Coolidge X-Ray Tube
Category : JEE Main & Advanced
(1) It consists of a highly evacuated glass tube containing cathode and target (also known as filament type X-ray tube). The cathode consist of a tungsten filament. The filament is coated with oxides of barium or strontium to have an emission of electrons even at low temperature. The filament is surrounded by a molybdenum cylinder kept at negative potential w.r.t. the target.
(2) The target (It is a material of high atomic weight, high melting point and high thermal conductivity) made of tungsten or molybdenum is embedded in a copper block.
(3) The face of the target is set at \[{{45}^{o}}\] to the incident electron stream.
(4) The filament is heated by passing the current through it. A high potential difference (\[\approx \] 10 kV to 80 kV) is applied between the target and cathode to accelerate the electrons which are emitted by filament. The stream of highly energetic electrons are focussed on the target.
(5) Most of the energy of the electrons is converted into heat (above 98%) and only a fraction of the energy of the electrons (about 2%) is used to produce X-rays.
(6) During the operation of the tube, a huge quantity of heat is produced in this target, this heat is conducted through the copper anode to the cooling fins from where it is dissipated by radiation and convection.
(7) Control of intensity of X-rays : Intensity implies the number of X-ray photons produced from the target. The intensity of X-rays emitted is directly proportional to the electrons emitted per second from the filament and this can be increased by increasing the filament current. So intensity of X-rays \[\propto \] Filament current
(8) Control of quality or penetration power of X-rays : Quality of X-rays implies the penetrating power of X-rays, which can be controlled by varying the potential difference between the cathode and the target. For large potential difference, energy of bombarding electrons will be large and hence larger is the penetration power of X-rays.
Types of X-rays
| Hard X-rays | Soft X-rays |
| More penetration power | Less penetration power |
| More frequency of the order of \[\approx {{10}^{19}}\,Hz\] | Less frequency of the order of \[\approx {{10}^{16}}\,Hz\] |
| Lesser wavelength range \[(0.1\,\overset{\text{o}}{\mathop{\text{A}}}\,-4\overset{\text{o}}{\mathop{\text{A}}}\,)\] | More wavelength range \[(4\,\overset{\text{o}}{\mathop{\text{A}}}\,-100\overset{\text{o}}{\mathop{\text{A}}}\,)\] |
You need to login to perform this action.
You will be redirected in
3 sec
