X Ray Interactions With Matter

Front 1

what three things may occur as an xray passes through matter?

Back 1

1. it can pass through unaffected

2. it can change direction and loose energy

3. it can be attenuated

Front 2

when an xray passed through matter and is unaffected, this is called

Back 2

transmitted

Front 3

when an xray passes through matter and changes direction and loses energy, this is called

Back 3

scattered

Front 4

when an xray passes through matter and is attenuated, this is called

Back 4

absorbed

Front 5

the reduction in the number of xray photons in the beam, and the subsequent loss of energy, as the beam passes through matter

Back 5

attentuation

Front 6

attenuation and scatter are the results of

Back 6

xrays interacting with matter at the atomic level

Front 7

what three things will xrays interact with?

Back 7

the whole atom

one orbital electron

the nucleus

Front 8

energy level when an xray interacts with the whole atom

Back 8

low energy

Front 9

energy level when an xray interact with one orbital electron

Back 9

intermediate energy

Front 10

what makes diagnostic xrays?

Back 10

when xrays interact with one orbital e-

Front 11

what energy level are diagnostic xrays?

Back 11

intermediate

Front 12

energy level when xrays interact with the nucleus

Back 12

high energy

Front 13

level of energy xrays used in radiation therapy

Back 13

high energy

Front 14

an atom has a __ charged nucleus surrounded by orbital e- that have _ charges

Back 14

positively charged; negative

Front 15

electrons surrounding the nucleus are held in place by what?

Back 15

their binding energy

Front 16

binding energy-

Back 16

the amount of energy required to remove an e- from its orbit

Front 17

the binding energy of an e- is determined by:

Back 17

1. the shell in which the e- resides

2. the atomic # of the atom

Front 18

the higher the Z number, the ___ the binding energy

Back 18

greater

Front 19

what is the K shell binding energy of tungsten? what is its Z #?

Back 19

69.5 keV; 74

Front 20

what is the K shell binding energy of molybdenum? Z#?

Back 20

20 keV; 42

Front 21

measure of energy

Back 21

electron volt (eV)

Front 22

the kinetic energy acquired when an electron is accelerated by a potential difference of one volt

Back 22

eV (electron volt)

Front 23

1 eV= ___ Joules

Back 23

1.6 x 10^-19 Joules

Front 24

1 keV= ___ eV

Back 24

1000

Front 25

electrons that are further away from the nucleus have a higher ___ than those close to the nucleus

Back 25

total energy

Front 26

e- closer to the nucleus are said to be in

Back 26

a "higher energy state"

Front 27

what happens when an outer shell electron drops into an inner shell?

Back 27

its total energy decreases

Front 28

5 basic interaction between xrays and matter

Back 28

1. coherent scattering

2. photoelectric effect

3. Compton scattering

4. pair production

5. photodisintigration

Front 29

coherent scattering is also called

Back 29

classical scatter, unmodified scatter, Thompson scatter or Rayleigh scatter

Front 30

coherent scattering on occurs with ___ energy x rays- below __ keV

Back 30

low;10

Front 31

when a low energy electron interacts with one or more electrons, its energy will be ___, but it will vibrate at the same frequency as the ___ xray.

Back 31

absorbed; incident

Front 32

the vibration will cause a ___ xray to be produced that has the same energy and wavelength as the ___ xray, but in a different __- the xray is ___.

Back 32

secondary; incident; direction; scattered

Front 33

when an xray is ___; no energy is transferred and the atom is not ionized

Back 33

scattered

Front 34

interaction in which no energy is transferred and the atom is not ionized

Back 34

coherent scattering

Front 35

why doesn't coherent scatter affect diagnostic radiographs very much?

Back 35

because it occurs at such low energy, most of the scatter does not hit the film

Front 36

coherent scatter can be a problem in which modality

Back 36

mammography

Front 37

who won the nobel prize in physics for photoelectric effect or photoelectric absorption; what year?

Back 37

Albert Einstein; 1921

Front 38

interaction in which the incident xray interacts with an inner K or L shell e-

Back 38

photoelectric effect or photoelectric absorption

Front 39

in photoelectric effect or photoelectric absorption, the incident x ray must have __ energy than the binding energy of the ___.

Back 39

more; orbital e-

Front 40

a photoelectric effect is most likely to occur when the incident xray has _____ energy than the e- that is interacts with

Back 40

just slightly more

Front 41

in a photoelectric effect, the xray is _____ by the e- and the photoelectron is _____.

Back 41

totally absorbed; ejected from its orbit

Front 42

the atom is ionized in what interaction

Back 42

photoelectric effect or photoelectric absorption

Front 43

the photoelectron has kinetic energy that is equal to the difference between

Back 43

the incident xray energy and the electron binding energy

Front 44

formula for finding the energy of the incident photon in a photoelectric effect

Back 44

Ei=Eb+Eke

Front 45

Ei=

Back 45

energy of the incident photon

Front 46

Eb=

Back 46

binding energy of the electron

Front 47

Eke=

Back 47

kinetic energy of the photoelectron

Front 48

the photoelectron can produce ___ ___ in other atoms, but it is usually very ___ energy.

Back 48

secondary radiation; low

Front 49

when an outer shell e- drops into the vacated inner shell after an e- is removed from its orbit

Back 49

cascade effect

Front 50

when the cascade effect occurs in a photoelectric effect, energy is given off in the form of what?

Back 50

a characteristic x ray- secondary radiation

Front 51

x rays created in the target of the anode

Back 51

primary radiation

Front 52

radiation produced somewhere other than the target

Back 52

secondary radiation

Front 53

because of the ______ of most atoms in the body (hydrogen, oxygen, carbon) the xrays in photoelectric absorption/effect are usually very ___ ___ and in a different ___ than the incident photon.

Back 53

low atomic number; low energy; directions

Front 54

the photoelectron can also ionize other atoms and create ____ ___ elsewhere, however usually very __ energy

Back 54

characteristic radiation; low

Front 55

three basic rules that govern the possibility of photoelectric interaction

Back 55

1. the energy of the incident xrays must be greater than the binding energy of the inner shell electron

2. the photoelectric interaction is more likely to occur when the xray photon energy and the electron binding energy are nearer to one another

Front 56

the third basic rule that governs the possibility of photoelectric interation

Back 56

3. the photoelectric interaction is more likely to occur with an electron that is more tightly bound in its orbit

Front 57

the ___ the keV, the chance of interaction becomes MUCH ___

Back 57

higher;less

Front 58

photoelectric effect =

Back 58

1/(energy)^3

Front 59

at 50 kVp, what % of the interactions are photoelectric; what % are Compton scattering?

Back 59

50.45%; 45.55%

Front 60

at 130 kVp- only _ % of the interactions are photoelectric and _% are Compton?

Back 60

24.78%; 75.22%

Front 61

the higher the kvp, the __ the percentage of photoelectric and the __ the percentage of Compton scattering

Back 61

less;greater

Front 62

the lower the kVp, the __ of the photons are absorbed (photoelectric) and the ___ are scattered (compton)

Back 62

more; less

Front 63

the probability of a photoelectric interaction ___ dramatically as the atomic number ___

Back 63

increases; increases

Front 64

photoelectric effect =

Back 64

(atomic number)^3

Front 65

bone has a higher average atomic number than does water, so __ xrays will be absorbed in bone than in water (soft tissue)

Back 65

more

Front 66

when more xrays are absorbed due to a higher atomic number in one tissue over another, this is called

Back 66

differential absorption

Front 67

what gives us radiographic contrast?

Back 67

differential absorption

Front 68

what is created by the incident xray interacting with an outer shell e-

Back 68

Compton scattering

Front 69

the photon has ___ energy than the e-, so it ejects the electron from its orbit

Back 69

more

Front 70

the photon is/is not absorbed in Compton scattering but it proceeds in a __ __ than the incident photon

Back 70

is not; different direction

Front 71

why isnt the photon absorbed in Compton scattering?

Back 71

because of the great difference in energies

Front 72

compton scatter has __ energy than the incident photon

Back 72

less

Front 73

what is the ejected e- called in a Compton effect?

Back 73

Compton electron or recoil electron

Front 74

Energy transfer formula for Compton effect

Back 74

Ei= Es+Eb+Eke

Front 75

Ei=

Back 75

energy of the incident photon

Front 76

Es=

Back 76

energy of the Compton scattered photon

Front 77

Eb=

Back 77

binding energy of Compton electron

Front 78

Eke=

Back 78

kinetic energy given to the Compton electron

Front 79

the amount of energy retained by the scattered photon is dependent on the

Back 79

angle of deflection

Front 80

the greater the angle, the __ energy is given to the Compton electron and the __ is retained by the scattered photon

Back 80

more;less

Front 81

0 degrees=

Back 81

no energy transfer

Front 82

180 degrees= ____; what is this called?

Back 82

maximum energy transfer; back scatter

Front 83

what contributes to the vast majority of scatter reaching the film?

Back 83

compton scattering

Front 84

what is the primary cause of occupational exposure to the radiographer?

Back 84

compton scattering

Front 85

pair production only occurs with __ __ energy photons, over __ MeV

Back 85

very high; 1.02

Front 86

MeV=

Back 86

mega electron volts

Front 87

in pair production, the photon interact with what?

Back 87

the nuclear field surrounding the nucleus of an atom

Front 88

what interaction with matter is occuring when the energy of the photon is absorbed and creates two pieces of matter

Back 88

pair production

Front 89

what two electrons are created in pair production?

Back 89

negatron and positron

Front 90

a negatively charged electron

Back 90

negatron

Front 91

a positively charged electron

Back 91

positron

Front 92

which electron is absorbed by another atom in pair production?

Back 92

the negatron

Front 93

which electron interacts with another electron?

Back 93

the positron

Front 94

what is it called when a positron interacts with another electron and turns matter into energy?

Back 94

annihilation reaction

Front 95

what are the products of an annihilation reaction?

Back 95

two .51 MeV xray photons

Front 96

annihilation reactions are a problem in which modality?

Back 96

radiation therapy

Front 97

in photodisintegration, a very high energy photon ( above __ MeV) will interact with what?

Back 97

10; the nucleus of an atom

Front 98

in which interaction is the photon absorbed and a piece (fragment) of the nucleus ejected?

Back 98

photodisintegration

Front 99

what can happen in photodisintegration with the nuclear fragment?

Back 99

it can ionize other atoms and cause biological damage

Front 100

photodisintegration does not occur within what? but only in what?

Back 100

diagnostic xray; radiation therapy