Mass separation spectrum

Y -y coincidences were performed. A group of strong Y-rays, with an average half-life of (12.1 0.6) s, was found to be coincident with Ka X-rays of Sm. In order to determine which Eu Sm mass chain was concerned, the coupling of the He-jet to the ion-source of the separator was realized. As shown in figure 6, the main y-rays with T1/ - 12 s are present in the mass-separated spectrum at A=138. I/Z... 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

The spark source is an energetic ionization process, producing a rich spectrum of multiply charged species (Af/2, Af/3, Af/4, etc.). These masses, falling at halves, thirds, and fourths of the unit mass separation can aid in the positive identification of elements. In Figure 2, species like Au and are labeled. The most abundant... 

The corresponding SIMS spectrum in Fig. 4.11 shows that the surface contains N atoms and NH2 species, whereas adsorbed NH and NH3 species are not observed. A separate study on the adsorption of NH3 on Rh(l 11) revealed that Rh2(NH3)+ peaks are clearly observable when NH3 is adsorbed [33]. Repeating the experiment with D2 instead of H2 enhances the mass separation between peaks and confirms the presence of N atoms and ND2 species. The interpretation is that the rate-determining step in the hydrogenation of N atoms on Rh(IIl) is the reaction from NH2 to NH3, The... 

The mass-separated beam of appropriate mass was directed down one of the UNISOR beam lines to a fast tape collection system. After a collection time of 24 s, the tape moved in 0.5 sec to a counting station where multi -spectrum scaling and gamma-gamma coincidence data were simultaneously acquired. The 138Eu decay was observed for about 20 hr and the 136Eu for only about 2 hr at a typical 8Ti beam level of 30 particle-nA. 

Figure 31a, b, show a measurement with the extended mass separator. The methane spectrum in Fig. 31a is shown with a hydrogen peak with m/z= 1. The spectrum in Fig. 31b was measured with a Xenon plasma, this allows to detect the 400 ppm argon in air. The current performance of the PIMMS is summarized in Table 4. 

An ion beam extracted from the ion source passes to the mass separation system where continuous changes in the voltages applied to the electrodes allow ions of the appropriate mass/charge (M/Z) ratio to achieve stability in the mass filter and pass to the detector. A spectrum is therefore generated giving the variation of the amplitude of the... 

Figure 4. ERD-TOF results from a Corning Glass 0211 target (a) mass spectrum, (b) mass separated energy spectra superimposed by total energy spectrum, and (c) composite depth profile of the observed elements.

Structural information about toxaphene components can be obtained by gas chromatography coupled to electron ionization mass spectrometry (GC/EI-MS), positive ion chemical ionization mass spectrometry (GC/PICI-MS) or negative ion chemical ionization MS(GC/NICI-MS). Mass separation is performed by low resolution quadrupole or high resolution magnetic field instruments, by ion trap systems (GC/IT-MS), or by tandem mass spectrometry (MS/MS) offering a broad spectrum of possibihties. 

Laser desorption REMPI time of flight mass spectrum of Demmim-SP . Ionization wavelength 193 nm. Major peaks represent parent masses, separated by the 166 Da mass of a repeat unit [Cp2]3-0. The numbers of units are indicated for some peaks. 

Finally, the ion current due to these mass-separated ions is measured, amplified, and displayed in the form of a mass spectrum. 

Unlike beam-type instruments, mass separation in a QIT is achieved by storing the ions in the trapping space and by manipulating their motion in time rather than in space. This task is accomplished with an oscillating electric field that is created within the boundaries of a three-electrode structure. The mass spectrum is acquired by changing the applied rf field to eject ions sequentially from the trapping field. 

Quadrupoles are the most widely nsed type of mass spectrometer. A qnadmpole is constructed from four parallel metal electrodes. The opposite electrodes are connected by dc and rf potentials. Mass separation is accomplished by the stable vibratory motion of ions in the high-frequency oscillating electric field thns created. Under the set of defined dc and rf potentials, ions of a specific mIq pass through the geometry of quadrupole rods. A mass spectrum is obtained by changing dc and rf potentials while keeping their ratio constant. 

Ions are ejected from the ion source and focused into a beam by a positive potential on a repeller plate positioned at the back of the ion source and a high potential, in the order of 5-10 kV at the front of the source. The beam then enters the analyzer section of the instrument for mass separation to form the spectrum. As the molecules are essentially ionized in the vapor phase, they must be stable at the temperatures needed to vaporize them. Many molecules do not fulfill these requirements but can be stabilized and made more volatile by derivatization. However, even with derivatization and heated ion sources, the technique is only applicable to molecules with masses less than 1000. 

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