Information on mass chains and nuclides available on this website:
6n has not been observed in the interaction of 700 MeV protons or of 400 GeV protons with uranium: the cross section is < 1.1 x 10-3 μb (TU77; 700 MeV), < 9 μb (TU77B; 400 GeV). See also (79AJ01).