Probing Exotic, Particle-Decay Isotopes: A New Application of the Recoil Distance Method*

The application of the Recoil Distance Method (RDM) with the NSCL/K\"{o}ln plunger [1] has proven useful in the study of picosecond-lifetime excited states of rare isotopes at the NSCL [2]. With precise control over target/degrader separation distances on the micrometer scale, replacing the passive degrader with an active silicon detector provides a new probe at fast beam fragmentation facilities for studies of exotic particle-decay isotopes with picosecond lifetimes along the proton drip line. A recent experiment at the NSCL utilized this resulting NSCL/K\"{o}ln ``particle plunger'' in a lifetime study of the two-proton emitter $^{19}$Mg, produced by the one-neutron knockout of a $^{20}$Mg secondary beam. The method and preliminary results for this commissioning particle plunger RDM investigation will be presented. [1] A. Dewald \textit{et al.}, GSI Scientific Report 2005, p. 38 (2006). [2] K. Starosta \textit{et al.}, Phys. Rev. Lett. {\bf 99}, 042503 (2007).