Proton-proton correlations observed in two-proton decay ofMg19andNe16

Abstract

Proton-proton correlations were observed for the two-proton decays of the ground states of 19 Mg and 16 Ne. The trajectories of the respective decay products, 17 Ne+p+p and 14 O+p+p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.PACS numbers: 21.10.-k; 21.45.+v; 23.50.+z The recently discovered two-proton (2p) radioactivity is a specific type of genuine three-particle nuclear decays. It occurs when a resonance in any pair of fragments is located at higher energies than in the initial three-body (p+p+"core") nucleus, and thus simultaneous emission of two protons is the only decay channel. Three-body systems have more degrees of freedom in comparison with two-body systems, hence additional observables appear. In the case of 2p emission, the energy spectra of single protons become continuous, and proton-proton (p-p) correlations are available, which makes them a prospective probe for nuclear structure or/and the decay mechanism. For example, the first p-p correlations observed in the 2p radioactivity of 94m Ag have revealed strong proton yields either in the same or opposite directions which called for a theory of 2p emission from deformed nuclei [1]. Two-proton emission can also occur from short-lived nuclear resonances or excited states (see, e.g., [2,3,4]). Though in this case the mechanism of 2p emission may depend on the reaction populating the parent state, such nuclei can be easily studied in-flight. E.g., the cases of 6 Be [2, 5] and 16 Ne [6]were studied by analyzing their p-p correlations in the framework of a three-body partialwave analysis developed for three-particle decays of light nuclei. In particular, the study of 6 Be revealed the existence of three-particle p+p+α correlations [2] which matched the three-body components found theoretically in the p-shell structure of 6 Be [7]. Very recently, p-p correlations were also observed in 2p radioactivity of 45 Fe [8,9] where both the lifetime and p-p correlations were found to reflect the structure of pf -shell 2p precursors [9]. Such a way of obtaining spectroscopic information is a novel feature compared to studies of two-particle decays.In the present paper, we study for the first time the p-p correlations in sd shell nuclei via examples of the 2p decays of 19 Mg and 16 Ne. These nuclei with very different half lives (T 1/2 ≈ 4 · 10 −9 s [10] and T 1/2 ≈ 4 · 10 −19 s [11], respectively) and presumably different spectroscopic properties may serve as reference cases illuminating the nuclear structure of other possible 2p emitters with sdwave configuration.The decay properties of the 16 Ne and 19 Mg ground states and the related resonances in 15 F and 18 Na are shown in Fig. 1 which compiles the data from Refs....

Observation and Spectroscopy of New Proton-Unbound IsotopesAr30andCl2

“…population. Previous studies of 16 Ne, 19 Mg populated in neutron-knockout reactions at intermediate energy [13,14,16] show that cross sections of the g.s. population contain a large part (of 10%-15%) of the excitation spectrum, which agrees also with studies of 6 Be, 12 O, and 16 Ne at lower energies [11,12,29].…”

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

“…[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.…”

Correlated two-proton decay fromC10

“…2 8 Be → α + α, (c) 6 Be → p + p + α∩ no 8 Be g.s. , and (d) 9 B → p + α + α∩ no 8 Be g.s. correlations.…”

“…Excellent cases for sequential decay (e.g., 12 O [4]) and nearly uniform sampling of three-body phase space (e.g., 6 Be g.s. [5][6][7], 16 Ne, 19 Mg [8,9], and 45 Fe [10]) exist. The 45 Fe case is a beautiful example of the single-particle orbital angular momentum of the protons in the parent being impressed on the three-body dynamics [10].…”