Radioactive Isotopes of Lanthanum

The radioactive isotope ${\mathrm{La}}^{140}$, known to be produced by deuteron and slow neutron bombardments of lanthanum is found to have a half-life of 40.0±0.3 hours. This isotope has now been produced by the reaction ${\mathrm{Ce}}^{140}\mathrm{}(n,p)\mathrm{}{\mathrm{La}}^{140}$. Evidence for the occurrence of a $d$, $y$ reaction has been obtained through the formation of ${\mathrm{La}}^{140}$ by the reaction ${\mathrm{Ba}}^{138}\mathrm{}(d,y)\mathrm{}{\mathrm{La}}^{140}$. The 40-hour isotope decays with the emission of 1.41±0.05-Mev electrons and 2.00±0.05-Mev gamma-rays. Deuteron and also proton bombardments of barium produce a new radioactive isotope of lanthanum of half-life 17.5±0.5 hours. This activity decays by the process of $K-\mathrm{e}\mathrm{l}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{n}$ capture with the emission of x-rays identified as the characteristic $K$ radiation of barium. The presence of a 0.88±0.1-Mev gamma-ray of low intensity indicates that the resulting barium nucleus may also be left in an excited state. This 17.5-hour activity is assigned to ${\mathrm{La}}^{137}$.