Comprehensive Guide to Atomic Structure, X-ray Production, and Radiographic Principles

Atomic number

The number of protons in the nucleus of an atom. In a neutral atom, it also equals the number of electrons.

Mass number

The total number of protons plus neutrons in the nucleus.

Proton

A positively charged subatomic particle located in the nucleus.

Neutron

A subatomic particle with no electrical charge located in the nucleus.

Electron

A negatively charged subatomic particle located in the electron shells surrounding the nucleus.

Nucleus

The dense central region of an atom containing protons and neutrons.

Dalton atomic theory

John Dalton proposed that matter is composed of atoms and that atoms of each element have unique characteristics.

Rutherford atomic model

Rutherford's model established that the atom has a small, dense, positively charged nucleus with electrons surrounding it.

Bohr atomic model

Bohr described electrons as occupying specific energy levels or shells around the nucleus.

Electron shell

A defined energy level surrounding the nucleus where electrons are found.

K shell

The innermost electron shell and the shell with the greatest electron binding energy.

L shell

The second electron shell surrounding the nucleus.

M shell

The third electron shell surrounding the nucleus.

Electron binding energy

The energy that holds an electron in its orbital shell.

Nuclear binding energy

The energy holding protons and neutrons together in the nucleus.

Ion

An atom that has gained or lost one or more electrons and therefore has a net electrical charge.

Positive ion

A positively charged atom produced when an atom loses one or more electrons.

Negative ion

A negatively charged atom produced when an atom gains one or more electrons.

Ionization

The removal of an electron from an atom.

Excitation

The temporary movement of an electron to a higher energy level without removing it from the atom.

Ion pair

A positively charged atom and the electron removed from it during ionization.

Neutral atom

An atom with equal numbers of protons and electrons and therefore no net electrical charge.

Atomic mass number formula

Mass number = number of protons + number of neutrons.

Number of neutrons formula

Number of neutrons = mass number - atomic number.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Electromagnetic radiation

Energy that travels through space as electric and magnetic disturbances.

Electromagnetic spectrum

The complete range of electromagnetic radiation arranged by energy, frequency, or wavelength.

Electromagnetic spectrum order

From lowest to highest energy: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays.

Ionizing radiation

Radiation with enough energy to remove electrons from atoms.

Nonionizing radiation

Radiation that does not have enough energy to ionize atoms.

X-rays

High-energy electromagnetic radiation capable of ionizing matter.

Gamma rays

High-energy electromagnetic radiation originating from the atomic nucleus.

Speed of electromagnetic radiation

All electromagnetic radiation travels at approximately 3 × 10^8 m/s in a vacuum.

Wavelength

The distance from the peak of one wave to the peak of the next wave.

Frequency

The number of waves or cycles that pass a given point per second.

Hertz

Unit of frequency equal to one cycle per second.

Amplitude

The maximum height of a wave.

Wavelength and frequency relationship

Wavelength and frequency are inversely related: as wavelength decreases, frequency increases.

Frequency and energy relationship

Frequency and energy are directly related: higher frequency means higher photon energy.

Wave equation

c = fλ, where c is the speed of light, f is frequency, and λ is wavelength.

Photon

A packet of electromagnetic energy.

Planck relationship

E = hf; photon energy increases as frequency increases.

High-energy electromagnetic radiation

X-rays and gamma rays have enough energy to ionize matter.

Wave-particle duality

Electromagnetic radiation can behave as both a wave and a particle depending on its energy and interaction.

Particulate radiation

Radiation consisting of particles that have mass, such as alpha and beta particles.

Alpha particle

A positively charged particulate radiation consisting of two protons and two neutrons.

Beta particle

A high-speed electron or positron emitted from an unstable nucleus.

X-ray tube

A vacuum tube that converts electrical energy into x-rays, with heat produced as a major byproduct.

Cathode

The negative electrode of the x-ray tube that supplies electrons.

Anode

The positive electrode of the x-ray tube that contains the target and receives electrons from the cathode.

Cathode function

The cathode provides and directs electrons toward the anode.

Anode function

The anode receives the high-speed electrons and provides the target where x-rays are produced.

Filament

A heated tungsten wire in the cathode that produces electrons through thermionic emission.

Thermionic emission

The boiling off or release of electrons from a heated filament.

Focusing cup

The negatively charged cup surrounding the filament that concentrates the electron cloud toward the focal spot.

Dual-focus tube

A tube containing two filaments that can produce different focal spot sizes.

Small filament

Produces the small focal spot and is generally used when greater recorded detail is needed.

Large filament

Produces the large focal spot and can tolerate greater heat loading.

Target

The area of the anode struck by electrons where x-rays are produced.

Focal spot

The area of the target struck by electrons from the filament.

Actual focal spot

The physical area of the target bombarded by electrons.

Effective focal spot

The apparent focal spot size as viewed from the patient/image receptor.

Line-focus principle

The angled anode target allows a large actual focal spot for heat dissipation while producing a smaller effective focal spot for image sharpness.

Why use the line-focus principle

To balance heat dissipation with image sharpness.

Small effective focal spot

Produces better recorded detail and sharpness.

Large actual focal spot

Spreads heat over a larger area of the target.

Target angle

An angle of the anode target face used to create the line-focus effect.

General-purpose target angle

Typically about 7° to 18°, with approximately 12° being common according to the textbook.

Anode heel effect

The reduction in x-ray intensity on the anode side because x-rays must pass through more target material before exiting.

Cathode side

The side of the x-ray beam with greater intensity because of the anode heel effect.

Anode side

The side of the x-ray beam with lower intensity because of the anode heel effect.

Rotating anode

A rotating target that spreads heat over a larger area and increases tube heat capacity.

Stationary anode

A fixed target generally used where lower heat loading is expected.

Rotor

The rotating component of the induction motor located inside the tube enclosure.

Stator

The electromagnets outside the tube envelope that cause the rotor/anode to rotate.

Induction motor

The motor system that rotates the anode through electromagnetic induction.

Tube envelope

The glass or metal enclosure that maintains the vacuum around the cathode and anode.

Vacuum

The absence of air inside the tube that allows electrons to travel from cathode to anode without air interference.

Protective housing

The lead-lined metal housing surrounding the x-ray tube that provides electrical insulation, thermal protection, physical protection, and radiation shielding.

Tube housing oil

The oil surrounding the x-ray tube that helps transfer heat away from the tube.

Cooling fans

Fans in the tube housing that help dissipate heat.

High-voltage cables

Cables that deliver the electrical energy required by the x-ray tube.

Target window

A thinned section of the tube enclosure that allows useful x-rays to exit while minimizing absorption.

Target window filtration

The target window contributes approximately 0.5 mm aluminum equivalent to inherent filtration in a general radiography tube head.

Leakage radiation

X-rays produced in the tube that travel in directions other than toward the patient.

Allowed leakage radiation

The protective housing is designed to reduce leakage radiation to less than 100 mR/hr at 1 meter according to the textbook.

Useful beam

The x-ray photons that exit through the tube window and are directed toward the patient.

Inherent filtration

Filtration naturally present in the tube housing and components, including the target window.

Added filtration

Additional filtration, generally aluminum, placed in the tube head to remove low-energy photons.

Total filtration

The combination of inherent and added filtration.

General radiography total filtration

The textbook describes approximately 2.5 mm aluminum equivalent total filtration for a general-purpose tube head.

Compensating filter

A filter used to compensate for differences in patient thickness or tissue density.

Aluminum filtration

Material commonly used to remove low-energy x-ray photons from the beam.

Why filtration is used

To remove low-energy photons that would mainly increase patient dose without contributing useful image formation.

Tungsten

Target material commonly used because of its high atomic number and high thermal capacity/high melting point.

Tungsten atomic number

Tungsten has an atomic number of 74.

Why tungsten is used

Tungsten combines a high atomic number, high melting point, and good ability to tolerate heat.

Tungsten K-shell binding energy

Approximately 69.5 keV.

Tungsten K-characteristic radiation

K-characteristic photons can be produced when the tube operates at approximately 70 kVp or higher because tungsten's K-shell binding energy is about 69.5 keV.

Copper in the anode

Copper is used because of its good thermal and electrical conductivity.