Chapter 9 Flashcards
What is Ionizing Radiation?
Capable of penetrating matter and possess sufficent energy to eject orbital electrons along its path
Two sources of Ionizing Radiation
Natural
Man-made
Types of Natural Radiation
Cosmic radiation from the sun
Uranium
Radium
Types of human made radiation
Nuclear industry - power plant accidents, weapons testing, disposal of by products
Radionuclides - smoke detectors
Medical and dental exposures - greatest source of human made radiation
Video monitors, suntan beds, microwave ovens
What is the smallest unit of radiation?
Photons
Quanta/Quantum when occuring in groups
What 3 things must exist for X-rays to be produced?
Electron source
Force to move them rapidly
Something to stop this movement abruptly
How are x-rays produced?
- Filament (electron source) is in cathode assembly - made of thoriated tungsten
- mA (electric current) is applied to the filament and it responds by boiling off electrons (thermionic emissions)
kV is applied to the tube terminals causing electrons to accelerate towards the anode end of the x-ray tube
- X-rays are produced when electrons strike anode
Both heat and energy are produced - 1% xrays and 99% heat
What can happen after X-rays strike matter?
Absorption
Scatter
Pass through unaffected - remnant radiation
What are the difference types of tissues by density?
Air
Soft Tissue
Fatty Tissue
Bone
Units of Measure
Gray - absorbed dose
Sievert - Equivalent dose or occupation dose
Coulomb/kg - Measures exposure in air
What is the heterogeneous beam?
Xray beam has many energies - measured in KeV
What is the primary beam?
Dirtected toward the patient through window
Most occupational exposure comes from:
Scatter
Who sets standards for radiation protection equipment?
Under the direction of the FDA, Center for Devices and Radiological Health (CDRH)
Who collects and distributes info on radiaiton awareness?
NCRP: National Council on Radiation Protection and Measurement
Enforced by the NRC: Nuclear Regulatory Commission
Two theories of effective dose limits:
- Non-threshold - no dose exist below which the risk of damage does not exist. No dose considered permissible
- The benefit to patient to perform exam must outweigh the risk of biological damage
Effective dose limit for occupational worker
50 mSv/year
Effective dose limit for public
5 mSv/year
Biological response to radiation (how radiation reacts with cells)
Ionizing radiation when absorbed by matter undergoes energy conversions that result in changes in atomic structure
In living tissue: major consequence on life of any organism
How to minimize time for patient
Minimize time in path of xray beam, use technique charts to determine correct dose, minimize repeats
When to shield gonadal area:
When gonadal area within 4-5 cm of primary beam
3 types of lead shields
Flat Contact Shields - placed directly over gonadal area
Shaped Contact - cup shaped and fits male patient
Shadow shield - mounted to the side of the collimator of xray tube on flexible extension arm
What is filtration?
In path of x-ray beam
Absorbs that lower energy xrays; reduces scatter and grays
When does fluoroscopy time go off?
5 minutes
Inverse Square Law
Int Inten (Fin Dis)^2
————– = —————
Final Inten (Int Dis)^2
How much lead is in lead aprons and gloves?
.25 to 1.0mm
How often does shielding need to be checked?
At least 1 time a year
What is the dose limit for unborn child?
5 mSv for entire pregnancy
.5mSv per month
What is dose limit if pregnancy not vocalized?
50 mSv/year
Who should wear a personnel monitoring dosimeter?
Any worker regularly exposed to ionizing radiation who may likely receive 10% or more of effective dose limits
What is OSL?
Optically Stimulated Luminescense Dosimeter
Properties of OSL?
Most common
Usually worn for 2 months
Heat sealed
Strip of aluminum oxide inside is exposed to laser light, which causes luminescent in proportion to amount of radiation exposure
Advatages/Disadvantages of OSL
Unaffected by heat, mosture and pressure
Inability to get immediate reading
What is Coherent Scattering?
Photon strikes an atom
Atom absorbs electron and becomes excited
Atom releases excess energy in the form of another photon
Proceeds in different direction
What is Photoelectric Absoprtion?
Photon strikes inner shell electron and ejects it
Travels until it combines with other matter
Outer shell electrons move to fill vacancies and they release energy in the form of xrays known as secondary radiation
What is Compton scattering?
Photon strikes atom and uses a portion of energy to eject outer shell electron
Remainder of energy proceeds in different direction - can react with patient or exit
Ejected electron travels until combined with matter
What is a primary protective barrier stuck by?
Primary beam
What is secondary protective barrier struck by?
Scatter or leakage radiation
What types of scattering occur within the diagnostic range of X-rays?
Coherent, photoelectric and Compton
What type of scattering occurs in therapeutic range of energies?
Pair production
Photodisintegration
What types of scattering directly influences patient and occupational work exposure?
Compton and photoelectric
