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LUND UNIVERSITY Department of Medical Radiation Physics

SIMS technique and its application for hot particle characterisation

Ylva Ranebo

PhD student currently at Medical Radiation Physics ­ the Radioecology group previously at Institute for Transuranium Elements (ITU), Joint Research Centre, Karlsruhe, Germany ­ Nuclear Chemistry unit & Nuclear Safeguards and Security unit

17/11/2009 Ranebo

Outline of presentation

Secondary ion mass spectrometry

· ·

Some technique background and its principles Examples of SIMS applications in particle studies

­

Nuclear Safeguards ­ IAEA working in verifying countries nuclear activities are in accordance with the NPT treaty and the countries` declarations Characterization of hot particles from contaminated areas

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Some analytical difficulties

SIMS instrumentation at ITU

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Secondary ion mass spectrometry (SIMS) ­ schematic illustration

Secondary part ­ mass analyser Primary part ­ producing the primary beam accelerated towards the sample

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Secondary ion mass spectrometry (SIMS) ­ schematic illustration

Secondary part ­ mass analyser Primary part ­ producing the primary beam accelerated towards the sample

Sample substrate: carbon planchet Ø = 2.5 cm

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SIMS ­ Secondary ion mass spectrometry Principle

· · ·

Primary beam of ions (O, Ar, Cs) Produce ions from a solid sample - sputtering Secondary ions transferred into mass analyser

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SIMS ­ Secondary ion mass spectrometry Principle

· · ·

Primary beam of ions (O, Ar, Cs) Produce ions from a solid sample - sputtering Secondary ions transferred into mass analyser

Work modes

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Static ­ only the most superficial layers of the sample are analysed Dynamic ­ larger depth of the sample is analysed

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SIMS ­ What kind of information can be obtained

· · · · ·

Imaging ­ mass filtered ion microscope Depth profiling ­ isotopic content vs. the depth of the sample Mass spectrum Isotopic ratios ­ relative information, semi quantitative analysis Line scans

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Uranium Particle analysis in Nuclear Safeguards

IAEA Safeguard inspectors perform environmental sampling Fission track ­ Thermal ionisation MS

Swipe samples - Billions of dust particles sampled on pieces of cloth

Samples sent to laboratories for Fission Track / TIMS and SIMS analysis SIMS

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U Particle analysis in Nuclear Safeguards

The aim ·Analyse the isotopic content of U particles ·Reflects past history of the facility ·Nuclear weapons production? An effective method ·Fine particles released at handling of material ·Particles representative of orginal material ·Particles are highly mobile ·Difficult/impossible to clean up or remove U classification 235U enrichment Natural 0.7%, depleted < 0.7%, nuclear fuel 3-5%, weapons material >20%, weapons grade >90%

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SIMS particle analysis in Nuclear Safeguards

TASK Search through billions of particles to find the particles of interest Each particle has to be analysed individually "A needle in a hay-stack"problem Make precise and accurate measurements of both major and minor uranium isotopes SIMS + Timeliness and throughput + Ability to locate the particles - Poor accuracy and precision in samples with background interferences

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Why improve the analysis?

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Extremely small amounts <10-12 g gives LOW signal CAMECA 4f at ITU

Minor isotopes - Interfering elements

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Analysis of hot particles of uranium and plutonium Characterization of hot particles from accidents with nuclear weapons ­ Thule/Greenland & Palomares/Spain · What kind of information can be obtained? · What are the limitations?

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SIMS characterization of hot particles (HPs)

SIMS depth profiling isotopic content of uranium and plutonium Depth ~ 5 m Constant 235U/238U ratio and varying 240Pu/239Pu inside a HP Before SIMS

After SIMS

Particle depth (a.u.)

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SIMS characterization of hot particles (HPs)

· ·

Estimated depth: ~ 10 m Varying 235U/238U ratio and constant 240Pu/239Pu inside a HP

Particle depth (a.u.)

Particle depth (a.u.)

After dp

Tilted

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SIMS characterization of hot particles (HPs)

· ·

235U/238U

vs. 240Pu/239Pu U of weapons usable grade, Pu of weapons grade (> 90%)

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SIMS: Analytical challenges in HP studies

Hydride formation leading to mass interference 236U affected in uranium spectra Peak stripping method

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SIMS: Analytical challenges in HP studies

Unknown hydride interference Solution: Estimate uncertainty in isotopic ratios due to the hydrides

Method, conservative overestimation: · Assume no 236U present m/z=236 only 235UH · Peak stripping 1, Uranium · Assume PuH = UH · Peak stripping 2, Plutonium

Overestimated case · 235U/238U uncertainty < 0.01% due to hydrides · 240Pu/239Pu uncertainty ~ 10-40 % due to hydrides

PuH have shown similar behaviour as UH (Simons, 1999, Stoffels et al., 1994) 17/11/2009 Ranebo

SIMS Results: U/Pu depth profiles

· · ·

Varying rel U:Pu ratios inside a HP, semi quantitative ratios: RSF! RSF = Relative Sensitivity Factor RSF = 2.4

Particle depth (a.u.)

Particle depth (a.u.)

After SIMS

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Summary

What kind of information have been obtained? - SIMS isotopic fingerprinting: hot particles of U weapon usable-grade and Pu weapon grade - SIMS "detailed" isotopic fingerprinting, ~ nm scale: U and Pu compositions, semi quantitative U:Pu distributions, RSF U:Pu = 2.4 - Depth profile of the isotopic content · What are the challenges - SIMS: Hydride interferences affecting Pu analysis, U not - SIMS: semi Destructive

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Thank you for your attention!

And thanks to all co-workers! Elis Holm, Mats Eriksson, Magnus Hedberg, Gertie Johansson, Per Roos, Fredrik Henricsson, Nicole Erdmann, Olivier Bildstein, Nedialka Niagolova, Jussi Jernström, Gabriele Tamborini, Maria Betti, Jerome Himbert, Olivier Druinnhausen, Adrian Nicholl, Evelyn Zuleger, Pete van Belle, Sten Littman, Kaj Ljunggren, Martin Whitehouse, Kris Ingeneri, Rafael García-Tenorio, Mª Carmen Jiménez, J.García-López, Maria Wallenius, Klaus Mayer, Hartmut Thiele, Bert Cramer, Thierry Wiss, Klaus Lützenkirchen m.fl.

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Thank you for your attention!

Any questions?

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