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Nuclear Forensics Summer School Radiochemical separations and quantification

Nuclear Forensics Summer School Radiochemical separations and quantification. Aqueous chemical behavior of key radionuclides Oxidation state variation Solution phase speciation General separations Ion exchange/column chromatography Solvent extraction Precipitation/carrier Quantification

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Nuclear Forensics Summer School Radiochemical separations and quantification

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  1. Nuclear Forensics Summer SchoolRadiochemical separations and quantification • Aqueous chemical behavior of key radionuclides • Oxidation state variation • Solution phase speciation • General separations • Ion exchange/column chromatography • Solvent extraction • Precipitation/carrier • Quantification • Radiochemical methods • Spectroscopic • BOMARC example (at a later date) • Provide basis for linking chemical behavior with separations • Provide range of techniques suitable for quantification of radionuclides

  2. Radionuclides of interest • Can differentiate fissile material and neutron energetics from fission products • A near 90 (Sr, Zr), 100 (Tc) and 105 (Pd) • Mass 110-125 (Pd, Ag, Cd, In, Sn, Sb) • Lanthanides (140 < A < 150) • Actinides • Polonium 235U fission yield

  3. Fundamentals of separations • Oxidation state • Elements of different oxidation states easier to separate • Anionic and cationic speciation • UO22+,TcO4- • Variation of oxidation state • Addition of reductants/oxidants to control speciation • Method for separation of Pu from U • Varied stability of oxidation states

  4. Fundamentals of separation • Ion size • Concentration of counter anion • Can form anionic species • ThCl4and PuCl5- will behave differently • Counter anion can effect overall charge • Varied by acid concentration or addition of salt • Ionic size difference basis of lanthanide separations

  5. Chromatography Separations • Sample dissolution • Adjustment of solution matrix • Based on column chemistry and other elements in solution • Retention of target radionuclide on column • Removal of other elements • Solution adjustment • Acid concentration, counter ion variation • Addition of redox agent • Elute target radionuclide • Can include addition of isotopic tracer to determine yield • Chemical behavior measured by distribution

  6. Solvent Extraction • Two phase system for separation • Sample dissolved in aqueous phase • Normally acidic phase • Aqueous phase contacted with organic containing ligand • Formation of neutral metal-ligand species drives solubility in organic phase • Organic phase contains target radionuclide • May have other metal ions, further separation needed • Variation of redox state, contact with different aqueous phase • Back extraction of target radionuclide into aqueous phase • Distribution between organic and aqueous phase measured to evaluate chemical behavior

  7. Sr separations • Sr only as divalent cation • Isotopes • 88 (stable), 89 (50.5 d), 90 (28.78 a) • 90Sr/90Y (3.19 h for metastable, 2.76 d) can be exploited • Eichrom Sr Resin • 1.0 M 4,4'(5')-di-t-butylcyclohexano 18-crown-6 (crown ether) in 1-octanol

  8. Sr separation • 8 M nitric acid, k' is approximately 90 • falls to less than 1 at 0.05 M nitric acid • Tetravalent actinide sorption can be limited by addition of oxalic acid • 90Sr determined by beta counting

  9. Technetium separation • Exploit redox chemistry of Tc • TcO4- in aqueous phase • Separation from cations in near neutral pH solution • Anion exchange methods • Interference from other anions • Nitrate • Use Tc redox chemistry • Remove nitrates • Precipitate Tc (tetrabutylamonium) • Solvent extraction • UREX (i.e., 1 M HNO3, 0.7 M AHA) • UO22+ and TcO4- extracted • Back extraction (pH 2 acid), separate

  10. Mass 110-125 (Pd, Ag, Cd, In, Sn, Sb) • Noble metals to group 15 • Divalent Pd and Cd • Monovalent Ag • Trivalent In • Sndi- and tetravalent • Sb stable as trivalent, pentavalent • Separation by changing conditions to target specific elements

  11. HDEHP Pd to Sb • Extraction with HDEPH • Vary aqueous phase • Basic (pH 10) • Citric acid at pH 8 • 6 M HNO3 • Elements into different fractions

  12. In, Sn, and Sb • Extraction with HCl and HI • Control of redox chemistry to enhance separations • Varied organics • Isoamyl acetate, benzene

  13. In, Sn, and Sb • The extraction behavior of In, Sn and Sb in HI and HCl examined • Extraction of Sb(V) from Sn(IV) in 7 M HCl solution with isoamylacetate. • Selective removal of Sn(IV) or In (III) from Sb(V) by extraction into benzene or isopropylether from HI

  14. Polonium • Essentially tracer chemistry due to short half-life of isotopes • 206Po 8.8 d EC to 206Bi; α to 202Pb • 207Po 5.80 h EC to 207Bi; α to 203Pb • 208Po 2.898 y EC to 208Bi; α to 204Pb • 209Po 102 y EC to 209Bi; α to 205Pb • 210Po 138.38 d α to 206Pb • Range of separations from environmental samples • Sediment • seawater

  15. Polonium extraction • From aqueous α-hydroxyisobutyric acid • Varied organic phase • dioctyl sulphide, Cyanex 272, Cyanex 301 or Cyanex 302 in toluene • 2 mL each phase

  16. Polonium extraction

  17. Polonium extraction • Extraction of Po from 1M α-HIBA increases • Cyanex 272 < DOS < Cyanex 302 < Cyanex 301 • Extraction of Po with 1M extractants without α-HIBA aqueous phase • DOS < Cyanex 301 < Cyanex 302 < Cyanex 272.

  18. Lanthanides • Size separations • Lanthanide and actinide by elution with ammonium a-hydroxyisobutyrate from Dowex 50-X4 resin columns • pH variation • Determination of peak position with pH

  19. Lanthanides HDEHP separations • Ln separation by HPLC using Di-(2-ethylhexyl) phosphoric acid (HDEHP) coated reverse phase column • a-hydroxy isobutyric acid for elution

  20. Th Solution chemistry • Only one oxidation state in solution • Th(III) is claimed • Th4+ + HN3 Th3+ +1.5N2 + H+ • IV/III greater than 3.0 V • Unlikely based on reduction by HN3 • Claimed by spectroscopy • 460 nm, 392 nm, 190 nm, below 185 nm • Th(IV) azido chloride species • Structure of Th4+ • Around 11 coordination • Ionic radius 1.178 Å • Th-O distance 2.45 Å • O from H2O

  21. Solution chemistry • Thermodynamic data • Eº= 1.828 V (Th4+/Th) • ΔfHº= -769 kJ/mol • ΔfGº= -705.5 kJ/mol • Sº= -422.6 J/Kmol • Hydrolysis • Largest tetravalent actinide ion • Least hydrolyzable tetravalent • Can be examined at higher pH, up to 4 • Tends to form colloids • Discrepancies in oxide and hydroxide solubility • Range of data • Different measurement conditions • Normalize by evaluation at zero ionic strength

  22. Solution chemistry • Complexing media • Carbonate forms soluble species • Mixed carbonate hydroxide species can form • Th(OH)3CO3- • 1,5 • Phosphate shown to form soluble species • Controlled by precipitation of Th2(PO4)2(HPO4).H2O • logKsp=-66.6

  23. Complexation • Inorganic ligands • Fluoride, chloride, sulfate, nitrate • Data is lacking for complexing • Re-evaluation based pm semiemperical approach • Interligand repulsion • Decrease from 1,4 to 1,5 • Strong decrease from 1,5 to 1,6 • Organic ligands • Oxalate, citrate, EDTA, humic substance • Form strong complexes • Determined by potentiometry and solvent extraction • Choice of data (i.e., hydrolysis constants) impacts evaluation

  24. Th analytical methods • Low concentrations • Without complexing agent • Indicator dyes • Arzenazo-III • ICP-MS • Radiometric methods • Alpha spectroscopy • Liquid scintillation • May require preconcentration • Need to include daughters in evaluation

  25. Th ore processing • Main Th bearing mineral is monazite • Phosphate mineral • strong acid for dissolution results in water soluble salts • Strong base converts phosphates to hydroxides • Dissolve hydroxides in acid • Th goes with lanthanides • Separate by precipitation • Lower Th solubility based on difference in oxidation state • precipitate at pH 1 • A number of different precipitation steps can be used • Hydroxide • Phosphate • Peroxide • Carbonate (lanthanides from U and Th) • U from Th by solvent extraction

  26. Pa Solution chemistry • Both tetravalent and pentavalent states in solution • No conclusive results on the formation of Pa(III) • Solution states tend to hydrolyze • Hydrolysis of Pa(V) • Usually examined in perchlorate media • 1st hydrolyzed species is PaOOH2+ • PaO(OH)2+ dominates around pH 3 • Neutral Pa(OH)5 form at higher pH • Pa polymers form at higher concentrations • Constants obtained from TTA extractions • Evaluated at various TTA and proton concentrations and varied ionic strength • Fit with specific ion interaction theory • Absorption due to Pa=O

  27. Solution chemistry • Pa(V) in mineral acid • Normally present as mixed species • Characterized by solvent extraction or anion exchange • Relative complexing tendencies • F->OH->SO42->Cl->Br->I->NO3-≥ClO4- • Nitric acid • Pa(V) stabilized in [HNO3]M>1 • Transition to anionic at 4 M HNO3 • HCl • Precipitation starts when Pa is above 1E-3 M • Pa(V) stable between 1 and 3 M • PaOOHCl+ above 3 M HCl • HF • High solubility of Pa(V) with increasing HF concentration • Up to 200 g/L in 20 M HF • Range of species form, including anionic

  28. Solution chemistry • Sulfuric acid • Pa(V) hydroxide soluble in H2SO4 • At low acid (less than 1 M) formation of hydrated oxides or colloids • At high acid formation of H3PaO(SO4)3

  29. Solution chemistry • Redox behavior • Reduction in Zn amalgam • Electrochemistry methods • Pt-H2 electrode • Acidic solution • Polarographic methods • One wave • V to IV • Calculation of divalent redox • Pa(IV) solution • Oxidized by air • Rate decreases in absence of O2 and complexing ions

  30. Solution chemistry • Pa(IV) • Precipitates in acidic solutions • i.e., HF • Spectroscopy • 6d15f1 • Peak at 460 nm

  31. Pa Analytical methods • Radiochemical • Alpha and gamma spectroscopy for 231Pa • Beta spectroscopy for 234Pa • Overlap with 234Th • Activation analysis • 231Pa(n,g)232Pa, 211 barns • Spectral methods • 263 lines from 264 nm to 437 nm • Microgram levels • Electrochemical methods • Potentiometric oxidation of Pa(V) • Absorbance • Requires high concentrations • Arsenazo-III • Gravimetric methods • Hydroxide from precipitation with ammonium hydroxide

  32. Pa Preparation and purification • Pa is primarily pentavalent • Pa has been separated in weighable amounts during U purification • Diethylether separation of U • Precipitation as carbonate • Use of Ta as carrier • Sulfate precipitation of Ra at pH 2 • Inclusion of H2O2 removes U and 80 % of Pa • Isolated and redissolved in nitric acid • Pa remains in siliceous sludge • Ability to separate Pa from Th and lanthanides by fluoride precipitation • Pa forms anionic species that remain in solution • Addition of Al3+ forms precipitate that carriers Pa

  33. Pa purification • Difficult to separate from Zr, Ta, and Nb with macro amounts of Pa • Precipitation • Addition of KF • K2PaF7 • Separates Pa from Zr, Nb, Ti, and Ta • NH4+ double salt • Pa crystallizes before Zr but after Ti and Ta • Reduction in presence of fluorides • Zn amalgam in 2 M HF • PaF4 precipitates • Redissolve with H2O2 or air current • H2O2 precipitation • No Nb, Ta, and Ti precipitates • Silicates • K, Na silicates with alumina

  34. Pa purification • Ion exchange • Anion exchange with HCl • Adhere to column in 9-10 M HCl • Fe(III), Ta, Nb, Zr, U(IV/VI) also sorbs • Elute with mixture of HCl/HF • HF • Sorbs to column • Elute with the addition of acid • Suppresses dissociation of HF • Lowers Kd • Addition of NH4SCN • Numerous species formed, including mixed oxide and fluoride thiocyanates

  35. Pa purification • Solvent extraction • At trace levels (<1E-4 M) extraction effective from aqueous phase into a range of organics • Di-isobutylketone • Pa extracted into organic from 4.5 M H2SO4 and 6 M HCl • Removal from organic by 9 M H2SO4 and H2O2 • Di-isopropylketone • Used to examine Pa, Nb, Db • Concentrated HBr • Pa>Nb>Db • Dimethyl sulfoxide

  36. Pa purification • TTA • 10 M HCl • PaOCl63- • With TBP, Tri-n-octylphosphine oxide (TOPO), or triphenylphosphine oxide (TPPO) • Triisooctylamine • Mixture of HCl and HF • 0.5 M HCl and 0.01 M HF • Used to examine the column extraction • Sorbed with 12 M HCl and 0.02 M HF • Elute with 10 M HCl and 0.025 M HF, 4 M HCl and 0.02 M HF, and 0.5 M HCl and 0.01 M HF • Extraction sequence Ta>Nb>Db>Pa

  37. Pa purification • Aliquat 336 • Methyl-trioctylammonium chloride • Extraction from HF, HCl, and HBr

  38. Uranyl chemical bonding • Bonding molecular orbitals • sg2 su2 pg4 pu4 • Order of HOMO is unclear • pg<pu<sg<< suproposed • Gap for s based on 6p orbitals interactions • 5fd and 5ff LUMO • Bonding orbitals O 2p characteristics • Non bonding, antibonding 5f and 6d • Isoelectronic with UN2 • Pentavalent has electron in non-bonding orbital

  39. f orbitals From LANL Pu chemistry

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