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Physics U6 &HW
| Question | Answer |
|---|---|
| Which of the following is NOT one of the five basic x-ray interactions with matter? | bremsstrahlung |
| which of the following x-rays would be most likely to undergo classical scattering? | 5 keV |
| Which of the following interactions contributes to image noise? | Compton scattering |
| Which of the following occurs in a Compton interaction? | An atom is ionized |
| If Ei= incident x-ray energy, E(s)=scattered x-ray energy, E(b) =electron binding energy, and E(KE)= secondary electron kinetic energy, then which of the following is true? | E(i) = E(s)+ E(b)+ E(KE) |
| If Ei= incident x-ray energy, E(s)=scattered x-ray energy, E(b) =electron binding energy, and E(KE)= secondary electron kinetic energy, then which of the following is true? | E(s) = E(KE)+E(i)-E(b) |
| During Compton effect, most of the incident x-ray energy is given to which of the following? | Scattered x-ray |
| After Compton scattering, the scattered x-ray has? | longer wavelength |
| Compton interaction affects the image by increasing which of the following? | Noise(fog) |
| The probability that an x-ray will interact with an outer shell electron is influence principally by | The energy of the incident x-ray |
| The compton effect is | independent of Z |
| The Compton effect is the principle source of | image noise(fog) |
| If 45keV x-ray interacts with the K-shell electron in an atom of molybdenum(E(b)=20keV) and ejects it with 8keV energy what will be the enrgy of the scattered x-ray? | 17keV |
| The probability that an x-ray will undergo Compton interaction decreases with | increasing x-ray energy |
| The compton interaction involves so-called "unbound" electron because | they have very low binding energy |
| Which of the following is the x-ray interaction that does NOT cause ionization? | Classical Scattering |
| Compton-scattered x-rays have | lower energy than an incident x-ray |
| If Ei= incident x-ray energy, E(s)=scattered x-ray energy, E(b) =electron binding energy, and E(KE)= photoelectric kinetic energy, then which of the following is true? | E(i) =E(b)+ E(KE) |
| If Ei= incident x-ray energy, E(s)=scattered x-ray energy, E(b) =electron binding energy, and E(KE)= photoelectric kinetic energy, then which of the following is true? | E(KE)=E(i)-E(b) |
| The photoelectric effect is principally associated with which of the following | Absorption of an x-ray |
| A 50 keV x-ray has a 0.02 chance of photelectric interaction with muscle(Z=7.4). What is the chance of interacting with bone(Z=13.8)? | .021024576 |
| Which of the following has the lowest effective atomic number? | fat |
| Photoelectric interaction with soft tissue is most likely with which of the following x-rays | 0.3keV |
| during photoelectric interaction | An electron is emitted from the atom |
| During operation at 80 kVp, which of the following photoelectric interactions is most probable? | 30keV x-ray and bone |
| The radiographic image is formed principally by which of the following | photoelectric interaction |
| the probability of photoelectric effect varies as the function of x-ray energy(E)? | E(-3) |
| As a result of photoelectric interaction | an electron leaves the atom |
| the photoelectric effect is | The complete absorption of an x-ray with the subsequent emission of an electron |
| Lead has a K-shell electron binding energy of 88keV therefore an | 84 keV x-ray can undergo photoelectric interaction with the L-shell electron |
| A 39keV x-ray interacts through photoelectric effect with a k-shell electron of barium(binding energy 37keV0 therefore | the photoelectron will have 2 keV energy |
| the probability of photoelectric effect varies as what function of target atomic number (Z)? | Z(3) |
| Anatomic structures that readily transmit rays are called | radiolucent |
| differential absorption, although a complicated process, is basically the result of differences between | photoelectric effect and transmission |
| when a radiograph is taken | low kVp is necessary when soft tissue is imaged because it leads to high photoelectric effect |
| At what approximate x-ray energy is the probavility of a photoelectric interaction in soft tissue equal to the probability of compton interaction | 20keV |
| which of the following has the greatest mass density | bone |
| The colon is imaged during a barium enema examination principally because of differences in | subject atomic number |
| Air-contrast studies such as a colon examination are successful principally for which of the following reasons | there are differences in effective atomic number && in mass density |
| To optimize x-ray mammography | the main x-ray interaction should be the photoelectric effect |
| Differential absorption between bone and soft tissue occurs principally for which of the following reasons | There is a difference in effective atomic number |
| Angiography with iodinated compounds | works principally because of the differences in effective atomic number |
| Differential absorption is | The difference between those x-rays that are absorbed and those that are transmitted |
| As kVp increases the relative number of x-rays | that interact with tissue decreases |
| In which of the following tissue does differential absorption most depend on differences in mass density | lung and bone |
| How is photoelectric interaction with tissue related to the mass density(p) of the tissue | it is proportional |
| Lungs are imaged on a chest radiograph principally because of the differences in which of the following | tissue mass density |
| Differential absorption between lung and soft tissue occurs principally because of which of the following | the difference in mass density |
| The reduction in intensity of an x-ray beam after it passes through tissue is called | attenuation |
| x-ray transmission decreases exponentially, which also means that | the number of x-rays is never reduced to zero |
| Which process contributes most to the radiographic image | photoelectric effect |
| High kVp in chest radiograph will | reduce patient dose |
| Increasing kVp in imaging will | reduce skin dose |
| In high kVp chest radiography contrast depends most upon | Mass density |
| Microcalcifications are imaged on mammograms principally because of | Atomic number |
| More contrast is present froma barium examination than from an iodine examination because | barium has a higher atomic number |
| Photoelectric effect is proprtional to | Z(3) |
| what will increase the energy of bremsstrahlung radiation | x-ray tube voltage |
| Compton interaction occur with outer shell electrons and result in | recoil electron + photon of lower energy && reduced gray scale |
| At 60keV in soft tissue what predominates | compton scattering |
| What does the interaction of the photons with matter depend on? | the energy(kVp)& nature of the radiation photon; the atomic number(Z) of the subastance being irradiated |
| What is the difference between x-ray and gamma radiation; what are they identical in? | their origin is different x-ray comes from the shells and gamma comes from the nucleus; Their therapeutic effects are identical |
| High energy photons liberate ____ ____ from the orbits of atoms by various types of interactions | secondary electrons |
| What is ultimately responsible for the biologic effects of x-ray and gamma radiation | the energy absorbed from the liberation of the secondary electrons and their spatial distribution |
| What is the name of the differnt types of electrons ejected from the energy shells of an atom by incident photons called | secondary electrons |
| Name two different types of secondary electrons | recoil electrons and photoelectrons |
| Only what contributes to biologic effects | absorbed energy |
| What are the 4 types of diagnostically significant interactions | transmission of photons unchanged; unmodified scattering; photoelectric effect with true absorption ; modified scatter |
| what are the 2 types of therapeutic radiology | pair production and photodiscentigration |
| What interaction cause the blackness(density) on the film | transmission of photons unchanged |
| what are the two key factors that the interactions depend on? | kVp and atomic number |
| Atoms consist largely of what in the transmission of photons unchanged interaction | empty space |
| The actual particles in the atom(protons, neutrons, and electrons) constitute about how much of the volume of the atom | 10(-12) or one-million-millionth |
| A number of photons in any given x-ray beam passes directly through the atom without encountering an electron is called what type of interaction | transmission of Photons unchanged |
| The bringing about of less orderly arrangement of photon's direction due to the deflection caused by charged particles(orbital electrons) interposed in the path of the beam is known as | Scattering |
| Charged particles is also called | Orbital electrons |
| What is another name for unmodified scattering? | classical or Thompson scattering |
| What are the two types of scattering | modified and unmodified |
| Unmodified scattering refers to the scattering of radiation by what | relatively free charged particles(electrons) or outer shell electrons of an atom |
| Eplain classical scattering(unmodified)(where do electromagnetic waves pass;what does the electrical field of radiation do; what happens to the photon; what happens to the electron; what stays the same in the photon and what changes) | near an electron;sets the electron oscillating w/the same freq. of the incident electromagnetic waves;disappears in the electron;the electron then forces the radiation out & stops ocillating; photon is traveling in a differ direct but has the same energy |
| What is the new photon or scattered photon called and why | "in step" b/c this type of scattering of primary/incident photon is caherent or equal to the orginal energy |
| There is NO______ of energy from photo to electron in unmodified scattering. The ONLY thing that has changed is what? | transfer; the direction of the Incident photon)(now called scattered) |
| When does classical scatter occur | only if the incident photon does not have sufficient energy to dislodge the orbital electron; its predominant below energies of 10 keV |
| Does unmodified scattering have practical use in the Diagnostic Radiology | NO |
| Photoelectric interaction with true absorption creates | secondary radiation |
| Where does photoelectric absorption take place aand how much energy does it have | takes place when an incident photon(the primary beam) interacts with an inner atomic electron and has enough energy to eject the electron from its shell |
| All the energy of the photon during photoelectric interaction with true absorption must be what | equal or exceed the binding energy of the electron |
| During photoelectric interaction with true absorption the photons energy will be transferred where | to the dislodged electron |
| The nam given to the ejected orbital electron | photoelectron |
| what is the process called when the electron is given kinetic energy | photoelectric process |
| What interaction gives the white or clear image on a film | photoelectric interaction with true absorption |
| What is the formula for the Photoelectric Interaction with True Absorption? | E(i)= E(b) + E(ke) |
| During the Photoelectric Interaction, the secondary radiation occurs when the atom _______ the now vacant hole left by the dislodged __________. | Fill; Electron |
| When is the secondary radiation created and what is it characteristic of? | Radiation is created when the hole is filled and is characteristic of the shell that is now filled |
| What is the energy of the secondary radiation? | The inner-shell (K) binding energy - the binding energy of the shell the electron was pulled from (usually L) |
| During the Photoelectric Interaction with True Absorption, what type of energy is the secondary radiation? | Weak and not of diagnostic importance |
| The probability of occurrence for Photoelectric Interaction with True Absorption is dependent upon what 2 things? | 1)The kVp of the incident photon 2)The atomic number of the irradiated substance |
| The probability of occurrence for Photoelectric Interaction is ______________ proportional to the _______ of kVp. | Inversely Proportional; Cube of kVp (1/kVpᶾ) (photon energy) |
| The probability of occurrence for the Photoelectric Interaction is __________ proportional to the ________ of the atomic number of the irradiated substance. | Directly Proportional; Cube of Z (Zᶾ) (Atomic #) |
| As probability increases kVp__, wavelength___, Fequency____, Hardness of the beam___, and quality of the beam___ | decreases;increases;decreases;decreases;decreases |
| As the Atomic # of the irradiated substance increases the probability of occurrence for the Photoelectric Interaction ___________. | Increases |
| If you know the energy of the incident photon and the atomic number of the irradiated substance, what is the formula for the probability of occurrence? | Probability = Zᶾ/kVpᶾ |
| What is the energy of the photon for the Photoelectric Interaction w/ True Absorption? | Up to 50 kVp numbers |
| Photoelectric Interaction w/ True Absorption usually occurs with atoms of ________ atomic numbers. | High |
| During Photoelectric Interaction w/ True Absorption, why is it possible to see contrast differences in substances that have close atomic numbers? | The Density of the substances |
| The greater the density of a substance being irradiated means the ___________ the probability of Photoelectric Interaction. | Greater |
| Modified scattering is also referred to as the ___________ __________. | Compton Effect |
| During Modified scattering, what kind of electron does the incident photon interact with? | Loosely bound outer-shell electron |
| The Compton Effect occurs at photon energies up to _______ kVp. | 100 kVp |
| During the Compton Effect, the electron that interacts with the photon becomes a __________ or (AKA) ___________ electron. | Recoil or (AKA) Compton Electron |
| The amount of energy gained by the recoil electron depends on the __________ it's hit by the incident photon | Angle |
| During the Compton Effect, what becomes of the energy from the incident photon? | Some is used dislodging the electron and the remainder is divided between the recoil |
| During the Compton Effect (Modified Scattering) the more direct the hit of the incident photon to dislodge the electron, the __________ energy will be transferred to the ___________ Electron. | More; Recoil |
| During Modified Scattering, the less direct the hit of the photon on the electron, the _________ energy will remain with the _________ photon. | Less; Scattered |
| During the Compton Effect, how is the scattered photon different from the incident photon? | Traveling in a different direction; Energy (frequency) is decreased and wavelength |
| Give the formula for the transfer of energy from the incident photon during the Compton Effect: | E(i)= E(s) + E(b) + E(ke) |
| Give the subscripts for the Compton Effect formula: 1)i, 2)s, 3)b, 4)ke | 1)i=Incident photon 2)s=Scattered photon 3)b=Binding energy of electron 4)ke=Kinetic |
| This is radiation that is scattered 180° from the direction of travel of the incident photon: | Backscatter Radiation |
| Backscatter radiation is also known as ________ and puts the _________ on the radiographic image. | fog; gray |
| 1)Photoelectric Interaction: Photon energy: 2)Compton Scattering: Photon energy: 3)Thompson Scattering: Photon energy: | 1)Up to 50 kVp 2)Up to 100 kVp 3)Below 10 keV |
| What interactions occur with INNERSHELL electrons? | Photoelectric Interactions w/ True Absorption |
| What interactions occur with OUTERSHELL electrons? | Unmodified Classical (Thompson) Scattering & Modified Scattering/Compton Effect |
| Which interaction is responsible for Fog? | Modified Scattering / Compton Effect |
| What interaction does not involve an electron? | Transmission of Photons Unchanged |
| Which interactions eject orbital electrons? | Photoelectric and Compton |
| Which interaction can cause images of the cassette locks on the back of the cassette to show up on the Radiograph? | Backscatter from Modified Scattering |
| Which interaction increases the scale of contrast and actually "degrades" contrast? | Compton Scattering |
| What devices are available to reduce the negative effects of Compton Scattering? | Collimation and Grids |
| Increasing the hardness (quality) of the beam and Increasing kVp will have what effect on the probability of Compton Scattering? | Decrease the probability( also increase of frequency and wavelength) |
| Increasing the photon energy ____________ the probability of Compton Scattering and ____________ the problem caused by Compton Scattering. | Decreases; Increases |
| Why does the problem with Compton Scattering increase as the energy of the incident photon increases? | The scattered photons produced from the interaction will be strong enough to (1) continue traveling in a straight line to the film & (2) are stronger when they reach the film |
| Why does the probability of occurrence decrease as the kVp increases? | Because the number of interactions will decrease as the photon's energy increases (it will not interact with an electron and go straight through the patient to the film) |
| What are some cassettes designed with to prevent backscatter | lead lined backs because it can cause images of back locks of the cassette to show up on the film if not |
| Pair Production occurs with photon energies of: | At least 1.02 MeV |
| What subatomic particle does the photon interact with during Pair Production Interaction? | The Nucleus |
| During Pair Production, a photon disappears into a ___________ of an atom and ejects 1 _____________ electron and 1 ____________ electron. | Nucleus; Negative; Positive |
| What is the name of and what becomes of the ejected negative electron during Pair Production? | Negatron; Behaves like any other electron |
| What becomes of the ejected Positron during Pair Production? | Slows by interacting with other atoms and combines with an electron |
| Why would a Positron combine with an electron from another atom? | Because it's charge is positive and will combine with subatomic negative particles (electrons) |
| After a Positron combines with an electron it forms a ___________. | Positronium |
| A Positronium is an _________ atom which is very ___________. The subatomic particles that created to form a Positronium _____________ eachother. | Exotic Atom; Very Unstable; Annihilate |
| When the Positronium explodes it creates _______ Photons of ___________ energies | 2; equal |
| If the incident photon was 1.02 MeV, what would be the energy of the resulting gamma photons be and how will they travel? | 0.51 MeV Each; Travel in opposite directions |
| During Pair Production the first conversion is from energy to ______. The Second conversion is from ____________ to __________. | Matter (photon to positronium); Matter to energy (positronium to 2 photons) |
| The reaction that causes the Positronium to produce 2 photons is called the _____________ Reaction. | Annihilation |
| Pair Production occurs with photon energies from _________ to __________. | 1.02 MeV to 10 MeV |
| What is differential absorption? | the difference b/t those x-rays absorbed photoelectrically and those not absorbed; this is how an x-ray image is formed |
| Differential Absorption increases as kVp is | decreased |
| Absorbed radiation and appears clear | radiopaque |
| Allows radiation to pass through and appears black | radiolucent |
| The interaction b/t x-rays and tissue is proportional to the mass density of the tissue | mass density |
| if mass density is doubled then what happens to the photoelectric interaction | it is doubled |
| Radiation that is absorbed by a given percent per each incremental thickness of matter | exponential attenuation |
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