Detectors high-speed

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. 

This sequence of events is quite rapid. If we take typical instrumental conditions of the LIMA 2A, where the UV laser pulse duration is 5-10 ns, the fight path is "2 m, and the accelerating potential is 3 kV, then an ion arrives at the detector i n approximately 3 ps, and a ion arrives at the detector in approximately 40 ps. Since the time width of an individual signal can be as short as several tens of nanoseconds, a high speed detection and digitizing system must be employed. 

Silicon drift detectors (SDD, Figs 4.8 and 4.9) now also provide sufficient resolution (FWHM = 0.175 keV) above a sample spot sized 2 x 2 to 100 x 100 mm, and enable high-speed operation (> 10 counts s ). SDD can be combined with microelectronics and applied in portable TXRF models for microanalytical applications [4.30]. They must be cooled by a Peltier element. 

Fay and Lewis (1977) used spherical gas samples inside soap bubbles whose volumes ranged from 20 to 190 cm. Typically, a sphere was ignited with resistance wire, and the combustion process was then filmed with a high-speed camera. The fireball s maximum height and diameter, as well as the time needed to complete combustion, were evaluated. The fireball s thermal radiation was sensed by a radiation detector. Figure 6.3 relates fireball burning time and size to initial propane... 

FIG. 1 Schematic drawing of the high-speed stirring (HSS) apparatus. An organic phase separated from the dispersed system by the teflon phase separator is continuously circulated through the photodiode array detector. 

Fig. 3. Schematic diagram of the Northwestern apparatus for IR laser kinetic measurements in the gas phase. D, and D2 are InSb detectors with D2 being a high speed photovoltaic detector. M = Mirror, I = iris, C = chopper, BS = beam splitter, P = photolysis cell. [Reproduced with permission from Ouderkirk et al. (75).]...

Detection Inlet heat exchangers Flow cell volume and geometry MS ion sources Sprayers (e.g., in evaporative light scattering detectors) Data filtering effects in high speed applications... 

Another data acquisition consideration is data file size. A high speed LC/MS data file can easily reach dimensions of 20 MB/min if maximal information is required and the detectors are set to broadest scan ranges and highest sampling rates without data reduction. LC/MS systems capable... 

A detector plays an important part in achieving overall performance when optimizing for very short run times with reasonable peak capacities. The detector should match the optimized LC conditions in terms of flow rate and dispersion. The electronics must accurately capture the peak form produced by the column this is most important for quantitative analyses. The data quality may be limited by the laws of physics at high speed. The amount of data produced over time can become an issue. 

Typical applications for these high speed IR detectors are characterized by strictly controlled, dark environments where a flash fire could originate. While simple high speed infrared systems have been available for several years, modern sensor and filter developments, coupled with state-of-the-art electronics, have resulted in systems tailored for the munitions industry. These systems are more selective within the electromagnetic spectrum, fast in response, and extremely flexible in application to suppression systems. 

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