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In Search of…The Lost Art of Analytical Radiochemistry
…The Last Crusade
David S. Sill
Radiological and Environmental Sciences Laboratory Department Of Energy
60th RRMC, Knoxville, TN October 27– 31 2014
Analytical Radiochemistry
“The responsibility of an analytical radiochemist is to accurately determine the analyte of interest in the sample being submitted for analysis.”
D.S. Sill
Accurate Analytical Results
Must Guarantee Complete and Total Dissolution of the Sample
Must Guarantee Isotopic Exchange of the Tracer with the Analyte of Interest
And if you do…
Accurate Analytical Results Are Almost Guaranteed.
Initial Dissolution of the Sample
Most Important Part of Any Analytical Procedure…and also
The Most Neglected Part of Most Analytical Procedures…
Total Dissolution vs. Leaching Techniques
Analyte of interest must be in an ionic form to undergo subsequent chemical separations
“Clear” Does Not Mean Dissolved
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20
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60
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Pu-238 Pu-239 Pu-238 Pu-239 Pu-239
MaS12 MaS18 MaS24
Perc
ent R
ecov
ery
Total Dissolution vs Leaching
Leached
Fused
Two Variables One Equation DilemmaThe Second Most Important Concept
Sample Analysis vs. Evaluation of Laboratory Performance
Sample Unknown Act + Lab Unknown Performance Accuracy Result Unknown
Sample Known Act + {Lab Performance} Accurate Result ?
Laboratory Known Performance + {Unknown Sample} Accurate Result
Properties PE Material Must Have:
Known Activities (NIST) - Not Analyzed No Laboratory Bias Smaller Uncertainties
Address Real World Analytical Issues Sample Matrix Chemical Form of the Nuclide Chemical Interferences / Separations
Homogeneous - At Some Sample Size, At Some Precision
Natural Matrix StandardsRadionuclides Deposited Naturally And Randomly
Activity and Nuclides Present are Random
Can’t Guarantee Homogeneity Pu, Cs
Unknown Chemistry of Nuclide Soluble vs Insoluble
“Known” Values Include Lab’s Bias Uncertainty is always larger than NIST standards
Proper Use of PE Material
Evaluate: Accuracy, Detection Limit, False Positives
Real Samples Should Never be Used to Evaluate Laboratory Performance.
“Round Robin” Intercomparisons are of Little Value.
Precision Does Not Infer Accuracy.
Use of Internal Laboratory Control Sample Does Not Infer Accuracy on Real Samples
Fusions Routinely Used at RESL
Potassium Fluoride – KF, KHF2 Dissolves Siliceous Material – Volatizes Silica as SiF4↑ Dissolves Metal Oxides and Minerals Sulfate System – Pt Dish
Pyrosulfate – S2O7-2
Does Not Dissolve Silica Dissolves Metal Oxides Sulfate System – Glass or Pt Dish
Lithium Metaborate – LiBO2 Dissolves Siliceous Material – Soluble Silicate – SiO2 ↓ Dissolves Metal Oxides and Minerals Nitrate System – Pt Dish
Potassium Fluoride Fusion
Fusion in Pt @ 858°C – Ionic Salt – High [F-] Volatizes Silica as SiF4
No Dissolution of Pt “Precursor” to a Pyrosulfate Fusion Flux Turns Alkaline with Time Due to Loss of HF
SiO2 or H3BO3 can be used to Acidify Flux
KF + SiO2 → [K2SiF6] + H2SO4 → SiF4↑+ HF ↑ + K2SO4
Pyrosulfate Fusion
Does Not Dissolve Siliceous Materials Fusion Can Be Performed in Glass Will Dissolve Pt Rapidly at High Temperatures Little Dissolution of Pt at Low Temperatures Na+ vs. K+
Reversible Reaction / Easily Prepared Precipitation of Anhydrous Metal Salts – Very Insoluble
Na2SO4 + H2SO4 → NaHSO4 → Na2S2O7 → Na2SO4 + SO3
Preparation of Pyrosulfate
Na2SO4 + H2SO4 → 2NaHSO4 → Na2S2O7 → Na2SO4 + SO3 ↑
O O O O‖ ‖ ‖ ‖
-O—S—OH..HO—S—O- → -O—S—O—S—O-
‖ ‖ ‖ ‖ O O O O
Lithium Metaborate Fusion
LiBO2 can be prepared easily from H3BO3 and LiOH Dissolves Siliceous Materials – Soluble Si Reprecipitation of SiO2 can occur w/high [H+] Dissolves Metal Oxides and Minerals No Dissolution of Pt Surface Tension and KI Transposed to a Nitrate System Excellent for Samples Containing High [Ca+2] and [PO4
-3]
OH OH| |
Li+ -OH + HO – B – OH Li+ -O – B – OH Li+ -O – B=O
Common Analytical Problems: Pu SolubilityOnce Soluble Always Soluble ? No
Hydrolysis of Large +3 and +4 Elements
Heating a Salt Containing an Anion of a Volatile Acid(Cl-, NO3
-, etc.)
Solubility Of Some Hydroxides
Compound Ksp pH for ppt. of OH
NaOH Soluble 50%, 12.5M solution
Ca(OH)2 E-6 11
Fe(OH)2 E-16 5
Fe(OH)3 E-38 3
Pu(OH)4 E-55 << 2
SrCO3 E-10SrSO4 E-7
NO3 NO3
| |O3N ─ Pu ─ NO3 + HOH + Heat => O3N ─ Pu+...NO3
- H+...OH-
| |NO3 NO3
OH OH| |
OH ─ Pu ─ OH + Heat (-HOH) => OH ─ Pu=O => O=Pu=O|
OH
Co-57 False Positive TestingEu-152 added as Interference
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60
MaS29 - 39% A RdF30 - 62% A
Labo
rato
ries
Not Acceptable
Acceptable
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400
500
600
700
800
250 300 350 400 450 500 550
Cou
nts
Channel
Natural Uranium
U-238
U-235
U-234
U-232
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200
300
400
500
600
700
800
250 300 350 400 450 500 550
Cou
nts
Channel
Depleted Uranium
U-238
U-235
U-234
U-232
Fractionation of Radionuclides from Non-Acidified Water Samples
1-L Water Samples – Not Acidified Spiked with NIST Traceable Radionuclides Delay Between Dispensing Aliquots Aliquot Sizes: 200 mL, 300 mL, 500 mL Entire 1-L PP Bottle Dissolved and Analyzed
Pu-239
Days Result - pCi Total Found Total Added5 0.82 ± 0.03 (200mL)
12 0.54 ± 0.02 (300mL)
19 0.26 ± 0.01 (500mL)
Bottle 4.17 ± 0.13 5.79 ± 0.19 5.91 ± 0.12
Pu-238
Days Result - pCi Total Found Total Added5 3.11 ± 0.03 (200mL)
12 1.02 ± 0.02 (300mL)
19 0.12 ± 0.01 (500mL)
Bottle 2.89 ± 0.13 7.1 ± 0.3 7.35 ± 0.15
Am-241
Days Result - pCi Total Found Total Added5 4.29 ± 0.03 (200mL)
12 2.29 ± 0.02 (300mL)
19 0.08 ± 0.01 (500mL)
Bottle 1.95 ± 0.13 8.6 ± 0.4 8.95 ± 0.18
Current State Of The Analytical Art
Accurate analytical results are difficult to obtain on a routine and reliable basis.
Laboratories continue to use “Leaching Techniques” even though experimental evidence demonstrates that incomplete sample dissolution is the major cause of the inaccurate results being routinely reported.
Analytical problems are not isolated to one analysis area.
What Worse Than Not Having a CRM ?
Having a CRM that: Has an Inaccurate Reference Value Is Inhomogeneous Does Not Test the Real World Analytical Conditions that
Need to be Tested
Elite Analytical Infrastructure and Methods Verification of Each Reference Value Homogeneity Testing Traceability to NIST
Analytical InfrastructureRadiological Traceability Program
National Institute of Standards and TechnologyA
nalyze PT Material
Prepare PT Material
Prep
are
PT M
ater
ial
Ana
lyze
PT
Mat
eria
l
Radiological & Environmental Sciences Laboratory
Introducing Bias Experimental Value vs Known Value
Nuclide Expt’l ResultsCs-137 2.98 +/- 0.13 E+3 2.95 +/- 0.13 E+3 (Fusion) 3.01 +/- 0.13 E+3 2.99 +/- 0.13 E+3
3.04 +/- 0.13 E+3 2.89 +/- 0.13 E+3
Mean: 2.98 +/- 0.05 E+3 Known Value: 3.31 +/- 0.06 E+3
Cs-137 3.39 +/- 0.14 E+3 3.28 +/- 0.13 E+3 (HF) 3.15 +/- 0.13 E+3 3.21 +/- 0.13 E+3
3.35 +/- 0.16 E+3 3.25 +/- 0.14 E+3
Mean: 3.27 +/- 0.09 E+3 Known Value: 3.31 +/- 0.06 E+3
~100mg Aliquots - pCi/g
Inhomogeneous “Standards”and
The Particle Problem
Different 1-g Aliquots of the "Same Sample"(Pu-239 pCi/g)
70 +/- 475 +/- 436 +/- 3
670 +/- 30490 +/- 2511 +/- 1
“Known” ~ 2000 pCi/g
Soil “Standard” Prepared From NIST SolutionsIndividually Spiked 10g Sample - Pu239
Experimental (pCi/g) Sample Size Total Act/Aliquot12.3 +/- 0.6 3.5 g 43.1 +/- 0.27.8 +/- 0.4 3.5 g 27.3 +/- 1.43.9 +/- 0.2 3.0 g 11.7 +/- 0.6
“Known” 7.6 +/- 0.3 pCi/g Total Act. Found 82 +/- 4 pCiTotal Act Added 76 +/- 3 pCi
Interlaboratory Comparisons
1g Soil Samples / Ra-226
1.64 +/- 0.45 pCi/g5.5 +/- 0.2
2.48 +/- 0.050.00 +/- 0.018. 6 +/- 2.5
1.05 +/- 0.281.72 +/- 0.04
2.0 +/- 0.33.3 +/- 1.7
Mean: 3 +/- 3
Duplicate Samples Used For PE Purposes
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25000
30000
35000
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45000
50000
250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500
Cou
nts
Channel
Cs-137
Co-60
"Duplicate" for H-3 Analysis
Co-60
15 min
Duplicate Samples Used For PE Purposes
0500
100015002000250030003500400045005000550060006500700075008000850090009500
10000
250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500
Cou
nts
Channel
60 min
Cs-137
Co-60
"Duplicate" for Sr-90 Analysis
Co-60
RESL Certified Reference MaterialsWhy?
Long history of producing CRM’s for internal use.
Numerous requests for unique CRMs that are not available anywhere else.
Soil, Vegetation, Water, Air Filters Fish, Kelp, Bone, Wheat, Milk Dehydrated Eggs – Actinide / Sr-90 Sausage – Co-60 Oil Exploration / Fracking – Ra-226
Verification ResultsCRM Cement 0813
Nuclide Known Expt’lAm-241 4.91 ± 0.13 E1 4.8 ± 0.2 E1Pu-238 4.89 ± 0.12 E1 4.88 ± 0.17 E1Pu-239 4.91 ± 0.13 E1 4.85 ± 0.17 E1U-238 5.05 ± 0.11 E1 5.0 ± 0.2 E1U-234 6.67 ± 0.15 E0 6.9 ± 0.3 E1Cm-244 6.75 ± 0.11 E1 ? ± ?
Sample Size 100mg pCi/g