Use of Eichrom Resins for Bioassay Pa-231

1. Use of Eichrom Resins for Bioassay Pa-231 Bob Timm - GEL Tim Chandler - GEL Bill Burnett - FSU Mike Schultz - PerkinElmer Instuments, ORTEC

2. Outline • What is Protactinium • Pa-231 procedure development • Conclusions

3. Protactinium • Originally called "protoactinium", Pa is one of the rarest and most expensive naturally-occurring elements • Pa-231 has a fast fission cross section nearly the same as 239Pu • Pa(V) forms a very stable, water-soluble complex with fluoride • Pa(IV) forms insoluble fluorides • Two naturally-occurring isotopes: 234Pa and 231Pa

4. Pa-231 • PARENT • U-235 half-life 7x10^8 yrs decays to Th-231 • Th-231 half-life 25.52 hrs decays to Pa-231 • Pa-231 half-life 3.3x10^4 yrs • DAUGHTER • Ac-227 Actinium 100.0 %

5. History • Method for Environmental developed by Burnett and Yeh. (1995) • The earlier procedure was only concerned with interferences from naturally occuring radionuclides. • A method for Bioassay was required. Bioassay samples could contain artificial radionuclides. • Made the decision to try developing method using a single column method.

6. Development Objectives • Try an analysis on TRU Resin and start determining corrective steps. • Begin making corrections to procedure based on results of testing. • Finalize procedure.

7. Load Solution for Test 1 • Perform a Ca(PO4) Precipitation on DI water containing Nat Th, Nat U, Pu-239, Am-241 and Pa-231. • Followed procedure on next slide.

8. . TRU Resin Test-1 2 mL 9M HCl 3 10 mL 2M HNO3 2 4 10 mL 4M HCL 1 20 mL 8M HNO3 - 1M Al(NO3)3 5 20 mL 0.1M HCl Pa Elution 20 mL 0.1M HCL - 0.1M HF 6 1-4 (discard) 6 Th (~90-95%) 5 Pa

9. Test 1 Results • Only about 50% Protactinium recoveries with ~100% Plutonium and small amounts of Thorium (Up to 10%) visible in spectrum. • Analyzed the fractions just before the Protactinium Elution and determined the remainder of the Protactinium was in the Thorium elution.

10. Test 2 • Decision made to elute Thorium with 1M HCL instead of 0.1M HCL to increase Protactinium recovery. • Decision to use a TiCl3 solution to elute Plutonium when eluting Americium. Added 0.5 mL of TiCl3 to 20 mL of 4M HCL. • Followed procedure on next slide.

11. . TRU Resin Test-2 2 mL 9M HCl 3 10 mL 2M HNO3 2 20 mL 4M HCL - 0.5 mL TiCl3 4 1 20 mL 8M HNO3 - 1M Al(NO3)3 5 20 mL 1M HCl Pa Elution 20 mL 0.1M HCL - 0.1M HF 6 1-4 (discard) 6 Th (~90-95%) 5 Pa

12. Test - 2 Results • Plutonium was separated as expected and Protactinium recoveries increased to near 90%. • We tested the procedure one additional time adding the same actinides as before but added Np-237 as well. Unfortunately Np-237 followed Pa through the procedure and gave a new challenge.

13. Test 3 • Added UTEVA column to remove Neptunium and provide additional Uranium and Thorium clean up. • Load solution changed to 2.5M HNO3 / 0.1M Ferrous Sulfamate. Added 1 mL of 1.0 M Ascorbic Acid to reduce Fe. This is optimal for Neptunium (IV) retention on UTEVA while Protactinium stays in the +5 oxidation state. • Followed procedure on next slide.

14. . . TRU UTEVA Resin Resin Test-3 2 mL 9M HCl 20 mL 2.5M HNO3 / 0.1 M FeS / Asc Acid 10 mL 2.5 M HNO3 (2x) 20 mL 4M HCL - 0.5 mL TiCl3 3 4 5 20 mL 1M HCl 1 2 6 Pa Elution 20 mL 0.1M HCL - 0.1M HF 2 1 1-5 (discard) 6 Pa

15. Test - 3 Results • 80 to 90% of the Neptunium was removed by the UTEVA. • We have not identified exactly why the Neptunium is not fully separated by the UTEVA resin. We have ruled out column overloading of any sort by adding a TEVA column to the sequence and still seeing Neptunium interferance. • One possibility is phosphate interferance with Neptunium’s retention on UTEVA. (see next slide)

16. Sensitivity to PO4 TRU.Resin UTEVA.Resin

17. Test - 3 Results cont’d • Another thought was to separate Neptunium using spectral separation. • ~84% of the energy lines can be used which do not have Neptunium interferance with them.

18. Spectral Separation of Np-237 from Pa-231

19. Oxalic Acid rinse • Began testing to see if the separation of Neptunium and Protactinium on TRUResin was possible using oxalic acid. • We loaded Neptunium and Protactinium onto a TRU Column and performed a rinse with 1M HCL/0.015 M Oxalic acid. • Neptunium did not show up in the Protactinium rinse. We proceeded with Test-4.

20. . TRU Resin Test-4 3 2 mL 9M HCl 10 mL 2M HNO3 2 4 20 mL 4M HCL - 0.5 mL TiCl3 1 20 mL 8M HNO3 - 1M Al(NO3)3 5 15 mL 1M HCl / 0.015 M Oxalic Acid 6 10 mL 1M HCl 7 Pa Elution 20 mL 0.1M HCL - 0.1M HF (Pa) 7 1-6 (discard)

21. Test - 4 Results • Tracer yields were ~50% and spectrums were free of interfering actinides. • Approximately 15% of the Pa tracer came off with the 10 mL rinse of 1M HCL. No other actinides were detected. This rinse can be combined with the Pa elution to obtain tracer yields of ~65%. • The remaining Protactinium tracer came off with the oxalic acid rinse containing Neptunium.

22. Test 5 • Increased the molarity of HCL with the Oxalic acid rinse to 2M HCL. Our thought was that maybe the total volume of 1M HCL rinses was causing the Protactinium to elute early. The Thorium will still elute with the 2M HCL rinse.

23. . TRU Resin Test-5 3 2 mL 9M HCl 10 mL 2M HNO3 2 4 20 mL 4M HCL - 0.5 mL TiCl3 1 20 mL 8M HNO3 - 1M Al(NO3)3 5 15 mL 2M HCl / 0.015 M Oxalic Acid 6 10 mL 1M HCl 7 Pa Elution 20 mL 0.1M HCL - 0.1M HF (Pa) 7 1-6 (discard)

24. Test - 5 Results • Tracer yields were ~95%. Spectrums had 1% of the Np-237 added. No other actinides were present. • Two tests are currently in progress. • a.) Increase the Oxalic rinse to 0.03M Oxalic acid. • b.) Perform the oxalic acid rinse under HNO3 conditions.

25. Conclusions • Eichrom Resins can be effectively utilized to separate Protactinium from other actinides for alpha measurements. • Np-237 if present may interfere. We can resolve this interference with spectral separation or by using an oxalic acid rinse. • A Ce(OH) method of co-precipitation is necessary for alpha counting. Flouride co-precipitations will not work with Pa(V).