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N_TOF fission data of interest for ADS

N_TOF fission data of interest for ADS. Nuclear data needs. Simulation and design of Gen-IV and ADS systems require accurate nuclear data Current data libraries present important discrepancies and lacks. Fission Cross Sections. 1eV. 1MeV. Neutron Capture.  decay. Thorium fuel.

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N_TOF fission data of interest for ADS

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  1. N_TOF fission data of interest for ADS

  2. Nuclear data needs • Simulation and design of Gen-IV and ADS systems require accurate nuclear data • Current data libraries present important discrepancies and lacks.

  3. Fission Cross Sections 1eV 1MeV

  4. Neutron Capture  decay Thorium fuel • 232Th + n  233Th  233Pa  233U (fissile) 232U 233U 234U 235U 236U 237U 238U 231Pa 232Pa 233Pa 234Pa 235Pa 230Th 231Th 232Th 233Th 234Th

  5. Experimental Campaign • A set of measurements of neutron-induced fission in actinides was launched within the FP5. • Fission measurements in the framework of the n_TOF Collaboration and construction of the n_TOF facility.

  6. n_TOF facility

  7. Fission Chambers @ n_TOF PPAC chamber FIC chamber

  8. … n_TOF Fission Ionization Chamber Assembly Ionization chamber Gas used: Ar (90 %) CF4 (10 %). Gas pressure: 720 mbar Electric field: 600 V/cm Gap pitch: 5 mm Deposit diameter: 5 cm Deposit thickness: 125 µg/cm Support thickness: 100 µm (Al) Deposits on both sides. Electrode diameter: 12 cm Electrode thick.: 15 µm (Al) Windows diameter: 12 cm (KAPTON 125 µm)

  9. Inside FIC1 Photo 2

  10. List of Targets ----FIC0---- 235U - 47mg (3 targets) 238U - 110mg (3 targets) 232Th - 80mg (2 targets) 236U - 20mg (2 targets) 237Np - 10mg (1 target) 234U - 34mg (6 targets) ----FIC1---- 235U - 30mg (1 targets) 238U - 90mg (2 targets) 241Am - 2mg (4 targets) 243Am - 10mg (4 targets) 245Cm - 2mg (2 target) 233U - 20mg (2 targets)

  11. Some FIC results

  12. Fission Chambers @ n_TOF PPAC chamber FIC chamber

  13. PPAC setup

  14. PPACs @ n_TOF • 10 detectors 9 targets • U-234(2) and Th-232(5) • Two reference targets: U-235 y U-238 • Less than 1 % of flux attenuation in the full setup.

  15. Measured isotopes • Minor actinide : 237Np • Thorium cycle : 233U, 234U, 232Th • Spallation target : 209Bi, natPb • Reference isotopes : 235U, 238U

  16. Fission Detection Setup • Fissile target in a thin backing sandwiched by two detectors  Detection of both fission fragments in coincidence. • Fission event reconstruction: target position and emission angle. Efficiency limited by the cut at large angles.

  17. U-234: singles U-234: coincidences Discrimination with coincidences

  18. Cathode Positioning (I) • Positioning by using stripped cathodes and delay line readout. • The cathode signal is split in the delay line and transmitted to both ends Stripped Cathode Delay Line

  19. Cathode positioning (II) Diagonal condition: (Tch1-Tanode)+(Tch2-Tanode)=DLT DLT: Total delay line length (~320 ns) The time difference between both cathode ends provides the position of the signal.

  20. Targets (I) Epoxy frame Uranium target 80 mm Ø 300 µg/cm2 2 µm Al backing

  21. Targets (II) • Measurement of thickness and homogeneity by alpha counting and/or proton scattering. • High purity samples (> 99 % for U-234). 234U Y (mm) X (mm)  activity

  22. The n_TOF Data Acquisition System • The n_TOF DAQ consists of 54 flash ADC channels with 8 bit amplitude resolution and sampling of 500 MSample/s. • The full history of EVERY detector (BaF2 crystals and monitors) is digitised during a period of 16 ms (0.7 eV < En < 20 GeV) and recorded permanently on tape. Very useful feature since the raw data can be always re-investigated. • The system has nearly zero dead time. • 7.5 TB disk space for temporary storage. • Typical data rate of 2-3 TB/day on tape after compression. • Pulse shape analysis is performed on the fly at the LXBATCH Linux Batch Farm at CERN (30 CPUs exclusively dedicated) and stored in highly compressed Data Summary Tapes. • Quasi on-line analysis of the data with full statistics. One of the big successes of n_TOF. Many TOF facilities are following the n_TOF example and moving to digital electronics!

  23. PPAC signal analysis • Negative loop should be first • Xpos-Xneg < constant • const1 < Hneg/Hpos < const2

  24. HFF LFF Light vs. Heavy Fission Fragments Target 0 Energy < 10 MeV (Assymetric fission)

  25. Light vs. Heavy Fission Fragments Cathode signals for En around 1 MeV

  26. Cross Section Analysis •  (E): fission cross section • n (x,y,E): fission rate obtained from raw data •  (x,y): surface density of the target •  (E): detection setup efficiency a(x,y,E)/ b(x,y,E) ≈ 1 ± 0.01 (1%)

  27. 50º 50º Angular acceptance Simulations Measurements

  28. Log E =6.0 Log E =5.8 Log E =5.9 Cos () Cos () Cos () Log E =5.4 Log E =5.6 Log E =5.5 Fission Fragment Angular Distribution U-234 FFAD for neutron energies near the fission threshold

  29. Dependence of anisotropy with energy 238U

  30. Y (mm) X (mm) n_TOF beam at fission campaign • Neutron spectrum in the whole energy range. • Beam profile

  31. Th-232 results

  32. U234(n,f) U234 resonances

  33. 234U Previous data (IRMM report) Better energy resolution achieved at nTOF

  34. Np237(n,f) Np237 resonances

  35. Conclusions • The coincidence method has been used to obtain the fission results for the extensive n_TOF neutron energy range. • Th233, U234, Np237 results have been already produced and U233 is in progress. • Important discrepancies have been found in the Np237 resonance region.

  36. Fission Chamber @ n_TOF PPAC chamber FIC chamber

  37. n_TOF CERN

  38. FIC Design • Gas – Ar 90%+CF4 10% • Pressure – 600 mbar • Distance – 5 mm • HV – 300 V • 17 targets in the beam • “noise” electrode

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