merge 4 Flashcards
the presence of radiation is indicated by ticking, chirping or beeping sound
PULSE MODE
the instrument response is
expressed in mR/hr or R/hr
RATE MODE
- Used in instruments designed to
measure the intensity of radiation - Accumulate the signal and respond
with a total exposure (mGya or Gya)
INTEGRATED MODE
- mGya or Gya
- The practice of measuring the intensity of radiation
DOSIMETRY
- Instrument designed to detect and
measure radiation - The radiation-measuring devices
DOSIMETERS
◼The earliest radiation detection device
◼ The primary means of radiation detection
and measurement
◼ Limited range, sensitive, and energy
dependent
PHOTOGRAPHIC EMULSION
◼Consist of a cylinder filled with air and a
central collecting electrode
◼ Cylinder of gas– ( air ) ( xenon– used to
measure xrays in some ct scanners)
GAS-FILLED RADIATION DETECTOR
instrument can detect very low radiation intensities
HIGH LEVEL OF SENSITIVITY
instrument can detect & precisely measure the intensity of radiation field
HIGH LEVEL OF ACCURACY
The instrument of choice for measuring radiation intensity
IONIZATION CHAMBER
- A portable ion chamber survey instrument
- The most familiar area survey
- used principally for area radiation surveys; wide range
PORTABLE SURVEY INSTRUMENT (CUTIE PIE)
- A configuration of an ion chamber
- Another application of precision ion chamber
DOSECALIBRATOR
- Most accurate ion chamber (specific measurement output
intensity) - used for precise calibration of the output intensity of diagnostic x-ray imaging system
ION CHAMBER DOSIMETER
- Sensitive instruments
- Detect only Alpha and Beta radiation
- Used primarily as stationary laboratory
instruments for the assay
of small quantities of radioactivity (low
intensity area)
PROPORTIONAL COUNTER
- A sensitive portable survey instrument- Capable of detecting and indicating
SINGLE IONIZING EVENTS - Least likely to be used as x-ray detector
- Application: Survey for low radiation levels
GEIGER-MULLER COUNTER
a material that
glow when heated; exhibiting thermally
stimulated emission of visible light
Thermo-luminescence
- Radiation dosimeter adapted for personnel monitoring (newest)
- Used for both patient and personnel radiation monitoring
OPTICALLY STIMULATED LUMINESCENCE DOSIMETRY (OSL)
OSL material
aluminum oxide (Al2O3)
- Pack of photographic film used for approximate measurement of radiation exposure to radiation workers
- Most economical type of personnel radiation monitor
- Consists of a small case w/ a piece of film placed b/n different filters
FILM BADGE / FILM DOSIMETER
- Sensitive devices for x-rays and gamma rays
- Measures radiation intensities as low a single-photon interactions
SCINTILLATION DETECTORS
- An imaging device used in nuclear medicine
- limited range, very sensitive, & stationary or portable instruments
GAMMA CAMERA
- Nearly all noble gasses
- Applications are rare– detection efficiency is very low and probability of interaction is small
GAS SCINTILLATION DETECTORS
- Biologic molecules are mixed with a liquid
scintillation phosphor - Used frequently to detect low-energy beta
emission from
carbon-14 and tritium
Detection: 100% for beta radiation
LIQUID SCINTILLATION DETECTORS
- Inorganic crystals ; most widely used scintillation phosphors
Ex:- Thallium-activated sodium iodide (NaI:Tl)
SOLID SCINTILLATION DETECTORS
- An electron vacuum tube
- Contains a number of elements
- Converts light flashes from the scintillator into an electronic signal of pulses
PHOTOMULTIPLIER (PM) TUBE
- Allows the light flash to be reflected internally to the window
- Also necessary to seal the crystal
ALUMINUM SEAL
a seal that prevents the
crystal from coming into contact with air or
moisture
Hermetic seal
- absorbs moisture
- NOTE: most scintillation crystals are BLANK
Hygroscopic
A device that emits electrons when illuminated
( cesium, antimony, bismuth)
PHOTOCATHODE
a process wherein
electrons are emitted from the photocathode
Photoemission
- The first series of plate-like elements
Function: amplify the electron pulse through secondary electron emission
DYNODES
provides structural
support for the internal elements anD maintains the vacuum inside the tube
Glass envelope
provides an initial state of
pulse amplification
PREAMPLIFIER
- When heated, it emits visible light
– is the emission of light by a thermally stimulated crystal following irradiation
THERMOLUMINESCENSCENCE
DOSIMETRY (TLD)
- Uses a scintillation detector as an
energy-sensitive device - Uses pulse height analysis
GAMMASPECTROMETRY:
- Has more molecules available for
ionization - more sensitive
LARGE CHAMBERS
- Applications: Greater no. of molecules are available for
ionization - Higher sensitivity
PRESSURIZED CHAMBER
other name for PORTABLE SURVEY INSTRUMENT
cutie pie
the minimum time
between ionizations that can be detected
RESOLVING TIME
where the
TLD phosphor is placed on
PLANCHET (SPECIAL DISK)
electronic instruments
designed to measure and
analyze radiation and automatically relate
this to exposure or dose
through a conversion factor
TLD ANALYZER
- most widely used TLD material
- Effective atomic no. of: 8.2; that has photon absorption properties similar to that of soft tissue (nearly a tissue equivalent dosimeter)
- Characteristic: sensitive; can measure dose as low as– 5mrad (5μGyt)
- Dose exceeding 10rad (100mGyt)
- Accuracy : better than 5%
LITHIUM FLUORIDE (LiF)
- Characteristic: more sensitive to ionizing radiation can measure doses: less than 1mrad (moderate accuracy)
- Principal use: environmental monitoring
CALCIUM FLUORIDE (activated with manganese) (CaF2:Mn)
Principle use: Research
LITHIUM BORATE (Li2B4O7:Mn)
Principal use: Environmental monitoring
CALCIUM SULFATE (CaSO4:Dy)
