A new method has been developed for increasing the sensitivity of collinear laser spectroscopy. The method utilizes an ion-trapping technique in which a continuous low-energy ion beam is cooled and accumulated in a linear Paul trap and subsequently released as a short ( $10–20\mu \mathrm{s}$) bunch. In collinear laser measurements the signal-to-noise ratio has been improved by a factor of $2\times {10}^4$, allowing spectroscopic measurements to be made with ion-beam fluxes of $\sim 50\mathrm{ions}{\mathrm{s}}^{-1\mathrm{}}$. The bunching method has been demonstrated in an on-line isotope shift and hyperfine structure measurement on radioactive ${}^{175}\mathrm{Hf}$.

Collinear laser spectroscopy was performed on Ga ($Z=31$) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes ($N=36–50$). A ground state (g.s.) spin $I=1/2$ is measured for ${}^{73}\mathrm{Ga}$, being near degenerate with a $3/2^{-}$ isomer ($75\mathrm{eV}\lesssim E_{\mathrm{ex}}\lesssim 1\mathrm{keV}$). The ${}^{79}\mathrm{Ga}$ g.s., with $I=3/2$, is dominated by protons in the $\pi f_{5/2}$ orbital and in ${}^{81}\mathrm{Ga}$ the $5/2^{-}$ level becomes the g.s. The data are compared to shell-model calculations in the $f_{5/2}p{g}_{9/2}$ model space, calling for further theoretical developments and new experiments.