Deflecting

If a shallow kick off in soft formation is required (e.g. to steer the borehole away underneath platforms) a technique using jet bit deflection or badgering is employed (Fig. 3.16). A rock bit is fitted with two small and one large jet. With the bit on bottom and oriented in the desired direction the string is kept stationary and mud is pumped through the nozzles. This causes asymmetric erosion of the borehole beneath the larger jet. Once sufficient hole has been jetted, the drill bit will be rotated again and the new course followed. This process will be repeated until the planned deviation is reached. 

To deflect the bit in the desired direction a bent sub (w th typically 1° to 2° bend) which can be oriented from surface is inserted in the string just above the motor. 

Application of ceramics allows using stainless steel as vacuum envelope. No surface charges ean deflect the electron beam. Mechanical elements and functions can be easily integrated into the envelope due to its stability. 

The physics of X-ray refraction are analogous to the well known refraction of light by optical lenses and prisms, governed by Snell s law. The special feature is the deflection at very small angles of few minutes of arc, as the refractive index of X-rays in matter is nearly one. Due to the density differences at inner surfaces most of the incident X-rays are deflected [1]. As the scattered intensity of refraction is proportional to the specific surface of a sample, a reference standard gives a quantitative measure for analytical determinations. 

The X-ray instrumentation requires a commercial small angle X-ray camera, a standard fine structure X-ray generator and a sample manipulator if scanning is requested. The essential signal is the relative difference between the refraction level Ir and the absorption level Ia. Both levels are measured simultaneously by two scintillation detectors. At fixed angles of deflection this signal depends solely on the inner surface density factor C and thickness d of the sample [2] ... 

Fig. VI-4. Illustration of the surface force apparatus with the crossed-cylinder geometry shown as an inset. The surface separations are determined from the interference fringes from white light travelling vertically through the apparatus. At each separation, the force is determined from the deflection in the force measuring spring. For solution studies, the entire chamber is filled with liquid. (From Ref. 29.)...

AFM Atomic force microscopy [9, 47, 99] Force measured by cantilever deflection as probe scans the surface Surface structure... 

Figure Bl.7.4. Schematic diagram of a reverse geometry (BE) magnetic sector mass spectrometer ion source (1) focusing lens (2) magnetic sector (3) field-free region (4) beam resolving slits (5) electrostatic sector (6) electron multiplier detector (7). Second field-free region components collision cells (8) and beam deflection electrodes (9).

Probably the simplest mass spectrometer is the time-of-fiight (TOP) instrument [36]. Aside from magnetic deflection instruments, these were among the first mass spectrometers developed. The mass range is theoretically infinite, though in practice there are upper limits that are governed by electronics and ion source considerations. In chemical physics and physical chemistry, TOP instniments often are operated at lower resolving power than analytical instniments. Because of their simplicity, they have been used in many spectroscopic apparatus as detectors for electrons and ions. Many of these teclmiques are included as chapters unto themselves in this book, and they will only be briefly described here. 

Diffraction is the deflection of beams of radiation due to interference of waves that interact with objects whose size is of the same order of magnitude as the wavelengths. Molecules and solids typically have... 

Coincidence experiments explicitly require knowledge of the time correlation between two events. Consider the example of electron impact ionization of an atom, figure Bl.10.7. A single incident electron strikes a target atom or molecule and ejects an electron from it. The incident electron is deflected by the collision and is identified as the scattered electron. Since the scattered and ejected electrons arise from the same event, there is a time correlation... 

Figure Bl.19.16. Schematic view of the force sensor for an AFM. The essential features are a tip, shown as a rounded cone, a spring, and some device to measure the deflection of the spring. (Taken from [74], figure 6.)...

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

Figure Bl.19.34. Cantilever deflection and corresponding frictional force in the v-direction as a fiinction of sample position as a mica sample is scaimed back and forth under a tungsten tip. (Taken from [124], figure 2.)...

Meyer G and Amer N M 1990 Simultaneous measurement of lateral and normal forces with an optical-beam-deflection atomic force microscope Appl. Phys. Lett. 57 2089... 

Figure Bl.20.1. Direct force measurement via deflection of an elastic spring—essential design features of a direct force measurement apparatus.

To measure friction and shear response, one has to laterally drive one surface and simultaneously measure the response of a lateral spring mount. A variety of versions have been devised. Lateral drives are often based on piezoelectric or bimorph deflection [13, 71] or DC motor drives, whereas the response can be measured via strain gauges, bimorphs, capacitive or optical detection. 

The critical requirements for the ion source are that the ions have a small energy spread, there are no fast neutrals in the beam and the available energy is 1-10 keV. Both noble gas and alkali ion sources are conunon. Por TOP experunents, it is necessary to pulse the ion beam by deflecting it past an aperture. A beam line for such experiments is shown in figure B1.23.5 it is capable of producing ion pulse widths of 15 ns. 

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