Neutron richGa73andAs79isotopes via the (α,p) reaction

The ($\alpha$,$p$) reaction at 26 MeV has been used to study ${}_{}{}^{73}{}_{}{}^{}\mathrm{Ga}$ and ${}_{}{}^{79}{}_{}{}^{}\mathrm{As}$ with 12 keV resolution full width at half maximum. The reaction behaves like a simple proton stripping ("spectator" zero coupled neutron pair) and the characteristic shapes of the angular distributions permit assigning new spins and parities. In ${}_{}{}^{73}{}_{}{}^{}\mathrm{Ga}$: $198 \mathrm{keV}\left(\frac{5}{2^{-}}\right)$, $1116 \mathrm{keV}\left(\frac{1}{2^{-}}\right)$, $1494 \mathrm{keV}\left(\frac{9}{2^{+}}\right)$. In ${}_{}{}^{79}{}_{}{}^{}\mathrm{As}$: $\mathrm{g}.\mathrm{s}.\mathrm{}\left(\frac{3}{2^{-}}\right)$, $233 \mathrm{keV}\left(\frac{5}{2^{-}}\right)$, $499 \mathrm{keV}\left(\frac{1}{2^{-}}\right)$, $777 \mathrm{keV}\left(\frac{9}{2^{+}}\right)$, $1806 \mathrm{keV}\left(\frac{9}{2^{+}}\right)$, $1891 \mathrm{keV}\left(\frac{1}{2^{-}}\right)$, $1964 \mathrm{keV}\left(\frac{9}{2^{+}}\right)$. The observed splitting of the $J^{\pi }=\frac{3}{2^{-}}$ strength in ${}_{}{}^{73}{}_{}{}^{}\mathrm{Ga}$, important as compared to the one observed in ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$, is attributed to a change of structure between $N=40\mathrm{} \mathrm{and} 42$.