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Study of the structure of bone by X-ray absorption spectroscopy (XAS) (CAT#: STEM-ST-0242-WXH)

Introduction

Bone is one of the most important biological structures in the field of biomineralization. From the viewpoint of a materials scientist, bone is a composite of an organic and an inorganic phase with highly hierarchical structure. Its main building blocks are long collagen fibrils of about 100-nm diameter that contain nanometer-sized carbonated apatite crystals (‘dahllite’). There is a clear relationship between the weight fraction of the mineral phase in bone and its mechanical properties. The skeletal system in vertebrates is subject to continuous dissolution and formation (‘remodeling’) by osteoclasts and osteoblasts.




Principle

X-ray spectroscopy works on the principle of the excitation of core electrons that are orbiting in the lower shell(s). As the electron absorbs x-rays, it becomes excited and jumps to a higher level. The X-ray region used ranges from 1 to 100 nm. When x-rays interact with electrons it excites electrons to the higher levels. Energy absorbed by the electrons has a characteristic value for each element one can distinguish with the X-ray absorption spectrum.
X-ray absorption spectroscopy (XAS) is the measurement of transitions from core electronic states of the metal to the excited electronic states (LUMO) and the continuum; the former is known as X-ray absorption near-edge structure (XANES), and the latter as extended X-ray absorption fine structure (EXAFS) which studies the fine structure in the absorption at energies greater than the threshold for electron release. These two methods give complementary structural information, the XANES spectra reporting electronic structure and symmetry of the metal site, and the EXAFS reporting numbers, types, and distances to ligands and neighboring atoms from the absorbing element

Applications

X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter.

Materials

• X-ray generating equipment (X-ray tube)
• Collimators
• Monochromators
• X-ray detectors