Nuclear Zeeman Effect in Iron-57
This data is from O. C. Kistmer and A. W. Sunyar, Physical Review Letters, 4, 412(1960). The energy levels of the iron nucleus, contained in an ordinary iron sample, are split by the nuclear Zeeman effect. The spectrum shows the transitions for iron-57 in an iron oxide lattice. The splittings are some 11 orders of magnitude smaller than the nuclear transition energy!
Tipler & Llewellyn