Produced by accelerating electrons with high voltage and allowing them to collide with metal target (anode), e.g, Tungsten. Three Events (Two types of x-ray) a) Heat X-Ray Tube b) bremsstrahlung (braking radiation) c) characteristic radiation emission, Photoabsorption or photoelectric absorption is the dominant interaction mechanism in the soft X-ray regime and for the lower hard X-ray energies. At higher energies, Compton scattering dominates. Which of the materials should be used to produce soft X-ray and hard x rays? Ba (Z = 56) W (Z = 74) preferred target Mo (Z = 42) Pb (Z = 82) Pd (Z = 64) 12/20/16 1
What is the minimum energy of the e -beam in the X-ray tube If an electron is ejected from the K shell. The vacancy is filled with a second electron from the M shell. The produced photon is referred to as: The direct interaction of an incident electron with the nucleus of an atom results in X-ray production g -ray production
The Interaction of X-Rays with Matter Attenuation A process by which radiation loses power (reduce intensity) as it travels through matter due to the interaction with it. half-value-layer (HVL) is the thickness at which the intensity/energy is reduced by half Deferential Absorption The deference of absorption of radiation (x-ray) by deferent body tissues. e.g., image of the bone is produced because more x-rays are absorbed by bone than by the surrounding soft tissue. Resulted from - Transmitted x-ray through tissue. - Compton scattering by tissue. - Photoelectric effect. Depends on 1) Incident radiation (x-rays) energy. 2) Tissue atomic number. 3) Tissue mass density
The Interaction of X-Rays (high energy photon) with Matter Attenuation 1) As x-ray energy increases - Less Compton scattering - Slight increase in photoelectric interaction - More transmission through tissue Absorption edge: when the photon energy reaches the binding energy level for, e.g. E K, interaction with the K-shell electron becomes possible and the probability of photoelectric absorption jumps to a higher value; The K-absorption edge occurs at different photon energies with different materials.
The Interaction of X-Rays with Matter 2) As tissue atomic number increases - Very slight effect on Compton interaction - More photoelectric effect - Less x-ray transmission They depend on number of electrons, rather than, the mass number of the matter, the valency of a target matter, the free binding energy E K (kev), and the Molecular configuration. 3) As tissue mass density increases - Increase in Compton interaction - Increase in photoelectric interaction - Reduction in transmission through tissue Attenuation
Exponential decay
Ionizing and Non-Ionizing Radiation photons Non-ionizing Radiation Has enough energy to move atoms in the molecular range or cause vibrational or rotational excitations, but not enough to remove electrons. Uses - Microwave radiation for telecommunications and heating food - Infrared to provide heat - Radio waves for broadcasting
Secondary Electrons and Ionization Photons with enough energy can ionize atoms through the photoelectric and Compton effects Secondary electron: the recoiled electrons and photoelectrons set moving in the material; - Secondary electrons will have enough energy to ionize more atoms. - As they travel through the material they interact with the outer shells of the atoms and excite (ionize) them; Effects of Ionization - Air and gases become electrically conducting (the measurement of X- and gamma-rays); - Cause biological damage; - The excitation of atoms makes them emit light (luminescence); - Photographic effect (silver, bromide); - Heating of the material
Non-ionizing radiation may cause electrical shocks and burns Ionizing radiation produce general health effects, with variation with different tissue types. - damage the process of normal cell leading to cancer Natural sources of radiation in the environment - Background radiation: naturally occurs in our environment from earth, sun, our galaxy, other galaxies, and universe background. It is very low intensity. One CT scan can be equal to several years of background radiation exposure -Radon: colorless, odorless gas that comes from decaying rocks and soil; Accounts for half of annual exposure to radiation of average individual. Second leading cause of lung cancer after smoking. - Cosmic and terrestrial radiation: 8% of our average yearly exposure to radation, e.g., UV rays. UV rays can damage DNA in the skin and cause cancer.