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# Physics

### Bushong Ch 10

x-rays interact with matter in the following five ways. 1) by coherent scattering, 2) through the Compton effect, 3) through the photoelectric effect, 4) by pair production, and 5) by photodisintegration.
What effects are important in making an x-ray image? Compton effect and photoelectric effect.
Eletromagnetic radiation interacts with structures that are similar in size to? The wavelength of the radiation
True or False: X-rays have very short wavelengths. True
The higher the energy of an x-ray, the (shorter or longer) is it's wavelength. shorter
moderate energy x-rays generally interact with what part of the atom and high energy x-rays generally interact with what part of the atom? electrons; nuclei.
Coherent scattering is sometimes called what? Coherent scattering is an interaction between what? Classical scattering or Thompsons scattering. Low energy x-rays (below 10 keV) and atoms
In Coherent Scattering the incident x-ray interacts with a target atom causing it to become? excited. Low energy x-rays cannot ionize an atom.
(Coherent Scattering) The excited atom immediately releases this excess energy as a scattered x-ray with a wavelength equal to the incident x-ray. True or Fase True. Because the atom is just excited instead of ionized the incident x-ray and the scattered x-ray have the same wavelength and energy.
(Coherent Scattering) The incident x-ray and the scattered x-ray have the equal wavelength and equal energy but the scattered x-ray moves in what direction? A slightly different direction.
The result of coherent scattering is a change in direction of the x-ray without a change in its? energy
(Coherent Scattering) There is no energy transfer, and therefore no? ionization.
Most coherent scattered x-rays are scattered in what direction? The forward direction.
Coherent scattering is of little importance to? Diagnostic radiology
(Compton Effect) The interaction of an incident x-ray with an outer-shell electron that scatters the x-ray and also reduces its energy and ionizes the atom is called? The compton effect or compton scattering.
(Compton Effect) The x-ray interacts with an outer shell electron and ejects it from the atom. This is called ionization
(Compton Effect) The ejected electron is called? A Compton electron or a secondary electron.
(Compton Effect) The x-ray continues in a what direction with how much energy? different; less
(Compton Effect) True or False. The energy of the Compton scattered x-ray is equal to the difference between the energy of the incident x-ray and the energy of the ejected electron. True
(Compton Effect) The energy of the ejected electron is equal to? Its binding energy plus the kinetic energy with which it leaves the atom.
The mathematical formula for the Compton Effect is? Ei=Es (Eb+Eke) Ei is the energy of the incident x-ray Es is the energy of the scattered x-ray Eb is the electron binding energy Eke is the kinetic energy of the electron.
During a Compton interaction, most of the energy is divided between? Scattered x-ray and the Compton electron.
Compton scattered x-rays can be deflected in any direction, including 180 degrees from the incident x-ray. True of False True
(Compton Effect) At a defelction of 0 degrees, how much energy is transferred? none
(Compton Effect) As the angle of defelction increases to 180 degrees, more energy is transferred to? The compton electron
(Compton Effect) Even at 180 degrees of deflection, the scattered x-ray retains at least approximately how much of it's original energy? Two-thirds
(Compton Effect) x-rays scattered back in the direction of the incident x-ray beam is called? Backscatter radiation
(Compton Effect) The probability of the Compton effect decreases as x-ray energy? Increases
The probability of the Compton effect is inversely proportional to x-ray energy (1/E) and independent of? atomic number
Compton scattering reduces? image contrast
Compton scattering in tissue can occur with all x-rays and therefore is of considerable importance in? x-ray imaging
Scattered x-rays provide what kind of information on the radiograph? No useful information
The photoelectric effect occurs when an incident x-ray is totally absorbed during the ionization of an inner shell electron. True or False? True
(Photoelectric Effect) The electon removed from the atom is called? a photoelectron
What happens to the incident x-ray during the photoelctric effect? The x-ray is totally absorbed.
(Photoelectric Effect) Photoelectric interaction produces what type of x-ray? a characteristic x-ray.
(Photoelectric Effect) Ejection of a K-shell photoelectron by the incident x-ray results in? A vacancy in the K shell
A photoelectric interaction CANNOT occur unless the incident x-ray has energy how much energy? equal to or greater than the eletron binding energy.
True or false. The probability of photoelectric effects is inversely proportional to the third power of the atomic number of the absorbing material. False. It is directly proportionalx-ray to the third power of the x-ray energy and inversely proportional to the third power of the absorbing material.
True or False: The probability of the photoelectric effect is inversely proportional to the third power of the x-ray energy. True
True of False: Pair production occurs during x-ray imaging. False. It does NOT occur during x-ray imaging.
If an incident x-ray has sufficient energy, it may escape interaction with electrons and come close enough to the nucleus of the atom to be influenced by the? Strong nuclear force field.
The interaction between the x-ray and the nuclear field causes the x-ray to???? and in it's place, ???? electrons appear, one ??? charged (positron) and one ????? charged. This is called disappear; two; positively; negatively; pair production
Pair production occurs with x-rays that have energies greater than? 1.02 MeV.
(Pair Production) The x-ray interacts with? the nuclear force field
(Pair Production) How many electrons that have opposite electrostatic charges are created. Two
(Pair Production) The energy equivalence of the mass of an electron has been calculated to be 0.51 MeV
Because two electrons are formed in pair production interaction with 0.51 MeV, the incident photon must have at least how much energy? 1.02 MeV
(Photodisintegration) X-rays with energy above approximately 10 MeV can escape interaction with electrons and the nuclear force field and will be absorbed by what? The nucleus.
(Photodisintegration) When the high energy x-ray is completely absorbed by the nucleus, the nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment. This process is called what? Photodisintigration
True or False: Photodisintegration does NOT occur in diagnostic radiology. True
Photodisintegration is an interaction between what type of x-ray energy (high, moderate or low) and what part of the atom? high energy; nucleus
(Photodisintegration) The x-ray is absorbed by the nucleus, and the nuclear fragment is emitted. True or False? True
(Differential Absorption) More important than the interaction of the x-ray by Compton or photoelectric effect is the x-ray transmitted through the body without interacting. True
(Differential absorption) occurs because of Compton scattering, photoelectric effect and x-rays transmitted through the patient. True
(Differential Absorption) Of the five ways an x-ray can interact with tissue, how many are important to radiology? Two, Compton effect and photoelectric effect.
(Differential Absorption) Compton scatter results in image noise. True of False? True
(Differential absorption) increases as kVp is increased or reduced? reduced.
(Differential Absorption)Approximately what percent of the x-rays incident on a patient reach the image receptor? 1%
(Differential Absorption) An x-ray image results from the difference between x-rays absorbed photoelectrically in the patient & those transmitted to the image receptor. This difference in x-ray interaction is called? Differential absorption
(Differential Absorption) The relative probability of interaction between bone and soft tissue (differential absorption) remains constant, whereas the absolute probability of each decreases with increasing energy. True or False True
(Differential Absorption) X-rays that undergo photoelectric interaction are absorbed and produce what areas of the radiograph? the absorbed x-rays produce the white images on the radiograph, such as bones.
(differential Absorption) At low energies, most x-ray interactions with tissue are photoelectric. At high energies, Compton scattering predominates. True of False. True
(Differential Absorbtion) The interaction of x-rays with tissue has what type of relationship to the mass density of the tissue regardless of the type of interaction? proportional. When mass density is doubled, the chance for x-ray interaction is doubled because twice as many electrons are available for interaction.
(Contrast Examinations)What compounds are needed as an aid for imaging internal organs with x-rays? When used in this fashion they are called? Barium and iodine compounds. Contrast agents.
Air is still used for contrast in some examinations of the colon along with barium; this is called? (Contrast Examinations) When used in this fashion, air is what type of contrast agent? A double-contrast examination. negative
(Exponential Attenuation) When x-rays are incident on any type of tissue, they can interact with the atoms of that tissue through any of these five mechanisms. Coherent scattering, Compton effect, photoelectric effect, pair production, and photodisintegration.
(Exponential Attenuation) The relative frequency of interaction through each of the five interactions with matter depends on what? The atomic number of the tissue atoms, the mass density, and the x-ray energy.
(Exponential Attenuation) An interaction such as the photoelectric effect is called an absorption process because the x-ray disappears. ABSORPTION is an all-or-none condition for x-ray interaction. True
(Exponential Attenuation) The total reduction in the number of x-rays remaining in an x-ray beam after penetration through a given thickness of tissue is called? Attenuation
(Exponential Attenuation) Attenuation is the product of? absorption and scattering
(Exponential Attenuation) X-rays are attenuated exponentially which means what? They do not have a fixed range in tissue.
(Exponential Attenuation) Attenuated x-rays are reduced in number by a given percentage for each incremental thickness of tissue they go through. True.