Question

what is the difference between x-ray imaging and the x-ray diffraction?

Answer 1

X-ray Imaging

X-rays are high energy electromagnetic radaitions whose wavelength is approximately between 0.02 to 100 where 1 = 10^-10 m. Since these are short wavelength radiations they are of very high energy (as energy and wavelegth are inversely proportional to each other according to relation E= h, where h is the planck's constant and is the frequency of radiation and wavelength, = 1/) they can easily peneterate into matter than visible light and can form images on photographic films or detectors. These x-rays are generated in vacuum tubes by making the high speed electrons bombard with metal target at a high potential difference. These radiations are made to fall on the part of the object whose t x-ray image is to be taken and then forms an image on a photographic film or digital recorder. Since fractures in bones have a different density than the bones the fractures can be easily identified in the x-ray image. And even tissues have different densities than bones.

X-ray diffraction

This technique was developed by Max von Laue and then using the Bragg's law it gained greater importance.This is a technique used to study the structure of crystals of various biological and non-biological molecules, an important example will be the determination of double helical structure of DNA using crystallographic techniques. Here, the crystals are considered to be a 3-D grating because crystals consists of an orderly arrangement of atoms and x-rays gets reflected from these planes of atoms. For understanding the crystal structure more the diffraction pattern of the waves that interact with the atoms of the crystal lattice is used.

However, visible light cannot be used for diffraction technique because for diffraction to occur the condition that the wavelength of the incident radiation must be of the order of atomic dimensions as the distance between atoms and molecules in a crystal are of the same order.

Here, the x-rays from different parallel planes, which are specifically designated by using the hkl values called the miller indices, gets reflected from these planes and interference of these waves occur either constructively or destructively.For constructive interference to occur the path difference of these reflected waves must be an intergral multiple of the incident radiations' wavelength. Thus a diffraction pattern of the x-ray beam is observed.

n = 2dsin ----- Bragg's law, which determines the angle at which diffraction intensities occur. Here, 'd' is called the interplanar spacing and 'n' is the order of diffraction. This also tells about the resolution od the pattern. A greater resolution means lower interplanar spacing ,d and therefore larger the angles at which the x-rays are diffracted.

X-ray diffraction is observed in crystals which gives the intensity of diffracted x-rays which later can be ued to get the structure of crystals whereas x-ray imaging is a mathod used to view inner parts of body in case of some defects.