China
Africa
Explore chapters and articles related to this topic
Diffraction
Published in Peter E. J. Flewitt, Robert K. Wild, Physical Methods for Materials Characterisation, 2017
Peter E. J. Flewitt, Robert K. Wild
Specimens with greater than 100 nm thickness can be examined by this technique but the beam is broadened as it passes through the foil, and this limits the spatial resolution obtained (Hutchins et al. 1979, Kyser and Geiss 1979) (see Figure 2.7). CBD patterns are very sensitive to strain fields from dislocations, precipitates or surface films, and it is essential that such regions are avoided. Contamination of the specimen can also cause problems and an area studied over long periods of time may contaminate, which will result in degradation. To achieve the best patterns from the technique, steps must be taken to reduce contamination, usually by obtaining a clean vacuum in the microscope and here a microscope operating at ultra-high vacuum pressures is invaluable (see Appendix 1). A cold finger, cooled to liquid nitrogen temperatures and placed close to the specimen, will reduce contamination.
Semiconductor Detectors
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
The HPGe detector crystal is mounted inside a mounting cup with standoffs to hold it in place. Usually the mounting cup is electrically attached as an outer contact to the crystal and a conductive pin is used as the inner contact within the hollow penetration. The mounted crystal is placed inside a housing, hermetically sealed, and evacuated. Older designs had the entire stem and housing evacuated; newer designs use a modular approach, in which only the detector compartment is evacuated. In the newer designs, an insulator plug partitions the electronics from the evacuated detector chamber. In either case, the detector crystal is shielded by the mounting cup and the housing, which unfortunately reduce efficiency for low-energy gamma rays. It is common to include a package of molecular sieve in the evacuated chamber to absorb residual gas molecules when the chamber temperature is lowered. The mounted detector is attached to a cold stem that is inserted into an LN2-filled dewar. The dewar is lined with “superinsulation”, made of multiple thin sheets of aluminized Mylar**textregistered**, to reduce LN2 losses and lengthen the time between periodic refills. The cold finger is usually made of copper, and is axially located inside a vacuum-tight jacket. This jacket is also partially filled with molecular sieve, used to getter residual gas molecules at low temperature. The preamplifier electronics are stationed close to the detector to reduce line capacitance. In many models, the preamplifer is situated adjacent to the detector house. In modern modular models, the entire preamplifier is situated next to the detector within the housing (see Figs. 15.33 and 15.34). The actual detector is much smaller in size than the housing, and often not exactly a perfect cylinder. From experience, some detectors may have a small section sliced from the crystal (to remove a twin or bad region). The actual spectroscopic performance is within the vendors specification, as is the quoted efficiency. However, casual solid angle calculations without taking into account possible geometry differences produces measurement error. The accepted method of calibrating a HPGe detector is documented in IEEE 325-1996 [Fairstein et al. 1996], which mostly negates problems with detector shape and size.
Review of Candidate Techniques for Material Accountancy Measurements in Electrochemical Separations Facilities
Published in Nuclear Technology, 2020
Jamie B. Coble, Steven E. Skutnik, S. Nathan Gilliam, Michael P. Cooper
Aqueous-based systems typically employ pneumatic sampling of solutions at various stages, allowing for isolated analysis of solutions outside of the high-temperature and radiation environment. This approach is not directly applicable to pyroprocessing because the salt within the electrorefiner must be kept at elevated temperatures to prevent freezing. Thus, measurements need to either be conducted within high-temperature, high-radiation environments or obtained via representative sampling. While salt sampling via cold finger distillation7 or microfluidic sampling8 is possible, significant challenges still exist with respect to sampling methods. In the electrochemical processing flow sheet plutonium is distributed within the system as various chemical forms, including as an oxide powder, molten salt, and solid metal. The distribution of material between these forms can contribute to issues of sample inhomogeneity,9,10 complicating sampling-based measurements. Likewise, the potential inhomogeneity of the electrolyte salt as a function of salt depth challenges representative sampling by any current sampling method.9 Additionally, cold finger techniques are susceptible to melt crystallization,11 resulting in fractional separation of fission products from the sample salt freezing process due to differences in melting points.7,11
Effect of pour point depressant (PPD) and the nanoparticles on the wax deposition, viscosity and shear stress for Malaysian crude oil
Published in Petroleum Science and Technology, 2020
N. Ridzuan, P. Subramanie, M. F. Uyop
Cold finger temperature has been identified as one of the most influential factor that affects the wax deposition based on our previous study done to screen out the factors influencing the wax deposition using design expert software (Ridzuan, Adam, and Yaacob 2016). The temperature difference between the bulk crude oil temperature and cold finger temperature, is calculated using the Eq. (2). where is the crude oil temperature in the vessel while is the cold finger temperature. As the increases more wax deposits can be observed. was constant at 50 °C while has been varied from 5 to 15 °C.
Study of wax deposition law by cold finger device
Published in Petroleum Science and Technology, 2019
Zhiyong Hu, Deli Meng, Yi Liu, Zhipeng Dai, Nan Jiang, Zhenggang Zhuang
The cold finger wax deposition experimental device is composed of the following parts: a cold finger (provides the deposition surface and cold flow channel), an oil tank (provides the oil storage space and heat flow channel), a temperature-controlled water bath (two sets, for controlling the cold finger and the wall thermometer of the oil tank) and the wax scraper (for the one-time removal of surface wax). The cold finger and the oil tank are made of stainless steel and exhibit good thermal conductivity. The cold finger has an inner diameter of 10 mm, an outer diameter of 76 mm, and a height of 210 mm. Meanwhile, the tank has an inner diameter of 130 mm, an inner height of 220 mm, an outer diameter of 170 mm, and a wall thickness of 3 mm. The temperature-controlled water bath (DCW/HDCW series) has a low-temperature thermostat, with temperature control ranging from −5 °C to 100 °C. The temperature control accuracy is °C. The scraper has a ring structure, and its inner hole diameter is 40 mm. It is covered with an elastic rubber pad and can produce a waxy layer to separate rapidly from the cold finger. The cold finger experimental device is shown in Figure 1.