A. J. Pacheco

Effect of the breakup on the fusion and elastic scattering of weakly bound projectiles on {sup 64}Zn

We study the behavior of the fusion, breakup, reaction, and elastic scattering of different projectiles on {sup 64}Zn, at near and above barrier energies. We present fusion and elastic scattering data with the tightly bound {sup 16}O and the stable weakly bound {sup 6}Li, {sup 7}Li, and {sup 9}Be projectiles. The data are analyzed by coupled channel calculations. The total fusion cross sections for these systems are not affected by the breakup process at energies above the barrier. The elastic (noncapture) breakup cross section is important at energies close to and above the Coulomb barrier and increases the reaction cross sections. In addition, we show that the breakup process at near and below barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly.

No evidence of break-up effects on the fusion of 9Be with medium-light nuclei

Abstract Fusion cross sections were measured for the 9 Be + 27 Al and 19 F + 9 Be , 12C systems, at energies above the Coulomb barrier, in order to investigate the possible effect of fusion hindrance due to the break-up of the weakly bound nuclei. Comparisons with one-dimensional barrier penetration models and with other similar systems, where no break-up is expected to occur, show no evidence of fusion hindrance.

Fusion of 16O + 144Sm at sub-barrier energies

Abstract Fusion cross sections have been measured for the system 16 O+ 144 Sm at bombarding energies in the range 63 MeV ⩽E lab ( 16 O )⩽72 MeV by observation of delayed X-rays emitted by the evaporation residues. Comparison of the present results for the magic nucleus 144 Sm with those already existing for the fusion of 16 O with other samarium isotopes shows that the enhancement of the cross sections at sub-barrier energies can be explained in terms of a one-dimensional barrier-penetration model that incorporates the quadrupole deformation parameter, s 2 . There is no need to invoke the neck degree of freedom.

Fusion, break-up and elastic scattering of weakly bound nuclei

We describe the behaviour of the fusion, break-up, reaction cross sections and elastic scattering of weakly bound nuclei, at near and above barrier energies. The total fusion cross sections are not affected by the break-up process at this energy regime. The elastic break-up cross sections are important at energies close and above the Coulomb barrier, even in systems with light targets, and increase the reaction cross sections. We also show that the break-up process at near and sub-barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly, named by us as break-up threshold anomaly.

Examination of nuclear measurement conditions in cold fusion experiments

The recent announcement of electrochemically induced nuclear fusion [1,2] has generated great interest and activity within the scientific community. In particular, there are several aspects related to the work of ref. 1 which are not fully understood and therefore deserve further investigation. One of them is the huge discrepancy between the amount of measured heat and the intensity of the supposedly accompanying nuclear radiation, namely neutrons and gamma rays. In view of the fact that the detection of nuclear radiation in the context of an electrochemical process is perhaps the most unequivocal fingerprint for the occurrence of fusion, we feel that a careful re-evaluation of the measurement conditions may be needed. In order to address this question, in the present paper we report on an attempt to observe this phenomenon and on the possible problems related to the detection techniques.

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.

The AMS system and research program at the TANDAR laboratory

Abstract Several aspects of the AMS program at the TANDAR laboratory are discussed. The current activities are focused on environmental and cosmological applications. One of the projects has been the study of the global fallout of the radioisotope 36Cl and its latitudinal distribution in the southern hemisphere. We have also undertaken some of the preparatory work to measure the concentration of several radioisotopes in extraterrestrial samples obtained from a meteorite fall in northern Argentina. An important fraction of our effort in pursuing these studies has been the optimization of the technique in our 20 UD tandem. We discuss the results of recent tests carried out to evaluate the current capabilities of the accelerator regarding general stability, predictability and transmission efficiency, following the upgrading and adaptation activities.

The AMS program at the TANDAR accelerator

Abstract The accelerator mass spectrometry (AMS) program that is under development using the 20UD electrostatic accelerator TANDAR at Buenos Aires is presented. Tests and measurements in order to evaluate and to improve the accelerator performance are described. Preliminary measurements have been done by tuning 14C beams using as detection system a ΔE-ER telescope. For the detection of heavier isotopes some new developments are being currently implemented in a quadrupole-dipole-dipole (QDD) magnetic spectrometer. Furthermore, work is in progress to construct a time-of-flight system using two micro-channel plates prior to the entrance to the QDD spectrometer.

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.

DEVELOPMENTS OF AMS AT THE TANDAR ACCELERATOR

Abstract Man-made long-lived radioisotopes have been produced as a result of different nuclear technologies. The study of accidental spillages and the determination of radioisotope concentrations in nuclear waste prior to final storage in a repository are subjects of great interest in connection with this activity. The accelerator mass spectrometry (AMS) technique is a powerful tool to measure long-lived isotopes at abundance ratios as low as 10−12–10−15 in small samples. Applications to the Argentine nuclear program like those mentioned above, as well as applications to archaeology, hydrology and biomedical research, are considered in an AMS program using the TANDAR 20 UD electrostatic accelerator at Buenos Aires. In this work we present the status of the program and a description of the facility.