X-rays properties , uses and method of obtaining X-rays by using Coolidge tube
X-rays are invisible electromagnetic waves of high energy and short wavelengths lie between the wavelengths of gamma rays and the ultraviolet rays , Rontgen discovered invisible electromagnetic waves of short wavelength ranges from 10−13 m to 10−8 m and they have high energy , He called them unknown rays ( X-rays ) because he didn’t know what they are .
Properties of X-rays
- They can penetrate media easily .
- They can ionize gases .
- They diffract in crystals .
- They affect sensitive photographic plates .
Method of obtaining X-rays by using Coolidge tube
- Hot filament as a source of electrons .
- Tungsten target .
- A source of high potential difference between the filament ( cathode ) and the target ( anode ) to accelerate the emitted electrons from the filament .
- Evacuated tube contains the filament and target .
When the filament is heated , negative electrons are produced and directed towards the target under the influence of the electric field , The electrons acquire large kinetic energy depending on the voltage difference between the filament and the target , When an electron collides the tungsten target , part or all of its kinetic energy is concerted into X-rays .
Spectrum of X-rays
Analyzing a beam of X-rays generated from a target to compounds of different wavelengths , we find that the spectrum consists of two components .
- The continuous spectrum of all wavelengths that does not change with changing the material of the target .
- The line spectrum corresponding to certain wavelengths characteristic of the target material , called the characteristic X-ray radiation .
Continuous spectrum ( connected ) of X-rays
They are called Soft X-ray spectrum , bremsstrahlung , such as braking radiation , They can be generated when the velocity of the colliding electrons ( coming from cathode ) is reduced upon passing through a retarding electric field due to the electrons of the target material , its energy decreases due to repulsion , collision and scattering .
According to Maxwell-Hertz theory , the decrease in the energy of the electrons converts into electromagnetic radiation contains all the different possible wavelengths because the electrons lose its energy gradually .
The factors affecting the wavelength : The potential difference between the filament and the target , ( λm ∝ 1 / V ) and it does not change with the changing of the target material .
Line spectrum ( characteristics ) of X- rays
They are called Hard X-ray spectrum or trough X-ray spectrum , They can be generated when an emitted accelerated electron ( coming from the cathode ) collides with an electron close to the nucleus of the target material atom then if the later electron receives sufficient energy , it jumps to a higher level or leaves the atom altogether and is replaced by another electron from a higher level .
The difference in energy appears as radiation with a definite wavelength which is determined from the relation : Δ E = E2 − E1 = h c / λ
λ = h c / ΔE
The factors affecting the wavelength :
- The wavelength of the characteristic radiation does not depend on the potential difference between the cathode and the anode , although it does not appear at low potential difference .
- It changes by changing the target material as the wavelength decreases by increasing the atomic number of the target element .
Conditions to obtain a line spectrum ( characteristic ) of a target material :
- Applying high potential difference between the filament and the target in Coolidge tube , to make the emitted electrons from the filament acquire high kinetic so , at colliding with the target , it produces X-rays of high energy .
- Accelerated electron collides with electron from levels ( K , L , M ) close to the nucleus of the target material atom .
Applications of X-rays ( uses )
Studying the crystalline structure of materials : one of the important features of X-rays is diffraction , as they penetrate materials , The atoms in the crystal act as a diffraction grating ( which is a generalization of diffraction from a double slit ) , forming bright and dark fringes depending on the difference in the optical path .
They are used to detect the defects in metallic structure because they have a great penetration power as the wavelength of X-rays is less than the spaces between the atoms , They are used in imaging bones and fractures and some other medical diagnoses because they have high ability for penetration .