Embed Size (px)
Citation preview
Rev. 9-27-2010
Please Be Courteous To Others Deactivate all cell phones and pagers at this
time!
Rev. 9-27-2010
Properties of Ionizing Radiation
Kyle Thornton
RADL 70
Rev. 9-27-2010
Ionizing Radiation
Produces positively and negatively charged particles
Man-made or natural Can be particulate or
electromagnetic waves https://www.youtube.co
m/watch?v=K_zc1WKT0CA
Rev. 9-27-2010
Picture of Alpha Particle
Rev. 9-27-2010
Particulate Radiation
Alpha radiation Made of four particles
Two protons – two neutrons Does not penetrate matter easily Large/slow moving Carries a lot of energy Interact with matter very quickly Could not penetrate a piece of paper Dangerous if taken inside the body Personnel monitoring is not normally sensitive to alpha
particles
Rev. 9-27-2010
https://www.youtube.com/watch?v=Lg9coTz43K0
Rev. 9-27-2010
Sources of Alpha Radiation
Alpha Emitter Atomic Number
Americium 241 95
Plutonium 236 94
Uranium 238 92
Thorium 232 90
Radium 226 88
Radon 222 86
Polonium 210 84
Rev. 9-27-2010
Sources of Alpha Radiation
Uranium decays to Radium which decays to Radon Radon is a gas, easily
inspired into the body Radon daughter (decay)
products include polonium, bismuth and lead
Rev. 9-27-2010
Uses of Alpha Radiation
Americium 241 Used to power smoke alarms by creating an
electrical current Radium 226
Used to treat cancer – brachytherapy implants Polonium 210
Used as a static eliminator in paper mills and other industries
Rev. 9-27-2010
Particulate Radiation - Beta
Produced only in or near nucleus of an atom Mass is about 1/2000 the size of a proton or
neutron Contains mainly high speed electrons Behave similarly to a speeding bullet
Rev. 9-27-2010
Beta Particle Production
Created when ratio of protons to neutrons is too high
An excess neutron is converted to a proton and electron
Gamma ray production often accompanies this process
Rev. 9-27-2010
Beta Radiation Production
Rev. 9-27-2010
Comparison of Particulate/Electromagnetic Energy https://www.youtube.co
m/watch?v=ec8iomUS34U
Rev. 9-27-2010
Sources of Beta Particles
Tritium Cobalt-60 Strontium-90 Technetium-99 Iodine-129 and -131 Cesium-137
Rev. 9-27-2010
Uses for Beta Particles
Iodine 131 Used to treat thyroid cancers and Graves disease
Carbon 14 Used to date organic matter up to 30,000 years
old Tritium
Used for luminous dials, i.e., wristwatches, etc
Rev. 9-27-2010
Electromagnetic Spectrum
Rev. 9-27-2010
Electromagnetic Types Of Ionizing Radiation Gamma Rays
Monoenergetic waves of energy, able to penetrate most matter
Identical to x-rays in energy, wavelength, and frequency
Produced in nucleus Generally emitted from radioactive materials
Rev. 9-27-2010
Uses of Gamma Rays
Cesium 137 Cancer treatment
Cobalt 60 Cancer treatment Pasteurizing food
Technitium 99m Diagnostic Imaging Studies
Rev. 9-27-2010
X-Rays
Similar to gamma – no mass or charge Produced outside nucleus
Accelerating electrons in a vacuum Having them strike a metal target
Highest energy of all electromagnetic waves shortest wavelength, highest frequency
Rev. 9-27-2010
Physical Properties Of X-Rays Most penetrating electromagnetic waves They are heterogenous Polyenergetic Travel in a straight line Isotropic - Travel in different directions Affect photographic film Ionize all matter including gases Cause biologic changes
Rev. 9-27-2010
Physical Properties Of X-Rays Cannot be focused by a lens Do not reflect off of surfaces Electrically neutral Produce secondary and scattered radiation Cause crystals to fluoresce
Rev. 9-27-2010
Uses Of X-Rays
Diagnostic Radiography Fluoroscopy Tomography Mammography Computed Radiography Computed Tomography Industrial uses Authenticate paintings
Therapeutic Radiology
Rev. 9-27-2010
Linear Accelerator
Rev. 9-27-2010
Schematic of Linear Accelerator
Rev. 9-27-2010
Linear Accelerator
Rev. 9-27-2010
Linear Accelerator
Therapeutic units operate below 20 mA Times are around 1 - 60 minutes Energies are around 4 - 40 MV for x-ray
beams For electron beams MeV is used Linear accelerators are used to treat
neoplastic growths, physics research, and to produce radionuclides
Rev. 9-27-2010
Filtration and Half value layer
Filtration Used to remove low energy, long wavelength x-ray
photons Inherent in the x-ray tube itself Filtration is added by placing aluminum, molybdenum,
or rhodium plates in the x-ray beam path Half-value layer
Measures beam quality Amount of material necessary to reduce beam to half its
intensity Reduces patient dose
Rev. 9-27-2010
History Of Radiation Units
Somatic damage apparent shortly after Roentgen’s discovery of X-rays
The need to limit exposure became apparent In order to limit exposure, a means of
measurement was necessary First unit was known as skin erythema dose
This amount corresponded to a few hundred rads
Skin erythema threshold varies from person to person
Rev. 9-27-2010
Evolution of Radiation Units
The failure of the skin erythema dose as a unit necessitated another means of measurement
The Roentgen took its place as the accepted unit of x and gamma radiation
Today, both the international and traditional systems are used
Rev. 9-27-2010
Radiation Units
Roentgen - Coulombs/Kilogram – Air Kerma Ionization in air
Produced by gamma or X-rays 1 R = 2.58 X 10 (-4) C/Kg Gya – Grays in air
Rev. 9-27-2010
Absorbed Dose
Rad - Gray Radiation absorbed dose
Amount of energy absorbed per unit mass of the object
Depends on atomic number of the tissue, mass density, and incoming photon energy
One Gray = 100 Rads Can be used for any type of radiation Biologic effect varies with type of radiation
1 rad of X-ray does less harm than 1 rad beta radiation
Rev. 9-27-2010
Occupational exposure
Rem - Sievert Radiation equivalent man Unit of biological effect Rem = Rad X Quality factor Used for personnel monitoring 1 Sievert = 100 Rem
Rev. 9-27-2010
Radioactivity
Curie - Bequerel Measures nuclear disintegration Not an exact measurement Curie = 3.7 X 10 (10) disintegrations/second Bequerel = One decay/second
Rev. 9-27-2010
Dose Equivalent
Provides a means to calculate effective dose for different types of ionizing radiation Protons - Charge is equal in magnitude to
electron Mass is 1800 X greater
Neutrons - Electrically neutral Mass slightly higher than proton
Equal absorbed doses of these types will produce different amounts of biological damage
Rev. 9-27-2010
Quality Factor
Used to determine dose equivalency Absorbed dose is multiplied by this factor Evaluates relative hazard associated with
different types of radiation X-rays, beta particles, gamma photons, slow
moving external protons have a QF of 1 Thermal neutrons - 5 Low energy internal protons – 20 Fast neutrons, alpha particles - 20
Rev. 9-27-2010
Linear Energy Transfer
Amount of energy transferred in a medium per unit of path length This is an average amount expressed in kiloelectron
volts/micrometer Low LET radiation does not transfer much energy in matter along
its path X-rays fit in this category
High LET radiation transfers a lot of energy to a small area and generally do more damage
High LET radiation penetrates poorly, and poses more of a risk internally High LET radiation has a high quality factor
Rev. 9-27-2010
Stochastic Effects
Nonthreshold, randomly occuring biologic effects from radiation Cancer Genetic abnormalities
Rev. 9-27-2010
Non-Stochastic Effects
Deterministic effects from known amounts of radiation Blood changes Temporary sterility
