Possibility to study a two-proton halo inNe17

Abstract

The nuclide17 Ne is studied theoretically in a three-body 15 O+p+p model. We demonstrate that the experimental condition for existence of a proton halo in 17 Ne can be reasonably quantified in terms of s/d configuration mixing. We discuss experimental evidences for a proton halo in 17 Ne. We define which kind of experimental data could elucidate this issue.PACS numbers: 21.60. Gx, 21.10.Sf, 25.60.Dz, 25.60.Gc The 17 Ne nucleus is an interesting and relatively poorly studied system. It is a Borromean nucleus, since none of the binary subsystems (15 O-p and p-p) are bound. It seems to be the only realistic candidate to possess a twoproton halo [1,2]. The level scheme was established not so long ago [3] in multineutron transfer reactions. Available experimental data include Coulomb excitation [4,5] and low energy nuclear fragmentation [6,7] configuration is predicted to dominate, while in paper [11] the dominating configuration is predicted to be d 2 . In paper [12] effects of the "halo" kind (connected with larger radial extension of WF on the proton side) were considered being irrelevant for the β-decay asymmetry problem [9]. However, in paper [14] the β-decay asymmetry was successfully explained in these terms. It seems that theoretical agreement about the basic properties of 17 Ne is still missing at the moment.In papers [7,15] the comparatively narrow core momentum distribution was interpreted as possible evidence for proton halo in 17 Ne. This is a reasonable approach to the problem, as among typical experimental evidences for halo (e.g. large interaction, electromagnetic dissociation, and nucleon removal cross sections), the momentum distributions should give most expressed signal for this system. The aim of this paper is to test three-body WFs, obtained in [2], against the most recent experimental data [5,7]. We demonstrate that the experimental question of the proton halo existence in 17 Ne formulated as in [7,15] is largely defined by s/d configuration mixing. As we have already mentioned, the exact s/d ratio in 17 Ne is difficult to obtain unambiguously by theoretical calculations. To derive it from experimental data it is necessary to know the sensitivity of various observables to this aspect of the dynamics. We show that currently available experimental data are insufficient to determine reliably the structure (and possible halo properties) of 17 Ne. We can, however, confidently define which kind of experimental data is required to resolve the puzzling issues of the 17 Ne structure. the admixture of excited core configurations was found to be below 5 %, which is not enough to change "bulk" properties of these nuclei significantly. The core matter radius enters the definition of the composite system radius, the core charge radius is used to define a Coulomb interaction (if needed). For 15 N the charge radius is known from electron scattering r ch ( 15 N) = 2.615 fm [18]. The corresponding matter radius is r mat ( 15 N) = 2.49 fm. We estimated the matter radius of 15 O in two ways (from known experim...

Exclusive measurements of nuclear breakup reactions of17Ne

“…While earlier experiments had already revealed certain indications for the halo characteristics of 17 Ne (e.g., an anomalous beta decay branching ratio [4], and large matter radius [5]), the more recent experimental and theoretical studies have focused on the s 2 -weight in the s 2 /d 2 configuration mixture of the valence proton pair in the 17 Ne ground state. Yet, there is no final conclusion: the three-body model of Grigorenko et al [6], which is the benchmark for our study, predicts a value of 48 %. Kanungo et al [7] have measured narrow longitudinal-momentum distributions of the 15 O core in connection with a large cross section in 2p-removal reactions from 17 Ne beams on a Be target.…”

“…Using the invariant-mass technique, the 15 Op relative kinetic energy distribution has been determined and is shown in figure 1(a), next to the 16 F level scheme (b), and a reaction scheme (c). In figure 1(a), the experimental data (black markers) 17 Ne core and halo states, as depicted in [6].…”

“…The goal is to clarify the 17 Ne ground-state structure and its long proclaimed candidacy as a 2-proton halo nucleus [3]. Like the famous 2n-halo nuclei 11 Li or 6 He, 17 Ne is a Borromean three-body system. Its binary subsystems (p-p and 15 O-p) are unbound, and it can be described as an 15 O core with two valence protons, predominantly in (1s 1/2 ) 2 or (0d 5/2 ) 2 configurations.…”

Search for 2p decay of the first excited state of Ne17

“…This is a borromean nucleus: its 16 F subsystem is unbound with S p ( 16 F) = −535 keV. The situation with 17 Ne separation energies is highly analogous to that with the "classical" two-neutron halo nucleus 6 He and thus the question about the existence of the two-proton halo in 17 Ne was formulated in Ref. [4].…”

“…The intrigue of this problem is enhanced by the fact that the 17 Ne nucleus is probably the only realistic candidate to possess a two-proton halo as in heavier proton dripline systems the specific spatial extension of the valence nucleon wave functions should be suppressed by the Coulomb interaction. The issue of two-proton halo in 17 Ne was discussed in the theory papers [5,6] and experimental works [7,8].…”