Nuclear Spins of Neutron-deficient Lanthanum and Cerium Isotopes

Abstract

Nuclear spins of some neutron-deficient lanthanum and cerium isotopes have been measured by the atomic-beam magnetic resonance method. The results are: 131La (59 min) I=3/2, 132La (4.5 h) I=2, 132mLa (25 min) I=6, 133La (4.0 h) I=5/2, 135La (19.4 h) I=5/2, 136La (10 min) I=1, 130Ce (25 min) I=0, 132Ce (4.2 h) I=0, 133Ce (5.4 h) I=9/2, 133mCe (97 min) I=1/2, 134Ce (72 h) I=0, 135Ce (17.0 h) I=1/2, 137Ce (9.0)h I=3/2, 137mCe (34.4 h) I=11/2, 139Ce (140 d) I=3/2. The spin values of nuclei with neutron numbers N⩾76 are in accordance with predictions of the spherical shell model. The results obtained on the isotopes further away from the stability line indicate stably deformed nuclear shapes; e.g. for the nuclei 131La, 133Ce and 133mCe. For the transitional nucleus 132La, no unequivocal interpretation can be made of the ground state and isomeric state spins.