TIME-OF-FLIGHT MASS-SPECTROMETRY USING MEGA-ELECTRONVOLT NEUTRAL BEAMS

Neutral carbon, nitrogen and oxygen beams with an energy range of 300 keV-2 MeV (velocity range of 0.2-0.6 cm ns-1) have been used to induce secondary ion emission from solid samples. In this work, results for the ion desorption yield for hydrogen and some organic species emitted by bombardment of neutral and low charge state carbon beams on a phen ylalanine target are reported. The positive and the negative ion mass spectra obtained for neutral projectiles show very similar features as those obtained for 1+-6+ charge state projectiles. However, the ion e mission yields corresponding to neutral beams are observed to be sligh tly smaller than those produced by positive ion beams. The secondary i on desorption yield dependence on the projectile velocity is also anal yzed. It is found that the hydrogen desorption yield slowly decreases with the projectile velocity, whereas the yields of the other desorbed ions show a second to third power dependence of the projectile stoppi ng power in the target.