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TOPIC 6: PERSONNEL DOSIMETRY & RADIATION MONITORING (DATA ANALYSIS /…
TOPIC 6: PERSONNEL DOSIMETRY & RADIATION MONITORING
RADIOLOGICAL MONITORING
Aim
Verify the
effectiveness
of radiation protective measures at workplaces
Identify
occurrence of abnormal radiation exposure situation in workplaces
Assess
radiation exposure situation according to regulatory equipments
:check:
Keep surveillance
over working environment
:check: Detect quantity and extent of contamination
MONITORING PROGRAM
Established by the
Basic Safety Standard (BSS)
regulations
systematically carry out
Measurement
Assessment of actual and potential occupational and public exposures
3 components
Workplace Monitoring
Environmental Monitoring
Personnel Monitoring
Carried out individually on personnel working in controlled areas
Occupational exposure
can be in form of
external radiation
internal contamination
External radiation + Internal contamination = Annual individual dose
Instruments for
external radiation
Dosimeter measure radiation from sources outside the body
should be suitable to type of radiation involved and range of
radiation exposure level
Film Badges
Thermoluminescent Dosimeter (TLD)
Direct Reading Dosimeter
Instruments for
internal radiation
Bioassay Method
indirect method to assess intake of radioactive materials into the body.
assess
alpha, beta and low energy gamma emitters
Whole Body Counting
Direct method of measuring intake of radioactive materials into body
spectrum analyzer
counter system
Sensitive enough to
detect weak gamma radiation
by radionuclides deposited in organ
2 types
Chair Type
a chair with 3 detectors positioned in directions that allow optimum measurement of radionuclides in lung, stomach, thyroid
Shielded Room Type
Low background counting room shielded from background radiation
MONITORING INSTRUMENT
Radiation Detector
LIQUID DETECTORS
SOLID STATE DETECTORS
GAS-FILLED DETECTORS
Interaction of radiation with molecules of air
3 common systems
Ionization chambers
Best used as
photon
measuring instrument
but can be modified for alpha, beta & neutron monitoring
Less sensitivity compared to Geiger Counter - but can be used in high counting rate situation
Good energy dependence characteristics
Eg: survey meter, Cutie-Pie
Proportional counters
Operates in higher voltage supply than ionization chamber
Phenomenon of
gas multiplication
Application: detection of low-energy radiation
Detection of
neuron
Geiger counters
/G-M detector
Monitor low-level beta and gamma radiation
Very high sensitivity
Operates in higher voltage supply than ionization chamber & proportional counter
Monitor
contamination
and
search of lost radiation source
Long dead time
unnecessary for accurate counting at high counting rates
SCINTILLATION DETECTORS
A medium detector produce scintillation light to detect ionizing radiation
Liquid scintillation counting technique
ionizing radiation in liquid form passes through medium detector then produces scintillation light
Production using
solid medium
sodium iodide thallium-activated detector Nal(TI)
Preferred to maximize ionizing radiation capture
Device employing semiconductors
Basic info carriers: electron-hole pairs which generate basic
electric signal from the detector
Solid state crystalline dosimeter
emits visible light when interact with radiation
Visible light
Fluorescence - relatively long
Phosphorescence - relatively short
due to electron excited into a 'trap' or lattice between valence & conduction band
Usually used with photomultiplier tube (PMT)
series of accelerating dynodes that amplify signal received by scintillation detector
DATA ANALYSIS / INTERPRETATION
Equivalent dose to skin
Equivalent dose to eye lens
Effective dose
Aim
Demonstrate compliance with dose limitation system & authorized limit
CALIBRATION & QUALITY ASSURANCE
Surveying & monitoring devices calibrated by manufacturer during production
Calibrate survey meters periodically as stipulated by appropriate authority