1. 2
Characteristics and Measurement of Radiation

2. Objectives Define the key words. Draw and label a typical atom.
Describe the process of ionization

3. Objectives Differentiate between radiation and radioactivity.
List the properties shared by all energies of the electromagnetic spectrum.
Explain the relationship between wavelength and frequency.

4. Objectives
Explain the inverse relationship between wavelength and penetrating power of x-rays.
List the properties of x-rays.
Identify and describe the two processes by which kinetic energy is converted to electromagnetic energy within the dental x-ray tube.

5. Objectives
List and describe the four possible interactions of dental x-rays with matter.
Define the terms used to measure x-radiation.
Match the Système Internationale (SI) units of x-radiation measurement to the corresponding traditional terms.
Identify three sources of naturally occurring background radiation.

6. Key Words Absorbed dose Absorption Alpha particle Angstrom (Å) Atom
Atomic number
Atomic weight
Background radiation

7. Key Words Beta particle Binding energy Characteristic radiation
Coherent scattering
Compton effect (scattering)
Coulombs per kilogram (C/kg)

8. Key Words Decay Dose Dose equivalent Effective dose equivalent
Electromagnetic radiation
Electromagnetic spectrum

9. Key Words Electron Element Energy Energy levels Exposure Frequency
Gamma rays

10. Key Words General/brems-strahlung radiation Gray (Gy) Hard radiation
Ion pair
Ionizing radiation
Ionization

11. Key Words Isotope Kinetic energy Microsievert (μSv) Molecule Neutron
Photoelectric effect
Photon
Proton

12. Key Words Rad Radiation Radioactivity Radiolucent Radiopaque Rem
Roentgen (R)
Secondary radiation

13. Key Words Sievert (Sv) Soft radiation Système Internationale Velocity
Wavelength
Weighting factor

14. Introduction
Patients often link dental x-rays with other types of radiation exposures read or seen on TV.
Patients assume that oral health care professionals are knowledgeable regarding all types of ionizing radiation exposures.
Understanding of matter and energy are essential.

15. Atomic Structure Elements Atom Molecule Energy levels Electrons
Protons
Neutrons
Molecule
Energy levels

16. Figure 2-1 Diagram of carbon atom
Figure Diagram of carbon atom. In the neutral atom, the number of positively charged protons in the nucleus is equal to the number of negatively charged orbiting electrons. The innermost orbit or energy level is the K shell, the next is the L shell, and so on.

17. Ionization
Ion
Ionization
Ion pair

18. Figure 2-2 Ionization is the formation of ion pairs
Figure Ionization is the formation of ion pairs. When an atom is struck by an x-ray, an electron may be dislodged and an ion pair results.

19. Ionizing Radiation
Radiation is defined as the emission and movement of energy through space in the form of electromagnetic radiation (x- and gamma rays) or particulate radiation (alpha and beta particles).
Any radiation that produces ions is called ionizing radiation.

20. Radioactivity
Radioactivity is defined as the process whereby certain unstable elements undergo spontaneous disintegration (decay) in an effort to attain a stable nuclear state.

21. Radioactivity
Unstable isotopes are radioactive and attempt to regain stability through the release of energy, by a process known as decay.
Dental x-rays do not involve the use of radioactivity.

22. Radioactivity
Scientists have learned to produce several types of radiation:
Ultraviolet waves are produced artificially for sunlamps, fluorescent lamps, etc.
Laser beam; the potential impact on oral health is still being explored.

23. Electromagnetic Radiation
Electromagnetic radiation is the movement of wave-like energy through space as a combination of electric and magnetic fields.
The electromagnetic spectrum consists of an orderly arrangement of all known radiant energies.
X-radiation: various rays, visible light, infrared, TV, radio, microwave, and radar.

24. Figure 2-3 The electromagnetic spectrum
Figure The electromagnetic spectrum. Electromagnetic radiations are arranged in an orderly fashion according to their energies.

25. Electromagnetic Radiation
All energies of the electromagnetic spectrum share the following properties:
Travel at the speed of light
Have no electrical charge
Have no mass or weight
Pass through space as particles and in a wave-like motion

26. Electromagnetic Radiation
All energies of the electromagnetic spectrum share the following properties:
Give off an electrical field at right angles to their path of travel and a magnetic field at right angles to the electric field
Have energies that are measurable and different

27. Electromagnetic Radiation
Electromagnetic radiation display two contradictory properties:
Believed to move through space as both a particle and a wave.
Wave theory assumes that electromagnetic radiation is propagated in the form of waves.
Electromagnetic waves: wavelength, frequency, and velocity.

28. Electromagnetic Radiation
Photons
Wavelength
Angstrom (Å)
Frequency (ν)
Hertz (Hz)
Velocity
Soft radiation
Hard radiation

29. Figure 2-4 Differences in wavelengths and frequencies
Figure Differences in wavelengths and frequencies. Only the shortest wavelengths with extremely high frequency and energy are used to expose dental radiographs. Wavelength is determined by the distances between the crests. Observe that this distance is much shorter in (B) than in (A). The photons that comprise the dental x-ray beam are estimated to have over 250 million such crests per inch. Frequency is the number of crests of a wavelength passing a given point per second.

30. Properties of X-rays
X-rays are believed to consist of minute bundles (or quanta) of pure electromagnetic energy called photons.
Photons have no mass or weight, are invisible, and cannot be sensed.
X-ray photons are often referred to as “bullets of energy.”

31. Properties of X-rays Are invisible Travel in straight lines
Travel at speed of light
Have no mass or weight
Have no charge
Interact with matter causing ionization
Can penetrate opaque tissues and structures

32. Properties of X-rays
Can affect photographic film emulsion (causing a latent image)
Can affect biological tissue
Dense materials appear radiopaque (white/light gray)
Less dense materials appear radiolucent (black/dark gray)

33. Production of X-rays
Bodies in motion are believed to have kinetic energy.
General/bremsstrahlung radiation is produced when high-speed electrons are stopped or slowed down by the tungsten atoms of the dental x-ray tube.

34. Production of X-rays
Characteristic radiation is produced when a bombarding electron from the tube filament collides with an orbiting K electron of the tungsten target.

35. Figure 2-5 General/bremsstrahlung and characteristic radiation
Figure General/bremsstrahlung and characteristic radiation. High-speed electron (A) collides with the nucleus and all its kinetic energy is converted into a single x-ray. High-speed electron (B) is slowed down and bent off its course by the positive pull of the nucleus. The kinetic energy lost is converted into an x-ray. The impact from both A and B electrons produce general radiation. Characteristic radiation is produced when high-speed electron (C) hits and dislodges a K shell (orbiting) electron. Another electron in an outer shell quickly fills the void and an x-ray is emitted. Characteristic radiation only occurs above 70 kVp with a tungsten target.

36. Interaction of X-rays with Matter
Absorption
No interaction
Coherent scattering
Photoelectric effect
Compton effect
“Do x-rays make the material they pass through radioactive?”

37. Figure 2-6 X-rays interacting with atom
Figure X-rays interacting with atom. X-ray (A) can pass through an atom unchanged and no interaction occurs. Incoming x-ray (B) interacts with the electron by causing the electron to vibrate at the same frequency as the incoming x-ray. The incoming x-ray ceases to exist. The vibrating electron radiates new x-ray (C) with the same frequency and energy as the original incoming x-ray. The new x-ray is scattered in a different direction than the original x-ray.

38. Figure 2-7 Photoelectric effect
Figure Photoelectric effect. The incoming x-ray gives up all of its energy to an orbital electron of the atom. The x-ray is absorbed and simply vanishes. The electromagnetic energy of the x-ray is imparted to the electron in the form of kinetic energy of motion and causes the electron to fly from its orbit. Thus, an ion pair is created. The high-speed electron (called a photoelectron) knocks other electrons from the orbits of other atoms forming secondary ion pairs.

39. Figure 2-8 Compton scattering
Figure Compton scattering. Compton scattering is similar to the photoelectric effect in that the incoming x-ray interacts with an orbital electron and ejects it. But in the case of Compton interaction, only a part of the x-ray energy is transferred to the electron and a new, weaker x-ray is formed and scattered in some new direction. The new x-ray may undergo another Compton scattering or it may be absorbed by a photoelectric effect interaction.

40. Table 2-1 Radiation Measurement Terminology

41. Units of Radiation
Système International (SI) units: modern version of the metric system
Coulombs per kilogram (C/kg)
Gray (Gy)
Sievert (Sv)
ADA Requires SI terminology to be used on national board exams.

42. Units of Radiation
Note that numerical amounts of radiation expressed using SI terminology do not equal the numerical amounts of radiation expressed using the traditional terms.
Traditional units: Obsolete
Roentgen (R)
Rad (radiation absorbed dose)
Rem (radiation equivalent in man)

43. Units of Radiation
For practical x-ray protection measurement the following are used:
Exposure
Absorbed dose
Dose equivalent
Effective dose equivalent

44. Background Radiation
Background radiation is defined as ionizing radiation that is always present in our environment

45. Background Radiation
Natural background radiation originates from the following sources:
Cosmic radiation from outer space
Terrestrial radiation from the earth and its environments
Background radiation from naturally occurring radionuclides (unstable atoms that emit radiations) that is deposited in our bodies by inhalation and ingestion

46. Figure 2-9 Annual effective dose equivalent of ionizing radiations
Figure Annual effective dose equivalent of ionizing radiations. This chart illustrates the approximate percentage of exposure of the U.S. population to background and artificial radiations. (Reprinted with permission of the National Council on Radiation Protection and Measurements,

47. Review: Chapter Summary
The three basic building blocks of an atom are protons, neutrons, and electrons.
Ionization is the formation of charged particles called ions.
Ionizing radiation is defined as any radiation that produces ions.
Electromagnetic radiation is the movement of wave-like energy through space.

48. Review: Chapter Summary
Electromagnetic waves exhibit the properties of wavelength, frequency, and velocity.
X-rays are invisible, travel in straight lines at the speed of light, interact with matter causing ionization, affect photographic film, and affect living tissue.

49. Review: Chapter Summary
Four x-ray measurement quantities include: exposure(C/kg; roentgen), absorbed dose (gray/Gy; rad), dose equivalent (sievert/Sv; rem), and effective dose equivalent (microsievert/μSv).
For practical x-ray measurement three quantities are used: exposure, absorbed dose, and dose equivalent.

50. Review: Chapter Summary
Dental and medical x-rays make up approximately 5 percent of the total radiation exposure to the U.S. population.
All medical uses of ionizing radiations including CT scans and nuclear medicine account for 48 percent of the total ionizing radiation exposure.

51. Review: Chapter Summary
Background radiation consisting of cosmic radiation, terrestrial radiations and radon gas, and naturally occurring radionuclides account for 50 percent of the total radiation exposure.

52. Recall: Study Questions
General
Chapter Review

53. Reflect: Case Study
While taking a full mouth series of dental radiographs on your patient, he begins to consider how many radiographs are taken in this operatory daily. He asks you, “How long do you have to wait after each exposure before you can re-enter the room?” and “Are the walls and equipment in this room becoming radioactive from all the exposures taken in here?”

54. Reflect: Case Study
Prepare a conversation with this patient addressing these two questions based on what you learned in this chapter on radiation physics.

55. Relate: Laboratory Application
Proceed to Chapter 2, Laboratory Application, to complete this activity.