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Accueil du site > Activités scientifiques et techniques > Physique et Radiochimie de l’energie Nucléaire > Physique de l’aval du cycle et de la spallation > Données nucléaires > n-TOF : Fission fragment angular distributions

n-TOF : Fission fragment angular distributions

The effective cross-sections of neutron induced reactions consitute key data in reactor simulations. But their quality varies greatly according to the target isotope. The prospect of transmutation or incineration of long life radioactive waste has given rise to planned measures for improving accuracy and extending the energy domain on certain isotopes. The IPN group, with help from the lab’s radiochemists, has developed a system for measuring effective fission cross-sections with a view to supplying very thin radioactive targets. Effective fission cross-sections of natPb, 209Bi, 232Th, 233.234.238U and 237Np have thus been measured on the n_TOF neutron beam at CERN, with a precision of 4–6% and, for the first time, on an energy range of 0.7eV to 1GeV. Data obtained on 237Np have led to previous evaluations of this nucleus being called into question.

At n_TOF in 2010 we started measuring fission fragment angular distributions, which provide information on the transition states of the fissioning nucleus and also on spin deposition in spallation reactions.

In the medium term, we intend to continue the activity of measuring effective neutron-induced fission cross-sections, whether at n_TOF or NFS-Spiral2. But the ability to make such measurements is entirely dependent on obtaining highly radioactive thin targets, therefore on the availability of CACAO (Actinide Chemistry and Radioactive Targets at Orsay - see paragraph 3.2), which is the only installation capable of producing such targets. We are particularly studying the possibility of measuring the fission of 231Pa, a major waste product of the 232Th/233U branches. Its effective cross-section has already been measured, including quite recently, and there are still substantial disagreements with previous measurements. This is especially the case with measurement by transfer reaction, which is the favourite method for studying 233Pa but which shows discrepancies compared with direct measurements.


 

IPN

Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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