Radioactivity Induced in the Rare Earth Elements by Fast Neutrons

With the exception of illinium, thulium and lutecium all the rare earth elements have been bombarded with slow and fast neutrons. The fast neutrons were obtained from the Li+D reaction. Deuterons of 6.3 Mev were produced by the cyclotron at the University of Michigan. The following periods for electron emission have been observed: ${\mathrm{La}}^{140}$ (31 hr.), ${\mathrm{Pr}}^{142}$ (19 hr.), ${\mathrm{Nd}}^{147}$ (84 hr.), ${\mathrm{Nd}}^{149}$ (2.0 hr.), ${\mathrm{Nd}}^{151}$ (21 min.), ${\mathrm{Il}}^{144}$ (12.5 hr.), ${\mathrm{Sm}}^{151}$ (21 min.), ${\mathrm{Sm}}^{153}$ (46 hr.), ${\mathrm{Eu}}^{152}$ (9.2 hr.), ${\mathrm{Tb}}^{160}$ (3.3 hr.), ${\mathrm{Dy}}^{165}$ (2.5 hr.), ${\mathrm{Ho}}^{164}$ (47 min.), ${\mathrm{Ho}}^{166}$ (30 hr.), ${\mathrm{Er}}^{169}$ (12 hr.) and ${\mathrm{Er}}^{171}$ (5.1 hr.) The following periods for positron emission have been observed: ${\mathrm{Ce}}^{139}$ (2.1 min.), ${\mathrm{Pr}}^{140}$ (3.5 min.), ${\mathrm{Eu}}^{150}$ (27 hr.), ${\mathrm{Tb}}^{158}$ (3.6 min.), ${\mathrm{Dy}}^{159}$ (2.2 min.) and ${\mathrm{Er}}^{165}$ (1.1 min.). There seems to be at least two isotopes which are isomeric: one is ${\mathrm{Gd}}^{159}$ (3.5 min., 17 hr.) and the other is ${\mathrm{Yb}}^{175}$ (2.1 hr., 14 hr.). From radioactivity data it is necessary to postulate the existence of four new stable isotopes: ${\mathrm{Gd}}^{152}$, ${\mathrm{Dy}}^{160}$, ${\mathrm{Er}}^{164}$ and ${\mathrm{Yb}}^{170}$. With the fast neutron bombardment seventeen $n-2n$ type of reactions have been found.