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The dynamic mechanism of the Thomas-Ehrman shift in three-cluster systems is studied by using the example of 16Ne and 16C isobaric mirror partners. We predict configuration mixings for 0+ and 2+ states in 16Ne and 16C. Large isospin symmetry breaking on the level of wave function component weights is demonstrated for these states and discussed as a three-body mechanism of the Thomas-Ehrman shift. It is shown that the description of the Coulomb displacement energies requires consistency among three parameters: the 16Ne decay energy ET, the F15 ground-state energy Er, and the configuration mixing parameters for the 16Ne and 16C0+ and 2+ states. Based on this analysis we infer the F151/2+ ground-state energy to be Er = 1.39-1.42 MeV. [ABSTRACT FROM AUTHOR]

The structure and decay of 26O are investigated in a three-body 24O+n+n model suitable for studies of the long-lived (including radioactivity time scale) states. We have found extremely strong effects of the subbarrier configuration mixing on the decay width of true 2n emitters due to core recoil and neutron-neutron final state interaction. This effect far exceeds the analogous effect in the true 2p emitters. Our calculations provide reasonably narrow boundaries for the lifetime vs decay energy dependence for the true 2n emission. An upper limit of ~1 keV for the decay energy of the unbound 26O is inferred based on the recent experimental lifetime value. [ABSTRACT FROM AUTHOR]

An unusually large value of the 22C matter radius has recently been extracted from measured reaction cross sections. The giant size can be explained by a very loose binding that is, however, not known experimentally yet. Within the three-body cluster model we have explored the sensitivity of the s-motion-dominated 22C geometry to the two-neutron separation energy. A low energy of a few tens of keV is required to reach the alleged experimental lower value of the matter radius, while the experimental mean radius requires an extremely tiny binding. The dependence of the22C charge radius on the two-neutron separation energy is also presented. The soft dipole mode in 22C is shown to be strongly affected by the loose binding and should be studied in the process of Coulomb fragmentation. [ABSTRACT FROM AUTHOR]

Exploratory studies of two-proton emission from the unbound ground states of 30Ar and 34Ca are performed in a three-body core+p+p model. The lifetime dependencies on the decay energy are provided. Observation of the products from the in-flight decay of nuclei, obtained in a fragmentation experiment seems to be an adequate technique for the broad range of 30Ar and 34Ca lifetimes. Predictions for the 45Fe lifetime are discussed in details. Various forms of quasiclassical estimates are compared with the calculation results for 19Mg, 30Ar, 34Ca, and 45Fe. We study conditions of applicability of these estimates and ways to overcome their internal problems. [Copyright &y& Elsevier]

We discuss perspectives of studies of two-proton emission from the unbound ground state of 19Mg. The structure of 19Mg and the emission process are studied in a three-body model. Accurate estimates of the decay energy are provided in order to estimate the lifetime. We conclude that observation of the fragments from the in-flight decay of the nucleus, created by high-energy fragmentation, is an adequate experimental technique for the broad range of possible lifetimes of 19Mg. The 17Ne nucleus is studied in a three-body model to calibrate the model for 19Mg. Basing on the Coulomb displacement energy analysis the weight of the s2 component in 17Ne is predicted to be 40–50%. [Copyright &y& Elsevier]

Modern few-body methods for investigating Borromean two-neutron halo nuclei are discussed together with recent experiments. Advances in the studies of [sup 6]He and [sup 11]Li are analyzed. Some new problems created by a large neutron excess and a halo phenomenon are considered. [ABSTRACT FROM AUTHOR]

Mechanism of simultaneous non-sequential four-neutron (4n) emission (or "true" 4n-decay) has been considered in phenomenological five-body approach. This approach is analogous to the model of the direct decay to the continuum often applied to 2n- and 2p-decays. It is demonstrated that 4n-decay fragments should have specific energy and angular correlations reflecting strong spatial correlations of "valence" nucleons orbiting in their 4n-precursors. Due to the Pauli exclusion principle, the valence neutrons are pushed to the symmetry-allowed configurations in the 4n-precursor structure, which causes a "Pauli focusing" effect. Prospects of the observation of the Pauli focusing have been considered for the 4n-precursors 7H and 28O. Fingerprints of their nuclear structure or/and decay dynamics are predicted. [ABSTRACT FROM AUTHOR]

Emission of two neutrons or two protons in reactions and decays is often discussed in terms of "dineutron" or "diproton" emission. The discussion often leans intuitively on something described by Migdal-Watson approximation. In this work we propose a way to formalize situations of dineutron emission. It is demonstrated that properly formally defined dineutron emission may reveal properties which are drastically different from those traditionally expected, and properties which are actually observed in three-body decays. [ABSTRACT FROM AUTHOR]

The interaction of an E/A = 57.6-MeV 17Ne beam with a Be target is used to populate levels in 16Ne following neutron knockout reactions. The decay of 16Ne states into the three-body 14O + p + p continuum is observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit T < 80 keV for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically. [ABSTRACT FROM AUTHOR]

The influence of the initial-state structure and the reaction mechanism on three-body decays is investigated using the example of the 6Be continuum populated in neutron-knockout reactions on 7Be. The sensitivity of the 6Be 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 O2+ and 22+ states in 6Be 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. [ABSTRACT FROM AUTHOR]

Coulomb and nuclear dissociation of 17Ne on light and heavy targets are studied theoretically. The dipole E1 strength function is determined in a broad energy range including energies of astrophysical interest. Dependence of the strength function on different parameters of the 17 Ne ground-state structure and continuum dynamics is analyzed in a three-body model. The discovered dependence plays an important role for studies of the strength functions for the three-body E1 dissociation and radiative capture. The constraints on the [ s ² ] / [ d ² ] configuration mixing in 17 Ne and on p -wave interaction in the 15 O + p channel are imposed based on experimental data for 17 Ne Coulomb dissociation on heavy target. [ABSTRACT FROM AUTHOR]

An unusually large value of the 22C matter radius, extracted by Tanaka et al. [Phys. Rev. Lett. 104, 062701 (2010)] from measured reaction cross sections, attracted great attention of scientific community. Since that time, several experimental works related to the 22C nucleus have appeared in the literature. Some of the experimental data, measured with high accuracy, allow us to fix 22C structure more reliably. Two limiting models reproducing 22C nuclear structure within the three-body cluster approach, that allow us to describe all existing experimental data, are presented. The 22C ground state, continuum structure, and geometry are obtained. With fixed 22C wave function, the prediction for the soft dipole mode in 22C, which is studied in the process of Coulomb fragmentation, is performed. [ABSTRACT FROM AUTHOR]

The lifetime of the recently discovered 2p emitter 67Kr was found to be considerably below the lower limit predicted theoretically. This communication addresses this issue. Different separation energy systematics are analyzed and different mechanisms for 2p emission are evaluated. We find that the most plausible reason for this disagreement is the decay mechanism of 67Kr, which is not "true 2p" emission but rather "transitional dynamics" on the borderline between true 2p and sequential 2p decay mechanisms. If this is correct, this imposes stringent limits of Er=1.35-1.42 MeV on the ground-state energy of 66Br relative to the 65Se-p threshold. [ABSTRACT FROM AUTHOR]

A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades 1 , with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far 2-4 , leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy 8 He beam was key., (© 2022. The Author(s).)

The ^{7}H system was populated in the ^{2}H(^{8}He,^{3}He)^{7}H reaction with a 26 AMeV ^{8}He beam. The ^{7}H missing mass energy spectrum, the ^{3}H energy and angular distributions in the ^{7}H decay frame were reconstructed. The ^{7}H missing mass spectrum shows a peak, which can be interpreted either as unresolved 5/2^{+} and 3/2^{+} doublet or one of these states at 6.5(5) MeV. The data also provide indications of the 1/2^{+} ground state of ^{7}H located at 1.8(5) MeV with quite a low population cross section of ∼25  μb/sr within angular range θ&#95;{c.m.}≃(17°-27°).

The most remote isotope from the proton dripline (by 4 atomic mass units) has been observed: ^{31}K. It is unbound with respect to three-proton (3p) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The 3p emission processes have been studied by the means of angular correlations of ^{28}S+3p and the respective decay vertices. The energies of the previously unknown ground and excited states of ^{31}K have been determined. This provides its 3p separation energy value S&#95;{3p} of -4.6(2)  MeV. Upper half-life limits of 10 ps of the observed ^{31}K states have been derived from distributions of the measured decay vertices.

Previously unknown isotopes (30)Ar and (29)Cl have been identified by measurement of the trajectories of their in-flight decay products (28)S+p+p and (28)S+p, respectively. The analysis of angular correlations of the fragments provided information on decay energies and the structure of the parent states. The ground states of (30)Ar and (29)Cl were found at 2.25(-0.10)(+0.15) and 1.8±0.1  MeV above the two- and one-proton thresholds, respectively. The lowest states in (30)Ar and (29)Cl point to a violation of isobaric symmetry in the structure of these unbound nuclei. The two-proton decay has been identified in a transition region between simultaneous two-proton and sequential proton emissions from the (30)Ar ground state, which is characterized by an interplay of three-body and two-body decay mechanisms. The first hint of a fine structure of the two-proton decay of (30)Ar*(2(+)) has been obtained by detecting two decay branches into the ground and first-excited states of the (28)S fragment.

We present a synthesis method to fabricate framed carbon-based nanostructures having highly anisotropic shapes, in particular, the nanofork and nanoscalpel structures which are obtained systematically under optimized growth conditions. A theoretical model is developed to explain the formation of such nanostructures on Si cantilevers and W etched wires exposed to a focused electron beam. We then demonstrate the potentials of these nanostructures as functional tips for scanning probe microscopy. Owing to their anisotropic shapes, such tips can be very useful for nanolithography, nanosurgery of biological objects, and precise manipulation with surface particles. Overall, our method provides a simple and robust way to produce functional scanning probe microscopy tips with variable shapes and enhanced capabilities for different applications compared to standard cantilevers., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The interaction of an E/A=57.6-MeV ^{17}Ne beam with a Be target is used to populate levels in ^{16}Ne following neutron knockout reactions. The decay of ^{16}Ne states into the three-body ^{14}O+p+p continuum is observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit Γ<80  keV for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.