1. Measurement of the 240 Pu(n,f) reaction cross-section at the CERN n_TOF facility EAR-2 47 th Meeting of the INTC CERN, June 25, 2014 A. Tsinganis 1, N. Colonna 2, R. Vlastou 1, P. Schillebeeckx 3, A. Plompen 3, J. Heyse 3, M. Kokkoris 1, M. Barbagallo 2, E. Berthoumieux 5, M. Calviani 4, E. Chiaveri 4, A. Stamatopoulos 1 and the n_TOF Collaboration 1) National Technical University of Athens (NTUA), Greece 2) Istituto Nazionale di Fisica Nucleare, Bari, Italy 3) European Commission JRC, Institute for Reference Materials and Measurements, Geel, Belgium 4) European Organisation for Nuclear Research (CERN), Geneva, Switzerland 5) Commissariat a l‘ Energie Atomique (CEA) Saclay - Irfu, Gif-sur-Yvette, France Spokespersons: A. Tsinganis, M. Kokkoris (NTUA) Technical Coordinator: O. Aberle (CERN)

2. Outline  Introduction and motivation  The 2010 240,242 Pu(n,f) proposal  The 240 Pu(n,f) measurement in EAR-1  Sample-induced damage to detectors  Advantages of EAR-2  Neutron fluence gain  Background suppression  Experimental  Samples, detectors etc.  Analysis  Software, simulations etc.  Beam request  Summary 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

3. The measurement in EAR-1: motivation  Proposal CERN-INTC-2010-042 / INTC-P-280 (21/05/2010)  An (n,f) measurement on 240,242 Pu  Both included in the NEA Nuclear Data High Priority Request List  Pu isotopes and minor actinides represent the main long-term contribution to waste radiotoxicity, persisting for ~ 10 5 y  240 Pu is produced in significant quantities in conventional reactors  Fission cross-sections of these isotopes are of great significance in the context of nuclear waste management and advanced nuclear systems, especially fast reactors (Generation IV, ADS)  Discrepancies ~ 10% exist above the fission threshold in 240 Pu data  Physics motivation has already been endorsed by the INTC  In addition, recent attempts at n_TOF and elsewhere within the ANDES project were not successful for different reasons 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014 1. ANDES: Accurate Nuclear Data for Nuclear Energy Sustainability, www.andes-nd.euwww.andes-nd.eu 2. Fission cross section measurements for 240 Pu, 242 Pu. Deliverable 1.5 of the ANDES project, DOI: 10.2787/81004 3. A. Plompen, “Minor Actinides, Major Challenges, the Needs for and Benefits of International Collaboration”, Nucl. Data Sheets (2014), Under publication

4. The measurement in EAR-1: detector degradation  An unexpected alteration of some detectors was observed after removal from the chamber  A distinct discoloration of the micromesh is visible in the 4 detectors used with the 240 Pu samples  Physical damage to the micromesh is visible under inspection with a microscope  A unique – if inadvertent – ageing test 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014 3cm Courtesy A. Teixeira (CERN)

5. The measurement in EAR-1: detector degradation  This leads to a deterioration of the electrical field  Separation of α-particles and fission fragments becomes impossible  A significant part of the data had to be discarded  Even under normal operation, the analysis would be challenging due to the long α-pile-up tail 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

6. The measurement in EAR-1: detector degradation  This leads to a deterioration of the electrical field  Separation of α-particles and fission fragments becomes impossible  A significant part of the data had to be discarded  Even under normal operation, the analysis would be challenging due to the long α-pile-up tail 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014 By comparison, 242 Pu…

7. Two experimental issues identified  Gradual deterioration of detector performance due to high current / high α-activity  Shorter measurement due to higher flux  High α-activity of the 240 Pu samples (>6MBq/sample)  Improved signal-to-background due to shorter acquisition window   Both issues can be addressed in EAR-2 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

8. Neutron fluence gain  Comparing EAR-2 (3cm diameter) with conditions of previous measurement in EAR-1 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014 x10-15x40-55x30-45 x7-10 x100-1000

9. Samples  Four 240 Pu samples manufactured at IRMM  3 cm diameter PuO 2 deposit  0.25 mm aluminium backing (5cm diameter)  The same samples used in the previous measurement 238 Pu0.0733% 239 Pu0.0144% 240 Pu99.8915% 241 Pu0.00041% 242 Pu0.02027% 244 Pu0.000046% Mass3.1mg Activity25.7MBq Surface density110 μg/cm 2 /sample 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014  Reference samples (to be manufactured)  235 U (≈ 70 μg/cm 2 )  238 U (≈ 340 μg/cm 2 )  Preferably of 3cm diameter to match the Pu samples  Could add 237 Np (≈ 60 μg/cm 2 ) as additional reference

10. Sample impurities 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014 NEA request range  Measurement unaffected by impurities above ~ 1keV and at selected resonances

11. Sample holders  Samples adapted to internal frame of the chamber  Samples kept in place by mechanical pressure only, “sandwiched” between to thin aluminium rings kept together by two-sided adhesive tape and two thick aluminium rings compatible with the chamber support frame.  Already designed & sample safety file in place 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

12. Experimental setup 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014  Detector chamber  Preamplifier module  Micromegas detectors  FINAL SETUP (picture from EAR-1)  Chamber support for EAR-2

13. Analysis software, simulations  Already developed for previous measurement  Peak-search routine, routine for high- energy data analysis etc....  Simulations of detector response: 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014  Simulated amplitude spectrum compared with experimental spectrum 

14. Beam request  2x10 18 protons on target  3-5 weeks, depending on beam delivery rate  240 Pu (435 μg/cm 2, 4 samples)  240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014  Statistical uncertainty  <3% above 10keV  <1% above 300keV  Expected systematic uncertainties ~ 3-4%  Detector efficiency  Amplitude threshold correction  Selected resonances will also be studied with good statistics

15. Summary  An important measurement  …especially in the light of recent not-so-successful attempts within ANDES  2x10 18 protons requested  Statistical uncertainty < 3% above 10keV, <1% above 300 keV  Improved conditions in EAR-2:  Shorter experiment (3-5 weeks) due to higher flux  Avoiding detector degradation  Shorter acquisition window  Stronger background suppression  Cross-check with different reference reactions  235 U(n,f), 238 U(n,f), 237 Np(n,f)  A useful study also for future measurements  Hardware already available  Procedures for Pu samples already in place  Analysis software already developed  Improvements, adjustments…  Could be ready to go on day 1  Only foreseeable delay could be sample manufacturing and transport  One PhD student (NTU Athens) starting in September 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

16.  Thank you for your attention… 240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014

17. Extra slides

18. Beam request  2x10 18 protons on target  Reference sample masses chosen to keep countrate <1 count/μs  235 U (70 μg/cm 2 )  238 U (340 μg/cm 2 )  240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014  237 Np (60 μg/cm 2 )

19. Beam request  2x10 18 protons on target  237 Np (60 μg/cm 2 )  240 Pu(n,f) measurement @ n_TOF EAR-2 47th INTC Meeting, CERN, June 25, 2014