HOW IT WORKS?
X-rays are electromagnetic radiation of wavelength of the order of 10‑10m to 10‑9 m.
X-rays have the following characteristics:
· It has high penetration power.
· It can darken photographic plates.
X-rays are produced when fast electrons collide with a heavy metal target in an x-ray tube.
X-ray of minimum wavelength is produced when the kinetic energy gained by an electron after being accelerated by a potential difference is completely converted into a photon of x-ray.
More than 90% of total kinetic energy of the accelerated electrons is converted into heat.
X-rays produced by an x-ray tube form a spectrum consists of:
· A continuous spectrum of various wavelengths.
· Characteristic line spectra. These spectra consist of a number of wavelengths of very high intensity.
Fast electrons from the cathode are decelerated on collisions with the target. Different percentages of the kinetic energy of the electrons are converted into x-ray photons. These x-ray photons of different wavelengths form the continuous spectrum.
A photon of characteristics line spectrum is produced when:
· An electron in the inner shell of the target atom is ejected by the fast electron from the cathode.
· The vacancy in the inner shell is filled by an electron from an outer shell. The difference in the energy is radiated as a photon of the line x-ray.
The wavelengths of x-ray in the line spectrum are characteristic of metal used as target in the x-ray tube.
X-rays can be diffracted by a crystal because:
· Atoms in the crystal are uniformly arranged in atomic planes.
· Separation between atoms in the crystal is of the same order of magnitude as the wavelength of the x-ray.