X-rays were discovered accidentally by Rontgen in 1895. The first Nobel Prize was awarded to Rontgen in 1901. This highly penetrating electromagnetic radiation has proved to be a very powerful tool to study the crystal structure, in material research, in the radiography of metals and in medical sciences. Laue, Henry and Lawrence Bragg, Barkla, Siegbahn were some of the Nobel Laureates who have made contribution to these studied. Gamma ray spectroscopy and electron-spectroscopy were some of the spin-offs of these studies apart from the discovery of elements.
Experimental production of X-rays and the Bragg spectrometer:
Electrons from a a heated element were accelerated by very high potential and made to impinge on the target (anode). The X-rays produced are collimated by parallel plates and are incident on a crystal (LiF, quartz, diamond, etc.) As the inter-atomic distance is of the same order as the wavelength of X-rays diffraction is produced and they are detected by counters or photographic plates.
PROPERTIES OF X-RAYS
(i) Short wavelength (0.1 A° to 1 A°) electromagnetic radiation.
(ii) Are produced when a metal anode is bombarded by very high energy electrons.
(iii) Are not affected by electric and magnetic field.
(iv) They cause photoelectric emission.
Characteristics equation eV = hvm
e = electron charge;
V = accelerating potential
vm= maximum frequency of X radiation
(v) Intensity of X – rays depends on number of electrons hitting the target.
(vi) Cut off wavelength or minimum wavelength, where v(in volts) is the p.d. applied t
(ix) Bragg’s Law 2 d sin theta= n lemda
(theta = angle for max intensity)
Note: (a) Binding energy = – [Total Mechanical Energy]
(b) Vel. of electron in nth orbit for hydrogen atom
c = speed of light.
(c) For x – rays
(d) Series limit of series means minimum wave length of that series.
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