Practical%20Whole%20Body%20Counting%20and%20Internal%20Dosimetry%20Tim%20Kirkham%20

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Practical Whole Body Counting and Internal
DosimetryTim Kirkham ENSR Corporation
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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 Transuranics 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
• 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 HTDs
• 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
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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
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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
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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 HTDs - TRUs, electron conversions, and
  beta (tritium mainly)
• Used mainly in DOE for TRUs 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
• TRUs - 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 HTDs

• Based upon easy-to-detects
• Normally Co-60 or Cs-137
• Used for
• alpha emitters
• pure beta emitters
• low activity gamma emitters

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Internal Dose Calculation

• Example Dose Calculation
• 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) Intake Estimate (Bq) Committed Lung Dose (mSv) Committed Lung Dose (mSv) Whole Body Committed Dose (mSv) Whole Body Committed Dose (mSv)
ICRP 30 ICRP 66 ICRP 30 ICRP 66 ICRP 30 ICRP 66
810 1373 200 104 51 19
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Human Interactions

• 10/90 rule
• Who is asking?
• Oh my gosh
• Empathy