Cadmium zinc telluride (CdZnTe) and cadmium manganese telluride (CdMnTe) semiconductor nuclear detectors have the ability to operate at room temperature without cryogenic cooling. Thus, they can be fabricated into portable nuclear detection devices that can be used at seaports and border security, and at nuclear facilities to monitor radiation levels. In this paper, we present results from the use of X-ray photoelectron spectroscopy (XPS) to study the surface compositions of CdZnTe and CdMnTe wafers. Our results showed that Cd, Te and TeO2 are the dominant species on these materials. Zn was also present on CdZnTe wafer, and Mn is present on the CdMnTe wafer. CdZnTe samples that were etched with high-energy ion beam did not show the presence of TeO2 on their surfaces. 

Cadmium zinc telluride selenide (Cd1−xZnxTe1−ySey or CZTS) is one of the emerging CdTe-based semiconductor materials for detecting X- and gamma-ray radiation at or near room temperature (i.e., without cryogenic cooling). Potential applications of CZTS sensors include medical imaging, X-ray detection, and gamma-ray spectroscopy. Chemical passivation of CZTS is needed to reduce the conductivity of Te-rich surfaces, which reduces the noise and improves the device performance. In this study, we focus on the effect of surface passivation of CZTS using a 10% aqueous solution of ammonium fluoride. The effects of the chemical treatment were studied on the leakage current, charge transport measured as the electron mobility-lifetime (µτ) product, and the spectral resolution measured as the full-width at half-maximum (FWHM) of specific peaks. After passivation, the leakage current increased and began to decrease towards pre-passivation levels. The energy resolutions were recorded for eight applied voltages between −35 V and −200 V. The results showed an average of 25% improvement in the detector’s energy resolution for the 59.6 keV gamma peak of Am-241. The electron µτ product was unchanged at 2 × 10−3 cm2/V. These results show that ammonium fluoride is effective for chemical passivation of CZTS detectors.