Acceleration region

Figure Bl.7.1. Schematic diagram of an electron ionization ion source source block (1) filament (2) trap electrode (3) repeller electrode (4) acceleration region (5) focusing lens (6).

The final total ion time of flight in the TOF mass spectrometer with a single accelerating region can be written in a smgle equation, taking all of the above factors into account. 

Ion Implantation Systems. An ion implantation system is used to accelerate ionized atomic or molecular species toward a target sample. The ionized species penetrates the surface of the sample with the resulting depth profile dependent on the implanted species mass, energy, and the sample target s tilt and rotation. An implanter s main components include an ionizer, mass separator, acceleration region, scanning system, and sample holder (168). 

Fig 4 is a diagram of an electron impact 1 source. The sample vapor is admitted into the ion source thru the slit in the back of the chamber and it passes thru a collimated electron beam b . On impact of electrons with the neutral molecules, positive ions (to a small extent negative ions) are produced. A small positive potential ( repeller potential ) between the back wall V of the ion source and first accelerator plate d , expels tile positive ions toward the accelerating region and at the same time attracts the negative ions which are then discharged at repeller plate c . The positive ions are accelerated by the potential difference applied to plates d and e , pass thru the exit slit T and continue toward the collector... 

The total pressure drop in the acceleration region can be expressed as... 

Mass spectrometric measurements require four components (1) an inlet to introduce the sample (2) a means of ionizing the species of interest (3) mass filtering/separation (4) detection of the ions. Accomplishing this under atmospheric conditions is difficult due to the high sample pressure, which is incompatible with the high voltages used in the ion acceleration region and mass analyzers, and to the complexity of the mixtures found in air. Special considerations imposed by atmospheric conditions are discussed briefly next. 

EDNA, and Tetryl consisting of velocity discontinuities, and 2) A smooth velocity-distance acceleration usually lasting ca 3 to 4 chge diams and associated directly with nonideal deton. The transient in 50/50-coarse/fine TNT mixt was much like that in the 80/20-AN/TNT mixt, except that transitions were more pronounced and the smoothly accelerating region less pronounced than in the latter case (Ref 52, p 54)... 

Figure 11.5. Pressure drop ratio as a function of mass flux ratio for 10 [im zinc particles in the acceleration region of Re = 53,000 (after Shimizu et al., 1978).

Much of the work in the early development of the preceding techniques incorporated pulsed electron-impact ionization sources or any of several types of laser ionization techniques. In almost all of these cases the ions were created in a pulsed fashion in vacuum and formed in or sent into the acceleration region of the mass spectrometer, where a static acceleration field present there injected them into the mass spectrometer. Such ion sources use the TOF-MS very efficiently because the repetition rate of the spectrometer is limited by the frequency of the ionization event itself. This arrangement allows the TOF-MS to mass analyze of all of the ions formed completely. However, many of the most popular ionization techniques being used in inorganic analysis today are continuous in nature. 

Although some early research did focus on introducing a pulsed external ion beam from a plasma jet into the acceleration region of the TOF-MS [12], it has not been until recently that continuous ion sources such as plasmas, electrospray devices, and other atmospheric-pressure discharges have been coupled with TOF-MS. Unfortunately, the inherently pulsed nature of the spectrometer can cause this marriage to be quite inefficient. The primary challenge in using the TOF-MS with... 

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