Rotating anodes

Unlike for synchrotron radiation, the maximum iatensity of x-rays from an x-ray tube is limited by how fast heat can be removed from the target to prevent its melting. In a conventional sealed tube, the target is stationary, relatively small, and must be continually cooled with water. In a rotating anode tube, the target is larger and is continually rotated so that the heat can be distributed over a larger surface. With such a tube the amount of heat, and hence. 

A very narrow window produces monochromatic radiation that is still several orders of magnitude more intense than the beam from conventional rotating anode x-ray sources. Sucb beams allow crystallographers to record diffraction patterns from very small crystals of the order of 50 micrometers or smaller. In addition, the diffraction pattern extends to higher resolution and consequently more accurate structural details are obtained as described later in this chapter. The availability and use of such beams have increased enormously in recent years and have greatly facilitated the x-ray determination of protein structures. 

Sealed conventional fine structure tubes with Mo, W, Cu, or Cr anodes are used as primary X-ray sources, as well as rotating anode tubes, or synchrotron radiation. The maximum energy of the X-ray quanta determines the range of elements acces-... 

The SAXS intensity distribution was measured with a rotating anode x-ray generator (Rigaku Denki, Rotaflex, RTP 300 RC) operated at 40 kV and 100 mA. The x-ray source was monochrolmatized to CuK (A = 0.154 nm) radiation. The SAXS patterns were taken with a fine-focused x-ray source using a flat plate camera (Rigaku Denki, RU-lOO). In the measurement of the solution sample, we used a glass capillary (< = 2.0 mm Mark-Rohrchen Ltd.) as a holder vessel. 

Other techniques utilize various types of radiation for the investigation of polymer surfaces (Fig. 2). X-ray photoelectron spectroscopy (XPS) has been known in surface analysis for approximately 23 years and is widely applied for the analysis of the chemical composition of polymer surfaces. It is more commonly referred to as electron spectroscopy for chemical analysis (ESCA) [22]. It is a very widespread technique for surface analysis since a wide range of information can be obtained. The surface is exposed to monochromatic X-rays from e.g. a rotating anode generator or a synchrotron source and the energy spectrum of electrons emitted... 

The diffractometer has gradually evolved in terms of maximum power of sealed X-ray tubes, rotating anodes, new X-ray optics, better detector efficiency, position-sensitive detection and, lately, real-time multiple-strip (RTMS) fast X-ray detection, which replaces a single detector by an integrated array of parallel detectors to provide an up to 100-fold increase in efficiency compared with traditional detectors without compromise on resolution. Time-resolved powder diffraction is... 

A variant of the typical X-ray tube described above is the rotating anode, which is capable of generating much higher intensities. Although rotating anode sources can and have been used in EXAFS experiments, the intensities are of such magnitude that data acquisition for extended periods of time is required and their application is furthermore limited to bulk samples. 

The progress achieved is closely linked to the development of both powerful detectors and brilliant X-ray sources (synchrotron radiation, rotating anode). Such point-focus equipment has replaced older slit-focus equipment (Kratky camera, Rigaku-Denki camera) in many laboratories, and the next step of instrumental progress is already discernible. With the X-ray free electron laser (XFEL) it will become possible to study very fast processes like the structure relaxation of elastomers after the removal of mechanical load. 

Rotating anode, conventional optics Rotating anode, Gobel mirror optics Synchrotron, bending magnet (DORIS, A2) Synchrotron, insertion device (ESRF, ID2)... 

The usability of the various available machines, in particular in regard to time-resolved measurements, is proportional to the flux that they are able to shine on the sample. Table 4.1 shows typical data. Modern laboratory instrumentation (rotating anode) is approaching the performance of older synchrotron light sources. 

Figure 4.2. Sketch of a laboratory setup comprising a rotating anode, conventional beam shaping optics, and an X-ray camera with the sample in normal-transmission geometry...

A rotating anode setup resembles a typical synchrotron beamline on a laboratory scale, and some progress concerning the optimum design of rotating setups was made by transferring sophisticated techniques for the optimization of beamline optics (Pedersen [72]) to rotating anode equipment. 

The maximum power of a conventional X-ray tube is 2.4 kW for broad focus (approx.. 2x 12 mm focal spot size). Modern rotating anodes consume 18 kW and deliver fine focus (approx.. 0.1 x 1 mm focal spot size). Most important for high intensity is not the power consumption, but the product of focal spot power density and focal spot size or, more accurately, the flux on the sample measured in photons/s (cf. Sect. 7.6). 

When the experiment has been set up at the beamline or the rotating anode, it is important to collect a complete set of data for later evaluation or the experiment will have to be repeated. Do not expect to be satisfied after the first time, because the collection of complete data is a matter of experience. The intention of this chapter is to reduce the number of repetitions. 

Typical exposure time is 4 - 8 hours using a rotating anode source, Gobel mirror, and a bent ID detector for simultaneous recording of the complete curve. 

Rotating electrode cell Wilson Process Systems Rotating cylindrical foil (usually stainless steel) or static cylindrical foil with rotating anode (larger cells) Discontinuous by manual scraping or flexing No V V ... 

Rotary style valves, 20 685 Rotary tackmeters, 14 316 Rotary tumble dryers, 18 732 Rotary vane pumps, 21 71 Rotating anode X-ray tube, 26 413 Rotating arc reactor, 1 211-213 Rotating biological contactor defined, 3 759t... 

A 0.4 m thick SPP layer was exposed to X-rays followed by a flood exposure using near UV radiation. The resist was then dip-developed in a 0.8 wt% TMAH solution for 60 s at 25 °C. We used two x-ray exposure systems to evaluate the characteristics of the SPP resist. One is SR-114 which has a source composed of a molybdenum rotating anode with a 0.54 nm Mo-La characteristic line. The exposure was carried out in air. The other has a synchrotron radiation source with a central wavelength of 0.7 nm (KEK Photon Factory Beam Line, BL-1B). The exposure was carried out in vacuum (<10-4 Pa). A positive resist, FBM-G,15) was used as a standard, because its sensitivity only weakly depends on the ambient. 

X-rays are commonly generated in three ways using a sealed tube, a rotating anode, or a synchrotron source. The use of sealed tubes is very uncommon, as both rotating anodes and synchrotron sources have greatly superior performance sealed tubes are thus not discussed here. 

The XAS spectrometer is similar to a UV-visible system in that it consists of a source, a monochromator, and a detector. The most favorable XAS source, synchrotron radiation, is tunable to different wavelengths of desirable high intensity. A laboratory instrument for analysis of solids and concentrated solutions may use a rotating anode source (further described in Section 3.3). The monochromator for X-ray radiation usually consists of silicon single crystals. The crystals can be rotated so that the wavelength ( i) of the X-rays produced depends of the angle of incidence (0) with a Bragg lattice plane of... 

---