Structure of Matter & Radiation – Vocabulary

A comprehensive set of vocabulary flashcards covering atomic structure, periodic groups, radiation types, and key radiologic science terms drawn from the lecture notes.

Atom

Smallest particle that possesses all the properties of an element; composed of electrons, protons, and neutrons

Subatomic Particle

A particle smaller than an atom, such as the electron, proton, or neutron

Electron

Negatively charged particle (−1) located in orbital shells; relative mass 1; 9.1 × 10⁻³¹ kg

Proton

Positively charged particle (+1) in the nucleus; relative mass 1836; 1.673 × 10⁻²⁷ kg

Neutron

Electrically neutral nuclear particle; relative mass 1838; 1.675 × 10⁻²⁷ kg

Nucleon

Collective term for protons and neutrons, which are themselves made of quarks and gluons

Atomic Mass Unit (amu)

Unit of mass equal to half the mass of a carbon-12 atom; used for atomic masses

Atomic Number (Z)

Number of protons in the nucleus of an atom; determines the element

Atomic Mass Number (A)

Total number of protons plus neutrons in the nucleus

Isotope

Atoms of the same element (same Z) with different numbers of neutrons (different A)

Isobar

Atoms with the same atomic mass number (A) but different atomic numbers (Z)

Isotone

Atoms with the same number of neutrons but different Z and A

Isomer

Atoms with identical Z and A but different nuclear energy states

Valence

Number of electrons in the outermost shell; determines chemical combining ability

Principal Quantum Number (n)

Shell number indicating the energy level of an electron

Electron Binding Energy (Eb)

Strength of attraction between an electron and the nucleus

Ionization Potential

Energy (≈34 keV for tissue) required to remove an electron from an atom

Radioactivity

Spontaneous emission of particles or energy from an unstable nucleus to achieve stability

Radioisotope

Radioactive atom of an element; same Z, unstable A

Radioactive Decay

Process by which an unstable nucleus emits particles/energy and transforms into another atom

Radioactive Half-life (T½)

Time required for half the radioactivity of a sample to decay

Radioactive Decay Law

Mathematical relation: Remaining Activity = Original Activity × (0.5)ⁿ, where n = number of half-lives

Beta Emission

Decay process in which a neutron converts to a proton and an electron (β⁻) is emitted, increasing Z by 1

Alpha Emission

Decay process in heavy nuclei emitting an alpha particle (2 p + 2 n), decreasing Z by 2 and A by 4

Alpha Particle (α)

Helium nucleus (2 p, 2 n); mass 4 amu, charge +2, 4–7 MeV energy

Beta Particle (β)

Light particle emitted from nucleus; charge −1 (electron) or +1 (positron); up to 7 MeV energy

Positron

Positive beta particle (β⁺); antimatter counterpart of the electron

Photon

Quantum of electromagnetic radiation with no mass or charge; travels at speed of light

X-ray

Photon originating from electron cloud interactions; 0–25 MeV; used in radiography

Gamma Ray

Photon originating from the nucleus during radioactive decay; 0–5 MeV

Particulate Radiation

Ionizing radiation consisting of particles with mass (e.g., alpha, beta)

Electromagnetic Radiation

Energy propagated as photons (e.g., x-rays, gamma rays); unlimited range in matter

Nonionizing Radiation

Radiation without sufficient energy to ionize atoms; used in ultrasound and MRI

Plum Pudding Model

J.J. Thomson’s atomic model with electrons embedded in positive ‘pudding’

Nuclear Model

Ernest Rutherford’s model featuring a small, dense, positively charged nucleus surrounded by electrons

Bohr Atom

Niels Bohr’s model of electrons orbiting the nucleus in fixed energy levels

Quantum Chromodynamics (QCD)

Theory describing the interactions of quarks and gluons within nucleons

Alkali Metals

Group 1 elements; soft metals that react vigorously with water and oxygen

Halogens

Group VII elements; easily vaporized and form water-soluble salts with metals

Noble Gases

Group VIII elements; chemically inert due to complete outer electron shells

Transitional Elements

Elements in which the orderly shell-filling scheme is interrupted; found in fourth period

Centripetal Force

Center-seeking force keeping an electron in its orbit

Centrifugal Force

Apparent force driving an electron outward, balancing centripetal attraction

Covalent Bond

Chemical bond formed by sharing electron pairs between atoms (e.g., H₂O)

Ionic Bond

Bond formed by electrostatic attraction between oppositely charged ions (e.g., NaCl)

Molecule

Smallest unit of a compound consisting of two or more atoms bonded together

Chemical Compound

Substance composed of only one type of molecule

Particle Accelerator

‘Atom smasher’ device used to probe nuclear structure by accelerating particles

CHON

Acronym for Carbon, Hydrogen, Oxygen, Nitrogen—elements making up ~90 % of the human body

Tungsten (W-74)

Element used as a primary x-ray tube target material

Molybdenum (Mo-42)

Element used in x-ray tube targets, particularly for mammography

Barium (Ba-56)

Element employed as a radiographic contrast agent

Iodine (I-53)

High-Z element used in radiographic and fluoroscopic contrast media