Coolidge X-ray tube & Application of X-rays
Coolidge X-ray tube
It consist of vacuum glass chamber in which filament is
connected to negative terminal of the battery (in several KV) & Copper
block is connected to the positive terminal of the battery. An arrangement is
made to heat the filament through heating coil which is connected to a small
battery (5-10 V). The front of the copper block is coated with tungsten. A
cooling arrangement is made at the back of copper block.
Working
When voltage is applied to the heating coil; heat is
generated. This heat; heated up the filament & because of thermionic
emission; filament generate electrons which have very low kinetic energy. When
these electrons comes out from filament, due to very high electric field between
anode (Target) & cathode (filament); these electrons get accelerated &
moves with very high kinetic energy towards the target. Electrons with high Kinetic
energy strike the target & X-rays are produced. Only few (say 1%) are
converted into x-rays rest are converted into heat & that’s why cooling
arrangement is made. The intensity of x-rays depends upon rate of emission of
electrons from filament.
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Expression for minimum wavelength (λₘₗₙ)
Consider continuous x-ray, the velocity of electron changes from V to V₁ due to deflection. If "m" is mass of electron then the energy of emitted photon due to radiation is
i.e; λₘₗₙ is inversely proportional to the applied voltage.
Application
- X-rays Photograph called radio-graph is used to detect fractures of bone & cavity of teeth.
- X-rays are used to detect bullet, stones etc. in human body.
- X-rays are used to destroy cancer cells.
- Hard X-rays are used to destroy tumors at the depth.
- X-rays are used in industries to check for cracks/ leakage in pipes.
- X-rays are used at airports, metro stations & railway stations to detect metals, weapons etc. in your luggage.
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