5+ Types Of Interaction of ionising radiation with matter And Compton Effect

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

We’ll focus on four procedures. The Photoelectric effect and the Compton effect are the two that have the most impact on diagnostic radiology. The processes should instead be discussed in a more logical order, beginning with one that is significant only at very low photon energies and concluding with the one that predominates at high photon energies. High photon energies are referred to as “hard” X-rays, whereas low photon energies are sometimes referred to as “soft” X-rays.

A firmly bound electron, or an atom as a whole (photoelectric effect, coherent scattering), the field of the nucleus, or an essentially free orbital electron are possible photon interactions (Compton effect, triplet production).
In the context of photon interactions, a tightly bound electron is an orbital electron with a binding energy of the order of or slightly larger than the photon energy, while a free electron is an electron with a binding energy that is much smaller than the photon energy.

During the interaction, the photon may completely disappear (photoelectric effect, pair production, triplet production), scatter coherently (coherent scattering), or scatter incoherently (incoherently) (Compton effect).

Compton effect (incoherent scattering)

The Compton effect, also known as incoherent scattering, is a type of scattering that occurs when a photon interacts with an atom. This interaction causes the photon to be scattered in a different direction and its wavelength to be altered. This phenomenon was first observed by Arthur Compton in 1923, and is an important part of quantum mechanics.

The Compton effect occurs when a high-energy photon interacts with an atom. When a photon strikes an atom, it causes the atom to become excited. The atom then releases a new photon with a slightly lower energy and the original photon is scattered in a different direction. The wavelength of the scattered photon is also altered due to the interaction.

The amount of energy and wavelength change that occurs during the Compton effect depends on the angle between the incoming and scattered photons. If the angle is small, the energy change is small. However, if the angle is large, then the energy change is larger. This is known as the Compton effect’s angular dependence.

The ratios of momentum and energy delivered to the electron and scattered photon, respectively, are governed by Φ and θ . The electron’s kinetic energy is quickly lost by ionisation, excitation, and finally heat in the medium. If no more interactions take place, a scattered photon with a lower energy than the initial photon emerges from the medium. The process is therefore one of energy scattering and partial absorption.

The Compton effect is used in many fields of science, from medical imaging to astronomy. For example, in medical imaging, the Compton effect is used to measure the density of tissue in the body. In astronomy, it is used to measure the age and composition of distant stars and galaxies.

The Compton effect is an important part of quantum mechanics and has been of great interest to physicists for many years. It demonstrates how light and matter interact and is a key part of understanding the universe.

It is a form of scattering that occurs when a photon is scattered by an atom or molecule in a medium. It is an important phenomenon in many areas of physics and is the basis for X-ray and gamma-ray spectroscopy. When the photon interacts with the atom it is scattered off in a random direction, transferring a portion of its energy to the atom.

It is the result of an electron in an atom being struck by a photon, resulting in the scattering of the photon and the ejection of the electron from the atom. This is an example of an inelastic scattering process, since the energy of the photon is increased or decreased by the interaction. It is also an example of a Compton scattering process, since the photon interacts with an electron and not a nucleus. The Compton effect is an important process in the production of X-rays and gamma rays, since it is the primary mechanism for the production of these high-energy photons.

Direction of Scattering Of Photon –

Photons are dispersed in all directions following Compton interactions. The scattered photons move more and farther forward as photon energy rises, although this shift is very minor in the diagnostic energy range, where a sizable part of X-rays may be back scattered. Compared to forward scattered photons, the mean energy of backscattered photons is smaller. The problem is further complicated for thicker objects, such as a patient, because both the original beam and the dispersed radiation would be attenuated.

Compton-Scattered Photons’ Effect on Image Quality: Controlling Factors 

Under extremely unfavourable circumstances, scattered photons that reach the image receptor may add up to 10 times as much radiation to the image as the source beam. Contrast is severely hampered by scatter. Although dispersion cannot be entirely eliminated, certain steps can be taken. Following the imaging procedure, the following factors might impact scatter:

1. Beam Collimation
2. Air Gap
3. Tube Voltage (kV) 
4. Body Thickness
5. Grid

Beam Collimation

Although field size has a significant impact on scatter, in practise it frequently has a greater bearing on patient dosage than on the amount of scattered radiation that reaches the imaging plane. The amount of scattered radiation reaching the imaging plane rises quickly at beginning but gradually increases to a maximum when the size of the X-ray field on the body increases from a very modest value. Beyond this size, the quantity of scatter reaching the image receptor is unaffected by increasing the field size.

As seen in the image, a narrow collimation (i.e., a limited x-ray field) causes a smaller irradiation region and a smaller patient volume where scatter can be created.

More of the body is exposed to radiation at once if we expand the x-ray field (i.e., make the total irradiated portions larger).

As seen in the image, a narrow collimation (i.e., a limited x-ray field) causes a smaller irradiation region and a smaller patient volume where scatter can be created.

More of the body is exposed to radiation at once if we expand the x-ray field (i.e., make the total irradiated portions larger).

Air Gap –

A patient and an image detector are separated by an air gap. Given that radiation is partially absorbed and dispersed in the air, the gap reduces the possibility that scattered x-ray radiation will reach the detector.

When necessary, mammography also employs these standard techniques for scatter reduction. The air gap approach could be an effective way to reduce dispersion for small field sizes. To keep resolution, the smallest focus point possible must be employed. In a mammography unit, the focus-image receptor distance is fixed, hence the focus-skin distance must be shortened. Although the sensitive breast tissue volume may decrease, the skin dosage will increase as a result.

Effect Of Tube Voltage kV –

Throughout the diagnostic range, the Compton effect produces dispersed radiation at a largely constant rate. However, as the kVp increases, the amount of scattered radiation that reaches the imaging receptor will increase noticeably because as more scattered photons go forward and have a greater energy, they are less attenuated by the patient and do not self-absorb. Overall, the dispersion increases with increasing kVp, while the dosage required to generate the picture on the patient decreases.

The average photon energy decreases with decreasing kV, increasing the number of photoelectric contacts and decreasing the fraction of scatter events as a result. Particularly when imaging bone, which includes a high atomic number material (Calcium, Z = 20), scatter is typically reduced at lower kV levels. In general, tabletop imaging of the extremities is possible due to two factors that help to reduce scatter: (a) thin body parts are easier to penetrate and can therefore use lower x-ray tube voltages (kV); and (b) the presence of bone (high Z) means that most interactions are photoelectric rather than Compton, which reduces scatter.

Body thickness –

The thickness of the anatomy we are employing for x-ray imaging affects X-ray scatter. As we already know, scatter results in an overall haze in the image’s backdrop.

The overall number of scattered photons will rise with the thickness of the body in the beam, but the quantity that reaches the image receptor stays constant for a given kVp because the body absorbs the scatter that is created in the top half of the body. Only very rarely may compression be used to change the thickness of the bodily portion being scanned.

When a patient has a thicker body or a bigger body habitus, the photons must travel a greater distance through the body, increasing the likelihood of scatter events.
More scattering events and background haze result from thicker tissues. It follows that the thinner the anatomy, the smaller the dispersion, and the thicker the anatomy, the larger the scatter.

This is the broad justification for why compression is desired in situations when it is practicable, like when taking x-ray pictures of the breast for mammography.

Grids –

Anti-scatter grids are commonly utilised for brain, spine, abdomen, breast, and contrast examinations but not for the tiniest anatomy, such as extremities. Increasing the percentage of dispersed x-rays that reach the detector is the main goal of using an anti-scatter grid.
By transmitting the bulk of primary radiation and rejecting specific scattered radiation, the grid is crucial for improving image quality in projection radiography. Lead or another x-ray attenuating material is frequently utilised for anti-scatter grids. Therefore, main photons will flow through the grid’s plates but scatter x-rays are more likely to be prevented. This device has a form factor that matches the size of the detector and is made up of a number of thin lead strips separated by radiolucent interspaces. The majority of grids are linearly shaped in one direction (usually along the long axis of the detector). Lead strips on parallel grids are focused to infinity (i.e. the primary x-rays have a parallel trajectory). To match the beam divergence from the focal spot to the detector at a certain source to detector distance, focused grids contain lead strips that are parallel at the centre (along the x-ray central axis) and increasingly tilted to the periphery.

The grid ratio is the proportion of the grid’s width to the height of the grid plate, also known as the grid septa.