Energy Levels inTm17269from the Decay ofEr17268

Abstract

The radioactive nuclide ${}_{68}{}^{}{}_{}{}^{}\mathrm{Er}_{}^{172}{}_{}{}^{}$ was produced in the Materials Testing Reactor, Arco, Idaho by the successive capture of two neutrons in erbium oxide enriched in ${\mathrm{Er}}^{170}$. In addition to three erbium activities and the radioactive ${\mathrm{Tm}}^{172}$ daughter, these samples contained six active contaminants from which the erbium was separated by use of an ion-exchange column. Scintillation studies, conducted with a 256-channel coincidence scintillation spectrometer, indicate the presence of at least eight gamma-ray transitions. Two of these transitions are either highly $K$ converted or their transition energies are approximately 50 kev. The energies of the other six transitions are about 610, 450, 408, 200, 160, and 125 kev. Beta-gamma coincidence experiments indicate the presence of two beta-ray components at approximately 310 kev (in coincidence with the 610-kev gamma ray) and 370 kev (in coincidence with the 408-kev gamma ray). The level scheme deduced for ${\mathrm{Tm}}^{172}$ has excited states at 408, 450 (or 160), 470±15, 530, and 610 kev. From the beta-ray intensities, the states at 530 and 610 kev are assigned spins of either 0 or 1 with positive parity. The spin and parity ($2^{-}$) of the thulium ground state have previously been assigned from the properties of the decay of ${\mathrm{Tm}}^{172}$.