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Motivations

This study aims to measure the angular distribution of fission fragments for 237Np and 232Th, providing valuable information on their spin properties. The angular distributions above 10 MeV are not well-known, and this research aims to fill this knowledge gap. Thin detectors, targets, and backings will be utilized, and the detection will be done in coincidence to discriminate fission events. By reconstructing the trajectory, the solid angle will be measured, despite the limitation of the accepted solid angle due to fragment stopping in electrodes. The detection efficiency will depend on the angular distribution cross-section measurement for 234U, which exhibits isotropic sideward peaking. By combining spins and orbital momentum, the angular distribution will vary with energy according to the vibrational resonances' (J, K). The experiment will take advantage of the full efficiency up to 45° and measure isotopes like 238U, 235U, and 232Th, allowing the evaluation of transferred momentum. The requested proton amount is 1.5 x 10^18, and flux ratios from 235U and 238U will be used. The ratios for 234U, 237Np, and 232Th will be measured against their mean values, along with the 238U/235U ratio and the cross-section measurements for 234U and 232Th.

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Motivations

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Presentation Transcript

  1. Motivations • Fission fragment angular distribution is an ingredient in the measurement of the fission cross section • Angular distribution gives information on the spin properties of fissionning nucleus • The angular distributions are not well known above 10 MeV

  2. f for 237Np

  3. Detection cell • Detection in coincidence of the 2 fragments (discrimination of fission) • Thin detectors, targets and backings • Limitation of the accepted solid angle (stopping of fragments in electrodes) • solid angle truncated but measured (trajectory reconstruction)

  4. Angle reconstruction (energy intervals) : 234U isotropic sideward peaking The detection efficiency depends on the angular distribution cross section measurement

  5. f for 234U

  6. Angular distribution : combination of spins • Basically : • J combines incident spins and orbital momentum • K projection along fission axis • If K << J forward peaking • If K ~ J sideward peaking (even-even nucleus) • The angular distribution may vary quickly with the energy according to (J,K) of the vibrational resonances

  7. Poor knowledge above 10 MeV 237Np 232Th nTOF well suited for describing the quick variations with energy

  8. 232Th Spallation domain ? Tutin et al., NIM A457 (2001) 646 Need to confirm the high anisotropy of 232Th at high energy

  9. Experiment • Take advantage of the full efficiency up to 45° • First isotopes to be measured : 238U, 235U, 232Th • Possibility of measurement of transfered momentum • Requested amount of protons : 1.5 1018

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

  11. Ratios : 234U target1/target0

  12. Ratios : 237Np targeti/mean

  13. Ratios : 232Th targeti/mean

  14. 238U/235U ratio

  15. f for 234U

  16. f for 232Th

  17. 232Th case : comparison to others

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