Off-axis detectors

The reflectron is situated behind the field-free region opposed to the ion source. The detector is positioned on the source side of the ion mirror to capture the arrival of ions after they are reflected. There are two common methods of positioning the detector. It may be coaxial with the initial direction of the ion beam. This detector has a central hole to transmit the ions leaving the source. However, the most common instrument geometry has the detector off-axis with respect to the initial direction of the ion beam. Indeed, adjusting the reflectron at a small angle in respect to the ions leaving the source allows the detector to be positioned adjacent to the ion source. 

Thorium. Multiple-collector measurement protocols by TIMS for thorium isotopic analysis typically involve the simultaneous measurement of Th and °Th (for silicate rocks), or Th and °Th, then Th and Th (for low- Th samples), using an axial ion counter and off-axis Faraday collector (Table 1). Various methods are used to correct for the relative gain between the low-level and Faraday detectors and 2a-uncertainties of l-5%o are typically obtained (Palacz et al. 1992 Cohen et al. 1992 McDermott et al. 1993 Rubin 2001). Charge-collection TIMS protocols enable Th, °Th and Th to be monitored simultaneously on a multiple-Faraday array and can achieve measurement uncertainties at the sub-permil level (Esat et al. 1995 Stirling et al. 1995). 

A non-invasive infrared (IK) method has been developed for the measurement of temperatures of small moving fuel droplets in combustion chambers. 7111 The IR system is composed of two coupled off-axis parabolic mirrors and a MCT LWIR detector. The system was used to measure the temperature variations in a chain of monosized droplets generated with equal spacing and diameter (200 pm), moving at a velocity of >5 m/s and evaporating in ambient air. The system was also evaluated for droplet temperature measurements in flames under combustion conditions. 

Figure 17.4 Schematic of the T-jump spectrometer described in the text. OAP, off-axis parabolic mirror PB, Pellin—Broca prism P, polarizer L, lens S, sample MCT, mercury cadmium telluride detector. The size of the pump relative to the probe at the point of overlap is shown in the lower left comer.

FIGURE 7.3 The rotary confocal fluorescence scanner used to detect pCAE chip separations. Laser excitation at 488 nm (100 mW) is directed up through the hollow shaft of a computer-controlled stepper motor, deflected 1.0 cm off-axis by a rhomb prism, and focused on the electrophoresis lanes by a microscope objective. The stepper motor rotates the rhomb/objective assembly just under the lower surface of the microchip at five revo-lutions/s. Fluorescence is collected along the same path and spectrally, and is spatially filtered before impinging on the four-color confocal detector [980]. Reprinted with permission from the American Chemical Society. 

Fig. 12.1. a Schematic diagram of the experimental setup (1) the off-axis //3 parabolic mirror, (2) the laser beam, (3) the specially designed pulsed conical nozzle, (4) the cluster gas jet, (5) the focusing spectrometer with the spherically bent mica crystal, (6) the vacuum-compatible X-ray CCD camera, (7) the ion detector for TOF measurements, b Typical X-ray CCD image measured at an intensity of... 

Fig. 5. Tandem quadrupole acceleration-deceleration mass spectrometer for NRMS studies. A - ion source B - quadrupole mass analyzer C - ion acceleration lens D - neutralization cell E - neutral drift region F - reionization cell G - ion deceleration lens H - energy filter I - quadrupole mass analyzer J - off-axis ion detector K - laser optics L - Ar-ion laser. Inset shows the drift region where residual precursor ions are reflected and the neutral beam overlaps with the laser beam...

Some instruments combine MALLS with 90° scattering at three wavelengths and orthogonal polarities to extend the size range to a lower size than is usually assumed possible for forward light scattering alone. Others use off-axis lasers and detectors to extend the size range... 

Microtrac FRA (Full Range Analyzer) has extended the lower size by using an off-axis low angle array with a separate collector lens in conjunction with the logarithmic line array detector (Figure 10.9). 

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