Y. Kalmykov

Complete electric dipole response and the neutron skin in 208Pb

A benchmark experiment on (208)Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in (208)Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

Pygmy dipole resonance in 208Pb

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208 Pb shows that, at very forward angles, J π = 1 − states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.

Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping

Abstract The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at E p = 200 MeV . Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states.

Complete dipole response in 208Pb from high-resolution polarized proton scattering at 0°

The structure of electric and magnetic dipole modes in 208Pb is investigated in a high‐resolution measurement of the (p,p′) reaction under 0°. First results on the E1 strength in the region of the pygmy dipole resonance are reported.

Distribution of the GT strength starting from the ground state of 14N

Two charge‐exchange reactions were performed at intermediate energies in order to investigate the Gamow‐Teller strength distribution starting from 14Ng.s. in β+ and β− directions: 14N(d,2He)14C and 14N(3He,t)14O. We describe here a few delicate details of the experimental techniques used in these investigations.

Structure of 7He studied with the 7Li(d,2He) reaction

A search for the Jπ = 1/2− spin–orbit partner of the Jπ = 3/2− ground state in 7He has been performed with the 7Li(d,2He) charge-exchange reaction. The results are incompatible with recent claims of such a state at very low excitation energy [Meister M et al 2002 Phys. Rev. Lett. 88 102501] but rather suggest a resonance with parameters Ex = (1.2+0.5 −0.4) MeV, Λ = (1.9+0.8−0.4) MeV. GT strengths deduced for the transitions to the lowest states in 7He are in remarkable agreement with ab initio quantum Monte Carlo calculations.