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Fission cross section measurements with a coincidence method

Fission cross section measurements with a coincidence method. Measured isotopes : 233 U, 234 U, 232 Th, 237 Np, and 209 Bi, nat Pb References : 235 U and 238 U. Focus on isotopes with several targets : 234 U (2 targets), 232 Th (5 targets), 237 Np (4 targets). Detection layout.

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Fission cross section measurements with a coincidence method

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  1. Fission cross section measurements with a coincidence method • Measured isotopes : 233U, 234U, 232Th, 237Np, and 209Bi, natPb • References : 235U and 238U • Focus on isotopes with several targets : 234U (2 targets), 232Th (5 targets), 237Np (4 targets)

  2. Detection layout

  3. Solid angle acceptance 237Np : 10 MeV < En < 15 MeV (2 targets) Target 1 Target 2

  4. f for 234U

  5. 238U/235U ratio

  6. f for 237Np

  7. Corrected counting rate of 237Np targets

  8. Raw counting rate of 237Np targets

  9. Raw counting rate of 232Th targets

  10. f for 237Np (raw)

  11. f for 232Th (raw)

  12. 238U/235U ratio (raw)

  13. Conclusion • The efficiency at 0° is lower than 1 when all localisation signals are • requested (unexpected) • The cross section based on anode signals is more reliable, and a • good reproducibility is obtained for different targets • Not protected against variations of angular distribution (between • 0.5 MeV and 50 MeV), and need of a normalisation factor. • A cross section accuracy better than 10% can probably be achieved

  14. Selection of fission Singles Coincidence

  15. Use of FADCs : pile up resolution 50 channels 500Ms/s Original signals - anode (black) - cathode right (red) - cathode left (green) Signals after filtered derivative (convolution)

  16. Use of FADCs : noise reduction Original signals Signals after filtered derivative (convolution)

  17. Energy resolution 235U around 10eV ( scaled and compared to ENDF) 234U around 570eV

  18. Targets • Thin layer (0.3mg/cm2) of 8cm in diameter • Electrodeposition on Al backing (2m thick) 234U Measured isotopes 237Np, 233U, 234U, 232Th, 209Bi, natPb Reference isotopes : 235U, 238U

  19. Emitting point distribution on the target 234U fission α activity Targets with Ø=8cm 209Bi natPb Extended targets

  20. Flux from 235U and 238U (JENDL above 20 MeV)

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