X ray physics part I


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  • X ray physics part I

    1. 1. Wilhelm Conrad Röentgen • Professor of Experimental Physics – Würzburg University • Discovered x-rays – 8 November, 1895 • Awarded first Nobel Prize for Physics – 1901
    2. 2. History of x-ray: • Roentgen placed his wife’s hands on photographic plate and exposed it to unknown radiation for 15 minutes. • When he developed the photographic plate, the outline of bones of her hand could be seen. • He named it x-ray.
    3. 3. Nature of the atom: • Simple substances are called elements. There are 105 elements. • The atom is the smallest particle of an element that has the characteristic properties of that element. • It consists of nucleus surrounded by orbital electrons. • The nucleus is composed of protons and neutrons and they are called nucleons.
    4. 4. • XAtomic number (Z): is the number of protons inside the nucleus that equal the no. of electrons . It determine the chemical properties of atom & identify the identity of element. • XMass number (A): the total number of protons & neutrons (nucleons). A • Nuclide is defined as zX
    5. 5. • Electrostatic force is a force between positively charges nucleus and negatively charged electrons (attracting force) balances the centrifugal force of rapidly moving electrons . • That keeps electrons maintained in their shells.
    6. 6. • Electron Binding energy (Ionization energy): • It is the energy required to remove electron from a given shell. • It should exceeds the eletrostatic force binding that electron to nucleus.
    7. 7. Atom (cont.) • The inner shells have more binding energy more than outer shells. • E.g. K-shell > L-shell> M-shell ..etc.
    8. 8. Ionization: • Atom is ordinary neutral as the number of electrons equal the number of protons. • If atom loses an electron, it becomes a positive ion and free electron is a negative ion. • This process of forming an ion pair is termed Ionization.
    9. 9. Ionization (cont.) • XIonization of inner shell electrons (K, L) require high energy to be ejected from their orbit (X-ray, Gamma rays or high energy particles) . • Ionization of electrons on outer shells require low energy particles (ultraviolet)
    10. 10. Nature of radiation: • X1- Corpuscular or particulate radiation: • A minute particles which have mass & charge traveling at straight line with high speeds. • A- Alpha Particles: composed of Helium nuclei (2P+2N) without orbital electrons. • Because of their double charge & heavy mass they loss their energy very quickly and have shallow tissue penetration .
    11. 11. Nature of radiation (cont.) • B- β- Particles: • They are emitted from nuclei of radioactive atoms & possess 1 unit of negative charge. • They are more penetrating than α-particles. • C- Cathode Rays (electrons): • Streams of electrons passing from the hot filament of cathode to anode target in x-ray tube.
    12. 12. Nature of radiation (cont.) • The capacity of particulate radiation to ionize atoms depends on its ; • Mass, velocity and charge. • The rate of loss of energy from a particle as it moves along its track through matter (tissue) is called Linear Energy Transfer (LET). • The slower heavy particles have higher LET.
    13. 13. Nature of radiation (cont.) • 2- Electromagnetic radiation: • It is a propagation of energy through space accompanied by electric and magnetic force field where they are perpendicular to each other. e.g. Xray & Gamma rays. • Electromagnetic radiations are arranged according to their energies in what is termed electromagnetic spectrum.
    14. 14. Nature of radiation (cont.) • Electromagnetic spectrum (EMS): • Energies in EMS are grouped according their wavelengths or energy of their photons . • They ranges from radio-waves to gamma & xrays.
    15. 15. Nature of radiation (cont.)             EM radiation regard as both a particle & wave. Particle concept: Discrete bundle of energy → Photons ( Quanta). Photons have no mass or weight travel in straight line & carrying EM energy. Wave concept: EM radiation → Waves characterized by; 1- Velocity →speed of wave (speed of light 3×108 m/s). 2- Wavelength (λ) → distance between the crest of one wave & the crest of the next. 3- frequency (F): refers to the number of wavelengths that pass a given point in a certain amount of time. C= λ√ (lambda × nu) C= velocity of light, λ= wavelength in meters, √= frequency in hertz (cycle per second).
    16. 16. Waves Short Wavelength Long wavelength • • • • wavelength All light waves travel at the same speed, c = 300,000 km/s Wavelength is the distance between two crests of the wave Frequency is the number of crests that pass by you in a second The longer the wavelength, the lower the frequency, the lower the energy of the photon
    17. 17. What are x-rays? • XA weightless bundles of energy (photons) without an electrical charge that travel in waves with a specific frequency at the speed of light. X-ray photons interact with the materials they penetrate and cause ionization.
    18. 18. Properties of x-ray X1- x-ray are invisible and weightless. 2- They travel in straight line. 3- They travel at the speed of light. 4- They have a wide range of wavelengths. 5- They can not be focused to a point; over distance the beam diverges like beam of light.
    19. 19. Properties of x-ray (cont.) 6- due to their short wavelengths , they penetrate materials that absorb or reflect visible light. 7- They are absorbed by matter; that depends on atomic structure of matter and wave-length of xray. 8- They cause certain substances to fluoresce ; to emit radiation of long wavelength (visible or ultraviolet rays). 9- they produce biologic changes in living cells. 10- they can ionize gases and materials they penetrate.
    20. 20. Interaction of x-ray with a matter: • When x-ray photons arrive at the patient , one of several events may occur; • 1- x-ray can pass through the patient without any interaction. • 2- x-ray photons can be completely absorbed by the patient. • 3- x-ray photons can be scatered.
    21. 21. Interaction of x-ray with a matter(cont.): • At the atomic level 4 interactions could be occur when x-ray photons interact with matter; • 1- No interaction. • 2- Absorption or photoelectric effect. • 3- Compton scatter. • 4- Coherent scatter.
    22. 22. 1- No interaction: • The x-ray photon passes through the atom unchanged and leaves the atom unchanged. • It is responsible for producing densities on film and make dental radiography possible.
    23. 23. 2- Absorption & Photoelectric effect: • Absorption: • X-ray photon may be completely absorbed by tissue. • At atomic level absorption occurs as a result of the photoelectric effect. • An x-ray photon collides with a tightly bound, inner shell electron and give up all of its energy to eject the electron from its orbit. • The ejected electron is termed a photoelectron and has a negative charge and absorbed by another atom. • The photoelectric effect accounts for 30% of dental x-ray.
    24. 24. 3- compton scatter • X-ray photon may be deflected from its path as it termed scatter. • In compton scatter , x-ray photon collides with loosely bound, outer shell electron and gives up part of its energy to eject it . • The ejected electron is termed a compton or recoil electron with negative charge. • Compton scatter accounts for 62% of the scatter in diagnostic radiology.
    25. 25. 4- coherent scatter: • A coherent or unmodified scatter occurs when a low energy x-ray photon interacts with outer shell electron. • No change or no ionization occurs. • The x-ray photon is scattered in different direction than the incident photon. • The x-ray photon is unmodified and simply change its direction without change in energy.