Types and Sources of Radiation

• Radiation has different types and sources
• Some radiation can damage biologic tissue
• Natural sources of radiation are always present in the environment
• Man-made or artificial radiation is created by humans

Types Of Radiation

• Mechanical vibrations of materials eg. Ultrasound
• Ultrasound is a mechanical vibration beyond the range of human hearing
• Electromagnetic waves are another type of radiation

Electromagnetic Waves

• Radio waves, microwaves, visible light, and x-rays are examples
• Electric and magnetic fields fluctuate rapidly as they travel
• Characterized by frequency and wavelength
• Frequency is the number of cycles per unit of time, measured in Hertz (Hz)
• Wavelength is the physical distance between crests of a wave, measured in meters
• Electromagnetic radiation exhibits a dual nature (wave-particle duality), travels as a wave and interacts as a particle (photon)

Electromagnetic Spectrum

• The full range of electromagnetic frequencies and wavelengths.
• Wavelength formula: C= λν
• C = speed of light (3 × 108 m/sec)
• λ = wavelength
• ν = frequency

Ionizing and Nonionizing Radiation

• Electromagnetic spectrum is divided into ionizing and nonionizing categories
• Ionizing radiation includes X-rays, gamma rays, and ultraviolet radiation [energy >10 eV]
• Nonionizing radiation includes visible light, infrared rays, microwaves, and ultraviolet radiation [energy < 10 eV]

Ionizing Radiation

• Ionization is where x-rays convert molecules to ions
• Conversion of atoms to ions makes tissues valuable for creating images
• This can result in damage to biologic material
• The amount of energy transferred to electrons by ionizing radiation is the basis of the radiation dose
• 2 Types of ionizing radiation:
• Electromagnetic Radiation such as x-rays and gamma rays
• Particulate Radiation

Particulate Radiation

• Includes alpha particles, beta particles, neutrons, and protons
• These are subatomic particles ejected from atoms at very high speeds
• They possess sufficient kinetic energy to cause ionization by direct collision
• Ionization does not occur when the subatomic particles are at rest

Alpha Particles & Beta Particles

• Alpha Particles:
• Originate from the nuclei of very heavy elements via radioactive decay.
• Contain 2 protons and 2 neutrons (Helium nucleus).
• Have a +2 charge.
• Are less penetrating and can be absorbed by a piece of paper.
• Are relatively harmless externally but very harmful internally.
• Beta Particles: Originate as a high speed electron.
• Contain 1 electron.
• Have a -1 charge.
• Are 8000x lighter than alpha particles.
• Are more penetrating than alpha and absorbed by a 1-cm thick block of wood or 1-mm thick lead shield.
• Are less harmful than alpha internally.

Radiation Dose Quantities

• Absorbed Dose (D):
• The amount of kinetic energy absorbed per unit mass.
• Measured in Gray (Gy).
• Equivalent Dose (EqD):
• Takes into account the type of ionizing radiation.
• Measured in Sievert (Sv).
• Effective Dose (EfD):
• Takes into account the type of ionizing radiation and the organs or tissues irradiated.
• Measured in Sievert (Sv).
• EfD is the best estimate of overall harm produced by radiation in human tissue.

Biologic Damage Potential

• Annual radiation limit amount for Technologists: 50 mSv

Radiation Exposure Effects

• 0.25 Sv: Blood changes like measurable hematologic depression.
• 1.5 Sv: Nausea, diarrhea
• 2.0 Sv: Erythema (redness over an area of skin)
• 2.5 Sv: Temporary sterility (gonads)
• 3.0 Sv: 50% chance of death (LD 50/30)
• 6.0 Sv: Death

Natural Background Radiation

• Terrestrial (radon, thoron) that may gain access:
• Crawl spaces under living areas
• Floor drains
• Sump pumps
• Porous cement block foundations
• Cosmic radiation (solar and galactic)
• Internal radiation from radioactive atoms (radionuclides):
• Potassium-40 (40K), Carbon-14 (14C)
• Hydrogen-3 (3H; tritium), Strontium-90 (9⁰Sr)

Man-Made Radiation

• Consumer products containing radioactive material
• Air travel
• Nuclear fuel for power
• Atmospheric fallout from nuclear weapons testing
• Nuclear power plant accidents: TMI-2 and Chernobyl
• Nuclear power plant accidents from natural disasters: Fukushima Daiichi
• Medical radiation

Medical Radiation

• Medical radiation results from diagnostic x-ray machines and radiopharmaceuticals.
• The 2 largest sources of artificial radiation are:
• Diagnostic medical x-ray: CT scanning, interventional fluoroscopy, radiography
• Nuclear medicine procedures
• 48% of the total collective EfD of the U.S. population comes from artificial sources of radiation as of 2006
• Patient dose for each examination varies with radiologic equipment, imaging procedures, and tech skills

Variability of Patient Dose

• Radiation dose may be measured in terms of:
• Entrance skin exposure (ESE), including skin and glandular dose
• Bone marrow dose
• Gonadal dose
• Fetal dose in pregnant women