Parasitic cross section

Uranium-233 is a superior fuel for use in molten fluoride-salt reactors in almost every respect. The fission cross section in the intermediate range of neutron energies is greater than the fission cross sections of U and Pu239 Thus initial critical inventories are less, and less additional fuel is required to override poisons. Also, the parasitic cross section is substantially less, and fewer neutrons are lost to radiative capture. Further, the radiative captures result in the immediate formation of a fertile iso-... 

As discussed later, the enclosure of an IPB may carry induced currents up to 95% of the current through the main conductors. Accordingly, the enclosure is designed to carry longitudinal parasitic currents up to 90-95% of the rated current of the main busbars. The cross-sectional area of the enclosure is therefore maintained almost equal to and even more than the main conductors to account for the dissipation of heat of the main conductors through the enclosure only, unless an additional forced cooling system is also adopted. The outdoors part of the enclosure exposed to atmospheric conditions is also subjected to solar radiation. Provision must be made to dissipate this additional heat, from the enclosure. 

To design a transistor with a 1.6-GHz intrinsic we should examine the factors that affect the of the transistor. A simplified cross section of the epitaxial emitter structure is shown in Figure 6.23. The stripe geometry has been assumed. All microwave transistors are fabricated more or less with this geometry. The intrinsic part, directly under the emitter, is the active part of the transistor. The extrinsic part, which connects the intrinsic base (under the emitter) to the base contacts, is the parasitic part of the transistor. The effects of these two parts on the transistor can be evaluated by the following formula [22] ... 

PIXE instruments are normally divided into two groups, those instruments suitable for macro-PIXE with a beam with cross-section of several mm, and those suitable for micro-PIXE with a beam spot of 1 tm cross-section. The obvious requirement for both PIXE facilities is the availability of an ion accelerator capable of producing beams of a few megaelectronvolts. In the early days of PIXE, parasitic use of accelerators purchased for research in nuclear physics was common. The majority of these... 

Figure 7.152 shows a cross section of a typical MOS capacitor using double polysilicon MOS technology together with the associated parasitic capacitors and an equivalent circuit model. Cpi is a sizable parasitic capacitance that exists from the bottom plate of the MOS capacitor C to the substrate. This is the capacitance of the siHcon dioxide layer under the first layer of polysilicon, as shown in Fig. 7.152. Typically, Cpi can have a value in the range of 5-20% of C. Cp2 is a small capacitance from the top plate of C to the substrate.

FIGURE 8.35 CMOS parasitic SCR (a) cross-section showing parasitic bipolar transistors, (b) equivalent circuit. 

The reactivity difference between an air (nitrogen) and a helium atmosphere in the reactor has been calculated to be 0.l6. The principal effect of nitrogen in the lattice is to Increase the parasitic absorptions and thus reduce the thermal utilization, f The thermal neutron absorption cross section of helium is zero. 

The neutron absorption cross-sections of any liquid salt for reactor applications must be low to avoid excessive parasitic capture of neutrons. For thermal and intermediate neutron spectrum reactors, this probably eliminates chloride salts with their higher nuclear cross sections, even if the high cross section Cl is removed. Only fluoride salts are candidates. A wide variety of atoms have low cross sections however, the realistic candidates are also restricted by the requirements of thermodynamic stability to ensure viable materials of construction for the container. Table XXVI-5 shows the primary salt options and their cross sections. If either lithium or boron is used as a salt component, isotopically separated lithium and boron are required to have a salt with a low absorption cross section. 

Discussion—It is approximately equal to the takeoff rate differing only by the parasitic heat losses. It is expressed in millilitres per hour for a head of any given internal diameter or millilitres per hour per square centimetre of cross-sectional area of the throat for comparative purposes. 

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