Transcript Whole Body Counting and Basic Internal Dosimetry Techniques

Practical Whole Body Counting and Internal
Dosimetry
Tim Kirkham – ENSR Corporation
Reasons for Study
– Increase knowledge of applied fundamentals.
– Enhance professionalism of radiological protection
technicians.
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Objectives
1.0
Describe the basic design/theory of operation of a
standard stand-up whole body counter
2.0
Identify artifacts present in:
 Background Count
 QCC count
 Personnel count
3.0
Explain why Transuranic’s and Hard-To-Detects are
included in internal dose calculations
4.0
Know why internal dosimetry is required and the
appropriate regulations and standards
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Objectives
5.0
Describe basic in-vitro sampling
6.0
Explain basic Internal dose calculations
7.0
Be able to draw conclusions concerning Human
Relations as it pertains to the Dosimetry Program
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Applicable Regulations and Guidance documents
– 10CFR20.1204
– Regulatory Guide 8.9 – Acceptable Concepts, Models,
Equations, and Assumptions for a Bioassay Program
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10CFR20.1204
– a) For purposes of assessing dose used to determine
compliance with occupational dose equivalent limits, the
licensee shall, when required under § 20.1502, take
suitable and timely measurements of-– (1) Concentrations of radioactive materials in air in work
areas; OR
– (2) Quantities of radionuclides in the body; OR
– (3) Quantities of radionuclides excreted from the body; OR
– (4) Combinations of these measurements.
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Part 20
– .1204 (b) Unless respiratory protective equipment is used,
as provided in § 20.1703, or the assessment of intake is
based on bioassays, the licensee shall assume that an
individual inhales radioactive material at the airborne
concentration in which the individual is present.
– Allowed to:
•
•
•
Adjust DAC or ALI to actual characteristics (requires prior NRC
approval)
Delay reporting if Class “Y” material
When a mixture of radionuclides exist in the air, may disregard
certain nuclides in the mixture
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Regulatory Guide 8.9
– Describes practical and consistent methods
acceptable to the NRC for estimating intake
– References ICRP 30, ICRP 54 and NUREG-4884
– Frequency of routine measurements
•
•
•
Baseline
Periodic
Termination
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Regulatory Guide 8.9
– Special monitoring
•
•
•
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High levels of facial
Entry without controls or into an area with unknown quantities of
airborne activity
Suspected ingestion/inhalation/wound
Failure of respiratory device
– Estimating Intakes
•
•
Evaluation levels
Investigation levels
– Type of Measurement
•
•
In-vivo
In-vitro
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Other “help”
– ICRP-66 replaces ICRP-30
– ICRP-68
– ICRP-78 replaces ICRP-54 because of ICRP publication 68
(1994) based on ICRP 60
•
New dose coefficients for intakes
– NUREG-4884 is very useful
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Theory of Operation (for most standup counters)
– Two 4” x 4” x 16” detectors
– Sodium Iodide scintillators
– 4” low cobalt steel
– Designed to count accurately 90% of all heights/weights
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More operations stuff
– Count is performed by each detector
– Signals are amplified (separately)
– Signals are converted to digital (separately)
– Signals are processed into a graphic spectrum (separately)
– Signals are summed
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More operations stuff
– Software searches according to the library,
– Software searches lastly on the spectrum,
– Software cannot separate all peaks so sometimes calls one
peak - two radioisotopes, or call it one isotope with extra
activity,
– Assigns activity based upon counts, efficiency at that
energy, and the gamma per second of that radionuclide
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Dose calculations by the software
– Calculates a dose based upon the “date of intake” input
at the time of the count.
– Accurate assuming no other radionuclides
– Does not include HTD’s
•
•
Dose calculation could easily double due to these radionuclides
Include tritium as well as alpha emitters
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Administration
– Background counts
– QCC counts
– Blind counts
– Calibration
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Background Counts
– Helps to ensure the counter is not contaminated (or source is present)
– Sources of Background include -
•
•
•
•
•
radon daughters
personnel in room at time of count
noble gases
electronic noise
Induced background
– Background subtracted from personnel counts
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Spectrum Artifacts
Background Spectrum
Counts
A
Channel
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Quality Control Counts
– Performed normally twice per day
– Ensures the spectrum has not drifted
– Compares itself to anticipated centroid locations and
activities
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Spectrum Artifacts
QCC Count
C
counts
A
C
B
Channel
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Blind Counts
– Administered by a third party
– Unknown radioisotopes and activities
– Must meet a predefined limit to pass
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Calibration
– Normally annually
– Energy/FWHM calibration
– Efficiency calibration
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Phantom
– Used to simulate a body (for calibration, blind counts, etc.)
•
Determines that software is calculating correctly
– Many different types
•
Japan Atomic Energy Research Institute (JAERI)
– Tissue equivalent
– Some are only anthropomorphic from a given direction
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Spectrum Artifacts
Worker Spectrum
Counts
A
B
Channel
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Accuracy
– Very geometry dependent
– Can increase activity by 50%
– Studies/QA program indicates a ± 20% accuracy: allowed 25% to +50%.
– Obviously influenced by statistics
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In-Vitro bioassay
– Secondary form of bioassay for most radionuclides,
– Verifies HTD’s - TRU’s, electron conversions, and beta
(tritium mainly)
– Used mainly in DOE for TRU’s and H-3
– Can be more sensitive depending upon the radionuclide
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In-Vitro Protocol
– Urine samples work best if over a 24-hour period
– Fecal samples - same restriction
– Gamma emitters - normally use fecal
– TRU’s - normally use urine
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Data Gathering
– Personnel Contamination Report
•
•
•
Work Location
SSN
Start time for exposure
– Dosimetric Assessment of Personnel Contamination
•
Type of analysis required (In-vivo, In-vitro)
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Data Gathering
– Decontamination
•
•
Must ensure the counter is detecting only internal contamination
Obtain documentation indicating decontamination (starting and
ending levels)
– Whole Body Counter
• Intake Date & Time
• Nuclides Identified
• Activity for each nuclide
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Data Gathering
– Air samples
– Swipes
– Lapel
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Scaling for HTD’s
– Based upon “easy-to-detects”
– Normally Co-60 or Cs-137
– Used for:
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•
•
alpha emitters
pure beta emitters
low activity gamma emitters
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Internal Dose Calculation
– Example Dose Calculation
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Gather Applicable Data
Identify isotopes and activity
Scale in Hard-to-Detect radionuclides
Compute intake
Compute WB and Organ dose (several different models)
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Comparisons between models
Intake Estimate
(Bq)
Committed Lung
Dose (mSv)
Whole Body
Committed Dose
(mSv)
ICRP 30 ICRP 66 ICRP 30 ICRP 66 ICRP 30 ICRP 66
810
1373
200
104
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Human Interactions
– 10/90 rule
– Who is asking?
– “Oh my gosh”
– Empathy
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