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J. Okolowicz

Publications and source records attributed to J. Okolowicz.

At least 19 recordsLinked to original sources
arXiv2019

Invariant-mass spectroscopy of $^{14}$O excited states

Excited states in $^{14}$O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast $^{15}$O beam and the invariant-mass technique was employed to isolate the 1$p$ and 2$p$ decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2$^{+}$ state that we find is in near degeneracy with the third 0$^{+}$ state. An interesting case of sequential 2$p$ decay through a pair of degenerate $^{13}$N excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons.

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arXiv2016

An above-barrier narrow resonance in $^{15}$F

Intense and purified radioactive beam of post-accelerated $^{14}$O was used to study the low-lying states in the unbound $^{15}$F nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E$\_R$=4.757(6)(10)~MeV with a width of $Γ$=36(5)(14)~keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a $^{12}$C core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the $2s\_{1/2}$ shell.

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arXiv2012

On the origin of nuclear clustering

Clustering is one of the most complex phenomena known to the structure of atomic nuclei. A comprehensive description of this ubiquitous phenomenon goes beyond standard shell model and cluster model frameworks. We argue that clustering is a consequence of an openness of the nuclear many-body system. To illustrate this point, we study the near-threshold behavior of exceptional points in ^16 Ne and ^24 S.

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arXiv2010

Open problems in theory of nuclear open quantum systems

Is there a connection between the branch point singularity at the particle emission threshold and the appearance of cluster states which reveal the structure of a corresponding reaction channel? Which nuclear states are most impacted by the coupling to the scattering continuum? What should be the most important steps in developing the theory that will truly unify nuclear structure and nuclear reactions? The common denominator of these questions is the continuum shell-model approach to bound and unbound nuclear states, nuclear decays, and reactions.

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arXiv2008

Degeneracies in a nonintegrable pairing model

The evolution pattern of exceptional points is studied in a non-integrable limit of the complex-extended 3-level Richardson-Gaudin model. The appearance of a pseudo-diabolic point from the fusion of two exceptional points is demonstrated in the anti-hermitian limit of the model and studied in some details.

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arXiv2008

Unexpected features of quantum degeneracies in a pairing model with two integrable limits

The evolution pattern of level crossings and exceptional points is studied in a non-integrable pairing model with two different integrable limits. One of the integrable limits has two independent parameter-dependent integrals of motion. We demonstrate, and illustrate in our model, that quantum integrability of a system with more than one parameter-dependent integral of motion is always signaled by level crossings of a complex-extended Hamiltonian. We also find that integrability implies a reduced number of exceptional points. Both properties could uniquely characterize quantum integrability in small Hilbert spaces.

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arXiv2006

Microscopic theory of the two-proton radioactivity

We formulate theory of the two-proton radioactivity based on the real-energy continuum shell model. This microscopic approach is applied to describe the two-proton decay of the $1^-_2$ state in $^{18}$Ne.

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arXiv2005

Description of the 17F(p,gamma)18Ne radiative capture reaction in the continuum shell model

The shell model embedded in the continuum is applied to calculate the astrophysical S-factor and the reaction rate for the radiative proton capture reaction 17F(p,gamma)18Ne. The dominant contribution to the cross-section at very low energies is due to M1 transitions J_i^pi = 2^+ --> J_f^pi = 2_1^+ whose magnitude is controlled by a weakly bound 2_2^+ state at the excitation energy E_x = 3.62 MeV.

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arXiv2003

Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States

We present the study of weakly bound, neutron-rich nuclei using the nuclear shell model employing the complex Berggren ensemble representing the bound single-particle states, unbound Gamow states, and the non-resonant continuum. In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body finite depth (Woods-Saxon) potential and a residual two-body interaction. We discuss the basic ingredients of the Gamow Shell Model. The formalism is illustrated by calculations involving {\it several} valence neutrons outside the double-magic core: $^{6-10}$He and $^{18-22}$O.

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arXiv2001

First-forbidden mirror beta-decays in A=17 mass region

The first-forbidden beta-decay of 17Ne into the 'halo' state J=1/2+ of 17F presents one of the largest measured asymmetries for mirror beta-decay feeding bound final states. This asymmetry is studied in the framework of the Shell Model Embedded in the Continuum (SMEC). The spatial extent of single particle orbits is constrained by the proton capture cross-section 16O(p,gamma)17F calculated in SMEC . This allows to estimate the mirror symmetry breaking in 17F/17O and 17Ne/17N nuclei.

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arXiv2001

Descritpion of Exotic Nuclei Using Continuum Shell Model

In weakly bound exotic nuclei, number of excited bound states or narrow resonances is small and, moreover, they couple strongly to the particle continuum. Hence, these systems should be described in the quantum open system formalism which does not artificially separate the subspaces of (quasi-) bound and scattering states. The Shell Model Embedded in the Continuum provides a novel approach which solves this problem. Examples of application in sd-shell nuclei will be presented.

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arXiv2000

Shell model description of 16O(p,gamma)17F and 16O(p,p)16O reactions

We present shell model calculations of both the structure of 17F and the reactions 16O(p,gamma)17F, 16O(p,p)16O. We use the ZBM interaction which provides a good description of the properties of 16O and neighbouring nuclei and, in particular it takes account for the complicated correlations in coexisting low-lying states of 16O.

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