Nuclear Spins of Neutron-deficient Lanthanum and Cerium Isotopes

Nuclear spins of some neutron-deficient lanthanum and cerium isotopes have been measured by the atomic-beam magnetic resonance method. The results are: 131 La (59 min) I =3/2, 132 La (4.5 h) I =2, 132m La (25 min) I =6, 133 La (4.0 h) I =5/2, 135 La (19.4 h) I =5/2, 136 La (10 min) I =1, 130 Ce (25 min) I =0, 132 Ce (4.2 h) I =0, 133 Ce (5.4 h) I =9/2, 133m Ce (97 min) I =1/2, 134 Ce (72 h) I =0, 135 Ce (17.0 h) I =1/2, 137 Ce (9.0)h I =3/2, 137m Ce (34.4 h) I =11/2, 139 Ce (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 131 La, 133 Ce and 133m Ce. For the transitional nucleus 132 La, no unequivocal interpretation can be made of the ground state and isomeric state spins.