Hot particle measuring techniques and applications. Mats Eriksson IAEA-MEL

Transcription

1 Hot particle measuring techniques and applications IAEA-MEL

2 Log-normal Particle size distribution Material dispersed after an explosion Mineral resources in the earth crust Pollutants in the air Log normal distribution - Size relation to Mass/Activity; Few large sized particles carry the majority of the mass released. Two ways of characterizing lognormal distributions, in terms of the original data (a) and after log-transformation (b).

3 Hot Particles 1.3 % of the particles carry 80% of the activity 1 Bq Pu particle diameter of 20µm Why Study Hot Particles? R.Pöllänen. Ph.D thesis, 2002 Formed in events involving explosions (e.g. the Chernobyl and the Thule accidents) and at nuclear installations (power and reprocessing plants) They carry the main fraction of the mass released, however they are very rare, leading to heterogeneous activity distribution Mostly a close-in fallout problem Contain some geochemical memory! However, a needle in a haystack problem

4 Focus on Hot Particles Finding and Identification of them Image techniques (e.g. image plates, beta camera, SEM, ) Analytical techniques SEM-EDX Synchrotron radiation techniques and PIXE µ-xrf µ-xrf tomography and µ-xanes Gamma and alpha spectrometry SIMS and ICP-MS

5 The Thule accident B-52 bomber, HOBO January, 1968 Particles spread to the marine and terrest enviroment The last flight path of HOBO 28

6 Arctic food web

7 Hot Particles Effects of ingestion is not well described and the dosimetry is complex and not well understood One study (B. Salbu, conf. proc., year 2002) on cheep have shown that 2 of 7 particles where incorporated in the GI tack of 2 animals. Also Dahlgaard et al, 2001, seen a similar effect in benthic biota. Surface chemistry unknown, related do dissolution rates of the particles Focus on particles consisting of alpha emitting radionuclides (e.g. Pu, U particles)

8 HR Pu Hot Particle 241 Pu T ½ =14.4y β Am T ½ =432y α γ : 59.5 kev 237 Np T ½ = y Hot particle separation technique Sampling splitting Fixation on adhesive carbon tape Tritium image plates Measurements for identification IDE Bioscope Beta camera 1 week exposure time 20 h acquisition time 1 h acquisition time

9 SEM EDX WDX Find position Morphology and elemental information: Simulation program DTSA From NIST sion/outputs/dtsa/dtsa.htm 1.40E E E E E E E E %Pu 50%U

10 What is Synchrotron Light Synchrotron light is the electromagnetic radiation emitted when electrons, moving at velocities close to the speed of light, are forced to change direction under the action of a magnetic field. The electromagnetic radiation is emitted in a narrow cone in the forward direction, at a tangent to the electron's orbit. Synchrotron light is unique in its intensity and brilliance and it can be generated across the range of the electromagnetic spectrum: from infrared to x-rays.

11 Properties of synchrotron light Synchrotron light has a number of unique properties. These include: High brightness: synchrotron light is extremely intense (hundreds to thousands of times more intense than that from conventional x-ray tubes) and highly collimated. Wide energy spectrum: synchrotron light is emitted with energies ranging from infrared light to hard x-rays. Tunable: it is possible to obtain an intense beam of any selected energy. Highly polarised: the synchrotron emits highly polarised radiation, which can be linear, circular or elliptical. Emitted in very short pulses: pulses emitted are typically less than a nano-second (a billionth of a second), enabling time-resolved studies.

12 SR-Fluorescence and Absorption Spectroscopy Fluorescence Spectroscopy: * elemental mapping (microfocused beam size mode) * high sensitivity to low concentrations (primary white light beam with its high flux mode) Absorption spectroscopy, elements between Al and Am: * information about the local atomic geometry (EXAFS) * chemical state of the absorbing atom (XANES). * investigations on ordered (crystalline) and disordered (amorphous, liquid) materials. Advantages * Nondestructive, surface / volume sensitive, * Multiple X-ray techniques with microfocus without sample remounting * Spectroscopy from light elements (Al) to Am at a single beamline

13 Why and how can these synchrotron techniques be used for radioecology studies Preferential leaching was observed in a time-series on totally dissolved U/Pu particles Mixed U/Pu particles, ICP-MS destructive, SR not! Uranium cross contamination not a problem in SR Homogenity of the particles? Preferential leaching (surface effects) Oxidation state determination, geochemical behaviour

14 Beam Line L in HASYLAB, and the micro confocal XRF setup

15 X-ray Fluorescent computer tomography (XFCT)

16 Synchrotron 3D XRF setup at ANKA The IAEA set-up at the synchrotron beamline

17 µ-xrf, X-ray attenuation I=I 0 exp(-µ en /ρ x) x [µm] I/I Scan Detector Fluorescence from all the elements -µ en /ρ = 73.9 cm 2 g -1 (22 kev) ρ 11 g cm -3 (80%UO 2 +20%PuO 2 ) Experiment set-up Irradiated volume I I 0 Monochromatic beam, Size: 2-20 micrometer Fluorescence from all the elements Monochromatic beam, Size~20 micrometer

18 SR µ-xrf study 3D-information on a 2D-projection (elemental distribution) New information about the structure (attenuation)

19 From 2D to 3D with Confocal µ-xrf (add. Information)

20 µ- XRF Tomography Pu (blue), U (green) and Fe (red)

21 Absorption Spectroscopy information about the local atomic geometry (EXAFS) chemical state of the absorbing atom (XANES) investigations on ordered (crystalline) and disordered (amorphous, liquid) materials.

22 More XANES problems No standard technique to analyse the XANES spectra's White line energy Fitting oxidation standard spectra's Fitting white line, first multiple scattering peak and the edge Polynomial fit, inflection point from df 2 /de 2 =0 Edge energy matrix dependent

23 Even more XANES problems (Radiolysis chemical changes)

24 XANES spectra's of some Thule HP Pu in the particles in the +4 state. i.e. in the less mobile state

25 µ-xrf Confocal vs. bulk analysis Particle ID Pu/U ratio Relative Pu/U ratio (voxel derived) ( 1 SD) uncertainty (summed spectra ) (1 SD) Thu ± 0.02 ( n= 67 ) ± Thu 97-1 N.A. N.A 0.20 ± 0.01 Thu ± 0.03 ( n= 622 ) ± Thu ± 0.33 ( n= 414 ) ± Particle ID Pu/U ratio μ-pixe Pu/U ratio μ-xrf (summed spectra) ( 1 SD) (summed spectra ) (1 SD) Thu ± ± Thu ± ± 0.01 Thu ± ± Thu ± ± Frequency T , Pu/U Lalfa ratio mean=0.43 +/ (1 sd) mean=0.28 +/ (ex ratio >0.5) Pu/U Lalfa ratio

26 Characteristic L-x-ray, 241 Am( 241 Pu) to Pu Two spectra groups: P = n A solution: n -1 P = A Counts Energy [kev] Zoom Relatively Low 241 Am/ Pu 0.13 Relatively High 241 Am/ Pu 0.17

27 Alpha spectrometry and fitting program AASI Alpha fit

28 Alpha spectrometry Two 238 Pu/ 239,240 Pu ratio groups Average ratio: 0.014±0.004 (n=328) 241 Am/ 239,240 Pu ratio??

29 ICP-MS on bulk samples 240 Pu/ 239 Pu mass ratio

30 SIMS (next talk by Ylva) Isotopic fingerprint

31 SIMS Results-Isotopic Ratio Thu 68-1 Thu 68-5 Thu U/ 238 U 240 Pu/ 239 Pu 1,37 5, ,36 5, ,39 5, ,38 5, ,38 5, U/ 238 U 240 Pu/ 239 Pu 1,31 5, ,31 5, ,32 5, ,32 5, ,32 5, U/ 238 U 240 Pu/ 239 Pu 1,42 3, ,42 3, ,46 3, ,46 3, ,45 3, Typical uncertainties 235 U/ 238 U %; 240 Pu/ 239 Pu 0.5-1% Thu U/ 238 U 240 Pu/ 239 P u 1,31 5, ,31 5, ,31 5, ,30 5, Dept. 1,31of Nuclear 5,80 10 Sciences -2 and Applications Thu U/ 238 U 240 Pu/ 239 P u 1,046 2, ,040 2, ,040 2, ,046 2, ,044 2, Thu U/ 238 U 240 Pu/ 239 P u 0,974 4, ,980 4, ,980 4, ,980 4, ,974 4,

32 Combined techniques: SR and SIMS

33 A new source in Thule y x High 235 U enriched particles 235 U / 238 U = 8.2 ± 0.1 Frequency All U voxels Frequency U with Pu voxels log((u[log(u) > -2])) log((u[pu > 0.05 & log(u) > -2])) Pure U voxels All voxels Frequency Frequency

34 Combined techniques SIMS depth profile Time [s] 5.4 µ-xanes Fig. 3. This figure shows the U (red-yellow pixel image) and the Pu (the superimposed iso-intensity lines) distribution in one crosssection of the particle shown in Fig 2. A line profile of the Pu/U ratio is also shown (blue line in the figure). The Pu/U ratio is multiplied by a factor of 100. C B Area A B C Rel Pu L3 Shift to Pu(+3) 1.74 ev 1.88 ev 0.88 ev A

35 Conclusions PARTICLES are important to consider in radiological studies! Particles are Site specific and difficult to extrapolate results to other sites! The use of advanced analytical techniques for hot particle characterisation Image techniques (e.g. image plates, beta camera, SEM, ) An obligation Analytical techniques Gamma and alpha spectrometry An obligation SEM-EDX-WDX Almost an obligation Synchrotron radiation techniques and PIXE µ-xrf Very useful, need improvement µ-xrf tomography Very useful, need improvement µ-xanes Needs seriously improvement before applied SIMS Very useful, need improvement ICP-MS Very useful Leaching experiments should be conducted to support the theoretical conclusions.

36 Hot particles a hot topic Ph.D thesis R.Pöllänen. Ph.D thesis, Nuclear fuel particles in the environment - characteristics, atmospheric transport and skin doses. STUK-A188. Helsinki p. J. Jernström, Ph.D thesis, Development of analytical techniques for studies on dispersion of actinides in the environment and characterization of environmental radioactive particles, University of Helsinki, 2006 O. C. Lind, Ph.D thesis Characterisation of radioactive particles in the environment using advanced techniques, Norwegian University of Life Sciences, 2006 M. Eriksson, On weapons plutonium in the arctic environment (Thule, Greenland), Riso-R-1321, Riso National Laboratory, Roskilde, Denmark, NEXT year Maria-Carmen Jimenez Ramos, Seville, Spain (Palomares particles)

37 Institute for Transuranium Elements Ylva Ranebo Nedialka Niagolova Olivier Bildstein G. Tamborini Maria Betti STUK R. Pöllänen SR Beam-line scientists: R. Simon (ANKA) G. Falkenberg (HASYLAB) Acknowledgements to: IAEA s XRF group : D. Wegrzymek Risø National Laboratory Henning Dahlgaard Jussi Jernström Per Roos CNA PIXE team, Sevilla M.-C. Jimenez Ramos R. Garcia-Tenorio J. Garcia Lopez