High intensity tubes

Conventional sealed tnbes are used at powers of about a few hundred Watts per square millimeter. In such conditions, the necessary exposure times, although highly dependent on the type of detector used and on the geometric configuration of the system, are commonly from a few tens of minutes up to several hours long (sometimes several days). It is important to reduce these exposure times, particularly when the samples are not stable or when conducting kinetic studies of structural evolution. It then becomes necessary to use a source of high intensity X-ray beams. 

The method commonly used consists of using a rotating anode tube. This rotation, which is done at high speeds (2,000 to 6,000 rpm), makes it possible to work at powers of several thousand Watts per square millimeter. 

We can show that the performances of such a tube are proportional to aVbv, where a and b are the dimensions of the electron spot and v is the anode s surface speed. The increase in power therefore implies an increase either of the diameter or of the anticathode s rotation speed. 

The anode is a hollow cylinder, typically about 10 cm in diameter, rotating at several thousand revolutions per minute in a vacuum of roughly lO Torr with a steady circulation of water at a typical flow rate of 20 liters per minute. Usually, a tuibomolecular pump is used for maintaining the very low pressure inside the tube. 

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Electron beam sterilisation is a high-voltage potential established between a cathode and an anode in an evacuated tube. The cathode emits electrons, as a cathodic ray or electron beam. A high intensity of electrons is produced. These electrons are accelerated to extremely high velocities. These accelerated electron intensities have great potential as a bacteriocide. Most electron beams operate in a vacuum. As a result the unwanted organisms in the media vanish and the media is sterilised. 

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). 

The first high-intensity sodium lamp was introduced in Europe in 1931. Figure 9.26 shows a schematic view of a sodium lamp it comprises a glass shell containing sodium vapour at low pressure, metal electrodes to generate a current, and neon gas. The pressure inside the tube is at a relatively low pressure of 30 Pa, so some of the sodium evaporates to become a vapour. The inner side of the lamp is coated with the remainder of the metallic sodium as a thin film. 

Figure 2.19 A detailed plot of the spectrum from a Cu X-ray tube, in the vicinity of the K lines, showing the area selected by the high resolution and high intensity settings of the beam conditioner shown in Figure 2,20...

In the discussion of the same paper (pp 286-8) M. Norrish suggested generation of shock waves by adiabatic heating of an isolated section of a gas sample by flash irradiation. Thus a H2/O2 mixture with a trace of NO2 as a sensitizer (and no added coolant gas) could be subjected to a high- intensity flash.at one end of a quartz tube, the rest of the tube (to the extent of possibly 5/6) being blacked out. In such a detonation, Thrush (Ref 8a) has observed the emission... 

Postcolumn photochemical reactions are another approach to the detection problem. High-intensity UV light, generally provided by a Hg or Zn lamp, photolyzes the HPLC effluent, which passes through a Teflon (47) or quartz tube. The photolysis reaction determines the nature of the subsequent detection. If the compound has a UV chromophore, such as an aromatic ring, and an ionizable heteroatom, such as chlorine, then the products of the reaction can be detected conductometrically. Busch et al. (48) have examined more than 40 environmental pollutants for applicability to detection with photolysis and conductance detection. Haeberer and Scott (49) found the photoconductivity approach superior to precolumn derivatization for the determination of nitrosoamines in water and waste water. The primary limitation of this detection approach results from the inability to use mobile phases that contain ionic modifiers, that is, buffers and... 

The current availability of small portable 14 MeV neutron generators and the future availability of high intensity 252Cf spontaneous fission neutron sources will certainly result in the wide spread use of activation techniques for non-destructive "on-stream" product analysis in industry. The cost of the required instrumentation for many types of activation analysis is not excessive, as compared to the cost of other modem analytical instrumentation. The simple off-on operation of the new sealed-tube neutron generators and minimal maintenance associated with the use of an isotopic Z5ZCf neutron source will permit operation of the analytical facility with technician-level personnel. The versatility of the activation technique justifies its inclusion among the other major analytical techniques employed in any modem analytical facility. 

The research at MIT has been done in the cold-wall vertical tube reactor shown in Figure 14. The wafer is aligned almost parallel to the flow on a vertical silicon carbide-coated susceptor. The wafer is heated by optical radiation from high-intensity lamps to a temperature of 775°C. Silane was introduced... 

As a variant of the end-on arrangement shown in Fig. 3.5-8d, the sample cuvette may be made very long, e.g., as a quartz tube of some tenths of a millimeter in diameter and several meters long. It can be used for trace analyses and for producing a very strong Raman spectrum with an unexpected high intensity of over- and combination tones (Schrader, 1960 Walrafen and Stone, 1972 Walrafen, 1974 Kiefer, 1977 Schmid and Schrotter, 1981). 

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