Radiation Physics

directly related

Relationship between frequency and photon _____

inversely related

frequency and photon energy are ______ related to wavelength

wavelength

refers to the distance between two consecutive wave crests

frequency

refers to the number of cycles per second

greater frequency

shorter wavelength = _____

heated cathode (-) filament

the source of the electrons is the ____

thousands of volts (kilovolts) are applied.

the electrons are driven across the anode’s focal spot when what is applied?

• interact with tungsten atoms

• kinetic energy is converted to HEAT and x-ray PHOTON energy

when high speed electrons are suddenly stopped at the focal spot they interact with what and what happens to their energy?

HETEROgeneous (polyenergetic)

What kind of energy is x-ray beam?

1. Bremsstrahluung (Brems) or “Braking” Radiation

2. Characteristic Radiation

Two interactions that are produced at the anode through energy conversion process

Bremsstrahlung (brems) radiation.

high speed electron is deflected from its path and the loss of kinetic energy is emitted in the form of an x-ray photon.

• High speed electron is accelerated toward a tungsten atom within the anode focal track

• The negative electron is attracted by the positive nucleus of the tungsten atom

• As a result, pulled off course and redirected towards the nucleus

• The electron’s deflection from its original course caused by the “braking” (slowing down) results in a loss of energy

What happens in brems radiation?

70%-90%

Brems radiation comprises how much of the primary x-ray beam?

• A high speed ELECTRON encounters a tungsten atom and ejects a K-shell electron

• Thereby leaving a vacancy in the K shell.

• An electron from a higher energy level shell FILLS the vacancy

• In doing so, because of the difference in energy level between the K and L shells, a K-characteristic x-ray photon is emitted.

What happens during Characteristic Radiation?

the difference in binding energy between the K and L shells.

The energy of the characteristic ray is equal to ______

69 keV energy

The K-characteristic x-rays from a tungsten target x-ray tube have what energy?

10%-30%

Characteristic radiation comprises the minor portion of the x-ray beam

attenuation

The gradual decrease in exposure rate as ionizing radiation passes through tissues is called ____

• Photoelectric effect

• Compton scatter

Two major types of interactions that occur between x-ray photons and matter (in diagnostic x-ray range of energy)

Photoelectric effect

A relatively low-energy (low-kV) x-ray PHOTON interacts with tissue and expands all of its energy (true/total absorption) to eject an inner shell electron.

• this leaves an innershell orbital vacancy

• An electron from the shell above drops down to fill the vacancy and gives up energy in the form of a characteristic ray

ALL of its energy

In the photoelectric effect, the incoming (low-energy) photon releases how much of its energy as it ejects an inner shell electron from the orbit?

absorbers having high atomic number (i.e. bone, positive contrast media)

The photoelectric effect is more likely to occur in _____ with low-energy photons

Short-scale contrast

The photoelectric effect produces what kind of contrast?

Compton scatter

A fairly high energy (high kV) x-ray PHOTON interacts with tissue atoms, giving up some of its energy to eject an outer shell

recoil electron

the ejected electron from compton scatter is called?

RETAINS

The photon in compton scatter changes direction (scatters) as it exits the body but ______ much of its original energy.

DOES NOT pose

Because the scattered photon exits the body, it does _____ a radiation hazard to the patient.

• image fog

• pose a radiation hazard to personnel.

The compton scatter contribute to the:

• High-energy

• short wavelength

• electromagnetic radiations that break apart electrically neutral atoms

Ionization is caused by:

• beam attenuation

• type of interaction that occurs between x-ray photons and tissue

exposure depends on:

• Radiation quality (kV)

• Subject being irradiated (thickness)

• Nature of part (atomic number of part)

Exposure dose is affected by: