Validation of radiochemical methods for the determination of difficult-to-measure nuclides using LSC Nóra Vajda, Zsuzsa Molnár, Edit Bokori, Szabolcs Osváth*, Dénes Párkányi**, Mihály Braun*** RADANAL Ltd., Budapest, 1121 Hungary National Research Directorate for Radiobiology and Radiohygiene (OSSKI), Budapest, 1221 Hungary Centre for Energy Research, Hungarian Academy of Science (MTA EK), Budapest, 1121 Hungary ISOTOPTECH Zrt., Debrecen, 4026 Hungary LSC 2017, Copenhagen, May 1-5, 2017
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Validation of radiochemical methods for the determination of difficult-to-measure nuclides
High detection efficiency (close to 100 %) Quench effect – quench correction possibilitiesNo absorption/self-absorption Poor energy resolution (around 10 %)
Continuous nature of β decay/spectra
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Channel No.
LSC spectrum of a processed waste sample
Sample, tSIE=204
BG, tSIE=290
ANALYTE
BACKGROUND
Which analyte?3H – 18 keV
63Ni – 67 keV151Sm – 77 keV
93Zr – 90 keV85Sr, 59Ni, 55Fe …
LSC measurement
Chemical separation procedureHigh selectivity - to remove interfering nuclides
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Channel No.
LSC spectrum of a processed waste sample
Sample, tSIE=204
BG, tSIE=290
Which analyte?3H – 18 keV
63Ni – 67 keV151Sm – 77 keV
93Zr – 90 keV85Sr, 59Ni, 55Fe …
Method validation
by either or the combination of any the following techniques1. calibration using reference standards or reference materials, 2. inter-laboratory comparisons, e.g. PT3. systematic assessment of the factors influencing the result, 4. assessment (of the uncertainty of the results) based on scientific understanding
of the theoretical principles of the method and practical experience,5. comparison of results achieved with other methods
ISO/IEC 17025 (2005): General requirements for the competence of testing and calibration laboratories
90Sr determination
Nuclide Half-life Decay βMax Specific
mode activity
keV Bq/g
90Sr 29.1 y β− 546 5,04E+12
90Y 64 h β− 2280 2,01E+16
Standard validation techniques:1. Use of CRM, 2. Participation in PTs3. Systematic assessment of the factors influencing the result - fish bone4. Assessment based on scientific understanding
Validation issue5. No good independent method for validation
Validation of the method for Radiostrontium determination
Conclusions
90Sr results can be validated by measurement of reference materials, byparticipation in inter-laboratory comparisons.
It is important to assess all influencing factors, such as the presence of other Srand Y isotopes, or other possible contamination (radionuclides of K, Ba, Pb) byperforming ingrowth/decay measurements as part of method validation.
93Zr determination
Validation issues: No 93Zr standardNo reference materialNo intercomparison exercise
Validation option:comparison of independent methods: LSC
ICP-MS
Nuclide Half- life Decay βMax Specific Occurance/
mode activityfield of application
keV Bq/g93Zr 1,53106 y β− 90 9,27E+07 DN WD
Carrier free tracers by NAA of UPurification on UTEVA γ spectrometry
Repeated separation on UTEVAto purify Zr
Yield: Zr: 60-90%Fluctuating significantly due to Zradsorption to surfaces.
Sample Net intensity Net intensity Ni-63 intensity Ni-63 Ni-63 Ni-63 Ni-63 Cu Nicode at mass 63 at mass 65 corrected concentration activity activity activity concentration concentration
(Ni-63+Cu-65) (Cu-65) for Cu-63 concentratio oncentratio oncentratio in waste* in wastecps cps cps ppb Bq/mL Bq/L waste Bq/L waste ppb ppm