Physics Chapter 7 Flashcards Preview

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Flashcards in Physics Chapter 7 Deck (37)
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Know what classical interactions is also commonly called:

Coherent scattering or Thomson Scattering


Be able to describe what low energy atom does in classical scattering:

the incident x-ray photon interacts with an orbital electron of a tissue atom & change direction


KNow what happens when the energy from an atom in classical scattering is reemitted in a new direction

becomes a scatter photon


Be able to describe what the low energy causes in classical scattering

most classical scatter photons are absorbed in the body through other interactions & do no contribute significantly to the image, but do add slightly to patient dose


Know when Compton scattering commonly occurs in the diagnostic range

moderate energy x-ray photons (20-40 keV)


Know the 3 things a Compton interaction does

*Ionizes the atom making it unstable
*Ejected electron (Compton Electron/Secondary electron) leaves the atom with enough energy to go through interactions of its own in adjacent places
*The incident photon is deflected in a new direction and is now a Compton scatter


Know what the problem is with a Compton scatter interacting with the IR

it is not following its original path through the body & strikes the IR in the wrong direction **creates fog


Know what the most prevalent interaction between x-ray photons and the human body is

Compton scattering


Know what is responsible for most of the scatter that fogs an image

Compton scattering/interactions


Know what Compton scattering does NOT depend on

Atomic number


Know what the probability of Compton scattering is related to

Energy of the photon


Know what happens in Compton interactions as the x-ray photon energy increases

the probability of that photon penetrating a given tissue without interaction increases


Know in which direction Compton scatter photons can travel

any direction


Know what a deflection of zero degrees means with Compton interactions

means no energy transferred


Know what it represents with a 180 degree scatter deflection

maximum deflection and energy transfer


Know how much energy a scattered photon retains

Two thirds of its energy


Know where a Compton scattered photon can end up after exiting the patient

Near the patient/could expose the radiographer


Know where the major source of occupational exposure comes from

Compton scattering


Know the diagnostic range that photoelectric interactions occur

20-120 kVp


Know how photoelectric events occur

*Photoelectric interactions occur throughout the diagnostic range (20-120 kVp) & involve inner-shell orbital electrons of tissue atoms
*the incident x-ray photon energy must be equal to or greater than the orbital shell binding energy


Know what the x-ray photon does in photoelectric interactions

interacts with the inner-shell electron of a tissue atom & removes it from orbit
--The incident photon expends all its energy & is totally absorbed


Know what the absorption if the photoelectric interaction contributes to

Patient dose


Know what is necessary to create an x-ray

Although some absorption is necessary to create an x-ray image, it is the radiographers responsibility to select technical factors that strike a balance between image quality (needed absorption & transmission of x-ray photons to produce a good image) & patient dose


know the importance of the inner shell vacancy in photoelectric interactions

what makes the atom unstable


know what the source of secondary photons contributes to

patient dose


Know what the probability of photoelectric interaction depends on

the energy of the incident photons & the atomic number of the tissue atoms with which it interacts


Know what has to happen for photoelectric interactions to occur

the incident x-ray photon energy must be greater than or equal to the inner-shell binding energy of the tissue atoms involved


Know what happens in photoelectric interactions when the kVp is to high

less absorption takes place & some absorption is necessary for image formation


Know what the probability of photoelectric events is directly proportional to

the third power of the atomic number of the absorber


Know what the cubic relationship means to you the radiographer

when he or she makes small changes in the kVp setting or there are small changes in the atomic number of the tissue( anatomic variations or a pathologic condition) large changes in the probability of photoelectric events will result


In regards to photoelectric events what happens to tissues with higher atomic numbers

the greater the number of photoelectric events


In regards to photoelectric interaction photons what does bone do

more photons are absorbed, which means fewer photons are exposing the IR, resulting in the lighter shades on an image


Know what must be done in regards to photoelectric events if a structure isn't visualized well on an image

contrast agents are added


Know when pair production occurs

only with very high energy photons of 1.02 MeV or greater


Know what happens in a pair production interaction

the interaction occurs when the incident x-ray photon has enough energy to escape interaction with the orbital electrons & interact with the nucleus of the tissue atom


Know why differential absorption is called "differential:

different body structures absorb x-ray photons to different extents


Know what absorption depends on

the density of body tissue in which photons are passing