First Observation of the Unbound NucleusNe15

Abstract

We report on the first observation of the unbound proton-rich nucleus 15 Ne. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u 17 Ne. The 15 Ne ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to 13 O with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2 − and 1 − states in 14 F is observed. The 15 Ne ground state is shown to have a strong configuration with two protons in the (sd) shell around 13 O with a 63(5)% ð1s 1=2 Þ 2 component.

Thomas-Ehrman effect in a three-body model: TheNe16case

“…This uncertainty is often larger than the provided errors of particular experiments. Even the most recent experiments [8,9], both declaring to have the best precisions ever, disagree with each other for E T values of 0 + state beyond the provided errors. Thus the overall experimental situation is unsatisfactory already for the 0 + 16 Ne ground state energies.…”

“…Among the experimental data given in Table II, the four experiments enlisted first [8,9,18,19] provide both the 0 + and 2 + positions and thus allow to consider a consistency of these data with theoretical TES results as was done for [9] in Figure 4. Such a comparison is provided in Fig.…”

“…[4]. The 12 O, 16 Ne, and their isobaric mirror partners 12 Be, 16 Recently 16 Ne was studied in three experiments using neutron knockout from a 17 Ne beam [7][8][9], and providing data with better statistics and quality than in the previous works. This inspired us to revisit the issue and consider the TES effect in 16 Ne/ 16 C also in the broader context including the first excited 2 + states.…”

“…(i) The formulation provided by Eq. (5) is a simplistic, but reasonable approximation for the neutron knockout reaction mechanism used to populate 16 Ne states in the recent experimental studies [7][8][9]. Therefore, the differences in the approaches (4) and (5) is physically motivated.…”

Strong Neutron Pairing in core+4n Nuclei

“…The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14 C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay 21 Oð−1nÞ 20 …”