Analytical Challenges of PreciseAnalyticalChallengesofPreciseRa Measurements in BrineZoltan SzaboU.S. Geological SurveyNORM in Produced Waters: Process-based studiesneed precise enough characterization of radionuclidesneedpreciseenoughcharacterizationofradionuclidesthat mechanisms of mobility and progressive changescan be determined• Characterizing U, Ra, other isotope ratios and mixtures inthe produced waters. What level of precision and detectioncapability is needed?• To determine solely whether activity level is too high to beacceptable likely does not need high precision or detectioncapacity, at least at a “screening” level?• For isotopic forensics for studying wasteproductsgeneration during the fracturing process, analyses requirehigh precision and accuracy to study progressive changes• Analytical challenges need to be overcome• Build an Approach:– Evaluateandtroubleshootexistinganalytical methodsu e d oub es oo e s g y c e ods– Identify matrix interferences and how they can be removed– Refine or modify analytical methods as neededNotes of concern for using“indicators”for NORM inforNORMinproduced waters• Isotopic forensics required forcomprehensive characterization of the wastesO h f h i i h b h i db•Once the nature oftheisotope mixtureshasbeen characterizedbydirect analyses, the more generalized gross gamma and alphaactivitymeasurements maybe enough (with care!) for screeningygpurposes to indicate those drilling and waste products of concern.• Characterize and monitor radionuclidesin other wastes: pipe scale,sludges salts For workers or residents might there be gammasludges,salts.Forworkersorresidents,mighttherebegammaexposure concerns? (Likely Yes). Gamma spectroscopytechniques ought to provide enough sensitivity for determiningconcentrations in these waste products of concern.Detection of gross alpha is extremely limited in waterwith increasing TDS (or SC) as illustrated below forwithincreasingTDS(orSC)asillustratedbelowfordrinking water samples. Co-precipitation methods withdilution and/or some ion-exchange clean-upneededSzabo et al.,in reviewNORM in produced waters: Isotope characterization is a must!Gross alpha varies considerablywith time of measurement afterl ll i b i f i f hli d i R224sample collection onbasis ofmix ofshort-livedisotopes.Ra-occurrence is common, here see effect in drinking-water supply).(Szabo et alin review)Analyses for Ra with High Precision, Low MDC(Process based studies or precise verification needs)• RadioactivityCountingg• -Radon emanation (Rn-em): Ra-226• -Alpha spectrometry, direct or of progeny (AS): Ra-226, Ra224, Ra-223• -Gamma spectrometry (GS): AllD l d C i id ti (DCC) All tl f R223• -DelayedCoincidence counting(DCC):All, mostlyforRa-,Ra-224• Atom(Mass)Counting) g• -Thermal Ionization Mass Spectrometry (TIMS): Ra-226• -Multiple Ion Counting Plasma Mass Spectrometry (MC-ICPMS): Ra-226, possibly Ra-228Precision BackgroundPrecision,BackgroundActivity=(Net (=Total-Background) counts/time)ActivityBackground)counts/(Yield)(Volume)(Detector Efficiency)(Branching Factor)Maximize total counts relative to background, yield, efficiencyFor efficient laboratory operations: minimize time, volumeMinimize background plus matrix interferenceCritical level (instrument response) is defined for a method basedon a distribution of blank samples and a probability of Type I erroronadistributionofblanksamplesandaprobabilityofTypeIerror(false detection).Clean-up/Extraction necessaryto remove interferences, andymaintaining high yield is necessary. These need to be assessedindependently of “blank” samples.Precision or Uncertainty( )( )( )( )( )6VVuuVtNtNVtttNtNcu222222BBSS222B2S2SB2BS2c⎥⎦⎤⎢⎣⎡+εε××ε⎟⎟⎠⎞⎜⎜⎝⎛−+×ε×××−×=αPrecisionorUncertaintyNet combined uncertainty becomes the square root of variancesfor the already considered terms;that is of Net Count rates (=TotalBackground count rates) ofYieldVolume and Detector-Backgroundcountrates),of,Volume,andDetectorEfficiency.Atomic counting minimizes, relative to activity counting, variancesin total counts by avoiding random radioactivity count errors.relative to background yield efficiencyrelativetobackground,yield,efficiencyStill need to minimize variances in background and efficiency.Stillnecessaryto remove interferences and to maintaininghighyield.g gyBarium(lead, strontium)sulfate co-preciitation)p• Used typically with all counting techniques except DCC•Poor yield with high Ca Sr waters (problem allPooryieldwithhighCa,Srwaters(problem,alltechniques): needs ion-exchange and/or EDTA addition tosupernatant• Uneven crystal size and heterogeneous planchetdistribution (problem, especially AS): seeding solutions,slow precipitation Empore disk as precipitation surfaceslowprecipitation,Emporediskasprecipitationsurface• Thorium interference (problem, especially GS): anionexchange pretreatment• For atomic counting, extraction is more difficult, usuallyrequiring a carbonate matrix precipitation and anion- andcation-exchange resin purificationsexchangeresinpurificationsManganese Dioxide or Other Resin Extraction(usually completed directly in the field)• Mostly used for DCC, but has been tested with success forall counting techniquesYi ld f i d b i l i i•Yieldoften estimatedby comparing relative concentrationson successive resin cartridges•Spiking directly of cartridges with Ra, Th isotope solutionsSpikingdirectlyofcartridgeswithRa,Thisotopesolutionsadded to cartridge with slow drip• Acidic and reducing waters (deep brines?) are limited byh i f h id O i d lk lithe properties ofthe manganese oxide;Oxic andalkalinewaters are optimal•Isotope specific resins being developed are more expensiveIsotopespecificresinsbeingdevelopedaremoreexpensive–yields from brines would still need to be demonstratedYield Monitoring• Ba-133 for any sulfate salt co-precipitate counted byGamma-spectroscopyD d i ld i h hi h C S l di f-DecreasedyieldwithhighCa,Sr waters; alsodivergentfromRa yield in such waters•Ra-228 and Th-229 tracers for Ra-226 and Th-228 for228andTh229tracersforRa226andTh228foratom counting (TIMS, MC-ICP-MS)-Ba interference: no easy fix-organic compounds could be especially a problem for thebrines; needs additional periods of thermal degassing forTIMS