# Commissioning

The FRS Ion Catcher experiment at GSI enables precision experiments with thermalized projectile and ﬁssion fragments. At the same time the FRS Ion Catcher serves as a test facility for the Low-Energy Branch of the Super-FRS at FAIR. The performance of the FRS Ion Catcher, from thermalization of relativistic exotic nuclei to high accuracy mass measurements, has been characterized in ﬁve experiments with $^{ 238}$U and $^{ 124 }$Xe projectile and ﬁssion fragments produced at energies in the range from 300 to 1000 MeV/u. The CSC was the first of its kind to be operated with exotic nuclei at cryogenic temperatures (70 to 100 K). A helium stopping gas density of up to 0.05 $mg/cm^3$ was used, about two times higher than reached before for a stopping cell with RF ion repelling structures. An overall efficiency of up to 15%, a combined ion survival and extraction efficiency of about 50%, and extraction times of 24 ms were achieved for heavy α-decaying uranium fragment. High-accuracy mass measurements of more than 40 projectile and ﬁssion fragments have been performed with the MR-TOF-MS at mass resolving powers of up to 450,000 with production cross sections down to the tens of nanobarn-level and at rates down to a few ions per hour. The versatility of the MR-TOF-MS for isomer research has been demonstrate by the measurements of 15 isomers, determination of excitation energies and the production of a pure isomeric beam.

The weighted mean of all relative deviations is 4.5 ± 5.3 × 10$^{-8}$ and the standard deviation is 3.5 × 10$^{-7}$.

Some references for the past results of the FRS Ion Catcher can be found here: