X-rays were discovered by German physicist Dr. Rongtgen in 1895. X-rays have very smaller wavelength or high frequency. The production of X-rays is the reverse process of photoelectric effect.
X-Rays
When ffast moving electrons strike on a matal surface, photon of very high energy (i.e. High frequency) are emitted known as x-rays.
Production
The experimental arrangement consists of a high vacuum tube. When cathode is heated by a filament, it emits the electrons which are accelerated towards the Anode. If V is the potential applied, then the K.E of electrons with which they collides the target is
K.E. = Ve
Continuous X-ray Spectrum
X-rays emitted in all directions with a continuous range of frequencies are called continuous X-rays. The continuous spectrum is due to the effect known as bremsstrahlung or breaking radiation.
When a fast moving electron bombarded the target, they are suddenly slowed down due to the electrostatic attractive forces of nucei of target. Spectrum is obtained due to deceleration of impacting electrons. These impacting electrons emit radiation as they are decelerated by the target.
Since the rate of deceleration is so large that electrons lose all the K.E in the 1st collision, the whole K.E appears as the X-rays photons of energy hf max. i.e.,
K.E = hf max = hc/wavelength
The wavelength corresponds to frequency. Other electrons do not lose all their energy in their first collision. They may suffer a number of collisions before coming to rest. This will give rise the photons of smaller energy or X-rays of longer wavelength. Thus the continuous spectrum is obtained due to the deceleration of impacting electrons. Other electrons do not lose all their energy in their first collision. They may suffer a number of collisions before coming to rest. This will give rise the photons of smaller energy or X-rays of longer wavelength. Thus the continuous spectrum is obtained due to the deceleration of impacting electrons.
Biological Effects of X-rays
X-rays are ionizing radiations. They may cause damage to the living tissue. As X-rays photons are absorbed in tissues, they break molecular bonds and creates highly reactive free redicals (such as H and OH) which in turn can disturb the molecular structure of proteins and especially the genetic materials. Young and rapidly growing cells are sensitive, hence X-rays are useful for selective destruction of cencer cells. The X-rays can cause cancer by excessive use. Even when the organism itself shows no apparent damage, excessive use may cause the changes in reproductive system that will affect the organism’s offspring.
Properties and Uses of X-rays
X-rays have many practical applications in medicine and industry because X-rays can penetrate several centimetres into a solid matter, so they can be used to visualize the interior of the material which are apaque to ordinary light, such as fractured bones or defects in structural steel.
How to Visualize an Object? (i.e. X-ray of an object)
To vVisualize the object, it is placed between an X-ray source and a large sheet of photographic film. The darkening of the film is proportional to the radiation exposure. A crack or air bulb allows greater amount of X-rays to pass. This appears as dark area on the photographic film. Shadow of bone appears lighter than the surrounding flesh.
It is due to the fact that bone contains greater proportions of the elements with high atomic number and so they absorbs great amount of X-rays than flesh. In flesh the number of light elements like carbon, hydrogen and oxygen greater, so these elements allow greater amount of incident X-rays to pass through them. Other electrons do not lose all their energy in their first collision. They may suffer a number of collisions before coming to rest. This will give rise the photons of smaller energy or X-rays of longer wavelength. Thus the continuous spectrum is obtained due to the deceleration of impacting electrons.
