Radiography: Matter, Mass, and Weight

Radiography

• Radiography is both art and science.
• Natural science studies the universe and its contents.
• Natural science divides into the study of:
  • Nonliving matter (physical science: physics)
  • Living matter (biological science: anatomy & physiology)
• Physics studies matter, energy, and their interrelationships
• Matter possesses mass and occupies space.

Mass & Weight

• Mass is a primary characteristic of matter
• Mass is used to describe the quantity of matter in an object and is measured in kilograms.
• Weight describes the force an object exerts under gravity's influence.
• Matter is commonly found as mixtures of substances.
• A substance is material with a definite and constant composition.
• A mixture combines two or more substances
• Air is an example of a mixture.
• An element:
  • Represents a simple substance
  • Cannot be broken down into simpler substances by ordinary means
  • 92 elements exist on the periodic table.
  • Examples include hydrogen (H), oxygen (O), calcium (Ca), barium (Ba), lead (Pb), and iodine (i).

Compounds, Atoms & Molecules

• A compound is a complex substance.
• Compounds consist of two or more elements chemically united in definite proportion.
• Examples include water (H2O) and sodium chloride (NaCl).
• An atom is the smallest particle of an element, retaining the chemical properties of that element.
• A molecule consists of two or more chemically united atoms.
• Molecules represents the smallest particle of a compound possessing the compound's characteristics.
• The degree of attraction between atoms or molecules determines the state of matter, whether solid, liquid, or gas.
• Attraction is weakest in gases and strongest in solids, largely influenced by temperature.

Energy

• Energy describes the capacity to do work, measured in joules (J).
• Radiation describes energy emitted and transferred through matter, like heat and light.
• Matter struck by radiation is considered exposed or irradiated
• Matter and energy are interchangeable, demonstrated by Einstein's theory of relativity: E = mc².
• The Law of Conservation states that matter and energy cannot be created or destroyed.
• The total amount of matter and energy in the universe remains constant.

Atomic Theory: Historical Overview

• Ancient Greeks believed the basic elements included air, water, earth, and fire.
• Dalton (early 1800s) separated elements based on mass, contributing to Mendeleev's periodic table.
• Dmitri Mendeleev (1834–1907) developed the first periodic table.
• Rutherford (1911) proposed a dense, positive nucleus surrounded by negative electrons.
• Bohr (1913) described the atom as a miniature solar system
• Schrödinger laid the foundation for modern physics and quantum mechanics.

Atomic Structure

• Z is the atomic number which represents the number of protons and/or electrons
• The nucleus:
  • Contains a small, dense center
  • Contains protons (positive charge) and neutrons (neutral charge), collectively known as nucleons.
• Electrons:
  • Orbit the nucleus in various planes and specific energy states.
• Electrons are fundamental particles that cannot be divided.
• Protons and neutrons comprise even smaller subnuclear structures called quarks.
• Basic atomic particles include:
  • Proton (p+): positive charge, mass # of 1
  • Neutron (n°): neutral charge, mass # of 1
  • Electron (e–): negative charge, very negligible mass (0)

Electrical Stability & Atomic Number

• Atoms achieve electrical stability with an equal number of protons and electrons.
• Atomic (Z) number distinguishes elements by the number of protons in the nucleus.
• Changing the atomic number changes the element, such as in radioactive decay.
• For example, Radium (Z# 88) emits an alpha particle and decays to Radon (Z# 86).
• Changing the number of neutrons or electrons does not alter the element.
• Isotopes are atoms with the same proton number but different neutron numbers.
• Isotopes share the same atomic (Z) number but differ in mass number (a).
• An ion is when an atom gains or loses an electron

Atomic Mass & Orbital Electrons

• Atomic mass (A) number is the total count of protons and neutrons.
• Orbital electrons are in constant motion around the nucleus
• The distance from the nucleus determines the energy level or shell an electron occupies.
• Each energy level has a certain electron binding energy, which is the energy needed to remove the electron from the atom.
• Electron binding energy is measured in keV.
• Binding energy relies on:
  • Electron proximity to the nucleus
  • The number of protons in the nucleus
• Eb increases as Z# goes up.

Electron Shells & The Octet Rule

• From the nucleus outwards, orbital shells are labeled K, L, M, N, O, P, Q.
• The maximum number of electrons in a shell is determined by 2n², where n is the orbital shell number.
• Octet Rule: an atom never holds more than 8 electrons in its outer shell.
• Some atoms begin filling the next shell before reaching maximum capacity in the current shell.
• Atoms with exactly 8 electrons in their outer shell are chemically stable (inert).
• The noble gases (He, Ne, Ar, Kr, Xe, Rn) are examples of atoms with full outer shells.

The Periodic Table

• A periodic table is an orderly arrangement of elements by atomic number
• Elements are arranged in families and groups:
  • 8 vertical groups contain elements with the same number of electron shells
  • 7 horizontal periods display elements with the same number of electrons in the outer (valence) shell
• Atomic nomenclature identifies elements using symbols, atomic weight (mass number), and atomic number (Z#).
• Atomic weight (mass number) is the larger number, comprised of neutrons and protons.
• Atomic number is determined by the amount of protons.

Valence

• Number of electrons in the outermost shell determines the chemical combining characteristic (valence).
• Chemical combining characteristic dictates how atoms bond with others.
• Elements with one electron in the outermost shell have a valence of (+1).
• Elements with seven electrons in the outermost shell have a valence of (-1).

Types of Energy

• Work equals force times distance.
• Force acting an object over distance expends energy.
• Mechanical energy:
  • Involves machines or physical movement
  • Potential energy: energy because of position (at rest)
  • Kinetic energy: energy of motion
• Chemical Energy:
  • Is energy released from a chemical reaction
  • The body converts chemical energy from food to mechanical energy.
  • A battery converts chemical energy to electrical energy
• Heat Energy:
  • Also known as thermal energy
  • Results from molecule movement.
  • Temperature measures thermal energy.
  • Examples; a toaster converts electrical energy to thermal energy
• Electrical Energy:
  • Involves electricity, which occurs in the conduction band of an atom.
  • Electricity results from electron movement in a conductor
  • A light bulb converts electric energy to light energy.
• Nuclear energy:
  • Is obtained from breaking bonds between particles within a nucleus.
  • Nuclear power plants convert nuclear energy to thermal energy, ultimately used to generate electricity.

Electromagnetic (EM) Energy

• EM energy results from electric and magnetic disturbances in space.
• EM energy comprises electric and magnetic fields traveling through space.
• The source of EM energy comes from acceleration of a charge
• EM radiation travels through mediums or a vacuum.
• EM radiation can be described with the wave/particle duality (acting as a wave or particle, depending on circumstances)
• EM energies are arranged into the EM spectrum based on wavelength and frequency.

Characteristics of EM Radiation

• Wavelength and frequency share an inverse relationship.
• Waves are disturbances in a medium, such as sound in air or waves in the ocean.
• Wavelength is symbolized by λ and measured in angstrom.
• Frequency (ν) is measured in cycles per second (Hertz or Hz)
• Velocity of EM radiation equals frequency times wavelength.
• The velocity of all EM radiation is constant (c), equal to the speed of light (3 × 108 m/sec).
• High-frequency EM radiation interacts with matter, behaving more like a particle than a wave.
• EM radiation acts as a small bundle of energy, also called a photon or quantum.
• Photon energy and frequency are directly proportional.

X-Ray Properties

• X-rays highly penetrate and are invisible
• X-rays are electrically neutral and unaffected by electric or magnetic fields.
• X-rays can be produced over a wide range of energies and wavelengths (polyenergetic and heterogeneous).
• X-rays release small amounts of heat when passing through matter.
• X-rays travel in straight lines at the speed of light (3 X 108 m/sec.) in a vacuum.
• X-rays have the ability to ionize matter and cause fluorescence (the emission of light) of certain crystals.
• X-rays can't be focused by a lens but do affect photographic film.
• X-rays can produce chemical and biological changes in matter through ionization and excitation; and produce secondary and scatter radiation.