Practical Whole Body Counting and Internal Dosimetry Tim Kirkham – Chesapeake Nuclear Services

1. Practical Whole Body Counting and Internal DosimetryTim Kirkham – Chesapeake Nuclear Services

2. Reasons for Study • Increase knowledge of applied fundamentals. • Enhance professionalism of radiological protection technicians.

3. 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

4. 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

5. Applicable Regulations and Guidance documents • 10CFR20.1204 • Regulatory Guide 8.9 – Acceptable Concepts, Models, Equations, and Assumptions for a Bioassay Program

6. 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.

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Administration • Background counts • QCC counts • Blind counts • Calibration

16. 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

17. Spectrum Artifacts

18. Quality Control Counts • Performed normally twice per day • Ensures the spectrum has not drifted • Compares itself to anticipated centroid locations and activities

19. Spectrum Artifacts

20. Blind Counts • Administered by a third party • Unknown radioisotopes and activities • Must meet a predefined limit to pass

21. Calibration • Normally annually • Energy/FWHM calibration • Efficiency calibration

22. 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

28. Spectrum Artifacts

29. Accuracy • Very geometry dependent • Can increase activity by 50% • Studies/QA program indicates a ± 20% accuracy: allowed -25% to +50%. • Obviously influenced by statistics

30. 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

31. 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

32. 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)

33. 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

34. Data Gathering • Air samples • Swipes • Lapel

35. Scaling for HTD’s • Based upon “easy-to-detects” • Normally Co-60 or Cs-137 • Used for: • alpha emitters • pure beta emitters • low activity gamma emitters

36. 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)

37. Comparisons between models

38. Human Interactions • 10/90 rule • Who is asking? • “Oh my gosh” • Empathy