Radioactive Isotopes of Praseodymium

New nuclear reactions ${\mathrm{Pr}}^{141}\mathrm{}\left(\mathrm{dp}\right)\mathrm{}$, ${\mathrm{Ce}}^{142}\mathrm{}\left(\mathrm{pn}\right)\mathrm{}$, and ${\mathrm{La}}^{139}\left(\alpha n\right)$ yielding radioactive isotope ${\mathrm{Pr}}^{142}$ have been observed. The decay curves obtained for ${\mathrm{Pr}}^{142}$ after chemical purifications showed a half-life of 19.3±0.1 hours, a value considered to be more exact than that previously reported. The negative beta-ray spectrum was measured with a recently constructed magnetic spectrometer of the 180° focusing type and was found to have an end point of 2.14±0.02 Mev. A weak gamma-ray approximately 1.9 Mev was found associated with this period. The isotope ${\mathrm{Pr}}^{140}$ has been formed by the reaction: ${\mathrm{Pr}}^{141}\mathrm{}(n,2n)\mathrm{}$. Its half-life was measured as 3.4±0.1 minutes. Cloud-chamber measurements yield an upper limit of 2.40±0.15 Mev for its positron spectrum.