Lifetime andγdecay of the isomeric 19/2−state inTi43

Abstract

The nucleus $^{43}\mathrm{Ti}$ has been studied by prompt and delayed $n\ensuremath{-}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences in the bombardment of $^{40}\mathrm{Ca}$ with 20-MeV $\ensuremath{\alpha}$ particles. A cascade of three $\ensuremath{\gamma}$ rays with energies of 114.7, 1094.0, and 1857.7 keV has been observed. The $\ensuremath{\gamma}$ cascade is emitted by an isomeric state of 3066.4-keV excitation energy; its mean life has been determined to be $\ensuremath{\tau}=810\ifmmode\pm\else\textpm\fi{}50$ nsec. By measuring the relative intensities of the three $\ensuremath{\gamma}$ rays the sequence in the $\ensuremath{\gamma}$ decay has been established. The close resemblance of this $\ensuremath{\gamma}$ cascade to the one in the mirror nucleus $^{43}\mathrm{Sc}$ leads to the conclusion that the 3066.4-keV state in $^{43}\mathrm{Ti}$ is an isomeric 19/${2}^{\ensuremath{-}}$ state which has the decay scheme ${\frac{19}{2}}^{\ensuremath{-}}\underset{114.7}{\ensuremath{\rightarrow}}{\frac{15}{2}}^{\ensuremath{-}}(2952.7)\underset{1094.0}{\ensuremath{\rightarrow}}{\frac{11}{2}}^{\ensuremath{-}}(1857.7)\ensuremath{\rightarrow}{\frac{7}{2}}^{\ensuremath{-}}(0)$. This conclusion is in agreement with the results of measured excitation functions which show that the maximum yield of the 1857.7-keV $\ensuremath{\gamma}$ occurs at the lowest \ensuremath{\alpha} energy and that of the 114.7-keV $\ensuremath{\gamma}$ at the highest. The $B(E2)$ value of the 19/${2}^{\ensuremath{-}}$\ensuremath{\rightarrow}15/${2}^{\ensuremath{-}}$ transition in $^{43}\mathrm{Ti}$ is larger by nearly a factor of 2 than the corresponding transition in $^{43}\mathrm{Sc}$. The slightly lower excitation energy (56.9 keV) of the 19/${2}^{\ensuremath{-}}$ state in $^{43}\mathrm{Ti}$ with respect to the corresponding state in $^{43}\mathrm{Sc}$ seems to be at least partially due to Coulomb shifts arising from the two valence protons in $^{43}\mathrm{Ti}$.NUCLEAR REACTIONS $^{40}\mathrm{Ca}(\ensuremath{\alpha},n\ensuremath{\gamma})$; prompt and delayed $n\ensuremath{-}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences with ${E}_{\ensuremath{\alpha}}=20$ MeV. Singles $\ensuremath{\gamma}$-ray spectra: $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}=f({E}_{\ensuremath{\alpha}},{E}_{\ensuremath{\gamma}})$. Deduced for $^{43}\mathrm{Ti}:{\frac{19}{2}}^{\ensuremath{-}}(3066.4 \mathrm{keV})\ensuremath{\rightarrow}{\frac{15}{2}}^{\ensuremath{-}} (2951.7 \mathrm{keV})\ensuremath{\rightarrow}{\frac{11}{2}}^{\ensuremath{-}}(1857.7 \mathrm{keV})\ensuremath{\rightarrow}{\frac{7}{2}}^{\ensuremath{-}}(0)$, ${\frac{19}{2}}^{\ensuremath{-}}$ state: $\ensuremath{\tau}=(810\ifmmode\pm\else\textpm\fi{}50)$ nsec.