Towards the Limits of Existence of Nuclear Structure: Observation and First Spectroscopy of the Isotope 31K by Measuring Its Three-Proton Decay

The most remote isotope from the proton dripline (by 4 atomic mass units) has been observed: 31K. It is unbound with respect to three-proton (3 p ) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The 3 p emission processes have been studied by the means of angular correlations of 28S +3 p and the respective decay vertices. The energies of the previously unknown ground and excited states of 31K have been determined. This provides its 3 p separation energy value S3 p of -4.6 (2 ) MeV . Upper half-life limits of 10 ps of the observed 31K states have been derived from distributions of the measured decay vertices.This work was supported in part by the Helmholtz International Center for FAIR (HIC for FAIR); the Helmholtz Association (Grant No. IK-RU-002); the Russian Science Foundation (Grant No. 17-12-01367); the Polish National Science Center (Contract No. UMO2015/17/B/ST2/00581); the Polish Ministry of Science and Higher Education (Grant No. 0079/DIA/2014/43, Grant Diamentowy); the Helmholtz-CAS Joint Research Group (Grant No. HCJRG-108); the Ministry of Education & Science, Spain (Contract No. FPA2016-77689- C2-1-R); the Hessian Ministry for Science and Art (HMWK)through the LOEWE funding scheme; the Ministry of Education, Youth and Sports, Czech Republic (Projects LTT17003 and LM2015049); the JustusLiebig-Universit¨at Giessen (JLU) and the GSI under the JLU-GSI strategic Helmholtz partnership agreement; DGAPA-PAPIIT UNAM IA103218. This work was carried out in the framework of the Super-FRS Experiment Collaboration. This article is a part of the Ph.D. thesis of D. Kostyleva