Synchrotron radiation brilliance

The use of synchrotron radiation overcomes some of the limitations of the conventional technique. The high brilliance of up to 10 ° photons s mm mrad /0.1% bandwidth of energy, and the extremely collimated synchrotron beam lead to a large flux of photons through a very small cross section (0.1-1 mm ). This allows measurements with samples of small volume if isotopi-cally enriched (with the relevant Mossbauer isotope, e.g., Fe). Measurements that were described earlier [4] and that require a polarized Mossbauer source now become experimentally more feasible by making use of the polarization of the synchrotron radiation. Additionally, the energy can be tuned over a wide range. This facilitates measurements with those Mossbauer nuclei for which conventional sources are available but with life times that are too short for most experimental purposes, e.g., 99 min for Co —> Ni and 78 h for Ga —> Zn. 

According to Coppens et al. [12], intensities of the monochromatic beam at the sample table as high as 6 x 1011 photons mm"2 s-1 can be obtained with the best synchrotron sources, while the flux achieved with sealed tubes is approximately 109 photons mm-2 s"1. Furthermore, the increase in brilliance is of 6 to 10 orders of magnitude as compared to sealed tubes. A few months ago the European Synchrotron Radiation Facility (ESEF) at Grenoble became operational and now offers fluxes several orders of magnitude larger than those ever obtained. 

Fig. 19. Comparison of the average spectral brilliance of different synchrotron radiation sources ...

Numerous experimental setups to perform GIXS were recently described in the open literature [31-34]. We just recall that in almost all cases, a high brilliance synchrotron radiation X-ray beam is needed, especially from 3 generation synchrotron radiation sources like the ESRF in Grenoble (France), and they always couple a large UHV chamber with standard sample preparation with a heavy duty high precision goniometer that allows the orientation of the sample and the detector. 

The last few decades of the 20 century transformed the powder diffraction experiment from a technique familiar to a few into one of the most broadly practicable analytical diffraction experiments, particularly because of the availability of a much greater variety of sources of radiation -sealed and rotating anode x-ray tubes were supplemented by intense neutron and brilliant synchrotron radiation sources. Without a doubt, the accessibility of both neutron and synchrotron radiation sources started a revolution in powder diffraction, especially with respect to previously unimaginable kinds of information that can be extracted from a one-dimensional projection of the three-dimensional reciprocal lattice of a crystal. Yet powder diffraction fundamentals remain the same, no matter what is the brilliancy of the source of particles or x-ray photons employed to produce diffraction peaks, and how basic or how advanced is the method used to record the powder diffraction data. 

The present modern positon-sensitive counters in general cope with the scattering intensity produced at the present synchrotron radiation sources. As an increase of the brilliance of synchrotron radiation by 1000 to 10000 is expected with planned electron storage rings, considerable effort has to go into the development of area detectors and their read-out systems. 

Fig. 10. Brilliance of the X-rays as a function of photon energy from a bending magnet and from a Wiggler beam line at the Stanford Synchrotron Radiation Laboratory. Notice the difference in the flux between the bending and the Wiggle magnets. [Adapted from A. Bienenstock, Nucl. Instrum. Methods 172, 13 (1980).]...

The nuclear resonant inelastic and quasi-elastic scattering method has distinct features favorable for studies concerning the microscopic dynamics (i.e., lattice vibration, diffusion, and molecular rotation) of materials. One advantageous feature is the ability to measure the element-specific dynamics of condensed matter. For example, in solids the partial phonon density of states can be measured. Furthermore, measurements under exotic conditions -such as high pressure, small samples, and thin films - are possible because of the high brilliance of synchrotron radiation. (For the definition of brilliance, see O Sect. 50.3.4.5 of Chap. 50, Vol. 5, on Particle Accelerators. ) This method is applicable not only to solids but also to liquids and gases, and there is no limitation concerning the sample temperature. 

The high brilliance of synchrotron radiation makes possible the phonon density of states to be measured even for small samples. The measurement of the phonon density of states under high pressures using a diamond anvil cell (DAC), where the sample size is usually below 1 mm, is effective for studying the core of earth and has been performed by Lubbers et al. (2000), Mao et al. (2001), and Lin et al. (2005). 

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