Monochromatic X-ray radiation

Powder X-ray diffraction patterns were recorded in a D-5000 Siemens diffractometer, using nickel-filtered CuK as monochromatic X-ray radiation. The patterns were recorded... 

Characteristic X-rays are introduced in Chapter 2 when discussing monochromatic X-ray radiation for the X-ray diffractometer. It is necessary, however, to further discuss the features of characteristic X-rays in this chapter because they are the essential signals used in X-ray spectroscopy for identifying chemical elements. 

Figure 7.6 Non-monochromatic X-ray radiation from an X-ray gun with an A1 target. The characteristic Alkaline is at about 1.5 keV. (Reproduced with permission from D. Briggs and J.T. Grant, Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications and Surface Spectra Ltd, Chichester. 2003 IM Publications.)...

Figure 6.1 Contributions to the observed profile for monochromatic X ray radiation.

Samples are exposed to monochromatic X-ray radiation (typically with an energy range of 12 keV but energies up to 10 keV may be used) and the characteristic energies of the emitted photoelectrons are measured to reveal information about the elemental composition, elemental distribution, and chemical bonding characteristics of the near surface region. 

Even these small changes may be detected experimentally by removal of electrons from the molecules by monochromatic X-ray radiation and subsequent measurement of the kinetic energy of the removed electrons. Those that were more strongly bound run slower. 

If monochromatic X-rays are used as the ionizing radiation the experimental technique is very similar to that for XPS (Section 8.1.1) except that it is the kinetic energy of the Auger electrons which is to be measured. Alternatively, a monochromatic electron beam may be used to eject an electron. The energy E of an electron in such a beam is given by... 

For the purposes of analytical chemistry, four kinds of monochromatic beams need to be considered. (The quotation marks are to remind the reader that the beams under discussion are not always truly monochromatic.) Three kinds of beams—those produced by Bragg reflection (4.9), filtered beams (4.6), beams in which characteristic lines predominate over a background that can be neglected— will be discussed later ( 6.2). The fourth kind of beam contains monochromatic x-rays that are a by-product of our atomic age and that promise to grow in importance they are given off by radioactive isotopes. These x-rays must not be confused with 7-rays (11.1), which also originate from radioactive atoms but which differ from x-rays because the transformation that leads to radiation involves the nucleus. 

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... 

Monochromatic x-rays are used and the diffracted x-rays are detected by their action on photographic flues or plates. They can also be detected by means of a radiation counter and electronic equipment feeding data to a computer. Since x-rays of a given wavelength are diffracted only for a certain specific orientations of the sample so if the sample is a single crystal it should be placed in all possible orientations during experiment. For this the sample is rotated or oscillated about one of its axes. This can also be achieved by using a sample made as a powder of a very small crystal, in such a powder the minute particles are randomly oriented and all possible orientations are included. 

A variety of alternating copolymers based on H-allyl- and N-(3-ethynylphenyl)maleimides, with substituted styrenes and vinyl ethers, have been prepared and their response to x-ray irradiation studied. Broadband and monochromatic x-ray exposures were conducted at the Stanford Synchrotron Radiation Laboratory. Sensitivities were observed to correlate with mass absorption coefficients of the copolymers and were found to be as high as 5-10 mJ/cm2. Preliminary fine line lithographic studies indicate 0.5 ion resolution capabilities. 

Hieda, K. Hirono, T. Azami, A. Suzuki, M. Furusawa, Y. Maezawa, H. Usami, N. Yokoya, A. Kobayashi, K. Single- and double-strand breaks in pBR322 plasmid DNA by monochromatic X-rays on and off the K-absorption peak of phosphorus. Int. J. Radiat. Biol. 1996, 70 (4), 437-A45. 

Hieda, K. Tomita, M. Takemura, T. Kobayashi, K. Do Auger events of phosphorus by monochromatic X-rays induce DNA double strand breaks efficiently Moriarty, M., Mother-sill, C., Se5unour, C., Edington, M., Ward, J.F., Fry, R.J.M., Eds. Proceedings of 11th International Congress of Radiation Research, Allen Press, 1999 142-145. 

Takakura, K. Auger effects on bromo-deoxyuridine-monophosphate irradiated with monochromatic X-rays around bromine K-absorption edge. Radiat. Environ. Biophys. 1989, 28 (3), 177-184. 

Takakura, K. Maezawa, H. Kobayashi, K. Hieda, K. Strand breaks in DNA in buffered solution induced by monochromatic X-rays around the K-shell absorption edge of phosphorus. In Synchrotron Radiation in Biosciences. Chance, B., Deisenhofer, J., Ebashi, S., Goodhead, D.T., Helliwell, J.R., Huxley, H.E., lizuka, T., Kirz, J., Mitsui, T., Rubenstein, E., Sakabe, N., Schmahl, G., Stuhrmann, H.B., Wuthrich, K., Zaccai, G., Eds. Oxford University Press Oxford, 1994 756-764 pp. 

A major recent innovation has been to use substrates that are unreactive but may be activated by, for example, photolysis (see Chapter 6). This has necessitated the introduction of crystallographic procedures that can gather data in fractions of a second, rather than the minutes or hours conventionally used. Conventional protein crystallography uses a beam of monochromatic x-rays. An older technique that has been reintroduced is that of von Laue, which uses a spectrum of polychromatic radiation. An intense beam from a synchrotron, spanning wavelengths from 0.25 to 2.5 A, enables data for the Laue method to be taken over a fraction of a second.46,47... 

The XPS spectra were recorded on a Surface Science Laboratories small spot system using a monochromatized A1K X-ray radiation source. The take-off angle used for these measurements was 35°. Full details of the methods used in interpreting the XPS data have been described elsewhere [14], Data reduction was done using Surface Science Laboratories software version 8.0. This software utilizes a least squares curve fitting approach with only chi square statistics for goodness of the calculated fit to the experimental data. 

---