Physics Chapter 7

Question 1

Know what classical interactions is also commonly called:

Answer 1

Coherent scattering or Thomson Scattering

Question 2

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

Answer 2

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

Question 3

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

Answer 3

becomes a scatter photon

Question 4

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

Answer 4

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

Question 5

Know when Compton scattering commonly occurs in the diagnostic range

Answer 5

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

Question 6

Know the 3 things a Compton interaction does

Answer 6

• 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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Compton scattering

Question 9

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

Answer 9

Compton scattering/interactions

Question 10

Know what Compton scattering does NOT depend on

Answer 10

Atomic number

Question 11

Know what the probability of Compton scattering is related to

Answer 11

Energy of the photon

Question 12

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

Answer 12

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

Question 13

Know in which direction Compton scatter photons can travel

Answer 13

any direction

Question 14

Know what a deflection of zero degrees means with Compton interactions

Answer 14

means no energy transferred

Question 15

Know what it represents with a 180 degree scatter deflection

Answer 15

maximum deflection and energy transfer

Question 16

Know how much energy a scattered photon retains

Answer 16

Two thirds of its energy

Question 17

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

Answer 17

Near the patient/could expose the radiographer

Question 18

Know where the major source of occupational exposure comes from

Answer 18

Compton scattering

Question 19

Know the diagnostic range that photoelectric interactions occur

Answer 19

20-120 kVp

Question 20

Know how photoelectric events occur

Answer 20

• 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

Question 21

Know what the x-ray photon does in photoelectric interactions

Answer 21

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

Question 22

Know what the absorption if the photoelectric interaction contributes to

Answer 22

Patient dose

Question 23

Know what is necessary to create an x-ray

Answer 23

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

Question 24

know the importance of the inner shell vacancy in photoelectric interactions

Answer 24

what makes the atom unstable

Question 25

know what the source of secondary photons contributes to

Answer 25

patient dose

Question 26

Know what the probability of photoelectric interaction depends on

Answer 26

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

Question 27

Know what has to happen for photoelectric interactions to occur

Answer 27

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

Question 28

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

Answer 28

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

Question 29

Know what the probability of photoelectric events is directly proportional to

Answer 29

the third power of the atomic number of the absorber

Question 30

Know what the cubic relationship means to you the radiographer

Answer 30

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

Question 31

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

Answer 31

the greater the number of photoelectric events

Question 32

In regards to photoelectric interaction photons what does bone do

Answer 32

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

Question 33

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

Answer 33

contrast agents are added

Question 34

Know when pair production occurs

Answer 34

only with very high energy photons of 1.02 MeV or greater

Question 35

Know what happens in a pair production interaction

Answer 35

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

Question 36

Know why differential absorption is called “differential:

Answer 36

different body structures absorb x-ray photons to different extents

Question 37

Know what absorption depends on

Answer 37

the density of body tissue in which photons are passing