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Introduction to Nuclear Instrumentation
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Two such systems, advanced at the time, were the systems developed by the European Organization for Nuclear Research (CERN) and the United Kingdom Atomic Energy Research Establishment. The European Standards community on Nuclear Electronics (ESONE), founded in 1961, also began working on a new standardized modular system. Along with these systems, numerous commercial companies began working on various modular nuclear electronics systems. Further, the independent U.S. national laboratories began developing modular nuclear electronics systems for their own purposes. As a result, numerous different nuclear electronics systems were under development, none of which was compatible with any of the other systems. Overall, research at nuclear laboratories was seriously limited by the compatibility of instruments, and researchers were forced to invest in numerous different modular nuclear components.
Doping Effects in Wide Band Gap Semiconductor Nanoparticles: Lattice Variations, Size Changes, Widening Band Gaps but no Structural Transformations!
Published in Nandakumar Kalarikkal, Sabu Thomas, Obey Koshy, Nanomaterials, 2018
The positron lifetime in principle is measured as the time interval between the emission of the positron from a radioactive source and its subsequent annihilation with an electron of the sample of interest. While (one of) the annihilation gamma rays will serve as the end signal, the start signal needs to be derived from a concomitant process so that the positron can enter and interact with the sample electrons. Fortunately, a versatile radioactive source22 Na exists which decays to the first exited state of its daughter nucleus22 Ne (Fig. 3.1) and the latter immediately (within ~1-2 ps) de-excites to the ground state by releasing the excess energy of 1.276 MeV as a gamma ray. The detection of this and one of the annihilation gamma rays enables the measurement of the positron lifetime using a slow-fast gamma-gamma coincidence spectrometer. The schematic diagram of the setup is shown in Figure 3.2. It consists of two BaF2 scintillators coupled with XP2020Q photomultiplier tubes serving as the radiation detectors and the associated nuclear electronics. The time resolution of this set up is ~170 ps (full width at half maximum). For coincidence Doppler broadening measurements, two high pure Germanium (HPGe) detectors are used. They had resolutions 1.27 and 1.33 keV at 0.511 MeV. The schematic diagram of the experimental setup is as shown in Figure 3.3. About a million coincidence counts are collected in each positron lifetime spectrum whereas the number of coincidence events generated in each CDB spectrum was about 20 million.
A numerical study on contact conditions, dynamic resistance, and nugget size of resistance spot weld joints of AISI 1008 steel sheets
Published in Numerical Heat Transfer, Part A: Applications, 2023
Prashanth Kumar Reddy Gillela, Jeevan Jaidi, Venugopal Gude, Sunil Kumar Pathak, Dinesh Srivastava
Resistance Spot Welding (RSW) is an electro-thermomechanical joining technique, widely used for mass production in automobile, aerospace, nuclear, electronics and packaging industries. Lap-joints of ferrous and non-ferrous similar and dissimilar sheets up to 2 mm thickness can be precisely welded by the RSW process. The sheets (workpieces) to be welded are held together by the electrodes and heat is generated by passing an electrical current. The nugget formed at the workpiece-workpiece interface (faying surface) is due to the bulk resistance (Joule heating) and contact resistance. Figure 1 depicts the three different stages of RSW process, and a weld schedule comprising of squeeze, weld and hold cycles (time periods). Stage 1 is the squeeze in which the workpieces are brought and held together by the electrode load (force). Stage 2 is the weld in which a high electrical current is passed through the electrodes while the load is maintained. Stage 3 is the hold in which the electrical current is cutoff and load is continued until the nugget cools down to room temperature. Due to extremely limited scope for measurements on contact temperatures and pressures during the RSW process, an accurate prediction of bulk and contact resistances and temperatures would immensely help in the process optimization, besides in-line process monitoring and control. The following subsections briefly discuss on experimental and simulation studies done by different researchers on RSW of sheet metals.
In Celebration of Professor John Richard Thome on His 70th Birthday
Published in Heat Transfer Engineering, 2023
Lixin Cheng, Guodong Xia, Afshin J. Ghajar
He has also been active in numerical modeling of two-phase flows, including work on condensation in circular and non-circular microchannels and micro-gravity flows, UDF modified versions of Fluent for two-phase flows, and a new 3D/ALE-FEM numerical code for two-phase flow and evaporation in microchannels. In this respect, he worked hard to validate all these codes against independent test data, thus bringing more general faith to the validity and practical use of two-phase numerical modeling. His experimental activities covered micro-PIV and newly developed micro-shadow-velocimetry (micro-PSV) of single- and two-phase flows in microchannels and orifices, in addition to annular down-flows. He has proposed the first flow pattern-based suite of macroscale methods for predicting flow pattern transitions, flow boiling heat transfer, condensation heat transfer and two-phase pressure drops. He has also proposed the leading methods for flow boiling and critical heat flux in microchannels, just now adding a flow pattern-based model to this topic and has also just developed the first experimentally validated simulation tool for combined heat spreading and flow spreading for multichannel micro-evaporators with non-uniform heat fluxes and hotspots. He has in recent years also proposed the first unified suite of annular flow models for predicting void fraction, entrainment, liquid film thickness, convective heat transfer and pressure drops in macro-and microscale annular flows, which so far are also proving there is not macro-to-microscale transition in annular flow. He has also extended his experimental research to cover two-phase flow control for electronics cooling and new hybrid cooling cycles, using speed control on oil-free pumps and compressors. His work is widely used in engineering practice in diverse industries: refrigeration, air-conditioning, petrochemical, nuclear, electronics cooling, high energy physics particle detectors, and LNG.