X-Rays: History, Generation, Application
Computed tomography is way of imaging the given particle or product in very thin layers. The image generation of the product that need to be inspected is done with the help of X-rays.
X-rays are a kind of electromagnetic radiation that are capable of travelling at the speed of light. X-rays can penetrate to objects and can create the internal images of the object on photographic films or fluorescent screens. It is not visible to human eyes.
The X-rays was discovered in the year 1895 by the German scientist Wilhem Roentgen and he received Nobel prize for this discovery. After some research, he came to notice that whenever X-rays passes through a body, it created a shadow of that body on the photographic plates. A few years since then X-rays became a vital diagnostic tool for medical science. X-rays could easily penetrate through soft particles however, it is quite difficult in the case hard objects.
The electromagnetic radiation is transferred in particles and waves. There are transmitted at varying wavelength and frequencies. All these waves, having different wavelength constitutes electromagnetic spectrum. This spectrum is classified into seven regions that includes radio, IR, UV, X-rays, gamma rays and visible light.
In electromagnetic spectrum, the rage of X-ray is from the frequency of 1016 Hz to 1020 Hz. And X-rays are classified in to two types, soft X-rays and hard X-rays. The soft X-rays have their high frequency- about 3 × 1016 Hz to about 1018 Hz and low wavelength about 10 nanometers (nm), to about 100 picometers (pm). Hard X-rays having frequency is from 1018 Hz to1020 Hz and wave lengths of about 100 pm to about 1 pm. The hard X-ray and Gamma rays have same position in electromagnetic spectrum but only difference is that gamma rays are produced by atomic nuclei and X-rays are produced by accelerating electrons.
X-ray generation
When electrons are emitted from a heated filament, it is accelerated by high voltage towards a metal target and the energy of that electron on hitting the target is converted to X-rays. Besides, a device called Synchrotron can also be used to produce X-rays. It is a kind of particle accelerator and will make the charged particles to follow a closed circular path by magnetic field. Meanwhile, the angular acceleration forces the particle to emit photon and at a particular point where the energy is high enough, the electrons emit X-rays.
Because of the special characterizes of X-ray and the ability to penetrate through certain substances, X-rays have huge number of applications. X-rays are used for non-destructive testing and evaluation specially to find the internal cracks and faults inside certain substances. From a source the X-ray is generated and let it pass through the specimen to be inspected. The X-ray penetrates through the soft parts of specimen and it stops once it hits the hard parts. The X-rays thus passed through the specimen reaches the photographic plate and interact with molecules in plate and make image of the specimen according to the density of penetrated X-rays that fall on the plate. Once the film is processed the soft parts appears in grey shade, the rigid parts appears in white shade and air gap appears in black shade.
The computed tomography is platform where large number of X-ray images are used together. The specimen is rotated around the source and the images from all direction is recorded with help of a computer and produces two dimensional and three-dimensional image of specimen.
