RPC

Length

Quantity measuring extent in space; SI unit meter (m).

Mass

Quantity measuring amount of matter; SI unit kilogram (kg).

Time

Quantity measuring sequence or interval of events; SI unit second (s).

Electric current

Quantity for rate of flow of charge; SI unit ampere (A).

Thermodynamic temperature

Quantity for hotness/coldness; SI unit kelvin (K).

Amount of substance

Quantity for amount of entities; SI unit mole (mol).

Luminous intensity

Quantity for luminous power per solid angle; SI unit candela (cd).

Speed

Distance covered per unit time (scalar).

Velocity

Displacement per unit time with direction (vector).

Acceleration

Rate of change of velocity.

Force

Product of mass and acceleration.

Weight

Gravitational force on a mass (mg).

Momentum

Product of mass and velocity.

Work

Force applied through a distance (F × d).

Power

Rate of doing work (W ÷ t).

Kinetic energy

Energy due to motion (½ m v²).

Potential energy

Energy due to position in a field.

Atom

Smallest particle of an element retaining chemical properties.

Nucleus

Central dense core containing protons and neutrons.

Electron

Negatively charged particle orbiting the nucleus.

Proton

Positively charged particle in the nucleus.

Neutron

Neutral particle in the nucleus.

Atomic number (Z)

Number of protons in the nucleus; defines the element.

Mass number (A)

Total number of protons and neutrons in the nucleus.

Isotopes

Atoms with the same Z but different A.

Isobars

Atoms with same A but different Z.

Isotones

Atoms with same neutron number but different Z.

Isomers

Atoms with same Z and A but different energy state.

Electron binding energy

Energy required to remove an electron from a shell.

Electron capacity rule

Rule for maximum electrons in a shell: 2n².

1 amu

Mass of a proton or neutron in atomic mass units (amu).

0.0005 amu

Mass of an electron in amu.

0.511 MeV

Rest mass energy of an electron.

Atomic weight

Weighted average of all isotope masses.

Ion

Atom with unequal numbers of protons and electrons.

Ionization

Removal of an orbital electron producing an ion pair.

Dalton model

Proposed that all matter is made of indivisible atoms; early 1800s.

J.J. Thomson

Discovered the electron; proposed the "plum pudding" model.

Rutherford model

Discovered the nucleus via gold foil experiment.

Bohr model

Proposed electrons in fixed orbits with quantized energy levels; 1913.

Quantum mechanical model

Current model describing electrons as probability clouds around the nucleus.

Gravitational force

Universal attractive force between masses; infinite range.

Electromagnetic force

Force between charged particles; binds atoms; infinite range.

Strong nuclear force

Force binding nucleons in the nucleus; very short range.

Weak nuclear force

Force responsible for beta decay; very short range.

Radiation

Energy transmitted through space or matter as particles or waves.

Ionizing radiation

Radiation capable of removing bound electrons.

Non-ionizing radiation

Radiation not capable of ionization.

Irradiation

Matter that intercepts and absorbs radiation.

Contamination

Material that becomes radioactive through contamination.

Wavelength

Distance between two wave crests.

Frequency

Number of wave cycles per second; unit hertz (Hz).

3 × 10⁸ m/s

Speed of electromagnetic radiation in a vacuum.

c = λ × f

Relationship between wavelength, frequency, and speed.

E = h × f

Energy of a photon equation.

6.626 × 10⁻³⁴ J·s

Planck’s constant value.

Radioactivity

Spontaneous emission of radiation from unstable nuclei.

Alpha decay

Decay emitting 2 protons and 2 neutrons; +2 charge; heavy particle.

Beta minus decay

Decay emitting an electron from the nucleus; -1 charge.

Beta plus decay

Decay emitting a positron from the nucleus; +1 charge.

Gamma decay

Decay emitting high-energy electromagnetic radiation from nucleus.

Half-life

Time for half the radioactive atoms in a sample to decay.

Becquerel (Bq)

Unit for nuclear disintegrations per second; 1 disintegration/s.

Curie (Ci)

Traditional unit for activity; 3.7 × 10¹⁰ disintegrations/s.

Cosmic radiation

Radiation from outer space.

Terrestrial radiation

Radiation from naturally occurring materials in the earth.

Internal radiation

Radiation from radionuclides within the body.

Man-made radiation

Radiation from human activity; largest component from medical imaging.

Exposure (X)

Electric charge per unit mass in air; SI unit coulomb per kilogram (C/kg); traditional unit roentgen (R).

Absorbed dose (D)

Energy imparted per unit mass; SI unit gray (Gy); traditional unit rad.

Equivalent dose (H)

Dose weighted by radiation weighting factors; SI unit sievert (Sv); traditional unit rem.

Effective dose (E)

Sum of weighted equivalent doses for all organs/tissues; SI unit sievert (Sv).

Relative biologic effectiveness (RBE)

Quantity used to compare biologic effectiveness of different radiations.

Air kerma

Radiation quantity representing kinetic energy released per unit mass of air; SI unit gray (Gy).

Wilhelm Conrad Roentgen

German physicist who discovered x-rays in 1895.

Anna Bertha Ludwig

First medical radiograph taken by Roentgen.

Clarence Dally

First X-ray fatality.

Crookes tube

Early experimental vacuum tube used to study cathode rays in the late 1800s.

1901

When was the first Nobel Prize in Physics awarded to Roentgen.

X-ray production

Conversion of projectile electron kinetic energy into x-rays in the anode target.

Bremsstrahlung radiation

Interaction where a projectile electron is slowed or deflected by the nucleus, releasing an x-ray photon.

Difference between entering and exiting electron kinetic energy

Energy of a Bremsstrahlung photon.

Equal to initial kinetic energy of incident electron (tube kVp)

Maximum photon energy in Bremsstrahlung production.

Electron energy loss varies with proximity to nucleus

Reason Bremsstrahlung photons have a range of energies.

Characteristic radiation

Interaction where a projectile electron ejects an inner-shell electron; outer-shell electron fills vacancy; photon released.

Difference between binding energies of involved shells

Energy of a characteristic photon.

K, L, M, N, O, P

Electron shells from innermost to outermost.

69.5 keV

Typical K-shell binding energy for tungsten.

69 kVp

Minimum tube voltage for tungsten K-shell characteristic x-rays.

K-shell characteristic photons

Most useful characteristic photons in diagnostic imaging.

Less than 1%

Fraction of projectile electron kinetic energy converted to x-rays in anode.

Heat

Form of energy produced by most interactions in anode.

Polyenergetic beam

X-ray beam containing photons of many energies.

Monoenergetic beam

X-ray beam containing photons of identical energy.

X-ray emission spectrum

Graph showing distribution of x-ray photon energies.

Continuous spectrum

Spectrum showing continuous range up to maximum photon energy.

Discrete spectrum

Spectrum showing discrete peaks from binding energy differences.

Increases amplitude only

Effect of increasing mA on spectrum.

Increases amplitude and shifts to higher energies

Effect of increasing kVp on spectrum.

Decreases amplitude, increases average photon energy

Effect of filtration on spectrum.