Ion acceleration

If V2 Vi and the ion starts its journey from the surface of the electrode of higher potential, then the ion will be exposed to the full range of the electrical potential difference across the electrode gap and will receive the maximum possible kinetic energy as a result of ion acceleration by the electric field. The kinetic energy, T, acquired by an ion of mass m (in kg) and charge q (in coulombs, C) as it reaches the other electrode is given by 

The kinetic energy attained by the ion as it arrives at the downstream mesh electrode will depend on its initial location when the voltage is switched on, as hinted at earlier. For example, an ion midway between the two electrodes will initially be subjected to an electrical potential of (V2 — 3 i)/2. It will then follow the field lines and move towards 

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Ions accelerated out of the ion source with keV translational kinetic energies (and m/z selected with the magnetic sector) will arrive in the FFR of the instrument in several microseconds. Ions dissociating on this... 

X-radiation can also be induced by high energy (several Me proton beams from ion accelerators. Such particle-induced x-ray emission (PIXE) (284) is useful for thin samples and particulates, having detection Hmits of g. Intense synchrotron x-ray sources have found appHcations in... 

Several million dollars for high-energy ion accelerator Large laboratory for accelerator... 

Figure 1 Schematic of DC glow-discharge atomization and ionization processes. The sample is the cathode for a DC discharge in 1 Torr Ar. Ions accelerated across the cathode dark space onto the sample sputter surface atoms into the plasma (a). Atoms are ionized in collisions with metastable plasma atoms and with energetic plasma electrons. Atoms sputtered from the sample (cathode) diffuse through the plasma (b). Atoms ionized in the region of the cell exit aperture and passing through are taken into the mass spectrometer for analysis. The largest fraction condenses on the discharge cell (anode) wall.

All the techniques discussed here involve the atomic nucleus. Three use neutrons, generated either in nuclear reactors or very high energy proton ajccelerators (spallation sources), as the probe beam. They are Neutron Diffraction, Neutron Reflectivity, NR, and Neutron Activation Analysis, NAA. The fourth. Nuclear Reaction Analysis, NRA, uses charged particles from an ion accelerator to produce nuclear reactions. The nature and energy of the resulting products identify the atoms present. Since NRA is performed in RBS apparatus, it could have been included in Chapter 9. We include it here instead because nuclear reactions are involved. 

Nuclear reactions are excited when projectile energies are typically in the MeV range. Medium size ion-accelerators are, therefore, necessary to obtain these projectile energies. Protons and a projectiles, typical projectiles in other ion-beam analysis techniques as RBS or PIXE, have few useful nuclear reactions. Deuteron beams excite many more nuclear reactions, but the use of deuteron beams instead of standard beams is more hazardous, because of efficient neutron production. Strict safety rules are necessary when high-energy deuteron beams are used. 

An alternative view of these addition reactions is that the rate-determining step is halide-assisted proton transfer, followed by capture of the carbocation, with or without rearrangement Bromide ion accelerates addition of HBr to 1-, 2-, and 4-octene in 20% trifluoroacetic acid in CH2CI2. In the same system, 3,3-dimethyl-1-butene shows substantial rearrangement Even 1- and 2-octene show some evidence of rearrangement, as detected by hydride shifts. These results can all be accoimted for by a halide-assisted protonation. The key intermediate in this mechanism is an ion sandwich. An estimation of the fate of the 2-octyl cation under these conditions has been made ... 

The addition of a minimum of 2% molybdenum content in type 316 stainless steel has been shown to reduce the tendency for pitting-type corrosion in chloride environments. Hoar and Mears postulated that chloride ions accelerate the corrosion of stainless steel by penetrating the oxide him. The chloride-contaminated him then loses its passivating quality and a local attack on the metal follows, creating a pit. The exact mechanism by which molybdenum strengthens the oxide him is not clearly understood. ... 

In general there does not appear to be any direct correlation between the rate of the chemical dissolution of oxides and the rate of scale removal, although most work on oxide dissolution has concentrated on magnetite. For example, Gorichev and co-workers have studied the kinetics and mechanisms of dissolution of magnetite in acids and found that it is faster in phosphoric acid than in hydrochloric, whereas scale removal is slower. Also, ferrous ions accelerate the dissolution of magnetite in sulphuric, phosphoric and hydrochloric acid , whereas the scale removal rate is reduced by the addition of ferrous ions. These observations appear to emphasise the importance of reductive dissolution and undermining in scale removal, as opposed to direct chemical dissolution. 

Impurities, such as heavy metal ions, accelerate the decompn and may cause an expln to occur at a lower temp. Open Cup flash pt is 105°F (Ref 12). Since the material is an extremely powerful oxid agent it must be handled with extreme caution and kept away from combustible mats (Ref 12)... 

The ratio of HeH +/H2 + as a function of electron energy is plotted on the same energy axis. Ion-accelerating voltage = 2500 volts repeller potential = 3.12 volts ionizing electron current = 10 iiamp. 

Figure 1. Source chamber and ion-accelerating system for m.e.v. proton bombardment of gases at relatively high pressures...

Evidence for molecular chlorine or bromine as the attacking species in these cases is that acids, bases, and other ions, especially chloride ion, accelerate the rate about equally, though if chlorine dissociated into Cl" and Cl , the addition of chloride should decrease the rate and the addition of acids should increase it. Compound 27 has been detected spectrally in the aqueous bromination of phenol. ... 

At [H ] = 0.1 M, U(IV) reacts about six times more rapidly with Np(IV) than with Np(V). Unlike nitrate and sulphate, chloride ion accelerates the reaction. 

Single-line sources are now available which cut down the number of resonance lines in a spectrum and thereby reduce the resolution problems considerably. Since many laboratories have access to electron and ion accelerators to produce the parent nuclides Co and Cu, the major experimental obstacles to Ni spectroscopy have been overcome and a good deal of successful work has been performed in recent years. Moreover, the development of synchrotron radiation instead of conventional Mossbauer sources is of additional advantage for future Mossbauer applications (see below). 

QMS Simple operation and maintenance low cost constant resolution (Am) Unear m/z scale low ion accelerating voltages... 

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