Velocity determination of neutron-rich projectile fragments with a ring-imaging Cherenkov detector

For the velocity determination of relativistic heavy ions (A>100) in the energy range 300A.MeV ≤ Ekin ≤ 2A.GeV a highly resolving, compact ring-imaging Cherenkov counter with large dynamical measurement range was developed. The Cherenkov light cone emitted in the flight of a relativistic heavy ion by a liquid layer (C6F14) is focused on the entrance window of a one-dimensional position-resolving VUV-sensitive photon detector. This gas detector is operated at atmospheric pressure with a mixture of 90% methane and 10% isobutane with 0.04% TMAE as photosensitive admixture. For 725A.MeV 129Xe ions a velocity resolution Δβ/β=1.8.10-3 and a nuclear charge-number resolution ΔZ/Z=5.1.10-2 was reached. The over the photon energy range 5.4 eV ≤ Eγ ≤ 7.2 eV averaged detection efficiency of the detector system was determined to εtot=2.8%>. At the 0deg magnet spectrometer Fragmentseparator of the GSI Darmstadt the RICH detector was for the first time applied for the identification of nuclear charge number and mass of heavy relativistic projectile fragments. In the experiment the production cross sections of very neutron-rich nuclei by fragmentation of 136Xe projectiles in the reaction 76A.MeV 136Xe on 27Al were determined. From the measured production erates for the production of the double-magic nucleus 132Zn in this reaction a cross section of σ=(0.4±0.30.6) μbarn can be extrapolated. (orig./HSI)