arXiv subjects

Tomohiro Oishi

Publications and source records attributed to Tomohiro Oishi.

25 records · Page 2Linked to original sources

arXiv2018

One-proton emission from the $^6_Λ$Li hypernucleus

One-proton (1p) radioactive emission under the influence of the $Λ^0$-hyperon inclusion is discussed. I investigate the hyper-1p emitter, $^6_Λ$Li, with a time-dependent three-body model. Two-body interactions for $α$-proton and $α$-$Λ^0$ subsystems are determined consistently to their resonant and bound energies, respectively. For a proton-$Λ^0$ subsystem, a contact interaction, which can be linked to the vacuum-scattering length of the proton-$Λ^0$ scattering, is employed. A noticeable sensitivity of the 1p-emission observables to the scattering length of the proton-$Λ^0$ interaction is shown. The $Λ^0$-hyperon inclusion leads to a remarkable fall of the 1p-resonance energy and width from the hyperon-less $α$-proton resonance. For some empirical values of the proton-$Λ^0$ scattering length, the 1p-resonance width is suggested to be of the order of $0.1-0.01$ MeV. Thus, the 1p emission from $^6_Λ$Li may occur in the timescale of $10^{-20}-10^{-21}$ seconds, which is sufficiently shorter than the self-decay lifetime of $Λ^0$, $10^{-10}$ seconds. By taking the spin-dependence of the proton-$Λ^0$ interaction into account, a remarkable split of the $J^π=1^-$ and $2^-$ 1p-resonance states is predicted. It is also suggested that, if the spin-singlet proton-$Λ^0$ interaction is sufficiently attractive, the 1p emission from the $1^-$ ground state is forbidden. From these results, I conclude that the 1p emission can be a suitable phenomenon to investigate the basic properties of the hypernuclear interaction, for which a direct measurement is still difficult.

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arXiv2017

Dependence of two-proton radioactivity on nuclear pairing models

Sensitivity of two-proton emitting decay to nuclear pairing correlation is discussed within a time-dependent three-body model. We focus on the $^6$Be nucleus assuming $α+ p + p$ configuration, and its decay process is described as a time-evolution of the three-body resonance state. For a proton-proton subsystem, a schematic density-dependent contact (SDDC) pairing model is employed. From the time-dependent calculation, we observed the exponential decay rule of a two-proton emission. It is shown that the density dependence does not play a major role in determining the decay width, which can be controlled only by the asymptotic strength of the pairing interaction. This asymptotic pairing sensitivity can be understood in terms of the dynamics of the wave function driven by the three-body Hamiltonian, by monitoring the time-dependent density distribution. With this simple SDDC pairing model, there remains an impossible trinity problem: it cannot simultaneously reproduce the empirical $Q$ value, decay width, and the nucleon-nucleon scattering length. This problem suggests that a further sophistication of the theoretical pairing model is necessary, utilizing the two-proton radioactivity data as the reference quantities.

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arXiv2017

Correlation Energy of Proton-Neutron Subsystem in Valence Orbit

Deuteron correlation energy (DCE) of the valence proton-neutron subsystem is evaluated by utilizing a simple three-body model. We focus on the $^6$Li and $^{18}$F nuclei assuming the doubly-closed core and the valence proton and neutron. Two interaction models, schematic density-dependent contact (SDDC) and Minnesota potentials, are utilized to describe the proton-neutron interaction. Evaluating DCE, we conclude that the proton-neutron binding in $^6$Li can be stronger than its counterpart of a deuteron in vacuum. On the other hand, in $^{18}$F, the energetic correlation is remarkably weak, and does not favor the bound, deuteron-like configuration. This significant difference between two systems can be understood from a competition between the proton-neutron kinetic and pairing energies, which are sensitive to the spatial extension of the wave function. This result indicates a remarkable dependence of the deuteron correlation to its environment and the valence orbits.

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arXiv2017

Diagonalization scheme for the many-body Schroedinger equation

A new convenient method to diagonalize the non-relativistic many-body Schroedinger equation with two-body central potentials is derived. It combines kinematic rotations (democracy transformations) and exact calculation of overlap integrals between bases with different sets of mass-scaled Jacobi coordinates, thereby allowing for a great simplification of this formidable problem. We validate our method by obtaining a perfect correspondence with the exactly solvable three-body ($N=3$) Calogero model in 1D.

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arXiv2015

Finite amplitude method applied to giant dipole resonance in heavy rare-earth nuclei

Background: The quasiparticle random phase approximation (QRPA), within the framework of the nuclear density functional theory (DFT), has been a standard tool to access the collective excitations of the atomic nuclei. Recently, finite amplitude method (FAM) has been developed, in order to perform the QRPA calculations efficiently without any truncation on the two-quasiparticle model space. Purpose: We discuss the nuclear giant dipole resonance (GDR) in heavy rare-earth isotopes, for which the conventional matrix diagonalization of the QRPA is numerically demanding. A role of the Thomas-Reiche-Kuhn (TRK) sum rule enhancement factor, connected to the isovector effective mass, is also investigated. Methods: The electric dipole photoabsorption cross section was calculated within a parallelized FAM-QRPA scheme. We employed the Skyrme energy density functional self-consistently in the DFT calculation for the ground states and FAM-QRPA calculation for the excitations. Results: The mean GDR frequency and width are mostly reproduced with the FAM-QRPA, when compared to experimental data, although some deficiency is observed with isotopes heavier than erbium. A role of the TRK enhancement factor in actual GDR strength is clearly shown: its increment leads to a shift of the GDR strength to higher-energy region, without a significant change in the transition amplitudes. Conclusions: The newly developed FAM-QRPA scheme shows a remarkable efficiency, which enables to perform systematic analysis of GDR for heavy rare-earth nuclei. Theoretical deficiency of photoabsorption cross section could not be improved by only adjusting the TRK enhancement factor, suggesting the necessity of beyond the self-consistent QRPA approach, and/or a more systematic optimization of the EDF parameters.

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arXiv2014

Role of diproton correlation in two-proton emission decay of the $^6$Be nucleus

We discuss a role of diproton correlation in two-proton emission from the ground state of a proton-rich nucleus, $^6$Be. Assuming the three-body structure of $α+ p + p$ configuration, we develop a time-dependent approach, in which the two-proton emission is described as a time-evolution of a three-body metastable state. With this method, the dynamics of the two-proton emission can be intuitively discussed by monitoring the time-dependence of the two-particle density distribution. With a model Hamiltonian which well reproduces the experimental two-proton decay width, we show that a strongly correlated diproton emission is a dominant process in the early stage of the two-proton emission. When the diproton correlation is absent, the sequential two-proton emission competes with the diproton emission, and the decay width is underestimated. These results suggest that the two-proton emission decays provide a good opportunity to probe the diproton correlation in proton-rich nuclei beyond the proton drip-line.

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arXiv2012

Time-dependent approach to many-particle tunneling in one-dimension

Employing the time-dependent approach, we investigate a quantum tunneling decay of many-particle systems. We apply it to a one-dimensional three-body problem with a heavy core nucleus and two valence protons. We calculate the decay width for two-proton emission from the survival probability, which well obeys the exponential decay-law after a sufficient time. The effect of the correlation between the two emitted protons is also studied by observing the time evolution of the two-particle density distribution. It is shown that the pairing correlation significantly enhances the probability for the simultaneous diproton decay.

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