Physics Chap 5

Front 1

the process by which a neutral atom acquires a positive or a negative charge

Back 1

ionization

Front 2

removal of an electron leaves the atom with a positive charge, resulting in what

Back 2

ion pair

Front 3

what particles are known as directly ionizing radiation

Back 3

charged particles like electron, protons, and alpha

Front 4

why are charged particles known as directly ionizing radiation

Back 4

they have sufficient kinetic energy to produce ionization by collision as they penetrate matter

Front 5

what is excitation

Back 5

when the energy lost by the incident particle is not big enough to eject an electron but raises the electrons to higher energy levels

Front 6

what particles are indirectly ionizing

Back 6

uncharged particles like neutrons and photons

Front 7

why are uncharged particles indirectly ionizing

Back 7

they liberate directly ionizing particles from matter when they interact with matter

Front 8

ionizing photons interact with the atoms of a material to produce high speed electrons by what 3 major processes

Back 8

photoelectric effect
compton effect
pair production

Front 9

mathematically, what is the fluence of photons

Back 9

dN/da

Front 10

in the fluence of photons, what is dN and da?

Back 10

dN is the number of photons that enter an area
da is the cross sectional area

Front 11

what is the flux of photons

Back 11

fluence per unit time

Front 12

what is flux of photons expressed mathematically

Back 12

d (symbol for fluence)/dt

Front 13

what is dt

Back 13

time interval

Front 14

what is energy fluence

Back 14

the sum of all energies of all the photons that enter a sphere or cross sectional area

Front 15

what is energy fluence mathematically

Back 15

dEff/da

Front 16

for a monoenergetic beam, dEff is what

Back 16

just the number of photons (dN) times energy (hn) carried by each photon

Front 17

what is the energy flux

Back 17

energy fluence per unit time

Front 18

in photon beam attenuation, the reduction in number of photons is proportional to what

Back 18

the number of incident photons and the thickness of the absorber

Front 19

what is photon beam attenuation mathematically

Back 19

dN=-uNdx

Front 20

in the photon beam attenuation equation, what does u stand for?

Back 20

constant of proportionality

Front 21

in the photon beam attenuation equation what is u called

Back 21

attenuation coefficient

Front 22

if the thickness, x, is expressed as a lenght, the u is called

Back 22

linear attenuation coefficient

Front 23

what is the half value layer

Back 23

thickness of an absorber required to attenuate the intensity of the beam to half its original value

Front 24

what does HVL equal

Back 24

.693/u

Front 25

exponential attenuation strictly applies to

Back 25

a monoenergetic beam

Front 26

the slope of the attenuation curve _______ (increases/decreases) with _______ (increasing/decreasing) absorber thickness

Back 26

decreases
increasing

Front 27

what does the absorber or 'filter' remove

Back 27

low energy photons

Front 28

what are the units for linear attenuation coefficient

Back 28

cm -1

Front 29

the attenuation produced by x thickness depends on what

Back 29

number of electrons presented in that thickness

Front 30

what does u depend on

Back 30

density of the material

Front 31

what is u/r

Back 31

mass attenuation coefficient

Front 32

why is the mass attenuation coefficient more fundamental that the linear coefficient

Back 32

b/c the density has been factored out and its dependence on nature of material doesn't involve density but the atomic composition

Front 33

what is the unit of mass attenuation coefficient

Back 33

cm2/g

Front 34

what is the equation for electronic attenuation coefficient

Back 34

(u/p)(Z/No) cm2/electron
where Z is atomic number

Front 35

what is the equation for No

Back 35

(Na x Z)/Aw
where Na is avagadro's number and Aw is atomic weight

Front 36

what is u/r

Back 36

mass attenuation coefficient

Front 37

why is the mass attenuation coefficient more fundamental that the linear coefficient

Back 37

b/c the density has been factored out and its dependence on nature of material doesn't involve density but the atomic composition

Front 38

what is the unit of mass attenuation coefficient

Back 38

cm2/g

Front 39

what is the equation for electronic attenuation coefficient

Back 39

(u/p)(Z/No) cm2/electron
where Z is atomic number

Front 40

what is the equation for No

Back 40

(Na x Z)/Aw
where Na is avagadro's number and Aw is atomic weight

Front 41

what is energy transfer coefficient?

Back 41

the fraction of photon energy transferred into kinetic energy of charged particles per unit thickness of absorber

Front 42

what is Etr

Back 42

average energy transferred into kinetic energy of charged particles per interaction

Front 43

most of the electrons set in motion by photons will loose their energy by ________ with atomic electrons of the material

Back 43

inelastic collisions

Front 44

a few electrons, depending on the atomic number, will lose energy by_____________

Back 44

bremsstrahlung interactions with nuclei

Front 45

what is the product of energy transfer coefficient and (1-g)

Back 45

energy absorption coefficient

Front 46

what does (1-g) represent

Back 46

fraction of energy of secondary charged particles that is lost to bremsstrahlung in the material

Front 47

for most interactions involving soft tissues or low atomic material, bremsstrahlung component is

Back 47

negligible
thus energy absorption coefficient equals energy transfer coefficient

Front 48

attenuation of a photon beam by an absorbing material is caused by what 5 interactions

Back 48

photodisintegration
coherent scattering
photoelectric effect
compton effect
pair production

Front 49

the photodisintegration reaction between photon and nucleus iss only important at what energies

Back 49

very high (>10 MeV)

Front 50

attenuation coefficients vary with what 2 factors

Back 50

energy of photon
atomic number of absorbing material

Front 51

coherent scattering is probably in (high/low) atomic number material with photons of (high/low) energy

Back 51

high
low

Front 52

what happens in photoelectric effect

Back 52

photon interacts with an atom and ejects an orbital electron

Front 53

in photoelectric effect, the kinetic energy of the ejected electron is equal to

Back 53

the photon energy minus the binding energy of that electron

Front 54

where does photoelectric effect take place

Back 54

K,L,M, or N shells

Front 55

what are Auger electrons

Back 55

monoenergetic electrons produced by the absorption of characteristic x rays internally by the atom

Front 56

the probability of photoelectric absorption depends on the

Back 56

photon energy

Front 57

below ____keV, the interaction is limited to M or high shell electrons in photoelectric

Back 57

15keV

Front 58

for low energy photon, photoelectron is emitted in what direction
high energy?

Back 58

90 degrees relative to direction of incident photons

more forward direction

Front 59

what are the 3 special cases of compton effect

Back 59

direct hit
grazing hit
90 degree photon scatter

Front 60

if a photon makes a direct hit with the electron, the electron will travel ______ and the scattered photon will travel _____

Back 60

frontward
backward

Front 61

if a photon makes a grazing hit with an electron, the electron will be emitted at _____ and scattered photon will go ____ direction

Back 61

right angles
forward

Front 62

in compton, the radiation scattered at right angles is _____ (independent/depedent) of incident energy and has maximum value of ___

Back 62

indepedent
.511MeV

Front 63

the radiation scattered backwards is (indepedent/depedent) of incident energy and has maximum value of ___

Back 63

independent
.255MeV

Front 64

the compton effect (increases/decreases) with increasing photon energy

Back 64

decreases

Front 65

compton scattering is (independent/dependent) or atomic number

Back 65

independent

Front 66

if the energy of the photon is greater than 1.02MeV, the photon may interact through what mechanism

Back 66

pair production

Front 67

what does pair production interact with

Back 67

electromagnetic field of atomic nucleus

Front 68

what does pair production result in

Back 68

an electron and positron

Front 69

what minimum energy is required to create the pair of electrons

Back 69

1.02MeV

Front 70

what is the threshold energy of pair production

Back 70

1.02MeV

Front 71

what is annihilation radiation

Back 71

when a positron combines with an electron to produce to photons

Front 72

probability of pair production (increases/decreases) with atomic number

Back 72

increases rapidly

Front 73

charged particles interact by

Back 73

ionization and excitation

Front 74

the charged particle collisions are mediated by what forces

Back 74

coulomb

Front 75

collisions between the particle and atomic electrons result in

Back 75

ionization and excitation of the atoms

Front 76

collisions between the particle and the nucleus result in

Back 76

radiative loss of energy or bremsstrahlung

Front 77

what is stopping power

Back 77

rate of kinetic energy loss per unit path length of the particle

Front 78

neutrons interact by what 2 processes

Back 78

recoiling protons from hydrogen and recoiling heavy nuclei from other elements
nuclear disintegrations