Interactions Of Ionizing Radiation Flashcards
characteristic radiation occurs from what effect?
from photoelectric effect
in elastic interaction, what happens to E of e-?
given to e- in target
in inelastic interaction, what happens to E of e-?
only partially given up to target
Brems aka
radiative collision interaction
what happens to photon in transmission
- photon passes w/no interaction
- no E exchanged
coherent scatter aka
aka classical, unmodified, thompson
photoelectric effect has what kind of absorption?
true E absorption
does photoelectric effect depend on E?
yes- as E increases, photoelectric effect decreases (inversely prop)
auger e-
-mono E e- produced by absorption of characteristic xrays by atom & reemission of E in form of orbital e- ejected from atom
photonuclear interaction (photodisintegration) occurs at what E?
15MeV
compton scatter aka
modified scatter
compton depends on
- E of photon- inv prop (Z does NOT affect it)= decr w/incr E
- e- density- depends on # of e- per gram
pair production occurs at what E?
higher E; 10 MeV
pair production depends on
Z (dir prop to z^2)
linear attenuation coefficient definition
- probability per unit thickness that any one photon will be attenuated
- fx of photons removed from a beam per cm of absorber
- fx of photons removed per unit thickness
linear attenuation coefficient affected by e- density?
yes, e- density of absorber
Co-60/1.25 MeV dmax
0.5 cm
4 MV dmax
1 cm
6 MV dmax
1.5 cm
10 MV dmax
2.5 cm
15 MV dmax
3 cm
18 MV dmax
3.5 cm
20 MV dmax
3.5 cm
25 MV dmax
5 cm
QF (quality factor) formula
dose equiv= absorbed dose * QF
xray QF
1
gamma QF
1
e- QF
1
thermal n QF
5
alpha particle QF
20
n QF
20
p+ QF
10
R (Roentgen) unit for
exposure in air
absorbed dose measured in
rad or Gy
250keV dmax
surface
6MeV dmax
1.2 cm
9MeV dmax
2.0 cm
12MeV dmax
2.5 cm
when streams of fast moving e- interact w/target of anode, 2 types of x-rays generated:
- brems
- characteristic
max electronic buildup
secondary e- are set into motion when high photons strike medium
characteristic radiation is what kind of interaction?
collision
characteristic radiation has what kind of spectrum?
discrete
in characteristic radiation e- interacts with ?
e- of target
characteristic radiation collisions are?
excitation or ionization
characteristic radiation happens when e- does what?
fills vacancy
characteristic radiation has no importance in what?
MV
characteristic radiation can produce ? e-?
auger
in elastic interaction, what is conserved?
momentum & KE?
in elastic interaction, what is not lost?
E
in inelastic interaction, what is conserved?
momentum; KE not
Brems most created for
therapy
in Brems, e- attracted to
nucleus
what happens to e- in Brems?
passes near, slows down, and loses KE
Brems has what kind of spectrum?
continuous
in Brems, intensity is proportional to ?
beam current
in Brems, x-rays emitted what direction?
any angle
in Brems, photon E is equal to ?
E lost by e-
in coherent scatter what happens to e-?
not enough E to free e- (vibrates) but E absorbed
what does coherent scatter produce?
very low E photon, scatters
photoelectric effect in what E range
10-30 kvp
in photoelectric effect, photon interacts with?
atom & ejects orbital e-
in photoelectric effect, what is the KE of photon?
initial photon E minus binding E
photoelectric effect involves what e-?
inner shell
in photoelectric effect, what is created?
vacancy= characteristic xrays
in photoelectric effect if angle is 90 deg, what kind of E?
low
in photoelectric effect if angle is 10 deg, what kind of E?
high
is photoelectric effect dependent on Z?
- yes, directly proportional to Z^3 (mass coef dependent)
- Z^4- atomic coef dependent
probability of Brems varies with ?
Z^2 of target material
is photoelectric effect dependent on E?
yes
photonuclear interaction aka
photodisintegration
photonuclear interaction (photodisintegration) is an interaction between what?
photon & nucleus
in photonuclear interaction (photodisintegration), makes nucleus unstable and emits ?
neutron (why we shield) & gamma
in photonuclear interaction (photodisintegration) what happens to incoming photon?
complete absorption
Compton scatter E range
60kVp-10MeV
Compton used in
radiation therapy
in Compton scatter, photon has how much E?
more thank outer shell e-
in Compton scatter, incoming photon interacts with?
outer shell e- (loosely bound)
what is a scattered e- called
recoil e-
in Compton scatter, E is?
both absorbed & scattered
pair production can only occur when what happens
photon has 1.02 MeV threshold dose
in pair production what happens to photon
complete absorption
in pair production what happens to photon E
converted to positron & e- (matter created)
in pair production, what happens to positron
loses KE & recombines with free e- (annihilation rxn)
what is is called when positron combines with free e-
annihilation rxn
linear attenuation coefficient formula
0.693/HVL
linear attenuation coefficient unit
1/cm or cm^-1
linear attenuation coefficient affected by E?
yes, increase E, decrease u (inv prop)
linear attenuation coefficient affected by Z?
yes, increase Z, increase u (dir prop)
linear attenuation coefficient is affected by ? of absorber
state
QF definition
-compares biological effectiveness of particulate radiation to std xray rad
R (Roentgen) only applies at what E
3 MeV
R (Roentgen) only applies to what radiation
x-ray & gamma
R (Roentgen) only happens when?
e- equilibrium exists
R (Roentgen) SI unit
C/kg
R (Roentgen) only measures what?
products of ionization- not photons
R (Roentgen) is NOT
E or intensity or absorbed
R (Roentgen) is? C/kg
2.58 x 10^-4 C/kg
1 R air kerma deposits ? of absorbed dose in air
0.877 rad
F factor is
the tissue dependent conversion from kerma to absorbed dose
absorbed dose defines
quantity
absorbed dose applies to
all types of radiation & E ranges
absorbed dose applies in areas where ?
e- equilibrium does NOT exist
max electronic buildup depends on
photon E & medium composition
Dmax is defined as
max dose obtained at depth where electron equilibrium reached
Binding energy per nucleon is
8 MeV per nucleon
Most important physical quantities that are conserved in a nuclear reaction are
- charge
- mass number
- linear momentum
- mass-energy
