Lecture 3: Types & Sources of Radiation

Radiation

defined as the kinetic energy that passes from one location to another and can be displayed in many ways

Moving subatomic particles passing through space from one location to another.

• Examples are:

• Protons

• Neutrons

• Beta Particles

• etc.

Electromagnetic Spectrum

Full range of electromagnetic waves

Types of Radiation

• Mechanical vibrations of materials

  • Ultrasound

• Electromagnetic Waves

  • Radio waves

  • Microwaves

  • Visible light

  • X-rays

Electromagnetic waves

• Electric and magnetic fields fluctuate rapidly as they travel through space

  • a limited range of these frequencies is interpreted by its reaction with human systems as visible light.

• Electromagnetic radiation has a dual nature referred to as wave-particle duality

• Meaning this form of radiation propagates through space in the form of a wave but can interact with matter as a particle of energy called a photon, so x-rays are described as both waves and particles

Two divisions of the electromagnetic spectrum

• ionizing radiation

• nonionizing radiation

Ionizing Radiation includes:

• High-energy ultraviolet radiation

• x-rays

• gamma rays

Nonionizing radiation

• These are radiations that do not have sufficient kinetic energy to eject electrons from an atom:

  • Low-energy ultraviolet radiation (less than 10 eV)

  • visible light

  • infrared rays

  • microwaves

  • radio waves

Ionization

• electromagnetic radiation that has a high enough frequency to transfer sufficient energy to some orbital electrons and remove them from the atom

• Ionization describes the interaction of x-rays with human tissue

  • It makes x-rays valuable for creating images but has the potential for producing some damage in the biological material

• The amount of energy transferred to electrons by the ionizing radiation is the concept of radiation dose

Particulate radiation

In addition to electromagnetic radiation, we have another category of ionizing radiation called _______.

• As opposed to x-rays and gamma rays (which are ER) _________ is a form of radiation that includes these subatomic particles:

  • alpha particles

  • beta particles (electrons)

  • neutrons

  • protons

Ionization continued

• The subatomic particles are ejected from atoms at very high speeds and have enough kinetic energy to cause ionization by direct atomic collision

• When these particles are at rest, there is no ionization

Radioactive decay

a naturally occurring process in which unstable nuclei relieve that instability by some type of nuclear spontaneous emission, like charged particles

Alpha particles (alpha rays)

• are emitted from the nuclei of very heavy elements during the process of radioactive decay

  • emitted from Uranium and Plutonium

Alpha particles have:

• 2 protons and 2 neutrons

• Large mass

• Are a simple helium atom minus their electrons

• Less penetrating than Beta particles

• Lose energy quickly as they travel short distances (stopped by superficial layers of the skin or piece of paper)

• They have a scattering probability

• Considered to be a harmless external source of radiation, but internally if emitted from a radioisotope, can cause damage to healthy epithelial tissue (brachytherapy)

Beta particle (beta rays) compared to electrons

• Are identical to high-speed electrons except for their origin

  • Electrons originate in atomic shells outside the nucleus

  • Beta particles are emitted from within the nuclei of radioactive atoms

Beta particle

• 8000 times lighter than alpha particles

• Have one unit of electrical charge (-1)

• They do not interact as strongly as alpha particles

• They penetrate further than alpha particles with less ionization along their path

  • Stopped by 1 cm piece of wood or 1mm thick lead shield, aluminum

Beta decay

• is a nuclear decay process where an unstable nucleus transforms and ejects particles to become more stable, beta ray is emitted

• During beta decay, the proton in the nucleus is transformed into a neutron and vice versa.

• If a proton is converted to a neutron, it is known as β+ decay. Similarly, if a neutron is converted to a proton, it is known as β– decay

Beta decay cont.

• β+ decay: a proton decays into a neutron, a positron, and a neutrino

  • Neutrinos are particles with little or no mass and are released in order to conserve energy during the beta decay process.

β+ and β– decay

Other sources of electrons

• Not all high speed electrons are beta radiation

  • alternative sources of high speed (high energy) electrons are commonly produced by linear accelerators (used to treat more superficial lesions)

Gamma Radiation

a high-energy form of electromagnetic radiation emitted from an atomic nucleus

Breakdown of Gamma radiation key properties

• Source: Originates from radioactive decay or nuclear reactions.

• Energy: Possesses the highest energy in the electromagnetic spectrum.

• Wavelength: Features the shortest wavelengths, Charge: Completely neutral with no electrical charge or mass.

• Penetration: Highly penetrating, requiring thick lead or concrete to stop.

• Hazard: Classed as ionizing radiation, meaning it damages living tissue.

Protons

• Positively charged part of an atom

• Isolated proton (ionized hydrogen atom) has more mass than electron by a factor of 1800

• Typically less penetrating that a high energy electron

• Remember: The number of protons in a nucleus of an atom determines its atomic number (Z) and placement on the periodic table and identifies it as an element

Neutrons

• Have no charge

• Neutrons have same mass as a proton

• If you have 2 atoms with the same number of protons but different number of neutrons in the nuclei then you have isotopes

• If a combination of protons and neutrons cause an unstable nucleus, then this combination is called a radioisotope

Quality Factor (Q)

• are values used in radiation protection to quantify the different biological effectiveness of various types of radiation

• Q factor is a specific value that accounts for the ability of different types of ionizing radiation to cause varying degrees of biological damage, in units of absorbed dose.

• In other words, they convert the absorbed dose (measured in Grays) to an equivalent dose (measured in Sieverts), providing a measure of risk that accounts for the greater harm from radiation types like alpha particles compared to gamma rays or X-rays.

Higher quality factor (Q)

• Means that this type of radiation is more damaging to cells than a radiation with a lower quality factor for the same amount of abosbred dose.

• In radiation safety/protection, not all radiation is equal. The quality factor is a multiplier used to convert the physical dose of radiation absorbed by a material into the actual biological risk to human tissue.

Examples of Radiation Types and their Q Factors:

• Photons (X-rays, gamma and beta particles) and Electrons: Have a Q factor of 1

• High Energy protons: have a Q factor of 10

• Alpha particles: Have a high Q factor of 20.

Sources of radiation

Natural & Manmade

Natural Sources of Radiation

• Radioactive elements in the Earth’s crust and in the human body can be classified as ______.

• Terrestrial – from radioactive occurring materials in the Earth’s crust

• Cosmic – from the sun and beyond the solar system

• Internal – from radioactive atoms (radionuclides) that make up a small percentage of the body’s tissue

Terrestrial source of radiation

• Naturally occurring radioactive materials found in the Earth's crust, rocks, soil, water, and living organisms.

  • Radon accounts for 37% of the natural background radiation exposure

Cosmic source of radiation

• ______ is of extra-terrestrial origin as a result of nuclear interactions between the sun and stars

• Earth’s atmosphere and magnetic field shield the Earth from cosmic rays

Internal souce of Radiation

• Tissues of the body contain naturally occurring radionuclides that have been ingested from various foods or inhaled particles in the air.

• Remember:

• A radionuclide is an unstable nucleus that emits forms of ionizing radiation to achieve stability

• Types of ionizing radiation released by radionuclides may include:

  • Alpha particles (helium nuclei)

  • Beta particles (electrons)

  • Gamma rays (MeV)

  • Emission of X-rays due to some type of radioactive decay

Manmade sources of radiation (Artificial Radiation)

• ionizing radiation that is manmade and can come from:

  • Consumer products containing radioactive material

  • Medical radiation

  • Nuclear power plant accidents

  • Air travel

  • Nuclear fuel for power generation

Consumer products that emit radiation:

• Airport surveillance systems

• Older televisions

• Electron microscopes

• Ionization–type smoke detectors

• Luminous dials on watches

Medical radiation results from the use of:

• CT scanning

• Interventional fluoroscopy

• Conventional radiography or fluoroscopy

• Nuclear Medicine

Equivalent dose (EqD)

• Provides an overall dose value that includes the different degrees of tissue interaction (harm) that could be caused by different types of ionizing radiation

  • The most common unit of measure of EqD is the millisievert (mSv)

• Takes organ or tissue into account

Sources of Radiation chart