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Kazuhiro Oyamatsu

Publications and source records attributed to Kazuhiro Oyamatsu.

27 records · Page 2Linked to original sources
arXiv2008

Difference between interaction cross sections and reaction cross sections

We revisit the commonly accepted notion that the difference between interaction and reaction cross sections is negligible at relativistic energies, and show that, especially in small mass number region, it is large enough to help probe nuclear structure. For analyses of the difference, we construct "pseudo data" for the reaction cross sections using a phenomenological black-sphere model of nuclei since empirical data are very limited at high energies. The comparison with the empirical interaction cross sections suggests a significant difference between the reaction and interaction cross sections for stable projectiles on a carbon target, which is of the order of 0-100 mb.

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arXiv2006

The symmetry energy at subnuclear densities and nuclei in neutron star crusts

We examine how the properties of inhomogeneous nuclear matter at subnuclear densities depend on the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate the size and shape of nuclei in neutron star matter at zero temperature in a way dependent on the density dependence of the symmetry energy. We find that for smaller symmetry energy at subnuclear densities, corresponding to larger density symmetry coefficient L, the charge number of nuclei is smaller, and the critical density at which matter with nuclei or bubbles becomes uniform is lower. The decrease in the charge number is associated with the dependence of the surface tension on the nuclear density and the density of a sea of neutrons, while the decrease in the critical density can be generally understood in terms of proton clustering instability in uniform matter.

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arXiv2006

Formula for proton-nucleus reaction cross section at intermediate energies and its application

We construct a formula for proton-nucleus total reaction cross section as a function of the mass and neutron excess of the target nucleus and the proton incident energy. We deduce the dependence of the cross section on the mass number and the proton incident energy from a simple argument involving the proton optical depth within the framework of a black sphere approximation of nuclei, while we describe the neutron excess dependence by introducing the density derivative of the symmetry energy, L, on the basis of a radius formula constructed from macroscopic nuclear models. We find that the cross section formula can reproduce the energy dependence of the cross section measured for stable nuclei without introducing any adjustable energy dependent parameter. We finally discuss whether or not the reaction cross section is affected by an extremely low density tail of the neutron distribution for halo nuclei.

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arXiv2005

Reaction cross section described by a black sphere approximation of nuclei

We identify a length scale that simultaneously accounts for the observed proton-nucleus reaction cross section and diffraction peak in the proton elastic differential cross section. This scale is the nuclear radius, $a$, deduced from proton elastic scattering data of incident energies higher than $\sim800$ MeV, by assuming that the target nucleus is a ``black'' sphere. The values of $a$ are determined so as to reproduce the angle of the first diffraction maximum in the scattering data for stable nuclei. We find that the absorption cross section, $πa^2$, agrees with the empirical total reaction cross section for C, Sn, and Pb to within error bars. This agreement persists in the case of the interaction cross section measured for a carbon target. We also find that $\sqrt{3/5}a$ systematically deviates from the empirically deduced values of the root-mean-square matter radius for nuclei having mass less than about 50, while it almost completely agrees with the deduced values for $A\gtrsim50$. This tendency suggests a significant change of the nuclear matter distribution from a rectangular one for $A\lesssim50$, which is consistent with the behavior of the empirical charge distribution.

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arXiv2004

Nuclear radius deduced from proton diffraction by a black nucleus

We find a new method to deduce nuclear radii from proton-nucleus elastic scattering data. In this method a nucleus is viewed as a ``black'' sphere. A diffraction pattern of protons by this sphere is equivalent to that of the Fraunhofer diffraction by a circular hole of the same radius embedded in a screen. We determine the black sphere radius in such a way as to reproduce the empirical value of the angle of the observed first diffraction peak. It is useful to identify this radius multiplied by $\sqrt{3/5}$ with the root-mean-square matter radius of the target nucleus. For most of stable isotopes of masses heavier than 50, it agrees, within the error bars, with the values that were deduced in previous elaborate analyses from the data obtained at proton incident energies higher than $\sim 800$ MeV.

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arXiv2003

Proton-nucleus elastic scattering and the equation of state of nuclear matter

We calculate differential cross sections for proton-nucleus elastic scattering by using a Glauber theory in the optical limit approximation and nucleon distributions that can be obtained in the framework of macroscopic nuclear models in a way dependent on the equation of state of uniform nuclear matter near the saturation density. We find that the peak angle calculated for unstable neutron-rich nuclei in the small momentum transfer regime increases as the parameter L characterizing the density dependence of the symmetry energy decreases. This is a feature associated with the L dependence of the predicted matter radii.

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arXiv2002

Saturation of nuclear matter and radii of unstable nuclei

We examine relations among the parameters characterizing the phenomenological equation of state (EOS) of nearly symmetric, uniform nuclear matter near the saturation density by comparing macroscopic calculations of radii and masses of stable nuclei with the experimental data. The EOS parameters of interest here are the symmetry energy S_0, the symmetry energy density-derivative coefficient L and the incompressibility K_0 at the normal nuclear density. We find a constraint on the relation between K_0 and L from the empirically allowed values of the slope of the saturation line (the line joining the saturation points of nuclear matter at finite neutron excess), together with a strong correlation between S_0 and L. In the light of the uncertainties in the values of K_0 and L, we macroscopically calculate radii of unstable nuclei as expected to be produced in future facilities. We find that the matter radii depend strongly on L while being almost independent of K_0, a feature that will help to determine the L value via systematic measurements of nuclear size.

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