Generators, rotating-anode x-ray

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. 

We do not always need a synchrotron or a rotating anode X-ray generator to... 

A more recent addition to the diverse array of x-ray based methods is x-ray absorption spectroscopy. In contrast to x-ray diffraction methods which derive their utility from the properties of well defined crystallites, x-ray absorption methods are atomic probes, capable of obtaining both electronic and structural information about a specific type of atom. The growing use of x-ray absorption methods is a result of the greater availability of synchrotron radiation sources which provide the intense broad band x-radiation required. In some instances laboratory based spectrometers utilizing either sealed tubes or rotating anode x-ray generators can also be used. 

Although the local count rate is limited by the space charge effect, as we have seen before, it is the read-out system which will be the limiting component of the system as a whole. Certainly with synchrotron radiation as a source, but already with a rotating anode X-ray generator, area detector systems will be saturated quickly. In addition, the demands concerning the data acquisition system become even more stringent. 

The system with a slow scan read-out is now routinely in use for SAXS-experiments on a rotating anode X-ray generator. 

Rotating anode X-ray generators, one of which is shown in Figure 7.3, have an arrangement of cathode and anode essentially the same as for the sealed tubes described above. The tubes, however, are not evacuated and sealed, but continuously pumped by a diffusion pump backed by a conventional roughing pump. The environment is therefore the same as the inside of the sealed tube. The second important feature of the rotating anode device is exactly that implied by its name. The anode, which is a hollow disc of copper (usually) several inches in diameter, is rotated at 3000 to 6000 rpm by an external motor so that the beam of electrons emitted from the cathode falls on a continuously changing surface. Water,... 

FIGURE 7.3 A modern rotating anode X-ray generator used in most laboratories to produce CuKa radiation. An image of the actual anode is shown in background. (Courtesy of Rigaku America Corp.)... 

In order to detect the diffraction data very rapidly, we have made a new photoncounting X-ray detector, MSGC, whose size is 10 cm x 10 cm. The detector can record one-shot data within 1 ms. If the crystal was rotated around the -axis on the four-circle diffractometer using the rotating anode X-ray generator and the MSGC detector, all the intensity data of a standard single crystal were collected within... 

For native RCs from the R26 and 2.4.1 strains, data collection has been previously described (1,3). For RCs with 1 quinone and RCs with terbutryn, data were collected using a multiwire area detector (7) mounted on a Rigaku rotating anode x-ray generator. Processing of these data utilized the ROCKS crystallographic package (8). T e results of data collection are summarized in Table 1. 

The combination of the rotating anode X-ray generators which are nowadays very stable, the robust one-, two-, three-, or four-circle singlecrystal diffractometers, the area detectors (image plate, wire counters, or CCD), and powerful PCs make solving the crystal structure of a mediumsized molecule a job of a few hours, of a few days, or exceptionally of a week for crystals that are relatively small (< 50 pm in one or all dimensions) and/or show greater disorder. 

The second group developed a new detector which can collect a whole intensity data of a crystal within a second. They succeeded that a whole intensity data of a standard sample were collected within 2 s and the structure was successfully analyzed, using the new gas detector developed, MSGC, and a rotating anode X-ray generator [58]. A crystal of the Pn complex was mounted on the diffractometer with... 

Small-angle X-ray scattering experiments were performed by a small-angle camera using Cu IC, characteristic line from a rotating anode X-ray generator (Rigaku, RU-200) at the power of 50 kV and 150 mA. We used a one-dimensional position-sensitive proportional counter (MAC science, PSPC-5) to measure the scattered beam. Temperature was controlled by a personal computer within an accuracy of 0.01 °C. 

The collimated beams, smooth energy spectrum, and high intensity of synchrotron radiation sources offer compelling advantages for XAFS experiments, compared to conventional fixed and rotating anode X-ray generators, although the latter are useful in some situations. 

---