Radioactivity ofSc44

The decay of ${\mathrm{Sc}}^{44}$ has been reinvestigated using a NaI gamma-ray spectrometer and a magnetic-lens spectrometer adapted to coincidence measurements. The main transition from the ${\mathrm{Sc}}^{44}$ ground state is to the first excited level of ${\mathrm{Ca}}^{44}$ at 1.159±0.003 Mev. The probability for positron emission is 0.932±0.015, in agreement with the theoretical value of 0.928 for an allowed transition ($E_{max}=1.471\mathrm{}\pm 0.005$ Mev). The conversion coefficients of the 1.16-Mev gamma ray and of the isomeric transition in ${\mathrm{Sc}}^{44}$ are 6.3±0.3×${10}^{-5\mathrm{}}$ and 0.139±0.003, compatible with $E2\mathrm{}$ and $E4\mathrm{}$ transitions, respectively. A weak allowed decay leads to a level in ${\mathrm{Ca}}^{44}$ at 2.54±0.03 Mev. The continuous spectrum of low-energy electrons previously reported by J. A. Bruner was found to depend strongly on the thickness of the source and the backing. For the thinnest sources the intensity was found to be $\frac{1}{3}$ of that previously reported. Coincidence measurements showed that more than $\frac{2}{3}$ of the electrons are not coincident with both the positrons and the gamma rays and are, therefore, not emitted in the process of positron decay. It is concluded that there is no indication for a disagreement between the experiment and the theory of atomic excitation during beta decay.