Chapter 002

Dental Radiography – Chapter Two Outline Radiation Physics Fundamental Concepts X-radiation X-ray Machine Production of X-radiation Interactions of X-radiation

Introduction Purpose To present the fundamental concepts of atomic and molecular structure To define and characterize x-radiation To introduce the x-ray machine To describe in detail how x-rays are produced

Fundamental Concepts Atomic and Molecular Structure Ionization, Radiation, and Radioactivity Ionizing Radiation

Atomic and Molecular Structure Matter Anything that occupies space and has mass When matter is altered, energy results Atom The fundamental unit of matter All matter is composed of atoms

Atomic Structure Atom A central nucleus and orbiting electrons The identity is determined by the composition of the nucleus and the arrangement of orbiting electrons

Nucleus Composed of protons and neutrons Protons have positive electrical charges Neutrons carry no electrical charge Most of the atom is empty space

Nucleus The number of protons and neutrons in the nucleus of an atom determines its mass number or atomic weight The number of protons inside the nucleus equals the number of electrons outside the nucleus and determines the atomic number Atoms are arranged in increasing atomic number on the periodic table of the elements

Electrons Tiny, negatively charged particles Have very little mass, approximately 1/1800 as much as a proton or neutron Electrons travel around the nucleus in well-defined paths known as orbits or shells

Electrons The shell located closest to the nucleus has the highest energy level The strongest binding energy is found closest to the nucleus in the K shell Measured in electron volts or kilo electron volts

Electrons Maintained in their orbits by electrostatic force between the positive nucleus and negative electrons Known as the binding energy of an electron Binding energy is determined by the distance between the nucleus and the orbiting electron

Molecular Structure Atoms are capable of combining with each other to form molecules Molecules are two or more atoms joined by chemical bonds, or the smallest amount of a substance that possesses its characteristic properties

Molecular Structure Molecules are formed in two ways: The transfer of electrons The sharing of electrons between the outermost shells of atoms

Ionization, Radiation, and Radioactivity Ionization Normally, most atoms are neutral A neutral atom contains an equal number of protons and electrons An atom with an incompletely filled outer shell attempts to capture an electron from an adjacent atom

Ionization If the atom gains an electron, it has a negative charge If the atom loses an electron, it has a positive charge An atom that gains or loses an electron and becomes electrically unbalanced is called an ion

Ionization When an electron is removed from an atom in the ionization process, an ion pair results The atom becomes the positive ion The ejected electron becomes the negative ion

Radiation and Radioactivity Radiation The emission and propagation of energy through space or a substance in the form of waves or particles Radioactivity The process by which certain unstable atoms or elements undergo spontaneous disintegration, or decay , in an effort to attain a more balanced nuclear state

Ionizing Radiation Radiation is capable of producing ions by removing or adding an electron to an atom Classified into two groups Particulate radiation Electromagnetic radiation

Particulate Radiation Tiny particles of matter that possess mass and travel in straight lines and at high speeds Four types

Particulate Radiation Electrons Beta particles: fast-moving electrons emitted from nucleus of radioactive atoms Cathode rays: streams of high-speed electrons that originate in an x-ray tube Electrons emitted by a manufactured device Alpha particles Emitted from the nuclei of heavy metals Exist as two protons and neutrons, without electrons

Particulate Radiation Protons Accelerated hydrogen nuclei Mass of 1 and charge of +1 Neutrons Accelerated particles Mass of 1, no electrical charge

Electromagnetic Radiation The propagation of wavelike energy (without mass) through space or matter Oscillating electric and magnetic fields are positioned at right angles to one another

Electromagnetic Radiation May be human made or occur naturally Arranged in the electromagnetic spectrum according to their energies

Electromagnetic Radiation All have common characteristics May be classified as ionizing or non-ionizing Only high-energy radiations are capable of ionization Believed to move through space as both a particle and a wave; both concepts m ust be considered

Particle Concept Characterizes electromagnetic radiation in terms of discrete bundles of energy called photons or quanta Photons are bundles of energy with no mass or weight Photons travel as waves at the speed of light and move through space in a straight line

Wave Concept Characterizes electromagnetic radiations as waves Velocity The speed of the wave Wavelength The distance between the crest of one wave and the crest of the next

Wave Concept Frequency The number of wavelengths that pass a certain point in a given length of time

X-Radiation A high-energy, ionizing electromagnetic radiation X-rays Weightless bundles of energy without an electrical charge that travel in waves with a specific frequency at the speed of light X-ray photons interact with the materials they penetrate and cause ionization

X-ray Machine Component Parts Control panel - #1 Extension arm - #2 Tubehead - #3

Control Panel - #1 Contains an on- off switch Indicator light Control devices Time, kilovoltage, milliamperage Plugged into an electrical outlet

Extension Arm - #2 Suspends the x-ray tubehead Houses the electrical wires that extend from the control panel to the tubehead Allows for movement and positioning of the tubehead

Tubehead A tightly sealed, heavy metal housing Contains the x-ray tube that produces dental x-rays Metal housing Surrounds the x-ray tube and transformers, protects tube and grounds high voltage components

Tubehead Insulating oil Surrounds x-ray tube and transformers, prevents overheating

Tubehead Tubehead seal Permits exit of x-rays from tubehead, seals the oil, filters x-ray beam X-ray tube Heart of generating system Transformer Alters voltage of incoming electricity

Aluminum Filter Aluminum disks Filter out non-penetrating, longer wavelength x-rays

Lead Collimator Also know as the lead diaphragm Restricts size of the x-ray beam – 2 ¾”

How the aluminum filter and lead collimator work together

Positioning-indicating device - PID Aims and shapes the x-ray beam Also, referred to as the cone

X-ray Tube A glass vacuum tube Measures several inches long by 1 inch in diameter Includes Leaded-glass housing Cathode Anode

Leaded Glass Housing A leaded glass vacuum tube Prevents x-rays from escaping in all directions One area has a “window” that permits the x-ray beam to exit the tube and directs the beam toward the aluminum disks, lead collimator, and PID

Cathode (-) The negative electrode Consists of a tungsten wire filament in a cup-shaped holder made of molybdenum

Cathode (-) Supplies the electrons necessary to generate x-rays The tungsten filament produces electrons when heated The molybdenum cup focuses electrons into a narrow beam and directs the beams toward the tungsten target

Anode (+) The positive electrode Consists of a wafer-thin tungsten plate embedded in a solid copper rod Converts electrons into x-ray photons The tungsten target serves as a focal spot and converts electrons into photons The copper stem functions to dissipate heat away from the tungsten target

X-ray Generating Apparatus Electricity and electrical currents Circuits Transformers

Electricity and Electrical Currents Electricity The energy used to make x-rays Electrical current A flow of electrons through a condu ctor

Electricity and Electrical Currents Direct current (DC) When electrons flow in one direction through a conductor – example: a battery Alternating current (AC) When electrons flow in two, opposite directions – example: electricity Rectification The conversion of alternating current to direct current – example: a dental x-ray machine

Alternating Current – Flows in two, opposite directions

Rectification – The conversion of alternating current to direct current

Electricity and Electrical Currents Amperage The measurement of the number of electrons moving through a conductor Current is measured in amperes (A) or milliamperes (mA)

Electricity and Electrical Currents Voltage The measurement of electrical force that causes electrons to move from a negative pole to a positive one Voltage is measured in volts (V) or kilovolts (kV)

Electricity and Electrical Currents Milliamperage adjustment Can increase or decrease the number of electrons passing through the cathode filament Kilovoltage peak (kVp) adjustment Can control the current passing from the cathode to the anode

Circuits Circuit A path of electrical current Filament circuit - mA Uses 3 to 5 volts Regulates flow of electrical current to the filament Controlled by milliampere settings High-voltage circuit - kVp Uses 65,000 to 100,000 volts Provides high voltage required to generate x-rays Controlled by kilovoltage settings

Transformers A device used to either increase or decrease the voltage in an electrical circuit Three transformers are used to adjust the electrical circ uits Step-down transformer Step-up transformer Autotransformer

Step-Down Transformer Used to decrease voltage from the incoming 110- or 220 -line voltage to the 3 to 5 volts used by the filament circuit More wire coils in the primary coil than in the secondary coil

Step-Up Transformer Used to increase incoming voltage to 65,000 to 100,000 volts used by the high-voltage circuit More wire coils in the secondary coil than in the primary coil

Autotransformer A voltage compensator Corrects for minor fluctuations in current Standardizes the electricity

Production of X-radiation Production of Dental X-rays Types of X-rays Produced Definitions of X-radiation

Production of Dental X-rays Electricity from the wall outlet supplies the power to generate x-rays The current is directed to the filament circuit and step-down transformer in the tubehead The filament circuit uses 3 to 5 volts to heat the tungsten filament in the cathode Thermionic emission occurs, the release of electrons

The process of the production of dental x-rays

Production of Dental X-rays The electrons stay in an electron cloud until the high-voltage circuit is activated When the exposure button is pushed, the high-voltage circuit is activated The molybdenum cup in the cathode directs electrons to the tungsten target in to anode When electrons strike the tungsten target, less than 1% of the energy is converted to x-rays, the remaining 99% is lost as heat

Production of Dental X-rays A small number of x-rays are able to exit the x-ray tube through the unleaded glass window portion of the tube X-rays travel through the unleaded glass window, the tubehead seal, and aluminum disks

Production of Dental X-rays The size of the x-ray beam is restricted by the lead collimator The x-ray beam exits the tubehead at the opening of the PID

Types of X-rays Produced X-rays differ in energy and wavelength Two mechanisms General (braking) radiation Characteristic radiation

General Radiation Many electrons that interact with the tungsten atoms undergo not one but many interactions within the target Most x-rays (about 70%) are produced in this manner Produced when an electron hits the nucleus of a tungsten atom or passes very close to the nucleus of a tungsten atom

Characteristic Radiation Produced when a high-speed electron dislodges an inner-shell electron from a tungsten atom and causes ionization of that atom The remaining orbiting electrons are rearranged to fill the vacancy Occurs only at 70 kVp and above

Definitions of X-Radiation Primary radiation The penetrating x-ray beam that is produced at the target of the anode Secondary radiation X-radiation created when the primary beam interacts with matter Scatter radiation A form of secondary radiation, the result of a x-ray that has been deflected from its path by an interaction with matter

Interactions of X-Radiation No interaction (#1) Absorption of energy and photoelectric effect (#2) Compton scatter (#3) Coherent scatter (#3)

No Interaction The x-ray photon passes through the atom unchanged and leaves the atom unchanged These photons are responsible for producing densities on film and make dental radiography possible

Absorption of Energy and Photoelectric Effect (30%) The x-ray photon is completely absorbed within matter or the tissues of the patient Absorption The total transfer of energy from photon to the atoms of matter Photoelectric effect An x-ray photon collides with a tightly bound, inner-shell electron, gives up all its energy to eject the electron from its orbit The ejected photoelectron is absorbed by other atom s

Compton Scatter (62%) The x-ray photon is deflected from its pa th during its passage through matter In Compton scatter, ionization takes place The x-ray photon loses energy and continues in a different direction at a lower energy level The ejected electron is termed a Compton electron

Coherent Scatter (8%) An x-ray photon that has its path altered by matter A low-energy x-ray photon interacts with an outer-shell electron No change in the atom occurs, and an x-ray photon of scattered radiation is produced

Summary Overview of the chapter Fundamental concepts of atomic and molecular structure Characterize x-radiation Introduce the x-ray machine Describe how x-rays are produced

Identify the parts of the dental x-ray tube

Identify the parts of the dental x-ray tubehead

ASSIGNMENT Chapter 1 – Lesson 1 on D2L in Dental Radiology 1 – under content View the power point – this has audio ( you can print it off if you want to so you can follow along) PRINT OFF - Chapter 1 – Lesson 1 Worksheet for points PRINT OFF - Chapter 1 – Lesson 1 Self-test for points

Chapter 002

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