Target ionization

Matrix-assisted laser desorption mass spectrometry (MALDI-MS) is, after electrospray ionization (ESI), the second most commonly used method for ionization of biomolecules in mass spectrometry. Samples are mixed with a UV-absorbing matrix substance and are air-dried on a metal target. Ionization and desorption of intact molecular ions are performed using a UV laser pulse. 

Figure 18 Ionization of water vapor by 2-MeV He and ions. The dashed line is an estimate of the contribution of target ionization by He obtained by interpolation from regions beyond the vicinity of electrons contributed by electron loss by the He ion. (From Ref. 68.)...

Figure 20 Doubly differential cross sections for ejection of electrons of 219 eV (16 Ry) from He by 2-MeV He ions. The points are measured cross sections and the calculated results are line A— projectile ionization, target remains in the ground state line B—projectile ionization with simultaneous target excitation line C— target ionization, projectile remains in the ground state and line D—target ionization with simultaneous projectile excitation. (From Ref. 70.)...

A variation of the method for determining ° Pb- ° Pb dates of whole single zircons by TIMS analysis that eliminates the need for zircon dissolution and chemical separation of lead was introduced by Kober (1986), with a slight, yet important, modification described a year later (Kober, 1987). In the modified method, usually referred to as the zircon evaporation method, a single zircon crystal is placed into a folded side rhenium filament (the evaporation filament), which is positioned opposite of a blank rhenium ionization filament. The evaporation filament is heated for a short time to evaporate lead onto the target ionization filament. The current to the evaporation filament is then mrned off and the ionization filament is heated until Pb ionization begins and lead isotopic ratios are measured in the normal fashion. Current to the ionization filament... 

At 30 keV/u we find the largest deviation between the measured stopping power and our calculated values of about 12%. This may be attributed to an overestimation of cross sections for multielectron processes because of the use of the independent particle model. We emphasize that the present calculation does not properly take into account events in which more than one electron is actively involved, e.g., double target ionization or excitation and simultaneous projectile and target ionization. 

New medical applications of yttrium include Taxol and °Y-labeled DOTA-pep-tide-ChL6 as radioimmunoconconjugates for targeting ionizing radiation to breast cancer model HBT 3477 (DeNardo etal.1997), as well as modem endoscopy therapy using a YAG laser (Alsolarman et al. 2002). 

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