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Compound-Nucleus and Doorway-State Decays of β -Delayed Neutron Emitters K 51 , 52 , 53
Z. Y. Xu (University of Tennessee at Knoxville), R. Grzywacz (Oak Ridge National Laboratory, University of Tennessee at Knoxville), A. Gottardo (Université Paris-Saclay, Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro), Miguel Madurga (University of Tennessee at Knoxville), Irene M. Alonso (Consejo Superior de Investigaciones Científicas, Instituto de Estructura de la Materia), Andrei N. Andreyev (Japan Atomic Energy Agency, Advanced Science Research Center), G. Benzoni (Istituto Nazionale di Fisica Nucleare, Istituto Nazionale di Fisica Nucleare, Sezione di Milano), M. J. G. Borge (Consejo Superior de Investigaciones Científicas, Instituto de Estructura de la Materia), T. Cap (National Centre for Nuclear Research), C. Costache (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), H. De Witte (KU Leuven), Botyo Dimitrov (Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy), Jutta Escher (Lawrence Livermore National Laboratory), Aleksandra Fijałkowska (Rutgers, The State University of New Jersey, University of Warsaw), L. M. Fraile (Universidad Complutense de Madrid), S. Franchoo (Université Paris-Saclay), H. O. U. Fynbo (Aarhus University), Basil C. Gonsalves (University of Helsinki), Carl J. Gross (Oak Ridge National Laboratory), L. J. Harkness-Brennan (University of Liverpool), J. Heideman (University of Tennessee at Knoxville), M. Huyse (KU Leuven), D. S. Judson (University of Liverpool), Toshihiko Kawano (Los Alamos National Laboratory), Thomas T. King (Oak Ridge National Laboratory, University of Tennessee at Knoxville), S. Kisyov (Lawrence Berkeley National Laboratory, Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), Karolina Kolos (Lawrence Livermore National Laboratory), Agnieszka Korgul (University of Warsaw), Ian H. Lazarus (Science and Technology Facilities Council), R. Lică (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering, European Organization for Nuclear Research), M. L. Liu (Sun Yat-sen University), L. Lynch (European Organization for Nuclear Research), N. Marginean (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), R. Mărginean (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), C. Mazzocchi (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering, University of Warsaw), D. Mengoni (University of Padua, Istituto Nazionale di Fisica Nucleare), C. Mihai (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), A. I. Morales (Consejo Superior de Investigaciones Científicas, Universitat de València), Robert D. Page (University of Liverpool), J. Pakarinen (University of Helsinki, Helsinki Institute of Physics), S. V. Paulauskas (University of Tennessee at Knoxville), Angel Perea (Consejo Superior de Investigaciones Científicas, Instituto de Estructura de la Materia), M. Piersa-Siłkowska (University of Warsaw, European Organization for Nuclear Research), Zs. Podolyák (University of Surrey), Ch. Sotty (Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering), S. Taylor (University of Tennessee at Knoxville), O. Tengblad (Consejo Superior de Investigaciones Científicas, Instituto de Estructura de la Materia), Piet Van Duppen (KU Leuven), V. Vedia (Universidad Complutense de Madrid), D. Verney (Université Paris-Saclay), Nigel Warr (University of Cologne), Cenxi Yuan (Sun Yat-sen University)
Résumé : We investigated decays of ^{51,52,53}K at the ISOLDE Decay Station at CERN in order to understand the mechanism of the β-delayed neutron-emission (βn) process. The experiment quantified neutron and γ-ray emission paths for each precursor. We used this information to test the hypothesis, first formulated by Bohr in 1939, that neutrons in the βn process originate from the structureless "compound nucleus." The data are consistent with this postulate for most of the observed decay paths. The agreement, however, is surprising because the compound-nucleus stage should not be achieved in the studied β decay due to insufficient excitation energy and level densities in the neutron emitter. In the ^{53}K βn decay, we found a preferential population of the first excited state in ^{52}Ca that contradicted Bohr's hypothesis. The latter was interpreted as evidence for direct neutron emission sensitive to the structure of the neutron-unbound state. We propose that the observed nonstatistical neutron emission proceeds through the coupling with nearby doorway states that have large neutron-emission probabilities. The appearance of "compound-nucleus" decay is caused by the aggregated small contributions of multiple doorway states at higher excitation energy.