Ch 9 X-ray Interaction With Matter Flashcards
x-rays interact with matter in 5 ways:
1) coherent scattering
2) Compton scattering
3) photoelectric effect
4) pair production
5) photodisintegration
absorption determines:
the degree of contrast of an x-ray image
electromagnetic radiation interacts with structures that are:
similar in size to the wavelength of the radiation
the higher the energy of an x-ray the ______
shorter its wavelength
x-rays with energies below ____ interact with matter by _____
energies below 10 keV interact with matter by coherent scattering
in coherent scatter the incident x-ray interacts with:
a target atom causing it to become excited, immediately releasing the excess energy as scatter
the released scatter x-ray has a wavelength ____
equal to that of the incident x-ray (λ=λ’) and therefore equal energy
the result of coherent scatter is ____ ; there is no ____ and therefore no _____
a change in the direction but not the energy of the x-ray; there is no energy transfer and therefore no ionization
*coherent scattering is:
of little importance to diagnostic radiology
Compton scattering is when there is interaction with:
outer shell electrons that not only scatters the x-ray but reduces its energy and ionizes the atom as well
the energy of the Compton scattered x-ray is equal to:
the difference between the energy of the incident x-ray and the energy of the ejected electron
Compton Effect
Ei =
Ei= Es + (Eb+Eke)
Ei: energy of incident x-ray
Es: energy of scattered x-ray
Eb: electron binding energy
Eke: kinetic energy if the electron
during Compton scattering most of the energy is divided between ______ but the ______ retains most of the energy
the scattered x-ray and the Compton electron but the scattered x-ray retains most of the energy
Compton scattered x-rays can deflect in __ direction including _____
any direction including 180 degrees from the incident x-ray
at a deflection of 0 degrees ____ energy is transferred
no energy
as the angle of deflection increases to 180 degrees:
more energy is transferred to the Compton electron
at 180 degrees of deflection the scattered x-ray retains:
at least 2/3 of its original energy
backscatter radiation is:
x-rays that scatter back in the direction of the incident x-ray beam
the probability of Compton scattering decreases as:
x-ray energy increases
*the probability of Compton scattering is _____ to x-ray energy and independent of ______
inversely proportional to x-ray energy and independent of atomic number
the probability of Compton scattering does not depend on _____
the atomic number of the atom involved
*Compton scattering reduces ____
image contrast
with the PHOTOELECTRIC EFFECT the x-ray is not _____ but ______; ionization of _____ electrons occurs
not scattered but totally absorbed; ionization of inner shell electrons occurs
*the photoelectric effect is _____
total x-ray absorption
(Bremsstrahlung/Characteristic) x-rays are produced after a photoelectric interaction
Characteristic
the electron released in the photoelectric effect has an energy equal to:
the difference between the binding energies of the shells involved
the probability of photoelectric effect is: (energy)
inversely proportional to the third power of the x-ray energy (1/E)³
photoelectric interaction cannot occur unless:
the incident x-ray has energy equal or greater than the electron binding energy
the probability of photoelectric effect is: (Z)
directly proportional to the third power of the atomic number (Z) of the absorbing material
photoelectric interaction is more likely to occur with _____
high-Z atoms
pair production involves:
one positive and one negative electron (an electron pair)
*pair production does not ______ because it requires _____
does not occur in x-ray imaging because it requires 1.02 MeV
*photodisintegration does not _____ because it required ____
does not occur in x-ray imaging because t requires 10 MeV
*differential absorption occurs because of:
Compton scattering, photoelectric effect, and x-rays transmitted through the patient
*differential absorption increases as the ____
kVp decreases
at low energies ____ is more common, at high energies ____ is more common
photoelectric, Compton scatter
*the interaction of x-rays with tissue is proportional to the:
mass density of the tissue
*probability of Compton scatter is _____
inversely proportional to the x-ray energy (1/E) and has no relation to atomic number
*probability of photoelectric effect is _____
inversely proportional to the third power of x-ray energy (1/E³) and directly proportional to the third power of the atomic number (Z³)
*photoelectric involves ___ electrons and has a ____ binding energy
inner shell electrons and has a higher binding energy
*Compton scatter involves ____ electrons and has a ____ binding energy
out shell electrons and has a lower binding energy
*Coherent = _____ = _____ = ______
Coherent = Classic = Thompson = Raleigh
*in Compton the wavelength entering is _____ than the exiting wavelength
shorter
*in coherent scattering the entering wavelength is _____ tot the exiting wavelength
equal to
*the exiting wavelength in Compton scattering ____
changes direction
*in photoelectric effect there is a _____ but no _____
is a entering ray but no exiting ray (is absorbed)
*probability of Compton scattering decreases as _____ increases
energy
*logarithmic scales allow you to:
plot a larger scale in a smaller area
*logarithmic change of 0.3 is:
2 (equal to doubling the mAs)
