registry 2025 - target and matter interactions

Bremsstrahlung

this interaction:

- happens in the tube

- incoming negative electron passes outer shell and gets close to positive nucleus

- slows down in trajectory and curves from the nucleus

- that slow down in kinetic energy causes a release of high energy xray photon

- most of the x-rays are from this type of interaction

- and each time that slowed down electron makes runs with other nucleus, that resultant photon has less and less energy

- is 70% to 90% of the xray beam

hetergeneous beam

- This is a quality in brems radiation

- also called polyenergetic

- called this because you have a variety of energy in the beam from high to low

characteristic radiation

this interaction:

- A projectile electron collides with an inner shell electron of a target atom and gets ejected from orbit and

ionizes the atom

- A hole exists in the inner shell from the vacated electron and an electron from an outer shell falls in to fill the hole

- Then when the electron falls in, energy is given off in the

form of an x-ray photon

- This creates a hole in its shell of origin, and an electron from the next outer shell falls in to fill this vacancy; this continues until the atom is stable again

- Each time an electron falls in to fill a hole, an x-ray

photon is given off and each x-ray photon has a specific energy, equal to the difference in the binding energies of the two shells involved

- Only x-rays produced at the K-shell are of sufficient energy to be used in diagnostic radiography

- These x-rays possess energy that's typical of the specific binding energies of the atom involved.

- these x-rays are produced at kVp levels greater than 70 but only in small numbers

- makes up 10% to 30% of the x-ray beam

discrete x-ray spectrum

This is a typical for characteristic radiation.

This is called this because energies involved are specific to the

target atom and are predictable.

Continuous x-ray spectrum

Typical of brems radiation

because these energies all are different (from the peak electron energy down to zero energy)

photoelectric

This interaction:

- is considered characteristic as the incoming x-ray photon hits the k-shell electron. That electron gets ejected.

- the photon becomes COMPLETLEY ABSORBED and ceases to exist

- occurs in tissues

- results in increased dose to the patient

- k-shell hole gets fills by the other electrons in the other shells releasing low energy photons.

- this produces contrast in the radiograph because of the differential absorption of the incoming x-ray photons in the tissues

Photoelectron

this happens in photoelectric interactions. Its the electron that got ejected from the k-shell.

it may get ionized or excite other atom until it deposits all its energy

Compton scatter (interaction)

- occurs in tissues

- also called modified scattering

- Incoming x-ray photon strikes a loosely bound, outer-shell electron

- Photon transfers PART of its energy to the electron

- Electron is removed from orbit as a scattered electron, referred to as a recoil electron

- Ejected electrons may ionize other atoms or recombine with an ion needing an electron

- Photon scatters in another direction with less energy than before because of its encounter with the electron

- Scattered photon may interact with other electrons, causing more ionization, additional scattering events, or photoelectric absorption; or it may exit the patient

- Scattered photons emerging from the patient travel in divergent paths in random directions

- Scattered photons may also be present in the room and expose the radiographer or radiologist

Recoil electron

happens in Compton scatter

- its the electron that get's ejected as a scattered electron.

- this electron can either ionize other atoms or recombine an ion that needs an electron to be stable

Coherent scatter (interaction)

this interaction;

- occurs in tissues

- also called classical

- Produced by low-energy x-ray photons

- electrons are not removed (this makes it not ionized) but vibrate because of the deposition of energy from the incoming photon (excited)

- As the electrons vibrate, they emit energy equal to that of the original photon. This energy travels in a path slightly different from the path of the original photon. This is what makes it called scatter

- Does not affect image less than 70 kVp

- May have negligible effect on fog greater than 70 kVp