arXiv subjects

J. Okołowicz

Publications and source records attributed to J. Okołowicz.

15 recordsLinked to original sources

arXiv2025

Deviations from the Isobaric Multiplet Mass Equation due to threshold states

Recent studies have completed the A=16 isospin quintets for states with spin/parity Jπ =0+ and 2+. The dependence of their masses as a function of isospin projection shows evidence for deviations from quadratic behavior indicating isospin violation beyond the expectation from two- body forces. The deviation is most pronounced for the 2+ states. Predictions from the Shell Model Embedded in the Continuum (SMEC) allow us to explain that this isospin violation is associated with a modification of the nuclear structure due to the open-quantum-system nature of the proton- rich members of the quintet. In particular, the 0+ and 2+ states in 16Ne and the 2+ state in 16F are threshold resonances located just above a proton-decay threshold where s-wave coupling to the continuum is expected. The measured deviations of these threshold states from the quadratic behavior of the remaining members of the multiplets makes it possible to obtain information on the magnitude and the energy dependence of the continuum-coupling energy correction. Continuum coupling is also indicated for the ground state of 8C, but this time through p-wave coupling.

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arXiv2022

Near-threshold resonances in 11C and the 10B(p,α)7Be aneutronic reaction cross section

The nucleus 11C plays an important role in the boron-proton fusion reactor environment as a catalyzer of the 10B(p,α)7Be reaction which, by producing a long-lived isotope of 7Be, poisons the aneutronic fusion process 11B(p,2α)4He. The low-energy cross section of 10B(p,α)7Be depends on the near-threshold states 7/2+1 , 5/2+2 , 5/2+3 in 11C whose properties are primarily known from the indirect measurements. We investigate the continuum-coupling induced collectivization of these resonances in the shell model embedded in the continuum. We predict a significant enhancement of the 10B(p,α)7Be cross section at energies accessible to the laser-driven hot plasma facilities.

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arXiv2022

$β^-{\rm p}$ and $β^-α$ decay of the $^{11}$Be neutron halo ground state

Beta-delayed proton emission from the neutron halo ground state of $^{11}$Be raised much attention due to the unusually high decay rate. It was argued that this may be due to the existence of a resonance just above the proton decay threshold. In this Letter, we use the lenses of real-energy continuum shell model to describe several observables including the Gamow-Teller rates for the $β^-$-delayed $α$ and proton decays, and argue that, within our model, the large $β^-{\rm p}$ branching ratio cannot be reconciled with other data.

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arXiv2021

Spectroscopic factors in dripline nuclei

Single-nucleon knockout reaction studies of the proton-dripline nuclei $^9$C and $^{13}$O suggest an appreciable suppression of spectroscopic factors. In this work, we calculate the one-neutron and one-proton spectroscopic factors for the mirror pair $^9$C-$^9$Li and $^{13}$O using two variants of the continuum shell model: the complex-energy Gamow Shell Model and the real-energy Shell Model Embedded in the Continuum. Our results indicate that the continuum effects strongly suppress the spectroscopic factors of well-bound orbits in the dripline systems, but have less impact on the spectroscopic factors of weakly-bound states.

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arXiv2019

Electromagnetic transitions in near-threshold resonances

Near-threshold collectivization of continuum shell model eigenstates is investigated in $^{20}$O on the example of B(E$λ$) decays of 4$^+$ states in the vicinity of elastic and inelastic neutron threshold. Changes of the electromagnetic transition probabilities as a function of the continuum-coupling strength are explained by the corresponding evolution of the double poles of the scattering matrix.

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arXiv2019

Convenient location of a near-threshold proton-emitting resonance in $^{11}$B

The presence of cluster-like narrow resonances in the vicinity of reaction/decay thresholds is a ubiquitous phenomenon with profound consequences. We argue that the continuum coupling, present in the open quantum system description of the atomic nucleus, can profoundly impact the nature of near-threshold states. In this Letter, we discuss the structure of the recently observed near-threshold resonance in $^{11}$B, whose very existence explains the puzzling beta-delayed proton emission of the neutron-rich $^{11}$Be.

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arXiv2019

Collectivity of the electromagnetic transitions in near-threshold resonances

Mixing of the shell model (SM) eigenstates due to the coupling via the common decay channel leads in many cases to the formation of a collective eigenstate which carries many features of the nearby decay channel. This generic mechanism in open quantum systems explains the phenomenological Ikeda diagram and generalizes it for various clusters/correlations in the vicinity of the respective cluster decay thresholds. The near-threshold collectivization of the SM states may also influence their electromagnetic decays. We discuss this phenomenon on the example of B(EL) decays of near-threshold 2+ states in 14C.

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arXiv2015

Consistent analysis of one-nucleon spectroscopic factors involving weakly- and strongly-bound nucleons

There is a considerable interest in understanding the dependence of one-nucleon removal cross sections on the asymmetry of the neutron $S_n$ and proton $S_p$ separation energies, following a large amount of experimental data and theoretical analyses in a framework of sudden and eikonal approximations of the reaction dynamics. These theoretical calculations involve both the single-particle cross section and the shell-model description of the projectile initial state and final states of the reaction residues. The configuration mixing in shell-model description of nuclear states depends on the proximity of one-nucleon decay threshold but does it depend sensitively on $S_n - S_p$? To answer this question, we use the shell model embedded in the continuum to investigate the dependence of one-nucleon spectroscopic factors on the asymmetry of $S_n$ and $S_p$ for mirror nuclei $^{24}$Si, $^{24}$Ne and $^{28}$S, $^{28}$Mg and for a series of neon isotopes ($20 \leq A \leq 28$).

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arXiv2013

Near-threshold correlations of neutrons

The appearance of charged-particle clustering in near-threshold configuration is a phenomenon that can be explained in the Open Quantum System description of the atomic nucleus. In this work we apply the realistic Shell Model Embedded in the Continuum to elucidate the emergence of neutron correlations in near-threshold many-body states coupled to l=1,2 neutron decay channels. Spectral consequences of such continuum coupling are briefly discussed together with the emergence of complex multi-neutron correlations.

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arXiv2012

Toward understanding the microscopic origin of nuclear clustering

Open Quantum System (OQS) description of a many-body system involves interaction of Shell Model (SM) states through the particle continuum. In realistic nuclear applications, this interaction may lead to collective phenomena in the ensemble of SM states. We claim that the nuclear clustering is an emergent, near-threshold phenomenon, which cannot be elucidated within the Closed Quantum System (CQS) framework. We approach this problem by investigating the near-threshold behavior of Exceptional Points (EPs) in the realistic Continuum Shell Model (CSM). The consequences for the alpha-clustering phenomenon are discussed.

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arXiv2012

Asymptotic normalization coefficients and continuum coupling in mirror nuclei

Background: An asymptotic normalization coefficient (ANC) characterizes the asymptotic form of a one-nucleon overlap integral required for description of nucleon-removal reactions. Purpose: We investigate the impact of the particle continuum on proton and neutron ANCs for mirror systems from $p$- and $sd$-shell regions. Method: We use the real-energy and complex-energy continuum shell model approaches. Results: We studied the general structure of the single-particle ANCs as a function of the binding energy and orbital angular momentum. We computed ANCs in mirror nuclei for different physical situations, including capture reactions to weakly-bound and unbound states. Conclusions: We demonstrated that the single-particle ANCs exhibit generic behavior that is different for charged and neutral particles. We verified the previously proposed relation [N.K. Timofeyuk, R.C. Johnson, and A.M. Mukhamedzhanov, Phys. Rev. Lett. 91, 232501 (2003); Phys. Rev. Lett. 97, 069904(E) (2006); N. K. Timofeyuk and P. Descouvemont, Phys. Rev. C 72, 064324 (2005)] between proton and neutron mirror ANCs. We find minor modifications if the spectroscopic strength is either localized in a single state or broadly distributed. For cases when several states couple strongly to the decay channel, these modifications may reach 30%.

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arXiv2009

Exceptional points in the scattering continuum

The manifestation of exceptional points in the scattering continuum of atomic nucleus is studied using the real-energy continuum shell model. It is shown that low-energy exceptional points appear for realistic values of coupling to the continuum and, hence, could be accessible experimentally. Experimental signatures are proposed which include the jump by $2π$ of the elastic scattering phase shift and a salient energy dependence of cross-sections in the vicinity of the exceptional point.

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arXiv2003

Dynamics of open quantum systems

The coupling between the states of a system and the continuum into which it is embedded, induces correlations that are especially large in the short time scale. These correlations cannot be calculated by using a statistical or perturbational approach. They are, however, involved in an approach describing structure and reaction aspects in a unified manner. Such a model is the SMEC (shell model embedded in the continuum). Some characteristic results obtained from SMEC as well as some aspects of the correlations induced by the coupling to the continuum are discussed.

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arXiv1995

Chaos induced by Pauli blocking

Dynamics of classical scattering in the system of fermions is studied. The model is based on the coherent state representation and the equations of motion for fermions are derived from the time-dependent variational principle. It is found that the antisymmetrization due to the Pauli exclusion principle, may lead to hyperbolic chaotic scattering even in the absence of interaction between particles. At low bombarding energies, the same effect leads to the screening of the hard, short-ranged component in the two particle interaction and thus regularizes the dynamics.

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arXiv1994

Molecular dynamics approach: from chaotic to statistical properties of compound nuclei

Statistical aspects of the dynamics of chaotic scattering in the classical model of $α$-cluster nuclei are studied. It is found that the dynamics governed by hyperbolic instabilities which results in an exponential decay of the survival probability evolves to a limiting energy distribution whose density develops the Boltzmann form. The angular distribution of the corresponding decay products shows symmetry with respect to $π/2$ angle. Time estimated for the compound nucleus formation ranges within the order of $10^{-21}$s.

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