What is X ray?
When highly energetic is made to strike a metal target then electromagnetic radiations come out. It is known as an x-ray. The wavelength of the major part of this radiation is approximately equal to 1 Angstrom.
X-rays detect bone breaks or fine fractures as they pass through flesh but not dense material like bones.
Radiographer precautions include wearing lead aprons and standing behind a lead screen to minimize exposure. Similarly, pregnant mothers are always advised to avoid exposure to X-rays.
Properties of x-ray
- X-ray travels in a vacuum with the velocity of light.
- X-rays produce fluorescence when it strikes Barium platinocyanide.
- It affects the photographic plate more strongly than visible light.
- It is not affected by the electric field and magnetic field, as it contains no charge.
- When it passes through a gas, it ionizes the gas.
- It can penetrate thin foils of metal.
When an electron strikes a metal target, it has energy, ‘eV’ where ‘e’ is the charge of the electron and ‘v’ is the acceleration voltage.
The electron may lose all of its energy during a collision. In this case wavelength of x-ray,
λ = hc/E
λmin = hc/E
This wavelength is known as the cut-off wavelength and it only depends on accelerating voltage.
When the current of the filament circuit is increased or filament voltage increased, the number of electrons emitted per second increases. Hence the intensity of the X-ray increases but the cut-off wavelength remains unchanged.
In solid crystals, atoms are arranged in a regular pattern with interatomic gaps of the order of 0.1 nm. Suppose an X-ray beam is an incident on a crystal, making an angle with the planes of the atoms.
These X-rays are diffracted by different atoms and the diffracted rays interfere. In certain directions the interference is constructive. The analysis shows that there will be a strongly reflected X-ray beam only if,
2dsinθ = nλ
where n=1 (first-order maximum)
2dsinθ = λ
This equation is known as Bragg’s law.
Characteristics of X-ray and Continuous X-ray
When highly energetic electrons strike the atom of metal and it knocks out of electron of K – shell, electrons of higher energy state makes a transition to fill up the vacancy of K – shell. Due to the transition of electron x-ray is produced and this x-ray is known as characteristics x-rays. It is named Kα, Kβ, and K γ, etc.
λ = hc/change E
When an electron strikes a metal target, energy lost during the collision is converted into an electromagnetic wave. Generally during the collision, a part of this lost K.E is converted into a photon and the remaining part increases the K.E. of the colliding particle.
The energy received by the colliding particle goes into hitting the target and the electron makes another collision with reduced kinetic energy. In this way obtained X-ray is known as a continuous X-ray.
Uses of X – rays
- In medical diagnosis because X–rays can pass through flesh but not through bones.
- In the study of crystals structure because X-rays can be reflected and diffracted by crystals.
- In radiotherapy to cure untraceable skin diseases and malignant growths.
- It is used to detect fractures, diseases inside the body, cancer therapy, material science research, metal detector, etc.
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