Explanation
By changing the filament current with the help of rheostat, thermionic emission intensity of X-rays can be changed.
Applied voltage must be greater than binding energy.
The potential difference across the filament and target determines the energy and hence the penetrating power of X-rays.
The energy of X-ray photon is obtained from a coolidge tube by an electronic transition of target atom such as Kα line is obtained from transition from L orbit in K orbit.
Hard X-rays are of higher energy and the energy of X-rays depends on the potential difference between the cathode and the target.
Penetration is directly proportional to the energy of radiations.
When applied voltage is greater then energy of K-electron, continuous and all characterstic X-rays arc emitted.
When current through the filament increases, number of emitted electrons also increases. Hence intensity of X-ray increases but no effect on penetration power.
In the presence of inert gas photoelectron emitted by cathode ionise the gas by collision and hence the current increases.
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