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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 > Measurement of effective cross-sections (n,gamma) by the “surrogate” method and the measurement of level densities in actinides.

Measurement of effective cross-sections (n,gamma) by the “surrogate” method and the measurement of level densities in actinides.

An experimentation programme is under way concerning the simultaneous measurement of effective cross-sections (n,g) and (n,fission) using the surrogate method, and the extraction of level densities in actinides. The information on level densities and on the g-ray strength functions is useful in applied physics (nuclear energy) and in fundamental physics because current calculation of effective cross-sections is based on level density models that can be very inaccurate. Indirect measurement of effective cross-sections is very useful when the activity of the targets is too high to allow direct measurement.

In the Oslo Cyclotron, these experiments can be carried out by detecting g particle coincidences in transfer reactions. The combining of the “Silicon Ring”, a 72-channel E/∆E Silicon multi-detector for detecting light charged particles, with “Cactus”, a high-efficiency g multi-detector, allows these coincidences to be measured. After initial success with 232Th targets, several important measurements are planned on 233U, 235U, and 231Pa targets supplied by the Lawrence Livermore National Laboratory (USA), CEA Saclay, and possibly CACAO. Indirect effective cross-sections (n,g) have recently, been extracted for 232Th, 230Th and 231Pa, three important nuclei in the thorium cycle.

In 2012, we complemented this configuration with specially developed fission detectors in order to create a unique spectrometer with unprecedented characteristics. The charged particles, gamma rays, and fission fragments will be detected in coincidence for the first time. The fission fragment detectors will offer up to 60% detection efficiency, thus enabling simultaneous measurement of the effective cross-sections of fission and capture, which will cancel out any systematic errors.



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

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