Creation/Production

What is a photon?

A packet of electromagnetic energy.

What type of energy do X-rays consist of?

Photons.

What is kinetic energy?

Energy of motion, such as the energy carried by a moving electron.

What is binding energy?

Energy required to remove an electron from its shell in an atom.

What defines an inner-shell electron?

An electron close to the nucleus that is relatively tightly bound to the atom.

What is an outer-shell electron?

An electron farther from the nucleus that is relatively loosely bound to the atom.

What is a shell vacancy?

An unoccupied electron position in an atomic shell.

What is ionization?

The removal or addition of an electron, leaving an atom electrically charged.

What is excitation?

An increase in an atom’s energy without ejecting an electron.

What does keV stand for?

Kiloelectron volt—a unit used to express photon or electron energy.

What is an incident electron?

An electron approaching a target atom, originating at the filament and accelerating toward the anode.

What is characteristic radiation?

X-rays emitted when an outer-shell electron fills an inner-shell vacancy, releasing energy equal to the difference between shell binding energies.

What is characteristic photon energy?

The inner-shell binding energy minus the binding energy of the shell from which the filling electron came.

What is a characteristic cascade?

A series of electron transitions that fill successive vacancies as electrons move into shells closer to the nucleus.

What is bremsstrahlung radiation?

X-rays produced when an incident electron changes motion and loses energy while interacting with a nucleus’s electric field.

What is bremsstrahlung photon energy?

The difference between the incident electron’s kinetic energy before and after the interaction.

What is the target material in x-ray production?

The anode material in which incident electrons interact to produce x-rays, commonly tungsten.

What is an incident photon?

An x-ray photon approaching an atom before an interaction.

What is photoelectric absorption?

An interaction in which an incident photon is completely absorbed and an inner-shell electron is ejected.

What is a photoelectron?

The electron ejected during photoelectric absorption.

What is Compton scattering?

An interaction in which an incident photon transfers part of its energy to an outer-shell electron, ejecting it.

What is a recoil electron?

The electron ejected during Compton scattering carrying kinetic energy transferred from the incident photon.

What is a scattered photon?

A photon traveling in a different direction after an interaction.

What is scattering angle?

The angle between the scattered photon’s direction and the incident photon’s original forward direction.

What is backscatter?

Radiation scattered back toward the source.

What is coherent scattering?

Scattering in which the photon changes direction without changing energy or ejecting an electron.

What is attenuation?

Reduction of the primary beam as photons are absorbed or scattered out of it.

What is pair production?

An interaction in which a high-energy photon converts into an electron and a positron in the electric field near a nucleus.

What is a positron?

The electron’s antiparticle, with the same mass but a positive charge.

What is annihilation?

An interaction in which a positron and electron convert their mass and energy into photons.

What is photodisintegration?

An interaction in which a nucleus absorbs a high-energy photon and ejects a nuclear particle or fragment.

What interacts with the anode target to produce x-rays in the x-ray tube?

High-speed electrons.

How are electrons released before they accelerate toward the anode?

By thermionic emission.

What causes electrons to accelerate toward the anode?

The applied tube voltage (kVp).

What percentage of incident electron kinetic energy becomes heat at the anode?

Approximately 99%; about 1% or less becomes x-rays.

What happens to photon production efficiency as incident electron kinetic energy increases?

The efficiency of photon production increases.

What are the two types of x-ray-producing anode target interactions?

Bremsstrahlung produces a continuous spectrum; characteristic interactions produce a discrete spectrum.

What does 'bremsstrahlung' mean?

Braking radiation, or slowing.

What attracts the negatively charged incident electron during a brems interaction?

The positively charged nucleus.

What happens to the incident electron during a brems interaction?

It loses kinetic energy, slows down or brakes, and its course is diverted.

What is emitted when the incident electron loses energy during bremsstrahlung braking?

An x-ray photon.

If an electron enters a brems interaction with 60 keV and exits with 20 keV, what is the photon energy?

40 keV.

Why does bremsstrahlung produce a continuous spectrum?

Individual brems photon energies vary over a range of energy levels.

What is the maximum possible brems photon energy?

The incident electron’s full kinetic energy.

Can one incident electron undergo more than one brems interaction?

Yes, a single incident electron can undergo multiple brems interactions.

What must an incident electron do to begin a characteristic interaction?

Eject an inner-shell electron from the target atom.

What happens to the incident electron after ejecting an inner-shell electron in a characteristic interaction?

It usually continues but in a slightly different direction.

What fills the inner-shell vacancy during a characteristic interaction?

An outer-shell electron.

What is released when an outer-shell electron fills an inner-shell vacancy?

The difference in shell binding energies is released as an x-ray photon.

In tungsten, which shell transitions produce characteristic photons useful for diagnostic radiography?

Transitions into the K shell.

What is the K-characteristic photon energy for a K-shell binding energy of 69.5 keV and an L-shell binding energy of 12.1 keV?

57.4 keV.

For the same inner-shell vacancy, what happens when the filling electron comes from a more distant shell?

A higher-energy characteristic photon is produced.

What does an x-ray emission spectrum show?

The number of photons at each energy, including bremsstrahlung and characteristic photons.

What does the horizontal axis represent on an x-ray emission spectrum?

Photon energy in keV.

What does the vertical axis represent on an x-ray emission spectrum?

The number of photons.

Which interaction produces most photons within the diagnostic x-ray range?

Bremsstrahlung target interactions.

About what fraction of kVp is the average brems photon energy?

About one-third of the kVp.

What happens to photon quantity when mAs increases?

Photon quantity increases proportionally.

What happens to the spectrum when mAs increases?

It becomes taller and its total area increases.

What happens to average and maximum photon energies when mAs changes alone?

They remain unchanged.

What happens to lower-energy photons when tube filtration is added?

They are absorbed.

How does added filtration affect photon quantity and average photon energy?

It decreases photon quantity but increases average photon energy.

What happens to maximum photon energy when added filtration is increased?

It remains unchanged.

What happens to average and maximum photon energies when kVp increases?

Both increase.

What happens to photon quantity when kVp increases?

Photon quantity increases.

How does the emission spectrum change when kVp increases?

It extends farther right and its total area increases.

At the same kVp and mAs, what does lower voltage ripple produce?

More photons and a higher average photon energy.

What happens to maximum photon energy when voltage ripple is lowered?

It remains unchanged.

What are the two reasons radiographers should understand x-ray interactions with matter?

To minimize unnecessary patient dose and understand effects on image contrast and anatomical visibility.

What is radiation emitted by the x-ray tube that has not yet passed through the patient?

The primary beam.

What is the remnant beam?

Radiation that exits the patient and reaches the image receptor.

What are the six categories listed as radiographic variables?

Technical variables, geometric variables, patient characteristics and condition, image receptor systems, image processing, and viewing conditions.

What is attenuation in x-ray imaging?

The reduction in x-ray beam intensity as photons are absorbed or scattered.

What are four possible fates of x-ray photons?

They may pass through matter without interacting, interact with the whole atom, interact with orbital electrons, or interact with the nucleus.

How does higher atomic number generally affect K-shell binding energy?

Higher atomic number generally means greater K-shell binding energy.

How do electron energy states change farther from the nucleus?

Electrons in shells farther from the nucleus occupy higher energy states.

As you move outward through electron shells, what happens to electron energy and binding energy?

Electron energy increases while binding energy decreases.

What are the two primary interactions affecting diagnostic images?

Photoelectric absorption and Compton scattering.

Which interactions are not encountered in diagnostic x-ray energies?

Pair production and photodisintegration.

During photoelectric absorption, which electron does the incident photon interact with?

An inner-shell electron.

What happens to the incident photon during photoelectric absorption?

It is completely absorbed.

What occurs after the photoelectron is ejected in photoelectric absorption?

An outer-shell electron fills the inner-shell vacancy and a characteristic photon is released.

What energy must the incident photon have to eject an electron?

More energy than the electron’s binding energy.

When is photoelectric absorption more likely?

When photon energy is just above the shell’s binding energy.

What material property favors photoelectric absorption?

Higher atomic number.

What is the kinetic energy of a photoelectron equal to?

Incident photon energy minus the electron’s binding energy.

Which materials favor photoelectric absorption due to their higher atomic number?

Iodine and barium.

How do differences in photoelectric absorption affect the radiographic image?

Differences in absorption contribute to subject contrast.

What are alternate names for the Compton effect?

Modified scattering or incoherent scattering.

Which electron does an incident photon interact with during Compton scattering?

A loosely bound orbital electron, usually in an outer shell.

What happens to the electron during Compton scattering?

It is removed from its shell and becomes a recoil electron.

What happens to the scattered photon during Compton scattering?

It exits the atom in a different direction and with less energy.

What is the incident photon’s energy used for during Compton scattering?

To free the electron and produce the scattered photon.

What type of radiation is a Compton-scattered photon?

Secondary radiation.

What two factors determine scattered photon energy in the Compton effect?

The incident photon’s energy and the scattering angle.

For the same incident energy, what happens to retained photon energy as scattering angle increases?

Less energy is retained by the photon.

What is backscatter radiation?

Radiation scattered back toward the source.

What is the major source of occupational exposure?

Compton scatter from the patient.

What happens when scatter reaches the image receptor?

It adds unwanted exposure (fog) and reduces contrast.

What are alternate names for coherent scattering?

Classical scatter or unmodified scatter.