EPJ Web of Conferences 232, 04002 (2020)
https://doi.org/10.1051/epjconf/202023204002

Structure of superheavy hydrogen ⁷H

¹ IGFAE – U. de Santiago de Compostela, E–15782 Santiago de Compostela, Spain.
² GANIL, CEA/DSM – CNRS/IN2P3, BP 55027, F–14076 Caen Cedex 5, France.
³ U. de Sevilla, E–41080 Sevilla, Spain.
⁴ Department of Physics, University of Regina, Regina, SK S4S 0A2, Canada.
⁵ KVI–CART, U. of Groningen, NL–9747 AA, Groningen, The Netherlands.
⁶ Instituut voor Kernen Stralingsfysica, KU Leuven, B–3001 Leuven, Belgium.
⁷ LPC de Caen, U. de Caen Basse–Normandie – ENSICAEN – CNRS/IN2P3, F–14050 Caen Cedex, France.
⁸ Yukawa Institute for Theoretical Physics, Kyoto University, 6068502 Kyoto, Japan.
⁹ IPN Orsay, U. Paris Sud, IN2P3 – CNRS, F–91406 Orsay Cedex, France.

^* e-mail: manuel.fresco@usc.es
^** e-mail: thomas.roger@ganil.fr

Published online: 6 April 2020

Abstract

The properties of nuclei with extreme neutron–to–proton ratios reveal the limitations of state-ofthe-art nuclear models and are key to understand nuclear forces. 7H, with six neutrons and a single proton, is the nuclear system with the most unbalanced neutron–to–proton ratio ever known, but its sheer existence and properties are still a challenge for experimental efforts and theoretical models. We report here the first measurement of the basic characteristics and structure of the ground state of ⁷H; they depict a system with a triton core surrounded by an extended four-neutron halo, built by neutron pairing, that decays through a unique four–neutron emission with a relatively long half-life. These properties are a prime example of new phenomena occurring in almost pure-neutron nuclear matter, beyond the binding limits of the nuclear landscape, that are yet to be described within our current models.