Development of a liquid scintillator based active fission target for FIPPS
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Special Article - New Tools and Techniques
Development of a liquid scintillator based active fission target for FIPPS F. Kandzia1,a , G. Belier2 , C. Michelagnoli1,b , J. Aupiais2 , M. Barani3 , J. Dudouet4 , Ch. E. Düllmann5,6,7 , Ł. W. Iskra8 , M. Jentschel1, Y. H. Kim1, U. Köster1, A. Turturica9 1
Institut Laue Langevin, 71 Avenue des Martyrs, 38042 Grenoble, France CEA, DAM, DIF, 91297 Arpajon, France 3 Dipartimento di Fisica, Universita degli Studi di Milano, Via Festa del Perdono 7, 20122 Milan, Italy 4 Université Lyon 1, CNRS/IN2P3, IPN-Lyon, 69622 Villeurbanne, France 5 Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany 6 GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany 7 Helmholtz Institut Mainz, 55099 Mainz, Germany 8 INFN sezione di Milano, Via Celoria 16, 20133 Milan, Italy 9 Horia Hulubei National Institute of Physics and Nuclear Engineering-IFIN HH, 077125 Bucharest, Romania
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Received: 14 April 2020 / Accepted: 12 July 2020 / Published online: 18 August 2020 © The Author(s) 2020 Communicated by Navin Alahari
Abstract An active fission target has been developed for the FIPPS instrument at ILL, enabling for the first time an efficient suppression of β-delayed γ rays in high-resolution and high-efficiency γ-ray spectroscopy of fission fragments at a neutron beam. The target is based on a liquid scintillator in which the actinide is dissolved, resulting in a 4π fragment detection. Measurements have been performed with 233,235 U, with a fission tagging efficiency of 97.8(25)%. The high efficiency, together with the good time resolution of the scintillator target, provide high-selectivity data for γ-ray spectroscopy studies of fission fragments.
1 Introduction In the last decades, γ-ray spectroscopy with germanium detector arrays has been established as a leading method for the determination of the structure of nuclei [1]. Various mechanisms are available to produce nuclei in excited states, one being nuclear fission. The spectroscopy of prompt γ rays from fission fragments allows to study neutron-rich isotopes in the mass range 80 < A < 160, with average spin states around 6–7 h¯ [2] and values up to 20 h¯ [3]. In the past, extensive studies have been performed with spontaneous fission sources e.g. with the EUROGAM/EUROBALL [4] and GAMMASPHERE [3,5] arrays as well as with neutroninduced fission, e.g. in the EXILL campaign [6] and heavya e-mail:
[email protected] (corresponding author)
b e-mail:
[email protected] (corresponding author)
ion induced fission [7,8]. In this kind of investigations, the identification of a given fission fragment relies on multiple γ-ray coincidence techniques. For this selection method to be efficient, high resolution, granularity and peak-over-total ratio are required from the γ-ray spectrometer. One limiting aspect of such studies, especially when investigating isotopes with small fission yields, is the γ-ray background originating from β decays of radioactive fission products, particularly compromising the quality of the coinciden
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