First experimental results of a cryogenic stoppingcell with short-lived, heavy uranium fragmentsproduced at 1000 MeV/u

A cryogenic stopping cell (CSC) has been commissioned with238U projectile frag-ments produced at 1000 MeV/u. The spatial isotopic separation in flight was performed with theFRS applying a monoenergetic degrader. For the first time, a stopping cell was operated withexotic nuclei at cryogenic temperatures (70 to 100 K). A helium stopping gas density of up to0.05 mg/cm3was used, about two times higher than reached before for a stopping cell with RF ionrepelling structures. An overall efficiency of up to 15%, a combined ion survival and extractionefficiency of about 50%, and extraction times of 24 ms were achieved for heavyα-decaying ura-nium fragments. Mass spectrometry with a multiple-reflection time-of-flight mass spectrometerhas demonstrated the excellent cleanliness of the CSC. This setup has opened a new field for thespectroscopy of short-lived nuclei.