Mass measurements of relativistic projectile fragments in the storage ringESR

Two experimental methods of measuring masses of exotic nuclei in the storag e ring ESR are presented. Bismuth and nickel fragments were produced via pr ojectile fragmentation, separated and investigated with the combination of the fragment separator FRS and the ESR: (i) Direct mass measurements of rel ativistic projectile,fragments were performed using Schottky mass spectrome try (SMS), i.e., exotic nuclei were stored and cooled in the ESR. Applying electron cooling, the relative velocity spread of circulating low intensity beams can be reduced below 10(-6). Under this condition a mass resolving p ower of up to m/Delta m = 6.5 . 10(5) (FWHM) was achieved in a recent measu rement. Previously unknown masses of more than 100 neutron-deficient isotop es have been measured in the range of 60 less than or equal to Z less than or equal to 84. Using known Q(alpha) values the area of known masses could be extended to more exotic nuclei and to higher proton numbers. The results are compared with mass models and extrapolations of experimental values. I n a second experiment with Bi-209 projectiles the area of the measured mass es was extended to lower proton numbers. Due to various improvements at the ESR the precision of the measurements could be raised. (ii) Exotic nuclei with half-lives shorter than the time needed for SMS (present limit: T-1/2 approximate to 5 sec) can be investigated by time-of-flight measurements wh ereby the ESR is operated in the isochronous mode. This novel experimental technique has been successfully applied in first measurements with nickel a nd neon fragments where a mass resolving power of m/Delta m = 1.5 . 10(5) ( FWHM) was achieved.