Open Access

Lou Sai Leong, Laurent Tassan-Got, Diego Tarrío Vilas, Laurent Audouin, Carlos Paradela Dobarro, Ignacio Durán, Claire Le Naour, Sebastian Altstadt, Jozef Andrzejewsky, Massimo Barbagallo, Vicente Bécares, František Bečvář, Fabio Belloni, Eric Berthoumieux, Jonathan Billowes, Vittorio Boccone, Damir Bosnar, Markus Brugger, Francisco Calviño Tavares, Marco Calviani, Daniel Cano-Ott, Carlos Carrapiço, Francesco Cerutti, Enrico Chiaveri, Michael Chin, Nicola Colonna, Guillem Pere Cortés Rossell, Miguel Antonio Cortés-Giraldo, Maria Diakaki, César Domingo-Pardo, Rugard Dressler, Nataliia Dzysiuk, Christos Eleftheriadis, Alfredo Ferrari, Kevin Fraval, Srinivasan Ganesan, Aczel Regino García Ríos, Giuseppe Giubrone, María Belén Gómez Hornillos, Isabel Maria Ferro Gonçalves, Enrique Miguel González Romero, Erich Griesmayer, Carlos Guerrero Sánchez, Frank Gunsing, Perumal Gurusamy, David Jenkins, Erwin Jericha, E. Kadi, Franz Käppeler, Dimitri Karadimos, Nikolay Kivel, Paul Koehler, Michael Kokkoris, Gunther Korschinek, Jiří Kroll, Milan Krtička, Christoph Langer, Claudia Lederer, Helmut Leeb, Roberto Losito, Athanasios Manousos, Justyna Marganiec, Cristian Massimi, Trinitario Martı́nez, Pierfrancesco Mastinu, Mario Mastromarco, AKM Moinul Haque Meaze, A. Mengon, Emilio Mendoza Cembranos, Paolo Maria Milazzo, T. Mingrone, Mihail Mirea, Willy Mondelaers, Andreas Pavlik, Jarosław Perkowski, Marco Pignatari, Arjan J. M. Plompen, Javier Praena, José Manuel Quesada Molina, Thomas Rauscher, R. Reifhart, Albert Riego Pérez, Faustin Laurenţiu Roman, Carlo Rubbia, Raul Sarmento, Peter Schillebeeckx, Stefan Schmidt, Dorothea Schumann, Jose Luis Taı́n Enríquez, Giuseppe Tagliente, Andrea Tsinganis, Stanislav Valenta, Gianni Vannini, Vincenzo Variale, Pedro Vaz, Alberto Ventura, Roberto Versaci, Mark J. Vermeulen, Vasilis Vlachoudis, V. Vlastou, Anton Wallner, Timothy Ware, Mario Weigand, Christina Weiß, Tobias Wright, Petar Žugec

• Above 1 MeV of incident neutron energy the fission fragment angular distribution (FFAD) has generally a strong anisotropic behavior due to the combination of the incident orbital momentum and the intrinsic spin of the fissioning nucleus. This effect has to be taken into account for the efficiency estimation of devices used for fission cross section measurements. In addition it bears information on the spin deposition mechanism and on the structure of transitional states. We designed and constructed a detection device, based on Parallel Plate Avalanche Counters (PPAC), for measuring the fission fragment angular distributions of several isotopes, in particular 232Th. The measurement has been performed at n_TOF at CERN taking advantage of the very broad energy spectrum of the neutron beam. Fission events were recognized by back to back detection in coincidence in two position-sensitive detectors surrounding the targets. The detection efficiency, depending mostly on the stopping of fission fragments in backings and electrodes, has been computed with a Geant4 simulation and validated by the comparison to the measured case of 235U below 3 keV where the emission is isotropic. In the case of 232Th, the result is in good agreement with previous data below 10 MeV, with a good reproduction of the structures associated to vibrational states and the opening of second chance fission. In the 14 MeV region our data are much more accurate than previous ones which are broadly scattered.