implementing a method for age determination of uranium ...chronometers • 230th/234u • 231pa/235u...
TRANSCRIPT
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Startbild med låst
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Foto: Försvarsmakten/David Gernes
Implementing a method for
age determination of
uranium using the 230Th/234U chronometer Anna Vesterlund, Petra Lagerkvist, Henrik Ramebäck
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Background
Nuclear forensics:
• What? Where from? Why?
• Comparative signatures
• Origin assessment
• Age determination – Predictive signature
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Chronometers
• 230Th/234U
• 231Pa/235U
• 214Bi/234U
• Assumptions
– Closed system
– No Th at t0
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Ingrowth and age
𝑁𝑇ℎ 𝑡 = 𝑁0𝑇ℎ𝑒−𝜆𝑇ℎ𝑡 −𝜆𝑈𝑁0𝑈
𝑒−𝜆𝑇ℎ𝑡 − 𝑒−𝜆𝑈𝑡
𝜆𝑇ℎ − 𝜆𝑈 𝑡 =
1
𝜆𝑈 − 𝜆𝑇ℎ∙ 𝑙𝑛 1 −
𝑁𝑟𝑒𝑓𝑇ℎ𝑁𝑟𝑒𝑓𝑈
𝜆𝑇ℎ𝜆𝑈− 1
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Outline of the method
1. Pre-analysis
2. Th separation
3. Measurement of 230Th and 234U
4. Calculations
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229Th tracer preparation
• No reference material certified
for 229Th mass
• In-house tracer
• Base material: IRMM-040a
• 229Th concentration
determined by reverse isotope
dilution with IRMM-060
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Thorium separation
• Based on Varga et al. – Varga Z., Surányi G., Production date
determination of uranium-oxide materials
by inductively coupled plasma mass
spectrometry, Anal. Chim. Acta, 599
(2007) 16-23
– Varga Z., Wallenius M., Mayer K., Hrnecek
E., Alternative method for the production
date determination of impure uranium ore
concentrate samples, J. Radioanal. Nucl.
Chem., 290 (2011) 485-492
1. Sample: 2M HNO3
TEV
A
2 ml
2. Wash: 8 ml 2M HNO3
3. Th-elution: 0.75 ml 0.02 M HF/0.02 M HNO3
Discard
Th
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Thorium separation
• Evaporation and dissolution in
2 M HNO3
• Separation repeated once
1. Sample: 2M HNO3
TEV
A
2 ml
2. Wash: 8 ml 2M HNO3
3. Th-elution: 0.75 ml 0.02 M HF/0.02 M HNO3
Discard
Th
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Measurement
• Element XR with Twinnabar
spray chamber and Micromist
nebulizer
• IRMM-073/1 used for mass
bias correction
• All calculations, including
dead time correction done
post-acquisition
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Participation in REIMEP-22
• 20 mg uranyl nitrate
• Approx. 4% enrichment
• Reported date: 2012-07-15 ± 19 d
• Reference date: 2012-07-09 ± 7.8 d
• Reference material: IRMM-1000
Ref: Venchiarutti C. et al., REIMEP-22 U
Age Dating – Determination of the
production date of a uranium certified test
sample: Inter-laboratory comparison, Report
to participants, ISSN 1831-9424, 2015
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Conclusions
• Chemical yield about 40%
• Matrix for measurement not optimal
• Clean room environment not necessary
• Still, happy with the results!
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