C. A. Bertulani

Electromagnetic Processes in Relativistic Heavy Ion Collisions

Abstract Here is presented a study of the processes generated by the electromagnetic interaction in relativistic nuclear, and atomic collisions. There is nowadays a vivid interest in this field due to the construction of relativistic heavy ion accelerators. Certainly, the most important purpose of these relativistic heavy ion machines is the study of nuclear matter under extreme conditions. In central nucleus-nucleus collisions one hopes to observe new forms of nuclear matter, like the quark-gluon plasma [Lu-84, Bay-86]. On the other hand, very strong electromagnetic fields for a very short time are present in distant collisions with no nuclear contact. Such fields can also lead to interesting effects, which are discussed here. There have been many interesting theoretical and experimental developments on this subject, and new ares of research were opened. Of special interest is, e.g., the case of nuclear fragmentation. This is accomplished through the excitation of giant resonances or by direct break-up of the nuclei by means of their electromagnetic interaction. It is shown that this process can be used to study nuclear structure properties which are n not accessible by means of the traditional electromagnetic excitation at nonrelativistic energies. The creation of particles is also of interest due to the large cross sections, specially in the case of electron-positron pair creation. Although one can develop very elaborate and complicated calculations to explain the many processes originated in this way, the results can be understood in very simple terms because of our almost complete comprehension of the electromagnetic interaction. For those processes where the electromagnetic interaction plays the dominant role this is clearly a very useful tool for the investigation of the structures created by the strong interaction in the nuclei or hadrons.

Solar fusion cross sections II: the pp chain and CNO cycles

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for {sup 8}B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

Coulomb Dissociation as a Source of Information on Radiative Capture Processes of Astrophysical Interest

Abstract Experimental studies of the break up of light nuclear projectiles in the Coulomb field of a heavy nucleus, acting as a source of virtual photons, are proposed as an access to information about the reverse reaction, the fusion of the fragment particles at small relative energies. The mechanism of Coulomb dissociation is studied and the cross section of such reactions, being potentially of astrophysical interest, is estimated. The conditions of dedicated experimental investigations are discussed.

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.

Effective field theory for halo nuclei: shallow p-wave states

Halo nuclei are a promising new arena for studies based on effective field theory (EFT). We develop an EFT for shallow p-wave states and discuss the application to elastic nα scattering. In contrast to the s-wave case, both the scattering length and effective range enter at leading order. We also discuss the prospects of using EFT in the description of other halos, such as the three-body halo nucleus 6 He.  2002 Elsevier Science B.V. All rights reserved.

Coulomb dissociation of 11Li.

Kinematically complete measurements for Coulomb dissociation of [sup 11]Li into [sup 9]Li+2[ital n] were made at 28 MeV/nucleon. The [ital n]-[ital n] correlation function suggests a large source size for the two-neutron emission. The electromagnetic excitation spectrum of [sup 11]Li has a peak, as anticipated in low-energy dipole resonance models, but a large post-breakup Coulomb acceleration of the [sup 9]Li fragment is observed, indicating a very short lifetime of the excited state and favoring direct breakup as the dissociation mechanism.

MEASUREMENT OF THE COULOMB DISSOCIATION OF 8B AT 254 MEV/NUCLEON AND THE 8B SOLAR NEUTRINO FLUX

We have measured the Coulomb dissociation of 8B into 7Be and proton at 254 MeV/nucleon using a large-acceptance focusing spectrometer. The astrophysical S17 factor for the 7Be(p,gamma)8B reaction at E{c.m.} = 0.25-2.78 MeV is deduced yielding S17(0)=20.6 \pm 1.2 (exp.) \pm 1.0 (theo.) eV-b. This result agrees with the presently adopted zero-energy S17 factor obtained in direct-reaction measurements and with the results of other Coulomb-dissociation studies performed at 46.5 and 51.2 MeV/nucleon.

Coincidence cross sections for the dissociation of light ions in high-energy collisions

We make an analysis of the influence of the nuclear and of the Coulomb interaction in the dissociation of weakly-bound and cluster-like nuclei in coincidence experiments at high-energy collisions. We use the theory of diffraction dissociation to account for the nuclear effects and compare it to the Coulomb dissociation in the description of the angular distribution of the fragments, as well as in the total cross sections. The nuclear and the electromagnetic dissociation have very different characteristics and we show how this may help to disentangle their contributions in the study of experimental data.

Scattering of radioactive nuclei 6He and 3H by protons: Effects of neutron skin and halo in 6He, 8He, and 11Li

In an experimental study of 6He+p and 3H+p collisions at ∼70 A MeV, the elastic scattering angular distributions were measured and the known excited state 6He1.8∗ was observed. Comparative analysis of existing experimental data on proton elastic scattering by 4He, 6He, 6Li, 8He, 9Li, and 11Li was performed. Effects of valence neutrons were investigated using the eikonal approach. A difference between 11Li and 6,8He was found.

Microscopic theory of the total reaction cross section and application to stable and exotic nuclei

Abstract The multiple scattering theory is used to develop a theoretical framework for the calculation of the heavy-ion total reaction cross section. Several important medium effects such as Pauli blocking, are included. The second-order double-scattering contribution to the ion-ion t ϱ 1 ϱ 2 interaction is calculated and found to contribute at most an effect of 10% on σ R . It is found that, whereas at intermediate energies the t ϱ 1 ϱ 2 accounts reasonably well for the total reaction cross section, indicating the predominance of single-nucleon knockout at these energies, it underestimates σ R at lower energies by a large amount. This is mainly due to the absence in t ϱ 1 ϱ 2 of fusion and inelastic surface excitation. The case of exotic (neutron- and proton-rich) nuclei is also discussed.