Angular distributions in the neutroninduced fission of actinides

Angular distributions in the neutron-induced fission of actinides 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 Me. V L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides f for 237 Np L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides 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 20/02/2006

Angular distributions in the neutron-induced fission of actinides Angle reconstruction (energy intervals) : 234 U isotropic sideward peaking The detection efficiency depends on the angular distribution cross section measurement L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides f for 234 U L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides 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 L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides Poor knowledge above 10 Me. V 237 Np 232 Th n. TOF well suited for describing the quick variations with energy L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides 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 20/02/2006

Angular distributions in the neutron-induced fission of actinides Experiment • Take advantage of the full efficiency up to 45° • First isotopes to be measured : 238 U, 235 U, 232 Th • Possibility of measurement of transfered momentum • Requested amount of protons : 1. 5 1018 L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides Flux from 235 U and 238 U (JENDL above 20 Me. V) L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides Ratios : 234 U target 1/target 0 L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides Ratios : 237 Np targeti/mean L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides Ratios : 232 Th targeti/mean L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides 238 U/235 U ratio L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides f for 234 U L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides f for 232 Th L. Tassan-Got & the TOF collaboration INTC 20/02/2006

Angular distributions in the neutron-induced fission of actinides 232 Th case : comparison to others L. Tassan-Got & the TOF collaboration INTC 20/02/2006