Unit 4 (X-Ray Production & X-Ray Interactions)
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list four conditions to achieving x-ray production:
- gap between filament and target
- velocity of accelertated electrons
- incoming electrons (incident electrons)
- departing photons
name two things that occur when the kinetic energy of incident electrons increases:
- an increase in quantity and quality
- an increase in the number of target interactions
how do electrons dissipate excess energy involved in x-ray production?
they can undergo 1000+ interactions (energy never disappears)
over how much area do target interactions occur?
within .25 to .5 mm of target surface
name three things that occur on the target surface during x-ray production:
- heat production
- bremsstrahlung interactions
- characteristic interactions
what percent of the incident electrons' kinetic energy is converted into heat?
where do incident electrons transfer kinetic energy to?
- outer shell electrons of the target atoms
- (causes them to emit infrared radiation, or heat)
what are the two most common target materials and why?
- tungsten and rhenium
- because of their high melting points and high atomic numbers
name the atomic number and melting point of both tungsten and rhenium:
- tungsten (W): 74Z#, 3370°C
- rhenium (Ru): 44Z#, 3170°C
what is the most common target material used in mammography and why?
- its lower atomic number is helpful due to the lower energies needed in mammography
name the atomic number of molybdenum:
molybdenum (Mo): 42Z#
german origin, meaning "breaking" or slow down
in discussing Bremsstrahlung, what does the incident electron interact with?
the electrostatic force field of the nucleus
in discussing Bremsstrahlung, what occurs with the presence of a strong nuclear force?
the force keeps the incident electron and the nucleus apart and deflects the incident electron
in discussing Bremsstrahlung, describe the result of a nucleus with a high atomic number and an incident electron with low energy:
the incident electron doesn't penetrate the electrostatic force field to reach the nucleus
name what is occuring in the following diagram and compare incident electron A to incident electron B:
- bremsstrahlung x-ray production is occuring.
- electron B has more energy than electron A. therefore, it passes closer to the nucleus, makes a greater curve or change in direction at the nucleus, and produces a higher energy bremsstrahlung x-ray photon compared to electron A
it is important to note that ____________ does not occur with bremsstrahlung interactions.
if an incident electron has 40kEv as it approaches the nucleus, and it has 20kEv as it leaves the nucleus, how much bremsstrahlung energy has occurred?
Brems interactions account for what percent of the x-ray beam?
in dealing with tungsten, what is the kEv needed to make characteristic x-ray?
what two things occur as incident electrons get closer to the nucleus?
- photon energy increases
- larger deflection of the incident electron
describe what we know about direct interaction between the nucleus and the incident electron:
this would be the maximum energy photon, and though possible, it is highly improbable
what do incident electrons interact with?
- the k-shell electron
- (then the incident electron continues in a slightly different direction)
in a characteristic interaction, the __________ energy must overcome the ___________ energy.
- (occurs in techniques using 70kVp or higher)
describe/explain what is occurring in a characteristic cascade:
there is a "hole" in an inner shell, and it must be filled by an electron from an outer shell. this creates an electron energy difference and secondary photons are produced.
only electrons that drop into _____________ will contribute to the beam.
describe how to find the brems energy if you know the binding energies of electron shells, give an example:
- subtract the binding energy of the more outer shell from the binding energy of the more inner shell to find the brems energy that will result:
- Ex: if a K shell is 40kEv, the L shell is15kEv, then the brems energy will be 25kEv (40-15=25)
name the graph:
- kVp emission spectrum chart
- this is on tungsten, you can tell because characteristic peaks are occurring at 69keV
compare average kVp to selected kVp:
- average is approximately 30-40% of the selected
- ex. 90kVp will produce an average of 30keV
name the graph:
- mA chart
- denotes a change in mA, time, or mAs
- changes the beam amplitude
in the emission spectrum, what happens when there is a change in kVp?
- changes in beam amplitude and average energy
- (due to an increase in the kinetic energy provided to incident electrons)
- NO increase in electrons striking the target
in a kVp emission spectrum chart, why does the number of xray photons increase on the chart as the keV increases?
there are the same number of electrons, but there are more interactions
name the graph:
- chart showing the emission spectrum with a change in generators (single phase to three phase)
- overall ave energy of single phase is 25keV
- overall ave energy of three phase is 30-35keV
- the top of the hump is the amplitude
what is attenuation?
reduction in the number of x-ray photons in the beam as it passes through matter
what atomic parts do x-rays typically interact with (attenuation)?
- entire atom
- orbital electron
- neucleus of an atom
when an x-ray interacts with the entire atom, this is a:
an interaction in which an electron is ejected from an atom results in _____________ and occurs with which types of interactions?
- compton scatter interaction
- photoelectric absorption
low energy photons interact with:
moderate energy photons interact with:
high energy photons interact with:
- low: the whole atom (coherent)
- moderate: orbital electrons (PE and compton)
- high: nucleus (pair production and photodisintegration)
the electrons close to the nucleus are __________, while electrons farther away fromt the nucleus are ____________.
name the five basic types of interactions between x-rays and matter:
- coherent scattering
- photoelectric absorption (PE)
- compton scattering
- pair production
name a type of interaction in which the incident photon energy is completely absorbed by an inner shell electron:
when is photoelectric absorption most likely to occur?
the the x-ray photon has just slightly more energy than the binding energy of a K or L shell electron
what is formed when an electron is ejected from the atom after an x-ray interaction?
an ion pair
when an electron is ejected from the atom after a photoelectric absorption interaction, it becomes known as:
when ionization from photoelectric absorption takes place, a vacancy in the K shell makes the atom __________ charged, so it is a ____________ until:
- it finds a free electron to stabilize it
what equation can be used to determine photoelectron energy?
- Ei = Eb + Eke
- (entrance electron = binding energy + kinetic energy)
name three characteristics of the photoelectron:
- kinetic energy (Eke)
- reabsorbs quickly (within 1-2mm of tissue)
inner shell electron vacancy makes the atom:
what happens with characteristic cascade?
- vacancy filled by an outer shell electron
- electron undergoes change in every level
- emits characteristic photon
be familiar with three definitions of secondary radiation:
- radiation originating from irradiated material outside the x-ray tube
- x-ray production similar to characteristic x-ray production within the target
- characteristic photons emitted from atoms of patient after PE absorption interaction has occurred
give three conditions for photoelectric absorption:
- incident photon energy must be greater or equal to binding energy of inner shell electron
- more likely to occur if the incident photon energy and inner-shell electron binding energy are close to each other
- more likely to occur in elements with a higher atomic number, and therefore, higher binding energy of inner-shell electrons
give the formula used to calculate the max number of electrons in an orbital shell:
- ex. K-shell is 1
- = 2(1)2 = 2 electrons in the K-shell
attenuation is greater at ____________ energies.
what is the inverse cubed relationship?
photoelectric effect 1/(energy)3
what is the direct cubed relationship?
- 3 x photoelectric effect = atomic number
low atomic number atoms experience photoelectric absorption interactions:
high atomic number atoms experience photoelectric absorption interactions:
- with the K-Shell (tissue)
- in the K, L, M-Shell (bone)
__________ interactions involve low energy photons; _________ or lower, specifically.
give the two types of coherent interactions:
- Thompson: (interacts with single outer-shell electron)
- Rayleigh: (all electrons of the atom)
what is important to know, concerning coherent scatter and ionization?
ionization does not occur in coherent interactions
in coherent scatter, the atom stabilizes itself by:
releasing a photon equal in energy to the incident photon, but in a different direction
name the type of interaction in which the incident photon (Ei) interacts with an outer-shell, loosely bound electron and ejects it
compton scatter interaction
when an electron is ejected from the atom after a compton scatter interaction, it becomes known as:
a recoil electron
in compton scattering, the photon transfers some of its energy to ________________ and continues on in a different direction.
give the formula to determine compton scatter energy:
- Ei = Es + Eb + Ekeincident electron = scattered energy + binding energy + recoil electron
the energy transferred to the recoil electron affects:
- the angle and energy of the scattered photon
- (therefore) frequency and wavelength of scattered photon
increase the energy given over two the recoil electron and the energy of the scattered photon will:
low kVp and high mAs makes what interaction?
high kVp and low mAs makes what interaction?
- photoelectric absorption
- compton scatter
a recoil electron travels until:
it fills a vacancy in another atom
compton scatter is a source of:
- occupational exposure
- radiation fog
how does most scatter travel?
in a forward direction
most of the x-ray beam is ______________, while some of the beam is ____________.
what type of interaction typically predominates within diagnostic x-ray energy range:
photoelectric absorption predominates in what three instances in diagnostic x-ray?
- lower energy ranges (25=45keV/40-70kVp techniques)
- in elements with higher atomic numbers
- introduction of contrast agents
when photoelectric absorption predominates, the resulting image will have:
short scale contrast
what type of technical settings will result in more photoelectric absorption?
low kVp, high mAs
when compton scatter interactions predominate, the resulting image will have:
long scale contrast
what type of technical settings will result in more compton scatter interactions?
high kVp, high mAs
in pair production interactions, incident photon energy must be:
1.02 MeV or higher
the process of matter being converted back to energy:
a ___________ is volatile and quickly combines with a negative electron, while a ____________ behaves like an
electron and is absorbed by a nearby atom.
a type of interaction where the photon energy is absorbed by the nucleus:
- pair production
in pair production, when the nucleus becomes unstable, how does it stabalize itself?
releases a positron and a negatron
______________ is unstable antimatter.
in which type of interaction does matter of particles convert into energy?
which type of interaction is more commonly found in radiation therapy?
in pair production, ___________ and ___________ have mass equal to an electron but with opposite charges.
- positron (positive)
- negatron (negative)
photodisintegration interactions, incident photon energy must be:
10 MeV or higher
type of interaction in which the nucleus releases an alpha particle:
which type of interaction is often seen when working with radioisotopes, as in nuclear medicine?
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