Open Access

Javier Moreno-Soto, Stanislav Valenta, Eric Berthoumieux, Abdelaziz Chebboubi, Maria Diakaki, Wissem Dridi, Emmeric Dupont, Frank Gunsing, Milan Krtička, Olivier Litaize, Olivier Serot, Oliver Aberle, Victor Alcayne, Simone Amaducci, Józef Andrzejewski, Laurent Audouin, Vicente Bécares, Victor Babiano Suarez, Michael Bacak, Massimo Barbagallo, Benedikt Thomas, Samuel Bennett, Jonathan Billowes, Damir Bosnar, Adam Brown, Maurizio Busso, Manuel Caamano, Luis Caballero Ontanaya, Francisco Calviño Tavares, Marco Calviani, Daniel Cano-Ott, Adrià Casanovas Hoste, Francesco Cerutti, Enrico Chiaveri, Nicola Colonna, Guillem Pere Cortés Rossell, Miguel Antonio Cortés-Giraldo, Luigi Cosentino, Sergio Cristallo, Lucia Anna Damone, Paul John Davies, Mirco Dietz, César Domingo-Pardo, Rugard Dressler, Quentin Ducasse, Ignacio Durán, Zinovia Eleme, Beatriz Fernández Domínguez, Alfredo Ferrari, Paolo Finocchiaro, Valter Furman, Kathrin Göbel, Aleksandra Gawlik-Ramiega, Simone Gilardoni, Isabel Maria Ferro Gonçalves, Enrique Miguel González Romero, Carlos Guerrero Sánchez, Stephan Heinitz, Jan Heyse, David Jenkins, Arnd Rudolf Junghans, Franz Käppeler, Yacine Kadi, Atsushi Kimura, Ingrid Knapova, Michael Kokkoris, Yuri N. Kopatch, Cem Deniz Kurtulgil, Ion Ladarescu, Christos Lampoudis, Claudia Lederer-Woods, Sarah Jane Lonsdale, Daniela Macina, Alice Manna, Trinitario Martinez, Alessandro Masi, Cristian Massimi, Pierfrancesco Mastinu, Mario Mastromarco, Emilio Andrea Maugeri, Annamaria Mazzone, Emilio Mendoza Cembranos, Alberto Mengoni, Veatriki Michalopoulou, Paolo Maria Milazzo, Federica Mingrone, Agatino Musumarra, Alexandru Negret, Ralf Nolte, Francisco Ogállar Ruiz, Andreea Oprea, Nikolas Patronis, Andreas Pavlik, Jarosław Perkowski, Luciano Piersanti, Cristina Petrone, Elisa Pirovano, Ignacio Porras, Javier Praena, José Manuel Quesada Molina, Diego Ramos Doval, Thomas Rauscher, René Reifarth, Dimitri Rochman, Marta Sabate-Gilarte, Alok Saxena, Peter Schillebeeckx, Dorothea Schumann, Adhitya Sekhar, Alastair Gavin Smith, Nikolay V. Sosnin, Peter Sprung, Athanasios Stamatopoulos, Giuseppe Tagliente, José Luis Taı́n Enríquez, Ariel Tarifeno-Saldivia, Laurent Tassan-Got, Pablo Torres-Sanchez, Andrea Tsinganis, Jiri Ulrich, Sebastian Urlaß, Gianni Vannini, Vincenzo Variale, Pedro Vaz, Alberto Ventura, Diego Vescovi, Vasilis Vlachoudis, Rosa Vlastou, Anton Wallner, Philip John Woods, Tobias Wright, Petar Žugec

• Background: The photon strength functions (PSFs) and nuclear level density (NLD) are key ingredients for calculation of the photon interaction with nuclei, in particular the reaction cross sections. These cross sections are important especially in nuclear astrophysics and in the development of advanced nuclear technologies. Purpose: The role of the scissors mode in the M1 PSF of (well-deformed) actinides was investigated by several experimental techniques. The analyses of different experiments result in significant differences, especially on the strength of the mode. The shape of the low-energy tail of the giant electric dipole resonance is uncertain as well. In particular, some works proposed a presence of the E1 pygmy resonance just above 7 MeV. Because of these inconsistencies additional information on PSFs in this region is of great interest. Methods: The γ-ray spectra from neutron-capture reactions on the 234U, 236 U, and 238 U nuclei have been measured with the total absorption calorimeter of the n_TOF facility at CERN. The background-corrected sum-energy and multi-step-cascade spectra were extracted for several isolated s-wave resonances up to about 140 eV. Results: The experimental spectra were compared to statistical model predictions coming from a large selection of models of photon strength functions and nuclear level density. No combination of PSF and NLD models from literature is able to globally describe our spectra. After extensive search we were able to find model combinations with modified generalized Lorentzian (MGLO) E1 PSF, which match the experimental spectra as well as the total radiative widths. Conclusions: The constant temperature energy dependence is favored for a NLD. The tail of giant electric dipole resonance is well described by the MGLO model of the E1 PSF with no hint of pygmy resonance. The M1 PSF must contain a very strong, relatively wide, and likely double-resonance scissors mode. The mode is responsible for about a half of the total radiative width of neutron resonances and significantly affects the radiative cross section.