Lesson 4 Flashcards
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 - Personnel monitoring
- Emulsion reading
PHOTOGRAPHIC EMULSION
TWOPRINCIPAL APPLICATIONS
OF FILM:
- The making of a radiograph
- The radiation monitoring of
personnel (film badge)
- Consist of a cylinder filled with air
and a central collecting electrode - Cylinder of gas- (air ) ( xenon
used to measure rays in some ct
scanners)
GAS-FILLED RADIATION
DETECTOR
- Used widely as a device to
measure radiation intensity - Used to detect radioactive
contamination
GAS-FILLED RADIATION
DETECTOR
THREE TYPES OF GAS-FILLED RADIATION
DETECTOR
- IONIZATION CHAMBER
- PROPORTIONAL COUNTERS
- GEIGER-MULLER COUNTER
- Has more molecules available for
ionization - more sensitive
LARGE CHAMBERS
The instrument of choice for
measuring radiation intensity
IONIZATION CHAMBER
- Survey for radiation levels mR/hr–
- Portable survey instrument
- Dose Calibrator
- Ion chamber dosimeter
IONIZATION CHAMBER
- A portable ion chamber survey
instrument - The most familiar
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 systems
ION CHAMBER DOSIMETER
- Sensitive instruments
- Detect only Alpha and Beta
radiation
ION CHAMBER DOSIMETER
- A sensitive portable survey
instrument - Capable of detecting and
indicating SINGLE IONIZING
EVENTS - Least likely to be used as x-ray
detector
GEIGER-MULLER COUNTER
- is the emission of light by a thermally
stimulated crystal following irradiation - When heated, it emits visible light
THERMOLUMINESCENCE
DOSIMETRY (TLD)
BASIC PRINCIPLE OF TLD:
- PLANCHET (SPECIAL DISK)
- PMTUBE(photomultiplier tube)
- TLD ANALYZER
where the TLD phosphor is placed on
PLANCHET (SPECIAL DISK)
light sensitive and light measuring
vacuum tube (convert photons into
electric signal)
PM TUBE (photomultiplier tube)
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; which has photon absorption properties similar to that of soft tissue (nearly a tissue equivalent dosimeter)
LITHIUM FLUORIDE (LiF)
- more sensitive to ionizing
radiation can measure doses:
less than - 1 mrad (moderate accuracy)
CALCIUM FLUORIDE (activated with
manganese) (CaF2:Mn)
- OSL monitors the amount of
radiation received by the amount
of light emitted - Radiation dosimeter adapted for
personnel monitoring (newest) - Used for both patient and
personnel radiation monitoring
OPTICALLY STIMULATED
LUMINESCENCE
DOSIMETRY (OSL)
OSL MULTISTEP PROCESS:
- Exposure to ionizing radiation
(exposed) - Laser illumination (read)
- Measurement of the intensity of
stimulated light emission
(analyzed)
Advantage of OSL over TLD
- More sensitive than TLD
- OSL has a precision of 10Gyt
one who interpret and record monthly
exposure records of each RT
HEALTH PHYSICIST / RADIATION
SAFETY OFFICER
- Pack of photographic film used
for approximate measurement of
radiation exposure to radiation
workers - Most economical type of
personnel radiation monitor - Consist of a small case w/ a
piece of film placed b/n different
filters
FILM BADGE / FILM DOSIMETER
FILM BADGE / FILM DOSIMETER Filters:
- Copper
- Tin
- Aluminum
- Plastic
- Sensitive devices for x-rays and
gamma rays - Measures radiation intensities as
low as single-photon interactions
SCINTILLATION DETECTOR
● Basis for the gamma camera
● Used as image receptor for
several types of digital imaging
system
● Used in the detectors arrays of
CT imaging system Used to
monitor the presence of
contamination
● Used to monitor low levels of
radiation
SCINTILLATION DETECTOR
TYPES OF SCINTILLATION DETECTOR IN STATE
● liquid
● gases
● solids
- An imaging device used in
nuclear medicine - Also used in CT and digital
radiography imaging system
GAMMA CAMERA
GAMMA SPECTROMETRY
- Uses scintillation detector as an energy-sensitive device
- Uses pulse height analysis
- Nearly all noble gases
- 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
- Thallium-activated sodium iodide (Nal:TI)
Incorporated into gamma camera - Thallium-activated cesium iodide (CsI:TI)
Incorporated into
image-intensifier (fluoro) tubes as
the input phosphor and into flat
panel DR image receptors
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 hermetically
ALUMINUM SEAL
one that prevents the crystal from coming into contact with air or moisture
Hermetic seal
absorbs moisture
NOTE: most scintillation crystals are BLANK
Hygroscopic
● The portion of the glass envelope that is coupled to the scintillation crystal
● Crystal window and PM tube window: sandwiched together with silicone grease
● Rationale: to provide optical coupling so that light emitted by scintillator is transmitted to the interior of the PM tube with minimum loss
WINDOW
● A device that emits electrons
when illuminated
● (cesium, antimony, bismuth)
● Photoemission- a process
wherein electrons are emitted from the photocathode
PHOTOCATHODE
- The first series of plate-like elements
- Function: amplify the electron pulse through secondary electron emission
DYNODES
the ratio of secondary electrons to incident electrons
Dynode Gain
provides structural support for the internal elements and maintains the vacuum inside the tube
Glass envelope
the last plate like element of the PM tube
Collecting Electrode / Collimator
a structure that provides support for the glass envelope and internal structure
BASE
provides an initial state of pulse amplification
PREAMPLIFIER
