Induced Radioactivity in Europium

Europium oxide has been bombarded with slow neutrons from the cyclotron for periods ranging up to about five months, and with 7-Mev deuterons for much shorter lengths of time. By reduction of the europium to its bivalent state, it has been possible to separate this element from neighboring members of the rare earth group. By slow neutron activation, two periods of induced radioactivity have been produced in europium; one, with a half-life of 9.4±0.2 hours, is assigned to ${\mathrm{Eu}}^{152}$, in accordance with the results of other investigators. This isotope probably decays both by the emission of negative electrons and by the capture of $K$ electrons. The beta-spectrum, as measured in the cloud chamber, has an upper limit of 1.83 Mev. The second period, produced only after long exposure, has not decayed appreciably in six months. It has been assigned to ${\mathrm{Eu}}^{154}$. Preliminary studies indicate that $K$-electron capture may also take place in the decay of this isotope. The upper limit of the beta-spectrum has been found to be 1.0±0.1 Mev. By relatively short deuteron bombardments, the 9-hour period has also been produced, and in addition two new periods of 12±4 minutes and 105±5 minutes have been obtained. These could not be separated from the 9-hour activity by chemical methods, which indicates that they are due also to isotopes of europium, probably to isomeric forms of ${\mathrm{Eu}}^{152}$ and ${\mathrm{Eu}}^{154}$, not produced appreciably by slow neutron activation.