STUDY OF THE EIGENVALUE SPECTRA OF THE NEUTRON TRANSPORT PROBLEM IN PN APPROXIMATION P. Saracco, N. Abrate, M. Burrone, S. Dulla and P. Ravetto EPJ Web Conf., 247 (2021) 03018 Published online: 22 February 2021 DOI: 10.1051/epjconf/202124703018