Atom gun

A gun is used to direct a beam of fast-moving atoms or ions onto the liquid target (matrix). Figure 4.1 shows details of the operation of an atom gun. An inert gas is normally used for bombardment because it does not produce unwanted secondary species in the primary beam and avoids contaminating the gun and mass spectrometer. Helium, argon, and xenon have been used commonly, but the higher mass atoms are preferred for maximum yield of secondary ions. 

Having considered the various parts of a dynamic-FAB system (atom gun, ionization, and matrix), it is now necessary to see how these are put together in a working inlet/ion source interface. 

In fast-atom bombardment (FAB), an atom gun is used to project heavy, fast atoms (often argon or xenon) onto the surface of a target solution (matrix). 

The passage of a component of a mixture over the atom gun target area is accompanied by first a rise and then a fall in the ion current, and a graph of ion yield against time is an approximately triangularshaped peak. 

The main features of f.a.b.-m.s. are shown schematically in Fig. 1. The hardware consists of (i) an atom gun (or ion gun, see later) which is either mounted on the source housing of the mass spectrometer or, if small enough, inside the housing on the source itself, (it) a sample probe to the end of which is attached a small metal target onto which the sample is loaded, and (Hi) suitable source-optics for the efficient extraction of ions into the analyzer of the mass spectrometer. 

Barber and coworkers made radical changes to the s.i.m.s. technique. They replaced the ion gun with an atom gun, redesigned the ion source to... 

Metal atoms applied to the surface of a solid body under mild conditions (low target temperature and flow intensity) e.g., by means of an atom gun [25] (the method of molecular beams), provided that diffusion... 

Fig. 3.10. Reaction cell. 1 - Atom gun 2 - Thermostate 3 - Metal evaporator 4 - Pt/Pt-Rh thermocouple 5/7 - Collimation holes (diameter 3 mm) 8 -Shutter 9 - ZnO semiconductor sensor 10 - Mobile quartz weight 11 - Platinum contacts terminals 12 - Vitrificated iron bars controlled by a magnet 13 -Quartz guides...

Both air and fuel are injected through the same atomizing nozzle in this burner. Fuel is injected at a low pressure while air is injected at a high velocity resulting in a finer spray than is provided by the high pressure atomizing gun. A secondary, external air supply is also provided. This type of atomizer is less susceptible to nozzle plugging. 

A- Gun, Same as Atomic Gun A-Gun Shell. Same as Atomic Gun Shell AHH Propellant is described in confidential "Propellant Manual," SPIA/M2, Johns Hopkins Univ, Silver Spring, Maryland( 1959),... 

Atomic Gun (A-Gun) Shell. See under Atomic Weapons and Ammunition... 

Static SIHS. Static SIHS spectra were obtained using a VG SIHSLAB instrument. The essential components of which are described in detail elsewhere (17) but consist of an ion/atom gun (19), a secondary ion energy analyzer after the design of Wittmaack (20) and a quadrupole mass spectrometer (VGMH 12-12, 0-1200 Daltons). 

Mass spectrometry, especially in the form of fast atom bombardment, has become a potent tool in the elucidation of the structure of phospholipids. In this technique, the phospholipid sample in amounts in the range of 15-100 ng (or more), dissolved in chloroform-methanol (1 1, v/v), is mixed with a glycerol or thioglycerol matrix and placed on a sample mount in the spectrometer. A fast atom gun is then aimed, at a 90° angle, at the sample and the resulting ionized particles are directed to a mass analyzer unit. Under these conditions, most of the energy of the beam is limited to the surface of sample matrix. Consequently, the bulk of the sample is unaltered and can be recovered by solvent extraction. In the case of phospholipids, a mass ion, MH+, is produced also, some fragments are useful for structural analysis. A more... 

Fig. 1. Schematic diagram of a simplified FAB source (1) probe, (2) fast-atom beam, (3) atom gun, (4) sputtered secondary ion beam, (5) source ion optics, (6) to mass analyzer.

The overall diagram of a fast-atom bombardment ion source is depicted in Fig. 5. This is fairly simple, consisting of three main elements (1) an atom gun, (2) a sample inlet, and (3) an ion-extraction system. 

The atom gun is made up of an evacuated chamber that encloses a plate to which a high voltage potential (nominally 8 kV) is applied. The gas to be used as the bombardment gas is allowed in the chamber, through an appropriate... 

If a functional coat is to be evaluated, the scale-up requires that critical process parameters that affect coating uniformity be evaluated. Coating conditions such as atomization, gun location, and bed movement become critical processes. The curing rate of the film must be evaluated. Drying conditions (temperature and humidity) and drying time must be defined and ranges validated. 

Besides El, Cl, FI or FD techniques for generating ions in the mass spectrometer, some other ionization techniques have been reported. One such technique is metastable atom bombardment (MAB), which Is based on Penning ionization. In MAB a metastable ion beam generated outside the ion volume is used to bombard the sample. The energy available for ionization is discrete (quantified) and can be fixed by the choice of the rare gas used in the atom gun (He, Ne, Ar, Kr, Xe). This energy ranges from 8 to 20 eV. 

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