1. Measurement of the 240 Pu(n,f) cross-section at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) A. Tsinganis 1,2, N. Colonna 3, R. Vlastou 1, P. Schillebeeckx 4, A. Plompen 4, J. Heyse 4, M. Kokkoris 1, M. Barbagallo 3, E. Berthoumieux 5, M. Calviani 2, E. Chiaveri 2, A. Stamatopoulos 1 and the n_TOF Collaboration 1 National Technical University of Athens (NTUA), Greece 2 European Organisation for Nuclear Research (CERN), Geneva, Switzerland 3 Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Bari, Italy 4 JRC-IRMM, Geel, Belgium 5 Commissariat à l'énergie atomique (CEA), Saclay, France 14 th International Conference on Nuclear Reaction Mechanisms Varenna, June 15-19, 2015

2. Outline  Introduction and motivation  The n_TOF facility and Experimental Area II  Experimental setup  A first look at the data  Summary Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015

3. Introduction  Pu isotopes have the biggest contribution to the long-term radiotoxicity and heat output of nuclear waste (even after 10 5 years)  Low burn-up efficiency in conventional reactors…  …but a more efficient reduction of the Pu and actinide inventory is possible in Generation-IV reactors (or ADS) with a fast neutron spectrum  Accurate knowledge of these cross-sections is essential  An (n,f) measurement on 240 Pu  Included in the NEA Nuclear Data High Priority Request List  Proposal CERN-INTC-2014-0451/ INTC-P-418 (05/06/2014)  https://cds.cern.ch/record/1706708/files/INTC-P-418.pdf https://cds.cern.ch/record/1706708/files/INTC-P-418.pdf  Already attempted in EAR-1 along with 242 Pu  Very long measurement  Sample-induced damage to detectors  Very poor α – FF separation Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 3

4. The n_TOF facility

5. The CERN n_TOF facility: a spallation neutron source  Pulsed proton beam (20 GeV) provided by PS  ~ 7x10 12 protons per bunch  7 ns width (r.m.s.)  Low repetition rate (<0.8 Hz)  No neutron bunch overlap  Water-cooled lead target (40 cm length, 60 cm diameter)  Cooling layer (1 cm)  Moderator layer (4 cm)  H 2 O (demineralised water)  H 2 O + H 3 BO 3 (boric acid, enriched in 10 B) Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 5

6. The CERN n_TOF facility: a spallation neutron source  High instantaneous flux  High energy resolution  Wide neutron spectrum (thermal to GeV)  Experimental Area I (EAR-1)  Type-A Work Sector  can handle unsealed radioactive samples  Neutron beam-line  Sweeping magnet  Shielding  Two collimators Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 6

7. n_TOF Experimental Area II (EAR-2) h [m] 0 9.8 18.2 24.5 Beam Dump EAR-2 Exp. Hall 2 nd Collimator Magnet Pit Shielding Target 1 st Collimator Filter Box Shielding To EAR-1 Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 7

8. Neutron flux gain – EAR-2 vs. EAR-1 x10-15x40-55x30-45 x7-10 x100-1000 Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 8

9. Experimental setup

10. Samples  Four samples received from IRMM  3 cm diameter PuO 2 deposit  0.25 mm aluminium backing (5cm diameter)  One 235 U reference sample ( ~ 90μg/cm 2 )  One 238 U reference sample ( ~ 110μg/cm 2 ) 240 Pu 238 Pu0.0733% 239 Pu0.0144% 240 Pu99.8915% 241 Pu0.00041% 242 Pu0.02027% 244 Pu0.000046% Total mass3.1mg Total activity25.7MBq Surface density (per sample) 0.10 – 0.13 mg/cm 2  Contamination found inside one sample container!  Sample not used! Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 10

11. Pu sample impurities  Dominant or measurable contribution from contaminants expected at certain energies Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 11

12. The Micromegas detector  MICRO-MEsh GAseous Structure  “Microbulk” variant  Low amount of material to minimise neutron interactions  Drift space  Primary ionisation and charge drift  Micromesh  Amplification region  Charge multiplication and read-out ~35 μ m ~50 μ m Courtesy A. Teixeira (CERN) Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 12

13. Setup in EAR-2  Chamber, sample holders, electronics reused from EAR-1 measurement  Chamber filled with circulating Ar:CF 4 :isoC 4 H 10 gas (88:10:2, 1 bar)  500 MHz sampling rate  16ms acquisition window  Lower energy limit ~ 7 meV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 13

14. First results

15. Amplitude spectra Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 15 235 U 240 Pu

16. Amplitude spectra: EAR-2 vs. EAR-1  Extremely improved conditions  Increased flux  higher fission rate  Better background suppression Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 16

17. Amplitude vs. E n – 235 U Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 17

18. Amplitude vs. E n – 240 Pu Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 18

19. Fission counts (2000 bins per energy decade) 235 U 240 Pu L = 19.2m Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 19

20. Subtracting contaminant contribution Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 20

21. A more detailed look... 0.1-10eV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 21

22. A more detailed look... 10-100eV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 22

23. A more detailed look... 100eV-1keV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 23

24. A more detailed look... 1-10keV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 24

25. A more detailed look... 3-30keV Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 25

26. Libraries: room for improvement NEA request range Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 26

27. Summary  As expected/hoped, the 240 Pu(n,f) measurement is feasible in EAR-2, despite the difficulties encountered in EAR-1  Many resonances visible, with structure observed also in the sub- threshold region, upper energy limit of at least a few MeV  Raw data analysis still to be optimised, detailed Monte-Carlo simulations of the neutron beam geometry and experimental setup will be performed etc.  These preliminary results highlight the usefulness and performance of EAR-2 for fission measurements of highly radioactive isotopes Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 27

28.  Thank you for your attention!

29. Detector gain & drift field optimisation Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 29

30. Detector response – γ-flash treatment  2D-histogram created with superposition of several bunches  Initial γ-flash signal (hundreds of ns)  Small oscillation follows (considerably lower than in EAR-1)… not negligible!  Subtraction of an “average” γ-flash signal from each raw data “movie” Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 30

31. Pulse-shape fitting  Average pulse-shape Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 31

32. Raw data analysis Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 32

33. Amplitude spectra (full and restricted range) Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 33 FULL RANGE >100keV

34. Statistical uncertainty @50bpd – 240 Pu Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 34

35. Monte-Carlo simulations  Simplified geometry created in FLUKA  Simulation of samples and active detector volume  Appropriate distributions of α-particles and fission fragments created inside the sample  Fission fragment distributions obtained from the GEF (GEneral Fission) code using an n_TOF-like neutron spectrum Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 35

36. Monte-Carlo simulations  Simplified geometry created in FLUKA  Simulation of samples and active detector volume  Appropriate distributions of α-particles and fission fragments created inside the sample  Energy deposition along y-axis is scored event-by-event  Electron drift velocity calculated for given gas mixture as function of drift voltage using GARFIELD  …we can thus calculate the current reaching the readout electrode (dQ/dt)  …and reproduce signals by applying appropriate shaping Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 36

37. Simulated amplitude spectra  Amplitude spectrum after smoothing, compared with experimental spectrum  (from 242 Pu measurement in EAR-1) Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 37

38. Plutonium in nuclear waste  Pu isotopes have the biggest contribution to the long-term radiotoxicity and heat output of nuclear waste (even after 10 5 years) Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 38

39. Plutonium in nuclear waste  Low burn-up efficiency in conventional reactors…  …but more efficient reduction of the Pu and actinide inventory in Generation-IV reactors (or ADS) with fast neutron spectrum  Accurate knowledge of these cross-sections is essential Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 39

40. The measurement  An (n,f) measurement on 240 Pu  Included in the NEA Nuclear Data High Priority Request List  Proposal CERN-INTC-2014-0451/ INTC-P-418 (05/06/2014)  https://cds.cern.ch/record/1706708/files/INTC-P-418.pdf https://cds.cern.ch/record/1706708/files/INTC-P-418.pdf  Already attempted in EAR-1 along with 242 Pu  Very long measurement  Sample-induced damage to detectors  Very poor α – FF separation Measurement of 240 Pu(n,f) at the CERN n_TOF facility: first results from Experimental Area II (EAR-2) 14 th International Conference on Nuclear Reaction Mechanisms – Varenna, June 15-19, 2015 40