Production of X-rays by Modern Coolidge Tube is best apparatus for the production of X-Ray safely and cheaply as
1) It can be produce x-ray for long time.
2)This can be operated in small voltage and large voltage(100V-2000V).
3)Quality and intensity of x-ray both can be controlled in the coolidge tubes.
Modern coolidge tube consists of a highly evaporated glass bulb. At one end of bulb,filament coil is placed and connected to low tension battery. A concave structure C placed near the coil which collect all the thermoionic electron and accelerated towards the target metal.
At other end of bulb target metal made up tungstein is mounted in the metal rod .Target metal is adjusted at an angle of 45° with the horizontal .
A copper tube circulating cold water is passed around the metal,which maintain the temperature of target metal.Metal rod is connected to positive terminal of High Tension DC supply at filament coil is connected to negative terminal of high tension DC supply.
The working principle of production of X-rays from coolidge tube is based on the principle of conservation of kinetic energy of electron into energy of X-Ray Photon.
At first filament coil F is heated by sending filament current from low tension battery . Filament coil emits for number of thermoionic electrons. These electron are accelerated to a target metal and continuously colides upon the target metal. Due to this continuous collision target metal emites x-ray radiation of short range. In this production of X-ray, quality as well as intensity both can be controlled.
A) Control of quality of X-ray
Here, workdone by accelerating voltage=Gain of K.Eof thermoionic electron.
eV= 1/2mv2 …..1)
If no heat energy is produced, then
1/2mv2 = hf …..2)
from eqn 1 and 2, we get
hf = eV
f is directly proportional to V.
Quality of x-ray refers to pentration and ionization power.Pentration and ionising power depends on Frequency. From above mathematical analysis frequency of X-Ray depends upon magnitude of accelerating voltage.
Hence,quality of X-Ray can be controlled by controlling a accelerating voltage applied between filament coil and targat metal.
B) Control of intensity of X-ray
Let I be mangitude of filament current supplying to the filament coil.
since, Q = It
or, n/t = I/e
or, no. of electrons per second = filament current/charge of electron.
so, Intensity of x-ray is directly proportion to filament current.
Intensity of X-Ray refers to number of x-ray photon produced per second. As we send high magnitude filament current,coil get heated highly and it starts to emits more number of thermoionic electrons.
If a large number of electrons strike the target metal. Target metal produces more x-ray Photon and intensity of X-Ray can be controlled by controlling the magnitude of filament current.
Characterstic of Target Metal
- High melting point and high atomic weight.
- high conductivity.
- low volatile.
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