D. Martinez Heimann

Exclusive Measurements of Breakup Reactions in the {sup 7}Li+{sup 144}Sm System

Breakup reactions induced by a 30 MeV {sup 7}Li beam on a {sup 144}Sm target were measured through the coincident detection of the light particles emitted in the reaction plane. The emphasis of the measurements and data analysis was placed in the complete characterization of the reaction by means of the identification of the breakup products and the experimental extraction of the physically relevant magnitudes. The coincident yield of the emitted light particles was compared with the results of kinematical calculations that were done assuming different distributions for these magnitudes and taking into account the geometric response of the detection system. The results of this comparison indicate in all cases a clear dominance of a process compatible with the breakup of {sup 6}Li through the 3{sup +} resonant state at 2.186 MeV following one-neutron transfer from the projectile to the target, over the breakup of the projectile itself. Relative cross sections as a function of the emission angle of the {sup 6}Li and the in-plane anisotropy of the subsequent emission of breakup products were extracted from the data.

Breakup Reactions and Exclusive Measurements in the 6,7Li+144Sm Systems

The breakup of the projectile‐like nuclei in reactions induced by 30 MeV 6Li and 7Li beams on a 144Sm target have been measured through the coincident detection of the in‐plane emitted light particles. The primary ion that undergoes breakup has been identified and the physically meaningful variables that characterize the reaction have been obtained on a purely experimental basis. Distributions have been obtained for both the binary emission angle and for the breakup emission angle in the reference frame of the breakup products.

Multifragment emission and the experimental characterization of breakup reactions

The production of three or more particles in nuclear reactions is discussed in terms of physically meaningful variables for the description of the asymptotic exit‐channel configuration. The emphasis is placed in a direct comparison between these basic variables obtained in a purely experimental way and the corresponding results of generic model calculations. Applications of this approach to a few examples of recent inclusive and exclusive measurements of breakup reactions in the 6,7Li+144Sm systems are presented.

Elastic scattering of nuclear systems induced by weakly bound projectiles

The influence of the breakup channel on the elastic scattering and on the fusion process for systems that involve weakly bound stable nuclei has been widely investigated in the last years. One of the most used approaches to address these problems is to investigate the energy dependence of the nuclear interaction potential. For tightly bound systems at energies close to the Coulomb barrier, this energy dependence exhibits the behavior known as threshold anomaly. On the other hand, for various weakly bound systems the nuclear potential as a function of energy has a completely different behavior known as breakup threshold anomaly. In this report we present an overview of the subject discussing the different experimental measurements and theoretical interpretations that have been published. In this framework, we present the results of the elastic scattering cross sections for the 6,7Li+80Se systems that have been recently measured at the TANDAR laboratory and we discuss the conclusions obtained from these stu...

Resonant breakup in the 6,7Li + 144Sm systems

Resonant breakup processes in the 6,7Li + 144Sm systems is studied through the results obtained in exclusive measurements performed at energies around the Coulomb barrier and a kinematical description of these phenomena is introduced. For the 7Li projectile, dominance of transfer breakup through the 6Li first excited state is observed. In the 6Li projectile case, elastic breakup through the same projectile-like excited state clearly dominates the experimental yield. Relative and absolute cross sections for both systems are calculated. A clear asymmetry is observed in the intrinsic angular distributions, in good agreement with results reported for other known systems.

Elastic Scattering of {sup 7}Li+{sup 27}Al at Backward Angles in the 7-11 MeV Energy Range for Application in RBS

We have measured elastic excitation functions for the {sup 7}Li+{sup 27}Al system, in an energy range close to its Coulomb barrier (E{sub lab} = 8.4 MeV) in steps of 0.25 MeV. For this purpose, an array of eight surface-barrier detectors was used. To get an insight on the background composition (mainly {alpha} particles), a telescope-detector was used for atomic-number identification. Identical measurements for the {sup 6}Li+{sup 27}Al system are planned for the near future.

Detection Efficiency of a ToF Spectrometer from Heavy‐Ion Elastic Recoil Detection

The detection efficiency of a time‐of‐flight system based on two micro‐channel plates (MCP) time zero detectors plus a conventional silicon surface barrier detector was obtained from heavy ion elastic recoil measurements (this ToF spectrometer is mainly devoted to measurements of total fusion cross section of weakly bound projectiles on different mass‐targets systems). In this work we have used beams of 7Li, 16O, 32S and 35Cl to study the mass region of interest for its application to measurements fusion cross sections in the 6,7Li+27Al systems at energies around and above the Coulomb barrier (0.8VB≤E≤2.0VB). As the efficiency of a ToF spectrometer is strongly dependent on the energy and mass of the detected particles, we have covered a wide range of the scattered particle energies with a high degree of accuracy at the lowest energies. The different experimental efficiency curves obtained in that way were compared with theoretical electronic stopping power curves on carbon foils and were applied.

Elastic Scattering Of {sup 6,7}Li+{sup 80}Se At Near And Above Barrier Energies

In this work we propose to study the elastic scattering of the weakly bound projectiles 6,7Li on an intermediate mass target 80Se. From the experimental results presented here, precise angular distributions at energies below, around and above the nominal Coulomb barriers of the systems were obtained. The final goal of our work is to determine the characteristic parameters of the optical potential and use them to address the question of whether the usual threshold anomaly or the breakup threshold anomaly are present or not in these systems.

Breakup coupling effects on near-barrier quasi-elastic scattering of {sup 6,7}Li on {sup 144}Sm

Excitation functions of quasi-elastic scattering at backward angles have been measured for the {sup 6,7}Li+{sup 144}Sm systems at near-barrier energies, and fusion barrier distributions have been extracted from the first derivatives of the experimental cross sections with respect to the bombarding energies. The data have been analyzed in the framework of continuum discretized coupled-channel calculations, and the results have been obtained in terms of the influence exerted by the inclusion of different reaction channels, with emphasis on the role played by the projectile breakup.

Quasi‐elastic Scattering Measurements in the 6,7Li+144Sm Systems

In the present work, results of measurements of quasi‐elastic scattering cross sections using a silicon‐telescope detector at backward angles are reported. They allowed us to deduce fusion barrier distributions from the first derivative of the corresponding excitation function (−d(dσqes/dσRut)/dE). We report data for the systems 6,7Li on 144Sm which are characterized by loosely bound projectiles onto a closed neutron shell target. The experimental excitation functions and the associated barrier distributions are compared for both systems.