1. OSL Albedo Neutron Dosimeter
Ikuo Kobayashi Ph.D.
April 2009

2. Overview How OSL albedo neutron dosimeter (OSLN) works
Dosimeter Design Concept
OSLN Type Testing and Comparison to OSL Characteristics
Neutron Energy Response
April 2009

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.
April 2009

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, # =
YA case will be used (OW, PL, Al, and Cu). Same configuration as XA.
* Density thickness of case only.
April 2009

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)
April 2009

6. OSLN Type Testing and Comparison to OSL Characteristics
Material tested using the International Electrotechnical Commission (IEC) standard
Material Linearity
Fade
Energy Response
Depletion
Optical Annealing
April 2009

7. Material Linearity
OSL and OSLN material response tested from 0 – 1000 R
Bias within 1% from R, 5% from R, and 10% from 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%).
April 2009

8. Fade OSLN fade estimated to be less than 4% annually.
Actual data from days extrapolated to 390 days.
No significant variation noted between OSL and OSLN fade.
April 2009

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.
April 2009

10. Photon Energy Response Curve
April 2009

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.
April 2009

12. Depletion Curve
April 2009

13. Optical Annealing
Optical annealing effectiveness studied from R 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
April 2009

14. Optical Annealing Curves
April 2009

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)
April 2009

16. OSL Albedo Neutron Correction Factor
Hn = Net OSLN / NCF
NCF ranges from 0.08 for higher energies to 5 for moderated fields.
Moderated 252Cf response off curve.
April 2009

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 (1990)
# N. Hertel and J. McDonald, Calculated Dosimetric Quantities for D2O Moderate 252Cf Sources, Radiation Protection Dosimetry, Vol. 35 No. 1 pp (1991)
April 2009

18. Comparison with Other Neutron Dosimeters+
+N. Stanford, Stanford Dosimetry, Three Whole Body Algorithms for the Pantex Plant Panasonic 802 TLD, February 1992
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
April 2009

19. Field Testing
Field testing conducted at Callaway Nuclear Power Plant, Lawrence Berkeley National Laboratory, Hanford Site, Georgia Power, and US Army.
April 2009

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)
April 2009

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.
April 2009

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.
April 2009