Search for non-paulian transitions in 23Na and 127I

A new search of non-paulian nuclear processes, i.e. processes normally forbidden by the Pauli exclusion principle, was carried out by determining an improved upper limit for the spontaneous emission rate of protons in 23Na and 127I. A large set-up of highly radiopure NaI(Tl) crystals was employed; it was placed deeply underground at the Gran Sasso National Laboratory of I.N.F.N. The upper limit on the unit time probability of non-paulian emission of protons with energy Ep ⩾ 10 MeV is λ ⩽ 4.6 · 10−33s−1. The corresponding limit on the relative strength (δ2) for the searched non-paulian transitions has been estimated to be δ2 ≲ 1.0 · 10−54.