Positron Spectra ofEu152andEu152m

An intermediate-image beta-ray spectrometer equipped with spiral baffles has been used to investigate positrons in the decays of ${\mathrm{Eu}}^{152}$ and ${\mathrm{Eu}}^{152m}$. Thirteen-year ${\mathrm{Eu}}^{152}$ emits a positron group to the 0.122-Mev 2+ first excited state of ${\mathrm{Sm}}^{152}$ with an end-point energy of 0.715±0.010 Mev and an intensity of 1.6×${10}^{-4\mathrm{}}$ per disintegration ($logft=11.9\mathrm{}$) and a positron group to the 0.366-Mev 4+ second excited state with an end point of 0.47±0.03 Mev and an intensity of 0.8×${10}^{-4\mathrm{}}$ per disintegration ($logft=11.5\mathrm{}$). 9.3-hr ${\mathrm{Eu}}^{152m}$ emits a positron group to the ground state of ${\mathrm{Sm}}^{152}$ with an end-point energy of 0.895±0.005 Mev and an intensity of 7×${10}^{-5\mathrm{}}$ per disintegration ($logft=8.65\mathrm{}$) and a positron group to the 0.122-Mev state with an intensity of 4×${10}^{-5\mathrm{}}$ per disintegration ($log ft=8.6\mathrm{}$). The shape of the latter group has not been established. However, its end point, when the alpha shape factor is applied, gives better agreement with the 0.122-Mev energy separation from the ground-state beta ray than the end point of the uncorrected spectrum. The result is consistent with, but not positive proof of, the assumed spin of 0- for ${\mathrm{Eu}}^{152m}$. The ${\beta }^{-}$ end-point energies of ${\mathrm{Eu}}^{152}$ and ${\mathrm{Eu}}^{152m}$ are 1.470±0.010 Mev and 1.855±0.010 Mev respectively. An energy separation of 0.050±0.015 Mev between ${\mathrm{Eu}}^{152m}$ and ${\mathrm{Eu}}^{152}$ is derived from the various ${\beta }^{+}$ and ${\beta }^{-}$ end-point measurements. No $L$-conversion electrons could be found in ${\mathrm{Eu}}^{152m}$ decay corresponding to a 0.05-Mev isomeric transition. An upper limit of 3×${10}^{-5\mathrm{}}$ per disintegration was obtained for the fractional decay of ${\mathrm{Eu}}^{154}$ by positron emission.