Sunday, July 13, 2008

X-rays - laws and theories

Moseley’s law

Moseley measured the frequencies of characteristic X-rays from large number of elements and plotted the square root of th frequency against its position number in the periodic table.

The observations can be mathematically expressed as

√(v) = a(Z-b)

v = the frequency of characteristic X-rays from the elements\
Z = atomic number
a, b are constants

Bragg’s law

2d sin θ = n λ

d = interplanar spacing of the crystal on which X-rays are incident
θ = is the incident angle at which X-rays are strongly reflected.
n = 1,2,3 …
λ = wave length of X-rays

Application of Bragg’s law:By using a monochromatic X-ray beam (having a single wave length) and noting the angles of strong reflection, the interplanar spacing d and several information about the structure of the solid can be obtained.

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