# Moseley’s Law & Diffraction of X- Rays

♦ Learn about : Moseley’s Law , Diffraction of X- Rays & Uses of X – Rays ♦
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Moseley studied the characteristic X-ray spectrum of a number of a heavy elements, and observed a simple relationship between them. He found that the spectra of different elements are very similar, and with increasing atomic number Z , the spectral lines nearly shift towards shorter wavelength or higher frequencies.

He plotted a graph of the k-series between the square root of frequency (√ν)and atomic number (Z) and found it very approximately to be a straight line.

He therefore concluded that the  square- root of the frequency of a K-line is closely proportional to the atomic number of the element. This is called Moseley’s Law and may be expressed as : a = proportionality constant

b = screening constant

a and b does not depend on the nature of target.

Diffraction of X- Rays :- (1)  According to Laue the wavelength of X-Rays is very small and the atoms in crystals are arranged in form of three dimensional lattice.

(2) The diffraction of X-Rays is not possible by ordinary grating because the size of grating element is much larger than the wavelength of X-Rays.

(3) Diffraction of X-Rays is possible by the crystals. Because the inter atomic spacing in a crystal lattice is of the order of wavelength of X-Rays.

(4) Diffraction of X-Rays was first verified by laue spots.

(5) Diffraction of X-Rays takes place according to Bragg’s law

• (a) 2d sin θ = nλ
• (b) For maximum wavelength nmin = 1

(sin θ)max = 1
λmax = 2d

Uses of X – Rays
(i) In Study of crystal structure

(ii) In Surgery

(iii)  In Medicine

(iv)  In Spying

(v)   In Engineering

(vi)   In Research in the laboratories

(vii)  In Industries