Anti-analog giant dipole resonances and the neutron skin of nuclei

A Krasznahorkay,N Paar,D Vretenar,M.N Harakeh

doi:10.1016/j.physletb.2013.02.043

A Krasznahorkay, N Paar + Show 2 more

Open Access

https://doi.org/10.1016/j.physletb.2013.02.043

Copy DOI

Abstract

We examine a method to determine the neutron-skin thickness of nuclei using data on the charge-exchange anti-analog giant dipole resonance (AGDR). Calculations performed using the relativistic proton–neutron quasiparticle random-phase approximation (pn-RQRPA) reproduce the isotopic trend of the excitation energies of the AGDR, as well as that of the spin-flip giant dipole resonances (IVSGDR), in comparison to available data for the even–even isotopes 112–124Sn. It is shown that the excitation energies of the AGDR, obtained using a set of density-dependent effective interactions which span a range of the symmetry energy at saturation density, supplemented with the experimental values, provide a stringent constraint on value of the neutron-skin thickness. For 124Sn, in particular, we determine the value ΔRpn=0.21±0.05 fm. The result of the present study shows that a measurement of the excitation energy of the AGDR in (p,n) reactions using rare-isotope beams in inverse kinematics, provides a valuable method for the determination of neutron-skin thickness in exotic nuclei.

Highlights

An interesting phenomenon in nuclear structure is the formation of a skin of neutrons on the surface of a nucleus, and its evolution with mass number in an isotopic chain [1]
A method to determine the size of the neutron-skin thickness in nuclei using data on the anti-analog giant dipole resonance has been discussed
Charge-exchange (p, n) reactions provide an excellent probe for the neutron-skin thickness, as already demonstrated by measurement of the isovector spin giant dipole resonance (IVSGDR) and Gamow–Teller resonance (GTR), and the analog giant dipole resonance (AGDR) provides a complementary approach

Summary

Introduction

An interesting phenomenon in nuclear structure is the formation of a skin of neutrons on the surface of a nucleus, and its evolution with mass number in an isotopic chain [1]. A detailed knowledge of the symmetry energy is essential for describing the structure of neutron-rich nuclei, and for modeling properties of neutron-rich matter in applications relevant for nuclear astrophysics. Radioactive ion beams (RIBs) have recently been employed to determine the neutron-skin thickness in unstable nuclei, in measurements of reaction cross-sections and pygmy dipole resonances [1,15,16]. By calculating excitation energies E(AGDR) and R pn in a fully selfconsistent theoretical approach, and comparing to available data, the feasibility of the method will be tested with the aim to provide a basis for future studies with RIBs. The Letter is organized as follows.

Charge-exchange AGDR and neutron-skin thickness

Theoretical analysis

Determination of the neutron-skin thickness of 124Sn

Method

Conclusion and outlook