Download Radiation Biology Ch 20 Part II 2012

RTMR 284
CHAPTER 20 PART II
 Prevents transmission of radiation through the room
walls
 Required for ALL diagnostic and fluoro rooms
 Protects against primary , secondary, & scatter
radiation
 Thickness depends on:
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Distance from the sources
Workload
Use of area on other side of wall
Amount of time beam is pointed at the wall
 Primary Radiation: direct, collimated, useful x-ray
beam.
 Typically 1/16th inch of lead
 What wall is ALLWAYS a primary barrier?
 If the floor and ceiling are concrete based, no added
shielding is needed
 There needs to be 7’ of
upward primary barrier
when the x-ray tube is
5-7’ from the wall
 Secondary Radiation: made up of scatter & leakage
radiation
 Typically 1/32nd inch of lead
 What area in the room is ALLWAYS a secondary
barrier?
 Glass is room needs 30% lead by weight
 Leakage radiation regulations
Require <100mR/hr at 1 meter
 Distance: Lead coverage is proportional to distance from
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primary radiation source
Occupancy: Control (<100 mR/wk)
vs.
Uncontrolled Area (2 mR/wk)
Workload: Thickness of barrier is proportional to work
load of the room (mA-min/wk)
Use: Amount of time x-ray beam will be directed at a
barrier. NCRP Primary Barrier factor = ¼ & Secondary
factor = 1 (always present)
HVL: Amount of shielding required to reduce radiation
intensity to half orig. value
TVL: Amount of shielding required to reduce radiation
intensity to 1/10 the orig. value.
 Gas-Filled Detectors: collect ions produced by
ionizing radiation producing an output signal.
 Geiger-Muller Counters: best at detecting Beta particles,
extra sensitive to low level radiation ~
survey/detection/calibration uses in field
 Ion Chambers : positive ions created from interaction of
air in chamber and radiation interaction leading to a
measureable charge to the electrode in the chamber.
Used for assment/pt. dose analysis/quality checks.
 Scintillation Detectors: use crystals that give off
light when struck by radiation.
 Used as detectors in CT scanners and nuc med gamma
cameras
 Gas-Filled Detectors: collect ions produced by
ionizing radiation producing an output signal.
 Geiger-Muller Counters: best at detecting Beta particles,
extra sensitive to low level radiation ~
survey/detection/calibration uses in field
 Ion Chambers : positive ions created from interaction of
air in chamber and radiation interaction leading to a
measureable charge to the electrode in the chamber.
Used for assment/pt. dose analysis/quality checks.
 Scintillation Detectors: use crystals that give off
light when struck by radiation.
 Used as detectors in CT scanners and nuc med gamma
cameras
 Film Badge Dosimeters: film responds to amount of
radiation received in relation to the copper, cadmium,
and aluminum filter to estimate the energy of incident
radiation.
 Measure exposures ranging from 0.1 mSv (1o mrem) to
20 Sv (2,000 rem) [total body exposure]
 Keep in cool dry place when not worn at work!
 Thermoluminescent Dosimeters: uses lithium
fluoride crystals that trap radiation energy. Heating to
over 100 degrees C release the energy as light to be
measured by a PM tube to get values.
 Can be small in size and used as ring detectors.
 Pocket Dosimeters: most sensitive and consist of a
writing pen sized thimble ionization chamber.
 Uses a charged voltage reading that is set to zero and
measured at the end of the day to convert what amount of
radiation is detected based on by how much that voltage is
lowered in charge.
 Time consuming and inaccurate at exposures above the set
range of the device
 Optically Stimulated Luminescence: uses crystal forms
of aluminum oxide and is based on the electrons that are
stimulated by radiation exposure. Light intensity after
released by green laser indicated exposure levels.
 Reports low doses at 1mrad making it most radiosensitive.
 Monitoring period is typically monthly. Badges and TLD’s are
sent back to monitoring company to generate reports.
 Report includes: mrem doses for the period, quarterly totals,
YTD, and lifetime totals. As well as deep dose, lens of eye,
and lifetime dose equivalents.
 Must be worn facing outward in the truck of the body and
outside protective aprons near the collar during fluoro
exams. Placing the badge in the same area during normal
conditions each day will provide the most accurate results.
 Pregnant radiographers get a “baby” badge to be worn on
the abdomen under the protective apron to measure the
dose to fetus.