Mehmet Can ÇAPAR 030070131, 5th week definitions


1-Neutron Diffraction (Measurement techniques)

(Old answer) (Better answer)
Neutron Diffraction (ND) is capable of measuring the elastic strains induced by residual stresses throughout the colume of relatively thick stess components with a spatial resolution as small as 1 mm^3. Such capabilities provide for residuals-tress measurement inside components without sectioning or layer removal. Principal ND methos, as with XRD methods, measure the spacing between crystallographic planes in a component, and this spacing is affected by residual and applied stress. The spacing between a selected set of a crystallographic planes is related to the angle of incidence and diffraction of where teh neutron radiation, which are equal, and the wavelength of the monochromaric radiation by Bragg's Law:

λ= 2 d sin θ

The elastic strain induced bt the residual stress perpendicular to teh diffracting crystallographic plane then is related to d by:

ε= (d-d0)/do= sinθ0(sinθ-sinθ0)

(Totten, G., Howes, M., Inoue, T., Handbook of Resifual Stress and Deformation, 1st Printing, March 2002, pg.113)

(New answer)



Neutron diffraction is the method of choice for many crystallographic experiments. The nature of the scattering of neutrons by atomic species is such that the method offers a description of all atoms in a structure at approximately the same level of precision. This "equivalance" of atoms is due to the  fact that neutrons are scattered by the nucleus rather than tje electrons in an atom, and hence the scattering power does not have the strong dependence on Z found for many other scattering techniques such as X-ray or electron diffraction. The nature of this interaction also means that the scattering power of atoms for neutrons does not fall off with scattering angle, which makes neutron scattering ideal for high resolution studies. Of course,  the scatteredintensity in a diffrection pattern will still decrease at higher angles due to the Debye-Waler factor, but the effect is considerably less severe for neutron experiments. The consequens ability to acces very high resolution data (low values of dhkl-"short d-spacings") makes neutron diffraction a highly preciese method of studying structure.


(Chick C. Wilson, Single crystal neutron diffraction from molecular materials, pg:22-23)