Cross section hydrogen

The remainder of the Fowler article is of great interest, but in detail that is beyond the scope of this encyclopedia. Topics covered by Fowler include early research on element synthesis stellar reaction rates from laboratory cross sections hydrogen burning in main-sequence stars and the solar neutrino problem synthesis of l3C and, 60 and... 

Keywords Absorption cross section Hydrogen peroxide Hydroxyl radical ... 

Fracture of massive brittle and ductile pieces are rather well understood. By taking proper account of the microstructure as well as the micro- and macro-defects, most catastrophic and fatigue failures find a satisfactory explanation within the scope of the linear elastic fracture mechanics or the elasto-plastic fracture mechanics. Metallic filaments are particular and in many respects deserve a treatment of their own. Particular fabrication methods, such as drawing, melt spinning or crystallization from the vapor phase for whiskers are needed to obtain their small lateral dimensions. These processes may give rise to particular textures, intrinsic and extrinsic defects. Thermal treatments may modify or eliminate such defects but in many cases fracture is initiated by defects that stem from the fabrication process. Moreover, the small lateral dimensions, especially in micro-wires, make metallic filaments prone to external influences. Corrosive attacks may rapidly affect an important fraction of their cross-section. Hydrogen, for instance, which usually results in a severe embrittlement, may diffuse up to the core in a rather short time. 

Schnieder L, Seekamp-Rahn K, Wede E and Welge K H 1997 Experimental determination of quantum state resolved differential cross sections for the hydrogen exchange reaction H -r D2 -> HD -r D J. Chem. Phys. 107 6175-95... 

In Figure 2, we show the total differential cross-section for product molecules in the vibrational ground state (no charge bansfer) of the hydrogen molecule in collision with 30-eV protons in the laboratory frame. The experimental results that are in aibitrary units have been normalized to the END... 

Figure 2. Total differential cross-section versus laboratory scattering angle for vibrational ground state of hydrogen molecules in single collisioins with 30-eV protons.

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. 

NRA is an effective technique for measuring depth profiles of light elements in solids. Its sensitivity and isotope-selective character make it ideal for isotopic tracer experiments. NRA is also capable of profiling hydrogen, which can be characterized by only a few other analytical techniques. Future prospects include further application of the technique in a wider range of fields, three-dimensional mapping with microbeams, and development of an easily accessible and comprehensive compilation of reaction cross sections. 

For atomic masses M2 4 Mj the recoil cross-section is almost independent of the atomic number, because the cross-section becomes proportional to (Z2/M2) and the ratio Z2/M2 is close to 0.5 for all elements. ERDA with heavy projectiles thus has the advantage of almost constant sensitivity for all elements. Only for hydrogen the ratio Z2/M2 is equal to 1, hence the intensity of hydrogen recoils is enhanced by roughly a factor of four. 

A large number of examples have been reported in the literature for the deuteration or tritiation of double bonds and for the hydrogenation of enones labeled at an allylic position. The following list of substrates, in addition to those already discussed, provides a representative cross section ... 

Pfortner (1985) reports experiments with hydrogen in a lane, 10 m long and 3 X 3 m in cross section, in which a fan was used to produce turbulence. In these experiments, a transition to detonation occurred at high fan speeds. 

Catalyst flux is defined as catalyst circulation rate divided by the full cross-sectional area of the stripper. For efficient stripping, it is desirable to minimize the catalyst flux to reduce the carryover of hydrogen-rich hydrocarbons into the regenerator. 

Rare-Gas-Hydrogen Reactions. Ion-molecule reactions in the rare gas-hydrogen system are of great interest both theoretically and experimentally. The properties of the reactants and products are well known or may be calculated, and the properties of the intermediate three-body complex pose a tractable theoretical problem. Systematic studies of cross-section energy dependence and isotope effects in these systems have been undertaken by Friedman and co-workers (29, 47, 49, 67), by Koski and co-workers (2, 3), and by Giese and Maier (15, 16). 

The argon-hydrogen and krypton-hydrogen systems are distinguished by the fact that the reaction occurs with comparable cross-sections via both hydrogen molecule ion and rare gas ion reactants— namely,... 

The results in Table IV suggest that the condensation reactions cannot be described adequately by the ion-induced dipole model. In this regard the results agree with conventional studies which have frequently found a higher power inverse dependence of the cross-section on the field strength E for condensation reactions than for hydrogen transfer reactions. 

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