Interaction of x ray with matter

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 1 st 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.

4. 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.

5. 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.

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

7. 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.

8. Lets start

9. 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: Coherent Scattering Photoelectric Effect Compton Scattering Pair Production Photodisintegration

10. 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.

11. Thomson scattering vs Rayleigh scattering

12. 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.

13. 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

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15. 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.

16. 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, E p= E s + E b + 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.

17. Factor determining the energy of Photon Initial Energy Angle of Deflection

18. 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.

19. 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.

20. Energy Transfer in Photoelectric Effect Energy Transform is 2 step process. The 1 st 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.

21. 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: Characteristic Radiation Negative Ion ( The Photo electron) A positive Ion ( An atom deficient one electron)

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

23. 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.

24. 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

25. 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)

26. 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.

27. 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.

28. Interaction of X – Radiation with Soft Tissue

29. 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.

30. 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%.

31. 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.

32. Thankyou Any Questions ?