Sensitivity of three-body decays to the reactions mechanism and the initial structure by example of6Be

Abstract

The influence of the initial-state structure and the reaction mechanism on three-body decays is investigated using the example of the 6 Be continuum populated in neutron-knockout reactions on 7 Be. The sensitivity of the 6 Be excitation spectrum and the three-body correlations to the different components of the model is demonstrated. It is shown that the spin composition of the initial state may have an overwhelming effect on the three-body continuum. The characteristics and structure of the second 0 + 2 and 2 + 2 states in 6 Be are predicted and the conditions for their reliable observations are formulated. The effects of interference and the alignment of three-body states on the three-body correlations are demonstrated.Introduction. The study of systems beyond nuclear driplines is an important trend in modern low-energy nuclear research. Many of these systems belong to the three-body or even few-body continuum, and the reaction theory for populating these states is not well developed. Modern high-precision experiments with exotic beams require complicated analyses and advanced theoretical treatment, and call for deeper insights in this field.Observables in reactions producing unbound systems depend on three major ingredients: (i) the structure of initial nuclei, (ii) the reaction mechanism, and (iii) the final-state interaction (FSI). For very narrow resonances (extremely long-lived states), the aspects (i) and (ii) lose importance as the structure formed in the reaction has enough time to "forget" how it was created. Then for a consistent description of the system, it is sufficient to study only the decay process (FSI effects) by itself. However, exactly when this approach becomes valid is not always clear in advance. Clarity in this issue is especially important for systems beyond the driplines, where the resonant states (often already the ground states) are quite broad.In this work, we demonstrate the importance of the reaction mechanism and the initial-state structure for investigations of few-body systems beyond the driplines using the example of 6 Be (three-body α + p + p continuum) populated in neutronknockout reactions from 7 Be projectiles. The first result of these studies has been published in Ref.[1], elucidating the mechanism of democratic decay. Good agreement with experimental data was demonstrated for both the excitation spectrum and the three-body energy-angular correlations over a broad range of excitation energy. However, in this compact experimental work, many important theoretical issues of broader interest were left aside. In the present work, we focus on the most interesting theoretical results arising from our studies of the data [1]. This is a timely message considering the recent interest in the 6 Be system [2-6]. We also think that these

Role of diproton correlation in two-proton-emission decay of theBe6nucleus

“…It has been considered now that the actual 2p-decays are often much more complicated than the simple diproton decays which Goldansky originally proposed [39][40][41][42][43][44][45][46][47]. Moreover, it has not been completely clarified whether the diproton correlation can be actually probed by observing 2p-decays.…”

Three-body correlations in direct reactions: Example of Be6 populated in the ( p,n ) reaction

“…The expression (11) is somewhat different from that stated in Ref. [9] as far as we explicitly provide summation over spin variables {S, M S } of the three-body channel, which are not measurable (at least in foreseen realistic experimental scenarios).…”

“…During the last decade, such an approach was applied to exotic neutron-and proton-rich systems beyond the driplines in the experiments at the Flerov Laboratory of Nuclear Reactions at JINR (Dubna, Russia). For example, the interference patterns for broad overlapping states with different J π were used for unambiguous spin-parity identification of low-lying 9 He continuous states decaying via 8 He + n channel [2]. An analogous method can be used for three-body systems, however in a technically much more complicated manner.…”

Anomalous population ofHe10states in reactions withLi11

“…It was shown in Ref. [22] how the three-body-correlation patterns become sensitive to the interference conditions and experimental bias. The correlations for the 1 − state by itself are given in Fig.…”