TOF-B$\rho$ Mass Measurements at the NSCL, MSU

The radioactive beam facilities such as the NSCL offer ideal opportunities for time-of-flight mass measurements of very exotic ions. We have recently implemented a TOF-B$\rho$ technique at the NSCL and performed a mass measurement of neutron-rich nuclides in the Fe region. Masses of neutron rich nuclei are important for r- process calculations, and for calculations of processes occurring in the crust of accreting neutron stars. At the NSCL, a primary beam $^{86}$Kr was accelerated in the K500 and K1200 coupled superconducting cyclotrons to the energy of 100MeV/u. A fast radioactive beam was then produced by fragmentation reactions in the 47 mg/cm$^{2}$ and 94 mg/cm$^{2}$ Be targets and separated in the A1900 fragment separator. For this experiment a 58 m long time-of-flight path was used starting at the extended focal plane of the A1900 and ending at the focal plane of the S800 spectrograph. Fast scintillation detectors provided a timing resolution of about $\sigma$=30 ps, the relative magnetic rigidity B$\rho$ was measured at the momentum dispersive plane of the S800 by position sensitive micro-channel plate (MCP) detectors. Details of the experimental technique will be discussed and preliminary results will be presented.