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OSL Albedo Neutron Dosimeter

OSL Albedo Neutron Dosimeter. Ikuo Kobayashi Ph.D. Overview. How OSL albedo neutron dosimeter (OSLN) works Dosimeter Design Concept OSLN Type Testing and Comparison to OSL Characteristics Neutron Energy Response. How It Works. Al 2 O 3 :C coated with 6 Li 2 CO 3 .

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OSL Albedo Neutron Dosimeter

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  1. OSL Albedo Neutron Dosimeter Ikuo Kobayashi Ph.D.

  2. Overview • How OSL albedo neutron dosimeter (OSLN) works • Dosimeter Design Concept • OSLN Type Testing and Comparison to OSL Characteristics • Neutron Energy Response

  3. How It Works • Al2O3:C coated with 6Li2CO3. • Neutron response is induced in the Al2O3:C when 6Li absorbs a neutron (1n0) and produces both tritium (3H) and alpha (4He) particles. 6Li + 1n0 = 4He2 (2.05 MeV) + 3H (2.75 MeV) • Alpha and beta particles give up their energy in absorber via coulomb interactions.

  4. Design Philosophy Maintained • Reader calibration protocols not impacted. • Sensitivity will be obtained from the slide. • 2D barcode on slide will have the OSLN and OSL sensitivity on board • NXXXYYY######, N = slide type, X = OSL sensitivity, Y = OSLN sensitivity, # = 1 - 999999 • YA case will be used (OW, PL, Al, and Cu). Same configuration as XA. * Density thickness of case only.

  5. Configuration Plastic (PL) 2D Barcode – communicates both OSL and OSLN sensitivity. Aluminum (Al) OSLN Detector in position 2 (E2) OSLN detectors have a slight pink tint. Copper (Cu)

  6. OSLN Type Testing and Comparison to OSL Characteristics • Material tested using the International Electrotechnical Commission (IEC) standard 62387-1 • Material Linearity • Fade • Energy Response • Depletion • Optical Annealing

  7. OSL and OSLN material response tested from 0 – 1000 R Bias within 1% from 0 - 100 R, 5% from 100 - 500 R, and 10% from 500 - 1000 R. Readers initially tested up to 1250 R OSLN:OSL response within ± 2% from 0 – 500 R but shows a slightly higher variation at 1000 R (+4%). Material Linearity

  8. Fade • OSLN fade estimated to be less than 4% annually. • Actual data from 0 - 180 days extrapolated to 390 days. • No significant variation noted between OSL and OSLN fade.

  9. Photon Energy Response • The typical energy dependence of the OSL material was also exhibited in the OSLN material. • The effects of the OSLN over response to photons in the 24 – 65 keV region were not as pronounced. • The 6Li2CO3 reduced the energy over response by approximately 10 to 20% over the 24 – 65 keV photon energy range.

  10. Photon Energy Response Curve

  11. Depletion • ~ 5% depletion was noted for both the OSL and OSLN detectors after 25 reads on the strong beam. • Similar depletion rate for OSLN as OSL material (rule of thumb ~10% depletion after 50 reads). • The re-readability of the detector materials was preserved.

  12. Depletion Curve

  13. Optical Annealing • Optical annealing effectiveness studied from 0 - 1000R using the InLight 50A Annealer. • Recommended anneal levels OSL = 5 converted values and OSLN = 10 converted values both based on 99% confidence interval. • 500 mrem can be annealed in 60 s • The annealing effectiveness of the OSLN and OSL material can be modeled using a classic decay curve (I = I0 * e-bt). • decay constant for bOSL = 0.246/s and bOSLN = 0.240/s

  14. Optical Annealing Curves

  15. Neutron Energy Response Testing • NPL • Monoenergetic neutrons 40 keV to 5 MeV • PNNL • Cf-252 bare (2 MeV), Cf-252 moderate (615 keV), and AmBe (4.4 MeV) • PTB • 14 MeV (irradiations in progress) • Landauer • AmBe (4.4 MeV)

  16. Hn = Net OSLN / NCF NCF ranges from 0.08 for higher energies to 5 for moderated fields. Moderated 252Cf response off curve. OSL Albedo Neutron Correction Factor

  17. Net OSLN Response to Various Neutron Fields ^ # ^ N. Hertel and J. McDonald, Calculations of Anisotropy Factors and Dose Equivalent for Unmoderated 252Cf Sources, Radiation Protection Dosimetry, Vol. 32 No. 2 pp. 77-82 (1990) # N. Hertel and J. McDonald, Calculated Dosimetric Quantities for D2O Moderate 252Cf Sources, Radiation Protection Dosimetry, Vol. 35 No. 1 pp. 23-30 (1991)

  18. OSLN and UD-802 same response/mrem characteristic Significant variations noted with all albedo neutron dosimeter for response:dose CR-39 response:dose the same for the 2 radiation fields Comparison with Other Neutron Dosimeters + +N. Stanford, Stanford Dosimetry, Three Whole Body Algorithms for the Pantex Plant Panasonic 802 TLD, February 1992

  19. Field Testing • Field testing conducted at Callaway Nuclear Power Plant, Lawrence Berkeley National Laboratory, Hanford Site, Georgia Power, and US Army.

  20. Field Testing • Data obtained from Callaway Nuclear Power Plant. • Average NCF of 1.57 as compared to CR-39 result (relative to AmBe response) • Neutron energy ~90 keV (determined from derived function)

  21. Using OSL Albedo Dosimeter • Field specific neutron corrections required. • Significant errors can result in inappropriate use of any albedo dosimeter. • Must know your neutron radiation environment. • Similar to other Albedo products on the market (Panasonic UD-802 and Harshaw TLD-760). • Neutron field must be know for neutron performance testing.

  22. Conclusions • OSLN material characteristics are similar OSL. • Specific corrections will be required to accurately assess the neutron dose similar to Harshaw or Panasonic Albedo Technique. • Provides a low cost alternative, quicker results, and easier dose determination than CR-39 neutron monitoring.

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