Low-Intensity Branches in theTi45Decay

Abstract

The decay of ${\mathrm{Ti}}^{45}$ (∼100% electron capture and ${\beta }^{+}$ to the ${\mathrm{Sc}}^{45}$ ground state) has been reinvestigated with the Argonne toroidal-field beta spectrometers and with lithium-drifted germanium gamma detectors. New low-intensity branches to levels in ${\mathrm{Sc}}^{45}$ at 725.1±0.8 [149±35], 1238±1.5 [16±6], and 1411.3±0.9 [112±30] keV have been found. Numbers in brackets are the intensities for ${10}^5$ decays. The 12.4-keV level in ${\mathrm{Sc}}^{45}$ previously seen in the $\beta$ decay of ${\mathrm{Ca}}^{45}$ is also populated in the ${\mathrm{Ti}}^{45}$ decay; its energy is ${12.40}_{-0.01\mathrm{}}^{+0.02\mathrm{}}$ keV and its intensity is [12±3]. The intensity of the first-forbidden unique decay ($\frac{7}{2}-$ to $\frac{3}{2}+$) to the 12.4-keV state is not known because of the unknown amount of gamma branching to the 12.4-keV state from higher levels in ${\mathrm{Sc}}^{45}$, but from the observed 12.4-keV intensity, $log{f}_{1}t>\mathrm{}8.1\mathrm{}$. No evidence was found for beta decay to the 376-keV level [<60] or to the 540-keV level [<9]. $\mathrm{Log}\mathrm{ft}$ values for beta decays to the three states at 725, 1238, and 1411 keV are 6.3, 6.8 and 5.6, respectively. In general, to the other states, $log\mathrm{ft}$ values are greater than 7, with the exception of the 1660-keV state for which our gamma intensity limit yields $log\mathrm{ft}>\mathrm{}5.7\mathrm{}$. The available data are consistent with spin and parity assignments of (${\frac{3}{2}}^{+}$) for the 12.4-keV state and (${\frac{3}{2}}^{-}$) for the 376-keV state. The end point of the positron spectrum, 1044±5 keV, indicates a total decay energy, ${\mathrm{Ti}}^{45}$ → ${\mathrm{Sc}}^{45}$, of 2066±5 keV, 20 to 40 keV higher than earlier measurements and in better agreement with reaction data, 2062±4 keV. Our half-life measurement of 3.08±0.01 h agrees with previous measurements.