Affiliation: | aThe Henryk Niedwodniczański Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Kraków, Poland bGesellschaft für Schwerionenforschung mbH, Planckstr. 1, D-64291 Darmstadt, Germany cACCEL Instruments GmbH, Friedrich-Ebert-Str. 1, 51429 Bergisch Gladbach, Germany dInstitut de Recherches Subatomiques, 23, Rue du Loess, 67037 Strasbourg, France eUniversity of Paisley, Paisley PA1 2BE, Scotland, UK |
Abstract: | A detector has been designed and built to assist in-beam γ-ray spectroscopy with fusion–evaporation reactions. It measures with high efficiency the evaporation residues that recoil out of a thin target into the angular interval from 1.8° to 9.0° at an adjustable distance of 1000–1350 mm from a target, in coincidence with γ-rays detected in a Ge-detector array. This permits filtering of such γ-rays out of a much stronger background of other reaction products and scattered beam. Evaporation residues are identified by their time-of-flight and the pulse height using a pulsed beam. The velocity vector of the γ-emitting recoil is also measured in the event-by-event mode, facilitating to correct the registered γ-ray energy for the Doppler shift, with the resulting significant improvement of the energy resolution. The heavy-ion detection scheme uses emission of secondary electrons caused by the recoiling ions when hitting a thin foil. These electrons are then electrostatically accelerated and focused onto a small scintillator that measures the summed electron energy, which is proportional to the number of electrons. The detector is able to operate at high frequency of the order of 1 MHz and detect very heavy nuclei with as low kinetic energy as 5 MeV. The paper describes the properties of the detector and gives examples of measurements with the OSIRIS, GAREL+ and EUROBALL IV γ-ray spectrometers. The usefulness of the technique for spectroscopic investigations of nuclei with a continuous beam is also discussed. |