This slide contains the Information regarding what changes takes place when the X-ray Interacts with matter.

1. Interaction of X-ray with
Matter
By : Anjan Dangal
Bsc.Mit 1st year

2. • Atom
• Electron Proton Neutron
• Binding Energy
• Attenuation
• Absorption
• Scattering
Key Terms

3. • Attenuation : is the Reduction of the Intensity of beam as it passes
through a medium.
• Absorption: Is the transfer of the Energy from the Radiation to the
medium
• Scattering : is a change in the direction of the photon with or without
the loss of energy by the photon.

5. X ray Overview
• X ray photon are created by interaction of Energetic electron with the
matter at atomic level.
• X rays have very shortwavelenght no larger than 10^-8 to 10^ - 9 m.
• Higher Energy shorter the wavelenght.
• Low energy x ray tend to Interact with whole atom.
• Moderate Energy x ray with Electron .
• High Energy X ray with Nucleus.

6. Importance of Interaction
• The selective interaction of x ray photon with Human Body produces
the Image.
• Interaction of x ray photon with receptor converts an x ray image into
one that can be viewed and recorded.
• Technical Factor Kvp and Mas required to image tissue and if choosen
appropriately may actually decrease the Radiation dose to patoent.
• Image Visibility entirely depend upon the Interaction of x ray with
matter.

7. Introduction
In diagnostic Radiography Interaction always occurs in orbital Electron.
• 3 possible fates awaits each photon
1. Penetration
2. Absorption.
3. Scattering

8. • Penetration:
penetrate section of matter without Ineraction.
• Absorption:
interact with matter and completely absorped by depositing its
energy.
• Scattering:
interact and be scattered or deflected from its original direction
and deposit part of its energy. No longer carries useful Information
because their direction is random, and are responsible for noise in the
Image.

10. Lets start

11. Absorption and Scattering Process
• There are five different process by which x rays may be absorbed or
scattered as they pass through the medium, the first three of which
play a role in Diagnostic Radiology and Nuclear Medicine:
1. Coherent Scattering
2. Photoelectric Effect
3. Compton Scattering
4. Pair Production
5. Photodisintegration

12. Coherent Scattering
• Reffered by variety of name including Thomson , Rayleigh , Classical
and Unmodified scattering .
• Name coherent is given to those Interaction in which radiation
undergoes change in direction without change in wavelenght.
• When the energy of Incoming x ray photon is substantially less than
the binding energy of strongly bound orbital electron , it may occur.
• JJ Thomson discovered classical scattering of x ray with an electron.
• John Rayleigh discovered x ray interaction and its momentarily
absorption by the entire cloud of electron collectively around an
atom.

13. Thomson scattering vs Rayleigh scattering

15. Scattering Process
• Low energy x rays those with energies below about 10 kev interact
with target atom and set them in vibration at the frequency of
radiation
• A vibrating electron because it is charged particle immidiately
releases the excess energy as radiation.
• Summarily : Absorption of Radiation
Vibration of the Atom and
Emission of Radiation
Atoms returns to Undisturbed state.

18. Properties
• Scattered Radiation is with the wavelenght equal to that of Incident X
ray.
• No energy Transfer.
• No Ionization.
• Accounts for less than 5 % in diagnostic Radiography.
• At 70 kvp, 3% x-rays goes classical scattering

19. NEXT

20. Compton Effect
• Also called a Inelastic, nonclassic, Modified and Incoherent
Scattering.
• Discovered by American Physicist, Arthur Compton.
• Interaction occurs between photons and outer sheel electron which
have negligible binding energy.
• Electron is ejected from atom and photon is scattered with some
reduction in energy
• Scatter x rays emerging from this interaction are called compton
scatter and ejected electron is reffered as recoil electron.

22. Energy Distribution
• Of the x ray photon’s original energy , an amount equal to the
binding energy goes into ejecting the electron from its orbit , a
small amount also translates into the kinetic energy or speed with
which the Electron is ejected and the remainder is reemitted as the
Compton scatter x ray. Mathematicall,
Ep= Es + Eb + E ke
• Ep = Energy of Incoming x ray photon
• Es= Energy of scatter X ray
• Eb= Absolute value of Binding Energy
• E ke= Kinetic energy of ejcted electron.

24. Factor determining the energy of Photon
• Initial Energy
• Angle of Deflection

25. Conclusion of Compton Scattering
• 97 % of scatter x rays originate from compton interaction.
• Photoelectric effect = subject contrast but compton scattering =
scatter radiation.
• Compton works in opposite to photoelectric effect.
• Scattered x rays from Compton interaction can create serious
radiation exposure hazard in Fluroscopy.

26. Photoelectric Effect
• The photoelectric effect can occur when an incident photon has energy
equal to or greater than the binding energy of electron in atom.
• Photon can ionize the atom by ejecting an electron from a shell.
• Photon gives all its energy to the atom.
• Secondary electron / Photoelectron ejected with K.E equal to the energy
equal to the energy of the incident photon minus the binding energy.
• Vacant site fulfilled by electron jumping inward from another shell farther
away from Nucleus , accompanied by emmission of characteristic X
radiation in the form of secondary photon whose energy is equal to
difference between the binding energies of two shells involved.

28. Energy Transfer in Photoelectric Effect
• Energy Transform is 2 step process.
• The 1st is , photon transfers all its energy to an electron located in one
of the atomic shell and the electron is ejected from the atom known
as photoelectron and begins to pass through surrounding matter
penetrates tissues but never out of patients body and never reach IR.
• Finally that Photoelectron deposits the energy in the surrounding.
• Summarily, photon energy is divided in two portion : A portion of the
energy is used to overcome electrons binding energy and to remove it
from atom. The remaining energy is transferred to electron as KE and
is deposited near interaction site.

29. Vacancy Fullfilment
• Since the interaction creates vacancy in one of the Electron shell,
typically K or L.
• An electron moves down to fill in.
• The drop in energy of filling electron often produces a characteristics
x ray photon which is the characteristics of each element.
• This effect yields three end product:
1. Characteristic Radiation
2. Negative Ion ( The Photo electron)
3. A positive Ion ( An atom deficient one electron)

30. Probability of Occurence
1. The Incident photon must have sufficient energy to overcome the
binding energy of the electron.
2. A photoelectric reaction is most likely to occur when the photon
energy and electron binding are nearly the same.
3. The tighter an electron is bound in its orbit , the more likely it is to
be involved in photoelectric reaction.

31. Pair Production
• Do not occur in Diagnostic Radiology
• The high energy photon interacts with the nuclues of an atom.
• Photon Disappers.
• Its energy is converted in into matter in the form of two particles.
• One is electron and other is positron , a matter with mass as an
electron but with positive charge .
• Cannot take place with photon energies less than 1.02MeV.
• Produces two electron with mass of one equal to 0.51 MeV.

33. Process of Pair Production
• Incoming X ray photon strongly interacts with nucleus.
• Energy of Photon is transformed into two new particle: A negatron (
an ordinary electron) and a positron ( positevely charged electron).
• They have same mass and magnitude but different sign.
• The electron loses its Kinetic Energy by excitation and Ionizing atoms
and is captured by an atom in need of electron.
• Positron acts destructively with nearby electron.
• During this Interaction positron and electron annihilate each other, a
conversion of mass into Energy inaccordance with Einsteins’s , theory
of relativity as E= mc 2

34. • This energy that appears from annihilation of electron and positron is
carried off by two 0.511 MeV photon moving in opposite direction.
• Annihilation Radiation is used in Positron Emission Tomography ( PET)

35. Photo Disintegration
• Occurs with energy more than 10 Mev.
• Part of Nucleus of atom is ejected by a high energy photon.
• The ejected portion may be a neutron, a proton, an alpha particle or a
cluster of Particles..
• The photon must have sufficient energy to overcome nuclear binding
energies of the order of 7 – 15 MeV.

37. Process of photodisintegration
• A high energy photon collides with the nucleus of an atom, which
directly absorps the photon energy .
• This energy excess creates an Instability that in result emits neutron
by the nucleus.
• Other types of emissions , a proton or proton neutron combination or
even alpha particles are possible if sufficient energy is absorbed by
the Nucleus.

38. Interaction of X – Radiation with Soft Tissue

39. Summary
• Two Interaction of x radiation : photoelectric absorption and
Compton scattering are of Important in Diagnostic Radiology
• The photoelectric Effect is the basis of Radiographic Imaging
wheareas the compton effect is its bane.
• Within the energy range of Diagnostic Radiology 23 to 150 kvp which
also includes mammography , when kvp is decreased the number of
photoelectric interaction increases but the compton interaction
decreases however dose to patient increases.
• When kvp is increased patient receives a lower dose but the image
quality is compromised.

40. • Compton Effect is responsible for vast majority of scatter Radiation.
• If coherent scattering accounts for the 5% of the interaction, compton
scattering for 20 % , and the photoelectric effect for 75%, the total
100%.

41. Reference
• Physical Principles of Medical Imaging , Perry Sprawls.
• Radiography in Digital Age , Quinn B. Caryol
• Christensen’s Physics of Radiography
• First year Physics for Radiographer.
• Essential Physics of medical Imaging.
• Radiation protection in Medical Radiography.
• Radiologic Science for Technologist.

42. Thankyou
Any Questions ?