Damage cross section

Figure 8.4 Static SIMS. Primary ion bombardment results in surface damage and emission of ions and neutral atoms. The damaged area is quantified by the damage cross-section (a ). In static SIMS the total primary ion dose should be limited so that only small portion of the surface is damaged, a, surface layer b, bulk c, damaged zone d, depth of damage zone r, radius of damage zone.

We can estimate the time scale in which the whole surface layer is affected by the primary ions. The lifetime of a surface may be simply estimated from the primary ion flux (Ip) and damage cross-section (er) generated by each impact. Ip is commonly measured in A cm-2 (1 A = 6.2 x 1018 charged particles per second). Assume that each primary ion generates a = 10-13 cm2. Then, 1013 primary ions cm-2 will affect the whole surface area of 1 cm2. It means that the lifetime of a surface with the flux density Ip= 1 pA cm-2 (= 6.2 x 1012 ions cm-2) is less than 1 second. Apparently, 1 p A cm-2 of flux density for primary ions is too high for static SIMS. Since it is commonly accepted for the static SIMS condition to limit the total amount of primary ions up to 1013 ions cm-2, for a 10-min duration of static SIMS examination a primary flux density of about 2.7 nA cm-2 is required to preserve the chemical structure of the surface top layer where the secondary ions are emitted. This flux is extremely low compared with that of dynamic SIMS, which requires a flux density of greater than 1 pA cm-2 to ensure a reasonable erosion rate of surface for depth profiling. 

Damage cross section is an important SIMS parameter and provides a measure of the surface area affected by the impact of a single primary ion. The magnitude of the incident ion dose establishes whether a dynamic or static SIMS experiment is performed. For dynamic SIMS, the number of incident ions exceeds the number of surface atoms on the sample and results in erosion due to sputtering and chemical damage to the surface. Dynamic SIMS is primarily used in quantitative elemental imaging applications. In contrast, static SIMS measurements are performed so that the number of incident ions is... 

The dependence of the cross section of the monitor reaction on the neutron energy must be exactly known and, moreover, it should be similar to that of the damaging cross section. Interference in the results caused by neutrons of other energy ranges should be small, so that a correction can be made with tolerable accuracy. This also applies to the burnup of the monitor nuclide by neutron capture, i. e. its neutron capture cross section should be small. 

Lower topography formation on the sample from the sputtering process and lower damage cross sections for depth profiling of molecules are additional advantages of the Cgo source compared to liquid metal ion sources [15]. These sources are most often used with TOE SIMS. 

Damage cross section A parameter used in Static SIMS for describing the damage imparted during sputtering... 

We have applied our model to plain concrete prisms sxabjected to uni axial eccentric compressive load (Fig.3). At any time, the damage factor gains the value D(M) due to the local stress history at each location M belonging to a damaged cross-section. Taking Eq.9 into account, the following expressions are easily derived from the equations of equilibrium ex pressed in terms of actual stress (see (1) for more details) ... 

These equations express the equilibrium of the "actual part" of the damaged cross section subjected to a fictitious loading depending on the residual strain distribution. As assumed above, the modulus of elasticity is constant throughout the section. Finally, the obvious solution of Eq.lO leads to the stress distribution, having regard to Eq.1 and Eq.2 ... 

Tn Eq.lO and Eq.ll, G, I and Q denote respectively the center of gravity, the moment of inertia and the area of the actual part (union of the dS areas) of the damaged cross section. 

The AUGUR information on defect configuration is used to develop the three-dimensional solid model of damaged pipeline weldment by the use of geometry editor. The editor options provide by easy way creation and changing of the solid model. This model is used for fracture analysis by finite element method with appropriate cross-section stress distribution and external loads. 

Another application areas of microtomography are biology and agriculture. Fig.4a shows an X-ray transmission image through the tulip bulb in wet conditions. Damaged area can be found in the surface of this bulb. Fig.4b shows the reconstructed cross section with information about depth of damaged volume. 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

SiHcon carbide s relatively low neutron cross section and good resistance to radiation damage make it useful in some of its new forms in nuclear reactors (qv). SiHcon carbide temperature-sensing devices and stmctural shapes fabricated from the new dense types are expected to have increased stabiHty. SiHcon carbide coatings (qv) may be appHed to nuclear fuel elements, especially those of pebble-bed reactors, or siHcon carbide may be incorporated as a matrix in these elements (153,154). 

In general, cavitation damage can be anticipated wherever an unstable state of fluid flow exists or where substantial pressure changes are encountered. Susceptible locations include sharp discontinuities on metal surfaces, areas where flow direction is suddenly altered (Fig. 12.5), and regions where the cross-sectional areas of the flow passages are changed. 

Graphitic corrosion is a slow corrosion process, typically requiring many years to effect significant damage. Complete penetration of thick cross sections has, however, occurred in as little as 2 years in adverse environments. On the other hand, cast iron components can be found in use in Europe after 160 years of service. Although graphitic corrosion causes a substantial reduction in mechanical strength, it is well known that corroded cast iron, when sufficiently supported, may remain serviceable when internal pressure is low and shock loads are not applied. 

Susceptibility to radiation damage must be considered seriously if reference samples are to be calibrated for use in place of absolute systems. For the measurement of absolute C He, H) cross sections, films of polystyrene (CH) (which is relatively radiation hard) have been used successfiiUy, the RBS determination of carbon providing implied quantitation for the hydrogen present in the film. For a durable laboratory reference sample, however, there is much to recommend a known ion-implanted dose of H deep within Si or SiC, where the loss of hydrogen under room temperature irradiation will be neghgible. 

It is important to recognize that all materials will have problems in certain environments, whether they are plastics, metals, aluminum, or something else. For example, the chemical effect and/or corrosion of metal surfaces has a damaging effect on both the static and dynamic strength properties of metals because it ultimately creates a reduced cross-section that can lead to eventual failure. The combined effect of corrosion and stress on strength characteristics is called stress corrosion. When the load is variable, the com-... 

Fig. 11—Observation of subsurface damage, (a) Cross section HTEM images of surface undergoing collision for ten minutes, (b) Electron diffraction pattern from an amorphous area.

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