B. Radiation physics Flashcards
___ is the number of waves that pass a given point in one second.
Frequency
wavelength
the measured distance between two specific points of the wave
ex - peak to peak
- valley - valley
velocity
how fast the wave is traveling
- x-rays travel at the speed of light (c) in a vacuum
Si unit for velocity is _____
3 x 10^8 m/sec
Amplitude
half of the distance from one crest to one valley
- photons have both wave and particles distances
- photons have no mass or charge and low LET
wavelength is measured in
meters
wavelength and frequency are inverse relationship
wavelength will be short and frequency will be long and vice versa
the beams intensity will ______ more as the thickness of attenuating material ______
decreases , increases
what is the formula for attenuation of matter
I(X) = I e^-ux
I = initial intensity
u = linear attenuation coefficient
x = thickness of absorption material
As the radiation beam travels through matter, it will diverge and decrease in intensity because of the
inverse square effect
As the radiation beam travels through matter, it will diverge and decrease in intensity because of the
direction than it travels through matter
____ is inversely proportional to square of distance from source
beam intensity
Different types of radiation have different beam qualities and can produce different ____
amounts of response
Quality factor (QF) are assigned to describe the type of
Radiation
x-rays, gamma rays , beta particles , electrons
Quality factor = 1
protons
quality factor = 2
neutrons
Quality factor = 3-10
heavy particles
quality factor = 20
____________ is when the photon interacts occurs with an outer shell atomic electron and the photon becomes REDIRECTED OR SCATTERED from its original path without any CHANGE IN ENERGY
Coherent (or elastic) scattering
coherent occurs with ______ energies and _____ z# (atomic number
usually occurs with energies less than ____
low energies and materials with high z#
usually occurs with energies less than 10 Kev
Photoelectric effect occurs more with low energy photons interacting with material with a
high z number
________ is when the photon interacts with the inner shell electron and is then absorbed by this electron, and its energy is transfered
- results in a photoelectron being ejected from the atom
photoelectric effect
Photoelectric effect occurs in diganostic energy ranges more than
therapy energy ranges
helps to create contrast on an x-ray image (black and white due to absorption)
the photon interacts with an OUTER SHELL ATOMIC ELECTRON and GIVES UP PARTIAL ENERGY BEFORE CHANGES DIRECTION
Compton scaterring
compton scattering interacts in ______ ________ in radiation therapy
- occurs in energy from _______
- soft tissues
- 25 kv - 10 MV
_______ incoming photon disappear and then reappears as an electron positron pair
pair production
IN pair production the electron pair become two
.511 MeV photons
threshold energy needed for pair production
> 1.022 MeV
_______ photon goes in to nucleus and neutron comes out
photon nuclear reactions (photon disintegration):
occurs in high Z# material such as collimating jaws
occurs in ______
7-15 MeV
neutron radiation occurs in the treatment room with energies greater than
10 MV
Common electron energies in linacs are
5-20 MeV
_______ is describes that some kinetic energy is lsot and reappears in another form of energy like excitation, ionization, bremsstrahlung, etc.
inelastic collision
______ the total kinetic energy before the collision is the same as the total kinetic energy after the collision
elastic collision
the differences in density will affect how the beam ______ though the matter and how it _____ as well (dose distribution)
pentrates
- scatters
Electron travel in a _______ path
“zigzag” or “tortured”
Electrons are easily scattered by high Z number material because
of their low mass
Electron interactions are
bremsstrahlung and characteristic
protons are 2,000 times heavier than
electrons
The body is made up of tissues with different
densities
The difference in the density of tissue will effect how the beam penetrates through matter and how i
scatters as well
The lungs density is about
0.25-0.33 g/cm^3 ( beam will penetrate easier)
Bone density is about
1.8 g/cm^3 ( beam will attenuate more)
