Mass Measurements of r-process Nuclei Using the TOF-B$\rho $ Technique at the NSCL*

The r-process plays a key role in the nucleosynthesis of more than half of the nuclei heavier than iron. Mass is one of the most fundamental nuclear data for r-process models because it is essential to calculate other nuclear properties such as Q-values for $\beta$-decays, neutron capture rates and equilibrium abundance distributions. The trends of masses along the isotopic chains towards N=82 can help us to test the models calculating the masses in the r-process path which is out of reach for current facilities. At the NSCL, we have conducted a mass-measurement experiment using time-of-flight--magnetic-rigidity (TOF-B$\rho$) technique for neutron-rich isotopes from Zr to Ru around N=70 produced by the projectile fragmentation of $^{124}$Sn. I will present the preliminary results of this experiment.