W/SiC x-ray multilayers optimized for use above 100 keV

Abstract

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100 -200 keV. Grazing-incidence x-ray reflectance at E ϭ 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W͞SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range Eϳ150 -170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E ϭ 120 -180 keV. We describe our experimental investigation in detail, compare the new W͞SiC multilayers with both W͞Si and W͞B 4 C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.

Optical constants for hard x-ray multilayers over the energy range E = 35 - 180 keV

“…Previously we measured the reflectance of prototype hard X-ray W/Si and W/SiC multilayers designed for use above 100 keV; we found that the measured reflectance did not agree well with calculations of the expected performance made using optical constants determined from theoretical atomic scattering factors and mass absorption coefficients. We were able to get better agreement however with calculations made using experimentally derived optical constants measured over the energy range E = 120 -180 keV, which we determined for W and SiC, as well as for Ni .93 V .07 and B 4 C. 6 The discrepancy between the measured and theoretical optical constants can be partly attributed to incoherent (Compton) scattering, which is a particular concern especially for lighter elements at these energies, and which might not be properly accounted for in the available scattering factors and mass absorption coefficients.…”

Gamma-ray Imaging Methods

“…The -in terms of imaging -ideal gamma-ray imager, a gamma-ray lens, is very difficult to realize due to the small angle of total reflection for gamma rays. Multilayer, diffractive optics systems have been built which are able to focus gamma rays up to 160 keV, however, these systems are characterized by a large focal length and very small field-of-view [9]. The FOV is typically less than 1 deg.…”

Characterization of trace embedded impurities in thin multilayer structures using synchrotron X‐ray standing waves

“…A multilayer structure consists of thin layers of alternating elements or compounds. [6,7] These multilayer materials offer unique structural, [8] magnetic [9,10] and electronic [11,12] properties for a wide range of applications. A multilayer structure such as an X-ray optical element is used in many technological applications like in X-ray astronomy, microscopy, spectroscopy, and as filters and monochromators for synchrotron radiation and free electron X-ray lasers.…”