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90 Cards in this Set

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characteristic radiation occurs when...?
e- interact with inner orbital e- instead of nucleus
incident e- knock out inner orbital e-
atom left in ionized state
incident e- leaves with energy (equation)
Ef=Eo-Et

Et=energy imparted to orbital e-
orbital e- leavew ith energy (equation)
Ee=Ef-Ek

Ek=binding energy
ionized atom then has lower level e- which ________and creates a __________
loses energy

creates a photon
photon created from lower level e- moving up and losing energy is called
characteristic radiation
equation for characteristic radiation (photon equation)
hv= Ek-El

Ek=binding energy of inner orbit

El=binding energy of outer orbit
characteristic radiation is .....
characteristic of where it takes place

L radiation = L shell knocked out
K radiation = K shell knocked out
as energy increases, characteristic radiation
decreases
relationship between energy and characteristic radiation is
indirectly proportional
relationship between characteristic radiation and megavoltabe x-ray machines?
none, characteristic radiation is not seen in megavoltage x-ray machines just bremsstralung
3 methods photons and e- interact
photoelectric interaction

compton interaction

pair production
as energy increases teh % of initial energy retained in photoelectric interaction__________
decreases at all angels except 0 degrees
what provides diagnostic contrast
photoelectric interaction
what is a photoelectron
an ejected e- from the inner shell knocked out by a photon
characteristic radiation aka
florescent radiation
electromagnetic radiation that causes 2nd e- called ______ to be ejected
auger e-
energy given to photoelectric e- (equation)
Ek= hv-Eb
k shell binding energy
.5 kev or 500 ev photon/electron=low
characteristic radiation is emitted w/an energy of
.5kev with little to no Bremstralung
with increasing Z materials
e- is held tighter
= increasing binding energy
greatest angle e- can be scattered
90 degrees
characteristic radiation
adv
dis
adv= mono energetic

dis= bremstrullungs are greater in # than characteristic radiation
absorbtion edges are associated with
photoelectric attenuation
at photon increases
photoelectric attenuation decreases
photoelectric attenuation coefficient increases abruptly when
energy of photon equals binding energy of shell
when photon energy =binding energy
produces discontinuities in attenuation curve= absorption edges
discontinuities in attenuation curve
absorption edges
photoelectric effects predominate in
H20 < 50kev (max 200kvp or 66kev)

Pb <500kev
photoelectric attenuation varies as
1/E3 of the photon

Z3 of the absorber- more probable in bone than tissue
Our friend
compton interaction
ther are more ___interaction than______
photoelectric interactions than compton interactiosn
interaction of photon w/unbound e- (outer e- with low binding energy)
compton effect
unbound e-
binding energy is low so considered free e-
type of interacition in compton effect
elastic
______composed of low atomic #
free electrons (soft tissue)
in _____ photon ejects e- and e- receives part of energy, photon receds from collison with reduced energy
compton effect
equation for compton effect
hv-hv1 + Ee
photon direct hit with e-

what angle?
e-travels straight forward
photon straight back
e= max energy
photon =minimum

degree angle= 180
photon grazes e-

what angle
photon straight forward
photon maintains all energy
e- receives non form photon

angle 90
Compton wavelength
change in wavelength of photon
Compton
low energy photon
e aquires little energy phon gets most energy
Compton
high energy photon
recoil e- gets most energy
how does Z affect comtpton effect?
it doesn't because Compton is independent of Z (atomic number)
as energy ____ probablity of compton interaction______
increases probability of compton decreases (indirectly related)
in soft tissue the range 60kev-20mev, ________ is more important than _____or ____________
compton is more important than pair production or photoelectic
soft tissue ranges for compton
60kev-20mev
does pair production occur in diagnostic range?
no! starts at 1.02 Mev
what is pair production
when a photon passes near the nucleus of atom and is subjected to the field of the nucleus. photon may disappear and become e- or e+
pair production relationship to E=mc2
energy of photon turned into mass (e- and e+
probability of pair production ___as photon energy ____
increases
increases
(directly related)
pair production relationship with Z
vaires as Z2
What is triplet production
same as pair production except interactons occurs with electron fields
what results from triplet production
e- e+ and initial e-
threshold for triplet production
2.04Mev
probability of triplet production
1-10% as often as pair production
above 20Mev-
pair production is the most important process by which energy is absorbed
fem heads get great dose with?
pair production and there is shadowing of the prostate
T/F
Can a 10Mev electron have a compton interaction in tissue
FALSE because its an e- and not a photon
types of interactions with e- and photons

e- =
photon=
e= collisions an bremstrulung

photon= photoelectic, compton, pair production
bone absorbs 6 times as much energy gm for gm as tissue
photoelectric
bone and tissue absorb the same amount gm for gm
compton
bone absorbs 2times as much energy gm for gm
pair production
why we treat with photons
skin sparing
goes deeper
carry energy deeper because they have no charge or mass when they interact they produce electrons= dose=biological changes
T/F photons don't give does, they carry energy which is released by electrons (production of an interaction)
true
compton
as energy of photon____ scattering angle___ for photon and e-
increases, decreases
(indirectly proportional)
compton
as energy of photon___, more energy is given to e-
increases
if photon is scattered at 90 degrees
max energy it can have is .511mev
e- scattered directly forward
if photon is scattered at 180 degrees
e- given max amount of energy and
photon gets minimum
if photon is scattered at 0 degrees
photon gets max amount
e is deftected at 90 degree angle
e gets no energy from incident photon
form of Co60
disk, cylinder, pellet, encapsulated in stainless steel capsule
type of capsule
dbl stainless steel to prevent leakage
use waffers to
fill inner capsule for varying amount of co60
housing around capsule
lead for shielding purposes
source of "on" "off" mechanism
1 rotation wheel
2. horizontally driven drawer
3. mercury switch
how are mechanisms "fail safe"
must have power for motor to keep open, when power goes off it closes
2 sets of collimators for co60
primary
secondary
primary is
stationary
close to the source
defined larges filed size possible
secondary is
variable collimators
fld size used to treat

multiplane, made of depleted uranium
inner surface always parallel to beam , diverge with source/beam
how do you avoid e- contamination in co60
have secondary collimators at least 15-20 cm away from patient
source diameter for co60
1-2cm in diameter
increase diameter of source=
stronger source
BUT
larger source diameter=large pneumbra
pneumbra equation
w=s ((SSD-SCD)/
SCD)

pneumbra= source diameter ((skin to source distance- source to collimator distance) / source to collimator distance)
other isotopes used for teletherapy in teh past
Ra Cs
Co60 developed in
1952
standard source strength
4000-10,000 RHM
1RHM=
1Ci
# of photons=
dose rate created
probability of making x-rays is
1%, the rest is heat
probability of making x-rays for linear accelerator
50%
type of x-ray used in both diagnostic and radiation therapy
bremsstrulung