For these vectors I am strongly in favor of the singular-plural pattern (for apple in apples) rather than putting struct and list in the name.  For example, this line would be `std::vector<mt_451> mt_451s;`.  Also, I am not familiar enough with the ENDF internals without looking at the spec (who is?!) but is a vector the best data type for this? It very well may be, but I want to make sure that there isn't some other value that we should be keying a map off of instead.