Radiologic Physics Lecture Notes

Vocabulary practice flashcards covering matter, energy, atomic structure, electricity, magnetism, x-ray production, and interactions with matter.

Matter

Anything that occupies space & has mass/weight and can be transformed from one size, shape & form to another.

Mass

The quantity of matter, which is constant and measured in the kilogram ($kg$); $1\,kg = 2.2\,lbs$.

Weight

The force exerted on a body under the influence of gravity, measured in pounds ($lb$) or Newton ($N$); $1\,lb = 4.5\,N$.

Energy

The ability to do work; its SI unit is the Joule ($J$), while in Radiology, the electron volt ($eV$) is used.

Potential Energy

The ability to do work by virtue of position or energy at rest, such as a rollercoaster on top of an incline.

Kinetic Energy

The energy of motion, possessed by all matter in motion, such as a turning windmill or a falling guillotine blade.

Chemical Energy

The energy released by a chemical reaction, such as energy provided to the body or dynamite exploding.

Electrical Energy

The work that can be done when an electron moves through an electric potential difference ($V$).

Thermal/Heat Energy

The kinetic energy of molecules in motion at the molecular level; measured in calories or joules ($J$).

Nuclear Energy

The energy that is contained within the nucleus of an atom, released in power plants or atomic bombs.

Electromagnetic Energy

The type of energy used in x-ray imaging, also including radio waves, microwaves, and visible light.

Law of Conservation of Matter

States that matter may be transformed from one form to another but cannot be created or destroyed.

Law of Conservation of Energy

States that energy may be transformed from one form to another but cannot be created or destroyed; total energy is constant.

Theory of Relativity

Albert Einstein's 1905 theory stating mass and energy are interchangeable, expressed as $E=mc^2$.

Atom

The fundamental building blocks of matter and the smallest particle of an element; it is neutrally charged.

Nucleus

The positively charged central core of an atom that contains nucleons and nearly all the atom's mass.

Element

A pure chemical substance distinguished by its atomic number ($Z$), representing the number of protons/electrons.

Compound

A substance composed of two or more elements chemically linked, such as $H_2O$ or $BaSO_4$.

Covalent Bond

The chemical union between atoms formed by sharing one or more pairs of electrons.

Ionic Bond

Bonding that occurs because of an electrostatic force between ions.

Atomic Mass Unit

The mass of a neutral atom of an element, where $1\,amu$ equals $1/12$ the mass of a carbon-$12$ atom.

Atomic Mass Number ($A$)

The total number of protons and neutrons in the nucleus; formula is $A = \text{protons} + \text{neutrons}$.

Atomic Number ($Z$)

The number of protons or electrons in an atom.

Electron

A particle located in orbital shells with a charge of $-1$ and a mass of $9.109 \times 10^{-31}\,kg$; discovered by John Joseph Thomson.

Proton

A particle located in the nucleus with a charge of $+1$ and a mass of $1.673 \times 10^{-27}\,kg$; discovered by Eugene Goldstein.

Neutron

A particle located in the nucleus with a charge of $0$ and a mass of $1.675 \times 10^{-27}\,kg$; discovered by James Chadwick.

Octet Rule

The rule stating that no outer electron shell can contain more than eight electrons.

Centripetal Force

The center-seeking force that keeps an electron in its orbit.

Centrifugal Force

The flying-out-from-the-center force that causes an electron to travel straight and potentially leave the atom.

Electron Binding Energy ($E_b$)

The strength of attachment of an electron to the nucleus; the energy required to completely remove an electron from an atom.

Radioactivity

The emission of particles and energy by an atom in order to become stable.

Curie ($Ci$)

A unit used to express the rate of decay or disintegration of radioactive material.

Becquerel ($Bq$)

The SI unit of radioactivity.

Radioactive Decay/Disintegration

The process by which a nucleus spontaneously emits particles and energy to transform into another type of atom to reach stability.

Physical Half-life ($T_{1/2}$)

The time required for a quantity of radioactivity to be reduced to one-half its original value.

Biological Half-life ($T_b$)

The time required for the body to eliminate one-half of the dose of any substance by biological processes.

Effective Half-life ($T_e$)

Encompasses both physical and biological half-lives, expressed by the relationship $\frac{1}{T_e} = \frac{1}{T_{1/2}} + \frac{1}{T_b}$.

Isotopes

Atomic nuclei that have the same atomic number ($Z$) but different atomic mass numbers ($A$).

Isobar

Atomic nuclei that have the same atomic mass number ($A$) but different atomic numbers ($Z$).

Isotone

Atomic nuclei that have the same neutron number ($N\#$) but different atomic numbers ($Z$) and mass numbers ($A$).

Isomer

Atomic nuclei that have the same atomic number ($Z$), mass number ($A$), and neutron number ($N\#$).

Alpha Decay

Decay occurring in very heavy radionuclides ($Z > 82$) resulting in the emission of an alpha particle ($2p^+$ and $2n^0$).

Beta Minus Decay

Decay where a neutron is converted into a proton, resulting in an increase of atomic number by $1$ and emission of a negatron and antineutrino.

Beta Plus Decay

Decay where a proton is converted into a neutron, resulting in a decrease of atomic number by $1$ and emission of a positron and neutrino.

Electron Capture

A process where a nucleus captures an electron (usually from the K-shell) and converts a proton into a neutron.

Electrostatics

The study of stationary electric charges and the distribution of fixed charges.

Coulomb ($C$)

The SI fundamental unit of electric charge; $1\,C = 6.3 \times 10^{18}\,e^-$.

Volt ($V$)

The unit of electric potential, defined as potential energy per unit charge ($1\,V = 1\,J/C$).

Electrification

The transfer or movement of electrons from one object to another created by friction, contact, or induction.

Coulomb's Law

States the electrostatic force is directly proportional to the product of charges and inversely proportional to the square of the distance ($d^2$).

Electrodynamics

The study of electric charges in motion.

Ohm's Law

States that the voltage across a circuit equals current times resistance ($V = IR$).

Conductor

Any substance through which electrons flow easily, such as copper, aluminum, and water.

Insulator

Any material that does not allow electron flow, such as glass, rubber, and clay.

Semiconductor

A material that under some conditions behaves as an insulator and as a conductor, such as silicon and germanium.

Superconductor

Any material that allows electrons to flow without resistance, such as niobium and titanium; must be very cold.

Electric Power

Measured in watts ($W$), where $1\,W = 1\,A \times 1\,V$; formulas include $P = IV$ and $P = I^2R$.

Faraday's Law

The first law of electromagnetic induction stating that an electric current is induced in a circuit if it is in a changing magnetic field.

Lenz's Law

The second law of electromagnetic induction stating that an induced current will oppose the direction of the current that induced it.

Transformer

A device that changes the intensity of alternating voltage and current through electromagnetic induction; operates only with AC.

Line-Voltage Compensator

A device that measures incoming voltage to the x-ray system and adjusts it to precisely $220\,V$.

Automatic Exposure Control (AEC)

A system that automatically terminates the x-ray exposure once a predetermined quantity of radiation has penetrated the patient.

Line Focus Principle

A design in x-ray tube targets that allows a large area for heating while maintaining a small effective focal spot.

Anode Heel Effect

A decrease in beam intensity at the anode end of the x-ray beam caused by absorption of x-rays in the heel of the target.

Off-Focus Radiation

Extrafocal x-rays produced when electrons bounce off the focal spot and land on other areas of the target.

Heat Units (HU)

A calculation of total heat produced during x-ray exposure; for single-phase: $HU = kVp \times mA \times s$.

Photon

The smallest quantity of any type of electromagnetic energy; also called a quantum.

Planck's Quantum Equation

The relationship $E = hf$, where $h$ is Planck's constant ($4.15 \times 10^{-15}\,eV\text{-}s$) and $f$ is frequency.

Linear Energy Transfer (LET)

A measure of the rate at which energy is transferred from ionizing radiation to soft tissue, expressed in $keV/\mu m$.

Characteristic Radiation

X-rays emitted when an outer-shell electron fills an inner-shell void in a target atom.

Bremsstrahlung Radiation

X-rays produced by the braking of projectile electrons by the electric field of the target nucleus.

Coherent Scattering

Interaction occurring at low energies ($< 10\,keV$) where the incident x-ray changes direction with no change in energy or wavelength.

Compton Effect

Interaction where a high-energy incident x-ray ejects an outer-shell electron and continues in a different direction with reduced energy.

Photoelectric Effect

Interaction where a low-energy incident x-ray is completely absorbed as it ejects an inner-shell electron.

Attenuation

The total reduction in the number of x-rays in a beam after penetration through tissue, resulting from absorption and scattering.