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X-Rays

The form of energy which emitted and absorbed by charged particles is known as Electromagnetic radiation or EM radiation or EMR. Electromagnetic radiation has both electric and magnetic field components, which oscillates perpendicular to each other as well as perpendicular to the direction of energy and wave propagation.

They travel with the speed of light in vacuum that is 3 x 108 cm/sec. The refraction of electromagnetic light produced a band of color like in a rainbow is termed as electromagnetic spectrum. The electromagnetic spectrum started from radio wave ended at gamma radiation of the short-wavelength and high-frequency end; hence it covers the wavelengths from thousands of kilometers down to a fraction of the size of an atom.

Different electromagnetic radiations with their frequencies and wave length us as follows.

 Region of the spectrum Frequency (Hz) Wavelength (Ã…) Radio waves 3 x 1014 to 3 x 1017 3 x 1014 to 3 x 1017 Microwaves 3 x 107 to 6 x 106 1 x 109 to 5 x 1011 Infrared 5 x 1011 to 3.995 x 1014 6 x 106 to 7000 Visible 3.95 x 1014 to 7.9 x 1014 7000 to 4000 Ultraviolet 7.9 x 1014 to 2 x 1016 4000 to 150 X-rays 2 x 1016 to 3 x 1019 150 to 0.1 Gamma rays 3 x 1019 to 3 x 1020 0.1 to 0.01 Cosmic rays 3 x 1020 to infinite Less than 0.01

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X-Ray Generation

X-radiations or X-rays are a form of electromagnetic radiation from the range of 0.01 to 10 nanometers wave length and the corresponding frequencies 3Å—1016 Hz to 3Å—1019 Hz. The energy associated with X-rays is in the range of 120 eV to 120 keV.

In electromagnetic spectrum, X-rays placed between Ultraviolet rays and gamma rays. X-rays discovered by Wilhelm Conrad Rontgen in the late 1800's during the experiment with a cathode tube and also termed as Rontgen radiation.

For the generation of X-rays, three main components are there in X-rays generator;
1. A source of electrons.
2. An accelerator for generate a high speeds electron.
3. A target material for the interaction with photo electron.

When free electrons interact with orbital electrons or nucleus, they give up some of their energy in the form of electromagnetic energy known as X-rays.
The interaction of free electron with orbital electrons can be possible through two different atomic processes.
1. Bremsstrahlung
2. K-shell emission

1. Bremsstrahlung

The term Bremsstrahlung is a German term stand for the "braking rays." In this process a high speed electron strikes to a material and get slowed or completely stopped by the forces of any atom it encounters. The speed of electron decreases due to interaction of a high speed electron with the negative force of the electrons of target atom.

According to the law of conversation of mass "the change in speed of electron must be equals to the amount of energy radiate in the form of electromagnetic radiation that is X-rays."

Some time the collision between photo electrons and the target completely stopped the electron due to the strong positive force of the nucleus and the radiated X-ray energy will have energy equal to the total kinetic energy of the electron. Such type of collision occurs with very large and heavy nuclei materials.

Generally white radiation or Bremsstrahlung is a continuous spectrum of X rays which form due to the collision of the accelerated electrons with the atomic electrons of the target atoms.
If in collision of photo electron and target all of the kinetic energy of an electron is converted into radiation, than the energy of the X-ray photon would be given by

Emax = h$\nu$max = eV

Where; h = Plank's constant,
$\nu_{max}$ = the largest frequency,
e = charge of an electron,
V = applied voltage.

The maximum frequency associated with maximum energy or minimum wavelength is called the Duane-Hunt limit.

h$\nu_{min}$ = $\frac{hc}{\nu_{min}}$ = eV

$\nu_{min}$ = $\frac{hc}{eV}$ = $\frac{12398}{V}$ (volts)

2. K-shell emission

When a proton beam interacts with K-shell electron, it's kicked out the electron and creates a vacancy in the K-shell. For keeping the atom at low energy level, some electron transit from higher levels like L, M, N to K-shell vacancy and emits its redundant energy in a form of X-rays.

The energy gap between K and L (or M, N, $\nu$) shell decided the energy of emitted X-ray photon.
One transition induced next transition, for example; when L-shell electron is shifted to K-shell, some electron from M-shell will move to the free position and will emit the energy difference between L and M shell in form of X-rays.

X-ray generator

X-rays generator consist of a tube, the high voltage generator, the control console, and the cooling system. A stream of high speed electrons strikes at a target material like tungsten. The interaction between high speed electron and heavy metal produced X-rays. This process accomplished in an X-ray tube which is a main component of an X-ray generator.

• The tube contains the cathode filament which is heated with a low-voltage current.
• The heating of the filament produces free electrons.
• Since there is a large electrical potential between the cathode and the anode due to high-voltage generator so electrons are strongly attracted to the anode target.
• The movement of electrons between the cathode and the anode creates current in tube.
• As the temperature increases, the number of electrons increases in tube.
• The control console regulates the filament temperature, which corresponds to the intensity of the X-ray output.

X-Ray Properties

1. X-rays are electromagnetic radiation; which can travel in a straight line with the speed of visible light that is 1,86,000 miles/sec.
2. X-rays are visible from eyes but cannot be heard or smelt.
3. They do not show any deflection, reflection or diffraction in magnetic or electric field. Just like visible light, they show wave properties like interference, diffraction and refraction.
4. They have tendency to produce electric field and magnetic field which is perpendicular to their path of propagation.
5. X-rays can travel in vacuum and not required an medium. They have enough penetration power and can penetrate liquids, solid and gases.
6. The penetration power depends upon the quality, intensity and wavelength of light beam.
7. They can be easily absorbed by matter and absorption power depends on the atomic structure as well as wavelength of X-rays.
8. Because of their penetration power, they can ionized any matter and can emitted visible light when interact with a certain material. This phenomenon is known as Fluorescence.
9. Certain substance like Methylene blue gets bleached with X-rays. Due to high energy, X-rays produced active free radical during any chemical reaction.
10. X-rays have wide applications in biological field also. They used in the treatment of malignant lesions. They have germicidal effect and can cause the destruction of enzymes.