Continuous X–Rays

In the electromagnetic spectrum, we have different kinds of radiation ranging from cosmic rays to radio waves. X-rays also constitute the EMR spectrum, and they are characterised by high energy frequency and low wavelength. Their wavelength is 10-8 to 10-12 metres, about the size of an atom. They are produced when a high-speed electron collides with the target and loses energy. As a result, it releases lots of energy, forming x-rays of two types – continuous x-rays and characteristic x-rays.

Continuous X-rays meaning

When an electron with high speed (or high kinetic-energy) is made to collide the target molecule with a high atomic number, it loses a lot of energy. Due to the principle of energy conservation, it cannot be destroyed. This means that the kinetic energy gets converted into heat and x-rays. Most of the energy gets wasted in the form of heat. But what leads to the remaining energy being converted to x-rays? It happens due to the interaction of electrons with the nucleus of the target atom.

Electrons with very high initial kinetic energies can penetrate deep into the target molecule’s atom. It comes in close proximity to the nucleus. The electron is negatively charged, and an atom’s nucleus is positively charged. The nucleus exerts an electrostatic force on the incoming electron, changing its initial trajectory. The speed of electrons decreases, and their energy also diminishes significantly. Thus, the x-rays do not have one fixed frequency, but they have a range (which goes up to a maximum frequency) due to the deceleration of electrons. 

It is also known as bremsstrahlung, which means breaking radiation. It is also referred to as white light since it comprises radiation of differing wavelengths, just like white light.

Production of continuous x-rays

To produce x-rays, we use an X-ray tube or a Coolidge tube. It is a glass tube having a vacuum environment inside. There is a cathode (mostly tungsten filament) at one end and an anode at another. Cathode produces high-speed electrons that hit the anode. 

The maximum frequency of continuous x-rays depends on the voltage of the anode. Let V be the accelerating potential of the X-ray tube or the potential difference between the anode and the cathode.

Maximum energy or minimum wavelength (𝝀min) photons are released by the kind of electrons which lose all their energy upon a single collision with the anode material. Their entire energy (denoted by eV) is transformed into radiation energy.

Now, we know that eV = hc/𝝀min

Rearranging the equation, we get 𝝀min = hc/eV

We know the values of h, c and eV

h = 6.6 x 10-34 Js

c = 3 x 108 ms-1 

eV = 1.602 x 10-19 V

Substituting these values in the equation, we get, 𝝀min = 12.4 x 103 Ao/V

Properties of Continuous X-rays spectra

1. The total energy emitted through x-ray per second is dependent on the atomic number of the target molecule and the current inside the X-ray tube (number of electrons striking the target per second). It is directly proportional to both these factors.
2. The intensity of a wave can be defined as the rate of flow of EMR energy in a direction that is perpendicular to the wave moving through the unit area. The intensity of continuous x-rays remains zero up to a certain wavelength, which is known as the short-wavelength limit or minimum wavelength.

   Once the short-wavelength limit is reached, the intensity of the radiation increases rapidly with an increase in wavelength and reaches a maximum value. Following this point, the intensity decreases even as the wavelength increases. An inverted bell-like curve is obtained.

3. The intensity of the radiation depends on the voltage inside the tube. When we increase the voltage inside the tube, the intensity of the x-ray increases at a given wavelength. Moreover, the short-wavelength limit shifts to a lower wavelength, and so does the wavelength at which maximum intensity is observed.

Conclusion

In this article, we learned that continuous x-rays are a type of electromagnetic wave with several applications, primarily in body imaging. We also saw how the production of continuous x-rays takes place and the properties of continuous x-rays spectra. They have many practical applications, the major being in body diagnosis. They are used in detecting body injuries and are also used by dentists to take a scan of our teeth.