Angular distributions in the neutroninduced fission of actinides
Angular distributions in the neutron-induced fission of actinides (extension) Extension to experiment INTC-P-209 Angular distributions in the neutron-induced fission of actinides L. Tassan-Got, L. Audouin, M. Mac Cormick, IN 2 P 3/IPN Orsay-France C. Paradela, I. Duran, D. Tarrio, USC-Spain V. Vlachoudis, CERN and the n_TOF collaboration L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Motivations • Fission fragment angular distribution is an ingredient in the measurement of the fission cross section (detector efficiency) • Angular distribution gives information on the spin properties of fissionning nucleus • Information on angular momentum deposition in the spallation domain • The angular distributions are not well known above 10 Me. V L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Poor knowledge above 10 Me. V n. TOF well suited for describing the quick variations with energy L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Spallation domain ? 232 Th Tutin et al. , NIM A 457 (2001) 646 Need to confirm the high anisotropy of 232 Th at high energy L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Experiment • Take advantage of the full efficiency up to 45° • Isotopes to be measured : 238 U, 235 U, 232 Th • Requested amount of protons : 1. 5 1018 L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) New situation : Working Sector A at n_TOF • Possible accomodation of more radioactive isotopes • Interesting isotopes for fission fragment angular distributions : 234 U and 237 Np L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Configuration modification • 9 targets interleaved with 10 PPAC • Original configuration : 7 x 232 Th, 1 x 235 U, 1 x 238 U Beam time : 1. 5 1018 protons • New configuration : 2 x 234 U, 1 x 237 Np, 4 x 232 Th, 1 x 235 U, 1 x 238 U Beam time : 2. 0 1018 protons L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Counts for 232 Th • 4000 counts per energy bin in region of interest • 70 bin/decade around 1. 6 Me. V L. Tassan-Got & the TOF collaboration 30 bin/decade around 6. 8 Me. V INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) Counts for 234 U • 4000 counts per energy bin in region of interest • 70 bin/decade around 0. 45 Me. V (oscillations in anisotropy) L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) 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 target nucleus) • The angular distribution may vary quickly with the energy according to (J, K) of the vibrational resonances L. Tassan-Got & the TOF collaboration INTC 23/06/2010
Angular distributions in the neutron-induced fission of actinides (extension) 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) L. Tassan-Got & the TOF collaboration INTC 23/06/2010
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