Cross section depletion

Since the specific activity of a radionuclide produced by particle-induced reactions is a direct function of the incident particle flux, an increase in the incident particle flux results in an absolute increase in the specific activity of the product This relationship is linear for simple reactions and nonlinear for complex reactions. It is important to note that the half-lives, production and depletion cross sections, and irradiation time are equally important. Several important radionuclides have long physical half-lives and low production cross sections requiring long irradiation periods even in the highest neutron flux available. An example in this category is tungsten-188 (half-life 69 days parent for rhenium-188). 

Figure 3 shows the metal transported across the numerical seafloor folded back onto cross section A-A. Figure 4 shows zinc addition and depletion in the domain. 

The direct detection of the S <- Sj absorption in organic compounds has so far been achieved by a nanosecond or picosecond laser flash photolysis method. The general features of transient absorption spectra of metalloporphyrins actually suggest the presence of strong absorption bands in visible or ultraviolet region (38-40). However, as the transient absorption of the state often overlaps with that of ground state depletion, it is usually difficult to evaluate the absolute absorption cross sections for the transition by... 

Fig. 5.11 (a) Pre-Columbian mask made of ternary alloy (ca. 43% Au, 35% Ag, 21% Cu), courtesy Museu de Arqueologia e Etnografia, USP, Brazil (b) Cross section SEM image and corresponding EDX mapping. The dashed line is the object s contour. Note the strong Cu depletion at distances up to 10-15 im from the surface... 

Several methods not based on DLTS have also been described. White et al. (1976) present a two-light source, scanned photocapacitance technique that yields a spectrum of the deep states in the depletion region of a junction. The method is fast and sensitive, but most useful as a survey technique because knowledge of the dependence of the photoionization cross section on photon energy is required to obtain accurate trap depths. 

The difference in efficiency between the large planar 18-cm.3 Ge(Li) detector and the small round 8-cm.3 Ge(Li) detector depends essentially on their cross-sections since they have approximately the same depletion depths. This is apparent in comparing the peaks from 10 pCi of 137Cs generated by the large and small detectors (Figure 9). The geometry of the aluminum can was determined to be less efficient by approximately a factor of 10 than a disc-mounted point source. 

Under this condition, there is complete depletion of O2 at the electrode next to the porous layer of Fig.6a or inside the cavity of Fig.6b. The constant depends on the diffusion constant of O2 (in its particular carrier gas), Dq, and the geometrical characteristics of the diffusion barrier. In the device of Fig.6b (sensor with integral cavity), the diameter of the aperture C (usually greater than 50 microns) is much larger than the mean free path of the gas molecules at 1 atm (about 1 micron) and bulk diffusion dominates. In this case(ll-12). D0 - K Ta/P and cr - (DgA)/(kTd), where K] is a constant, P is the absolute pressure, a is a constant having a value between 1.5 and 2 and A and d are the cross-sectional area and length of the aperture C. Representative values for D0 are about 1.5 cm2/s at 700 °C and 0.15 cm2/s at 20 °C. Since Pg — cP with c the percentage of O2 molecules in the gas, we have... 

Fig. 10 (a) 3D-sketch of the cell cross section according to Fig. 12. (b) Sketch of the laser focus, (c) The laser beam is scanned along the y-direction. Right phase contrast image of arbitrary pattern written into critical sample. The bright regions show an enrichment of PDMS, the dark ones a depletion (enrichment of PEMS)... 

Figure 17. Schematic cross sections of a photopolymer material in which a grating pattern is being written, (a) The image exposure forms polymer and depletes the monomer concentration, (b) Additional monomer diffuses into the exposed areas, (c) An overall development exposure completes the polymerization to give a polymer with a modulated density.

Cross section of a p-n photodiode (a) and potential energy diagram or the junction region b). Absorption of a photon with energy in excess of the band gap produces charge separation of the resultant electron-hole pair to produce a voltage across the depletion layer. 

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