Loses out to New College, Oxford (as bonzer noted), founded in 1379 and known by that name since before 1400. And probably to some other structures already mentioned as well.
I know you didn’t intend this as a serious contender because the word “neutron” is recently coined. But actually, “neutron” doesn’t even qualify as a name signifying “new”.
It means the “neutral” particle, from Latin neuter which is derived from ne uter, “not one nor the other”, rather than from German neu, “new”.