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The Small-angle X-Ray Scattering Investigation of Advanced Beryllium Materials

The small-angle X-ray scattering (SAXS) technique allows to determine size distributions of inhomogeneities in materials and to predict their properties in Xray optics devices. A number of beryllium materials for the manufacturing of X-ray optics (refractive lenses and speckle suppressors) have been studied by the SAXS. Various composite materials based on porous beryllium have been studied. The effect of adding detonation nanodiamonds to the beryllium matrix on the scattering ability of the material is discussed.


INTRODUCTION
Small angle X-ray scattering (SAXS) is a non-destructive technique for investigation of distribution of inhomogeneities in materials at resolution from angstroems to hundred nanometers. The technique is based on the analysis of X-ray scattering intensity from fluctuations of electron density at small angles (less 10 ∘ ). Investigation of features of SAXS images gives one information of distribution and particle (pore) size which allows to predict properties of X-ray optics devices. Recently it was reported [1,2] that manufacturing technology of metallic beryllium influence SAXS features, and some recommendations of using beryllium materials for fabrication of composite refractive lenses (CRL) were given.
X-ray radiation is typically obtained with X-ray tubes and at synchrotron stations.
Synchrotron sources provide beams of high intensity, brightness, degree of polarization and coherence. The use of X-ray optics devices may significantly increase the informative value of X-ray research results. Beryllium is one of the most important materials for X-ray optics, in particular, for refractive lenses. It is also promising for manufacturing various X-ray filters, especially speckle-suppressors [3,4], which are produced from ultradisperse materials that allow to diffuse x-ray radiation and obtain images without speckles. Such ultra disperse materials, e.g. a spinning thin disc or amorphous boron powder, were used earlier as effective x-ray diffusers [4]. Using a rotating random-phase screen allows to reduce the degree of radiation coherence and enhance speckle elimination in transmission images [5]. Speckle-suppressor using porous beryllium was demonstrated efficiency of porous beryllium due to its high level of X-ray scattering. It is known that the solid dense beryllium has a relatively low scattering and absorption of X-rays in the range of low energies. For example the absorption of the 1 mm nanoberyllium plate is about 1% at 12 keV [3]. The use of speckle-suppressor with porous beryllium makes it possible to significantly increase the scattering and thus to destroy the beam coherence and to supress image speckles. Thus porous beryllium may be considered an advanced media for X-ray optics intended for shading corrections. For the material to be effective, it is necessary to reduce dimensions of structural inhomogeneities which is to increase the scattering ability. This may be achieved by injection of nanosize particles with a different electron density into the porous structure.

Materials
Detonation nanodiamonds (DND) with characteristic sizes from 4 to 6 nm as a component for the modification of porous beryllium are of a particular interest [6]. Nanodiamonds powder is usually manufactured as an explosion product of carbon-containing explosive [6].
The porous beryllium samples with different contents of nanodiamonds were manufactured and studied (

Techniques
The measurements of X-ray scattering intensity were performed on an automatic small-angle x-ray diffractometer "AMUR-K" which is equipped with a linear position- Experimental data were normalized by intensity of incident X-ray beam. After that a correction of collimation distortions were performed following by subtraction of scattering from empty chamber to compensate residual intensity of the primary beam [8]. The measure procedure was carried out in certified techniques that are approved for «AMUR-K» installation [9,10].
The calculation of size distribution of inhomogeneities was performed using the program POLYMIX which is an advanced version of the program MIXTURE, which, in turn, is included in the package ATSAS [11].

EXPERIMENTAL RESULTS AND DISCUSSION
Scattering curves are presented in Fig. 1 and 2. One could observe increasing SAXS intensity in the range from 0.5 to 2.5 nm −1 with the growth of nanodiamond concentration. This correlates with the shape of scattering image obtained from the pure nanodiamond powder. (Fig. 1).
It is interesting to note that in the region of very small angles at s < 0.05 nm −1 , the scattering intensity of beryllium composite samples with a nanodiamonds content 45-55%wt significantly exceeds the scattering intensity of each of materials (nanodiamond powder and porous beryllium without nanodiamonds) individually (Fig. 2).
The occurrence of submicron inhomogeineties in the porous Be matrix should increase scattering from beryllium composite in the region close to central beam which, together with the enhancing of wide-angle scattering provided by nanodimand phase, should increase efficiency of the material as a speckle-suppressor. A further studying of inhomogeneities distribution at sizes greater than 50 -100 nm will be performed at synchrotron facilities of ultra-small-angle scattering.