# A detector for filtering $\gamma$-ray spectra from weak fusion–evaporation reactions out of strong background and for Doppler correction: The recoil filter detector, RFD

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 \gamma-rays detected in a Ge-detector array. This permits filtering of such \gamma-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 \gamma-emitting recoil is also measured in the event-by-event mode, facilitating to correct the registered \gamma-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 \gamma-ray spectrometers. The usefulness of the technique for spectroscopic investigations of nuclei with a continuous beam is also discussed.
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Submitted on : Friday, October 5, 2007 - 11:30:51 AM
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### Citation

W. Meczynski, P. Bednarczyk, J. Grebosz, J. Heese, M. Janicki, et al.. A detector for filtering $\gamma$-ray spectra from weak fusion–evaporation reactions out of strong background and for Doppler correction: The recoil filter detector, RFD. Nuclear Instruments and Methods in Physics Research, Elsevier, 2007, 580, pp.1310-1326. ⟨10.1016/j.nima.2007.07.132⟩. ⟨in2p3-00176994⟩

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