Interaction of ionising radiation with matter & Thomson scattering, Rayleigh scattering & Mie scattering

Interaction of ionising radiation with matter –

When ionising radiation interacts with matter, it can cause changes in the physical and chemical properties of the material. Depending on the type of radiation and the material, interactions can lead to changes in the structure of atoms and molecules, the formation of new compounds, or the release of energy. In biological materials, ionising radiation can cause changes in DNA, leading to mutations and other cellular damage.

When ionising radiation interacts with matter, it can cause changes in the structure of atoms. This is known as ionisation. When an atom is ionised, it can become unstable and cause a chain reaction, resulting in the production of secondary particles such as electrons and protons. The interaction of ionising radiation with matter can also cause changes in the molecular structure of molecules, leading to the production of new molecules. This process is known as radiolysis. Finally, ionising radiation can also cause changes in the physical properties of materials such as those of metals, plastics, and even living cells, resulting in changes in their electrical, optical and thermal properties.

The Processes of Interaction

There are following type of Radiation Interaction With Matter process

1. Compton effect
2. Thomson scattering & Rayleigh scattering & Mie scattering
3. Photoelectric effect
4. Pair production & Triplet production
5. Photodisintegration

Thomson scattering & Rayleigh scattering & Mie scattering

Thomson scattering Of radiation 

Thomson scattering is the nonrelativistic limit of the Compton scattering of photons by free electrons. When a free-charged particle is present, a sort of elastic scattering of electromagnetic radiation called Thomson scattering occurs.

Electrons may pick up vibrational energy when X-rays are in close proximity to an atom. Resonance is the process that causes the electron to oscillate at a frequency similar to that of the X-ray photon. The electron soon emits this energy in all directions at the same frequency as the incoming photons since this is an unstable condition. Without absorption, the process consists of scattering and attenuation.

The process is favoured when the bulk of the electrons behave as bound electrons because the electrons that vibrate in this manner must remain bound to their nuclei. This happens when the electrons’ binding energy is high, meaning the scattering material’s atomic number is high, and when the bombarding photons’ quantum energy is comparatively low.

Classical electromagnetism can explain this behaviour. The low-energy limit of Compton scattering is what is known as Thomson scattering. But when the photon energy is less than the mass-energy of the particle, this lower limit is possible.  Additionally, when taking into account the low-energy limit, the charged particle may be accelerated by the incident wave’s electric field, which causes it to emit radiation at the same frequency as the incoming wave.

The wave disperses as a result. J.J. Thomson was the first to describe Thomson scattering. Thomson scattering of radiation is an important process in astrophysics, which describes the scattering of electromagnetic radiation off free electrons. This process is responsible for the Sun’s visible light, and it is also responsible for the light emitted by stars and galaxies. It is also used to map the distribution of free electrons in space and in the interstellar medium. Thomson scattering can also be used to study the properties of hot gas, such as the temperature, density and velocity of the gas.

Rayleigh scattering

The term “Rayleigh scattering” refers to the scattering of electromagnetic radiation by particles whose radii are smaller than or equal to one-tenth the wavelength of the radiation. The scattering of light by atmospheric particles is known as rayleigh scattering. The quantity of light scattering is inversely related to the wavelength’s fourth power, as stated by Rayleigh’s scattering law. Shorter wavelengths scatter more, as seen by the relationship between scattering and wavelength. Blue light scatters more because it has a shorter wavelength than red light. Lord Rayleigh, who published a paper outlining this occurrence in 1871, has been honoured by having the process bear his name.

Since the photon energies of the scattered photons are unaltered, Rayleigh scattering may be thought of as elastic scattering. Raman scattering is a type of scattering in which the scattered photons have either a greater or lower photon energy. This type of scattering often includes excitation of a molecule’s vibrational mode, which results in a lower scattered photon energy, or excitation of a molecule’s excited vibrational state, which scatters off and adds vibrational energy to the incident photon.

Rayleigh Scattering Law

Rayleigh Scattering law expresses that the amount of scattering of light is conversely relative to the fourth power of the wavelength.

The mathematical form of the above statement is:

 I =1/λ⁴

Here,

I  = intensity

This suggests that in the case of a shorter wavelength, then more likely, the light is bound to be scattered in contrast with longer frequency, because of the inverse relationship between the two.

• With frequency, Rayleigh scattering rises.
• Red light is therefore less spread than blue light.
• The blue colour of the sky is due in part to the fact that blue light scatters more lateraly than the other colours of the visible spectrum when it interacts with our atmosphere.

Blue light, which is at the short wavelength end of the visible spectrum, will be scattered much more strongly than long wavelength red light because the angle through which sunlight in the atmosphere is scattered by molecules of the constituent gases varies inversely as the fourth power of the wavelength. Since the viewer only sees dispersed light in directions other than towards the Sun, this causes the sunlit sky to have a blue hue. The patterns of forward and backward scattering from single particles are completely symmetrical, which is a result of the Rayleigh laws’ prediction that the intensity of scattered light will vary with direction. They also forecast the dispersed light’s polarisation.

Mie scattering 

Mie scattering is the elastic scattering of light by particles with a diameter that is equal to or greater than the incoming light’s wavelength. The square of the particle diameter determines the Mie signal.

In Mie Scattering, electromagnetic waves (like light) strike the particles and, after reflection, return to the environment with an equal distribution of wavelengths.

• Mie scattering depends on the wavelength.
• Because of Mie’s dispersion, the clouds seem white.

Mie scattering is a possible source of interference for this weaker light scattering mechanism since it is substantially stronger than Rayleigh scattering. Successful Mie imaging investigations must take into account the scattered intensity’s considerable angle dependence, especially for tiny particles. Particle Image Velocimetry is frequently used to assess flow velocities via Mie scattering (PIV).