Environmental Sample Analysis Advances and Future Trends

Transcription

1 Environmental Sample Analysis Advances and Future Trends D.Donohue Office of Safeguards Analytical Services Environmental Sample Laboratory International Atomic Energy Agency

2 Contents Introduction Bulk Analysis Particle Analysis Scanning Electron Microscopy Particle Chemical Analysis Secondary Ion Mass Spectrometry Future Directions

3 Analytical Challenges Assumptions: When nuclear material is handled in a location, traces are left behind. The detection probability of ES depends on the amount of material released, the type of process, and the effectiveness of cleaning or concealment. Therefore, HIGH SENSITIVITY is needed to find small releases or where cleaning has been extensive. Often, the signature of an undeclared activity is mixed with declared material or the natural background. To distinguish small differences, HIGH SELECTIVITY is needed, enhanced by HIGH PRECISION and ACCURACY.

4 Methods of Environmental Sample Analysis Radiometric Screening Presence and approx. amount of U, Pu, Am Fission/activation product ratios Bulk Analysis Particle Analysis

5 Bulk Analysis Bulk analysis means ashing and dissolution of the whole sample, chemical separation and measurement of U, Pu, Am by mass spectrometry. Sensitivity for Pu is in the low femtogram range (10-15 g). Such low levels may not appear as discrete particles.

6 Particle Analysis Particle analysis involves the removal of particles from the swipe, their location, manipulation and analysis of their elemental and isotopic composition. A 1 μm UO 2 particle weighs about 5 picograms (5 x g). 100 μm 5 μm

7 Requirements for Success Bulk analysis Clean handling and chemistry low blanks. Efficient chemical recovery High sensitivity mass spectrometry (ICP-MS) Attention to interference and background effects Particle analysis Efficient recovery of particles from swipes Low cross contamination risk Optimized particle location and choice Efficient use of limited sample material

8 Bulk Analysis in the ESL Ashing of Swipe Dissolution and Separation ICP-MS Measurement

9 238 Pu Analysis by Alpha Spectrometry Alpha Spectrometry avoids the interference between 238 U and 238 Pu suffered by most mass spectrometry methods. However, the sample must contain more than 1 pg of Pu to give sufficient signal.

10 Bulk Analysis Performance Element/Isotope Ratio Amount Uncertainty Method U ng 0.1 ng IDA ICP-MS Pu pg 0.10 pg IDA ICP-MS Pu pg pg IDA ICP-MS Pu pg pg IDA ICP-MS U-234/U TIMS U-235/U TIMS U-236/U TIMS Pu-238/Pu AS IDA = isotope dilution analysis, ICP-MS = inductively-coupled plasma mass spectrometry, TIMS = thermal ionization mass spectrometry, AS = alpha spectrometry

11 Particle Analysis - SEM Scanning electron microscopy with energy and wavelength dispersive X-ray spectrometers allows the study of particle morphology and chemical composition.

12 Particle/Chemical Analysis Manipulating 1 micrometer particles is feasible using both the SEM and optical microscopes. Age dating of Pu particles is accomplished with SEM-WDX measurement of the Am/Pu ratio, followed by chemical separation and ICP- MS measurement of the 241 Pu abundance.

13 SIMS Cameca IMS-4f U particles are located with PSEARCH software and the 235/238 ratio measured to ± 5% uncertainty by microprobe analysis. Minor isotopes, 234 U and 236 U are more problematic.

14 SIMS Cameca IMS 1280 Laure Sangely at the controls of the s LG-SIMS in Paris

15 235 cts Comparison 4f Screening Results False positive data showing high-enrichment IMS4F (SAL) IMS1280 (CAMECA) /238 ratio

16 Ground Breaking on 31 March 2010

17 The Clean Laboratory Extension (CLE) Existing Clean Lab Total area = 1280 m 2 (on 3 levels) Laboratory Space = 520 m 2 Support Rooms = 460 m 2 Cost = 4 M Euro

18 Future Directions - 1 Improved Bulk Analysis for Pu Multi-collector ICP-MS (2011) Sensitivity ~ 10 times higher Detection Limit for Pu < 1 fg Caveats: Better separation of interferences Concentration control Ultimate sensitivity - may see fallout background

19 Future Directions - 2 Age Dating of HEU Particles Preliminary screening by LG-SIMS Particle manipulation and chemistry MC-ICP-MS measurements of 230 Th/ 234 U and 231 Pa/ 235 U Caveats: Works better for large (>2 μm) and old (>10 years) particles Distinguish historical from recent

20 Future Directions - 3 Laser Ablation MC-ICP-MS Rapid measurement of enrichment in U particles Allows hundreds of particles to be sampled Complementary to SIMS (20-50 particles/sample) Caveats: Requires rich samples Requires pre-selection by SEM, SIMS or fission track

21 Future Directions - 4 Speciation of U (Pu) compounds in particles SEM-WDX measurements for O/U or O/F/U ratios Electron Backscattered Diffraction (EBSD) in SEM EBSD pattern for U 3 O 8 particle (1 μm) J.Small and J.Michael, J. Microscopy 201 (2001)

22 Who We Are Photo: D. Calma,