alt:
  if !isdefined(:rel_nuclides) # standard values
    rel_nuclides = ["Co60", "Cs137", "Fe55", "Ni63", "Sr90", "Am241"]
  end

neu:
  if isempty(rel_nuclides3) # standard values
    rel_nuclides = ["Co60", "Cs137", "Fe55", "Ni63", "Sr90", "Am241"]
  else
    rel_nuclides = [rel_nuclides3[i].name for i=1:length(rel_nuclides3)]
  end