A. E. Negri

(129)I dispersion in Argentina: concentrations in fresh and marine water and deposition fluences in Patagonia.

Measurements of total iodine (I) and iodine-129 ((129)I) concentrations in rivers and lakes of Argentina are presented. Their latitudinal distribution can be explained by taking into account their main sources (oceanic emissions and biomass burning for I, and atmospheric nuclear tests for (129)I), transport mechanisms, and fallout patterns. From the measured (129)I concentrations in the studied lakes, deposition fluences for their catchment areas were estimated. These results agree with a model of the global deposition pattern due to the (129)I released by atmospheric nuclear weapon tests and with other fluences reported for the southern hemisphere. In addition, the first measurements of (129)I in shallow seawater from the South Atlantic Ocean are presented and discussed.

Iodine-129 in animal thyroids from Argentina

(129)I and (127)I concentrations in animal thyroids coming from several regions of Argentina were determined by accelerator mass spectrometry (AMS) and gas chromatography (GC), respectively. The measured (129)I/(127)I ratios, ranging from 3 × 10(-12) to 4 × 10(-10), are significantly lower than those typical for areas in the northern hemisphere (10(-10)-10(-7)). The (129)I concentrations show a clear dependence with latitude and season, which can be understood considering tropospheric circulation patterns, possible (129)I sources and regional precipitation rates.

Assessment of 53Mn deposition on Earth via accelerator mass spectrometry

The 53Mn flux onto Earth is a quantity relevant for different extraterrestrial and astrophysical questions. It is a proxy for related fluxes, such as supernova-produced material or interplanetary dust particles. In this work, we performed a first attempt to assess the 53Mn flux by measuring the 53Mn/10Be isotopic ratio in a 1400 L sample of molten Antarctic snow by AMS (Accelerator Mass Spectrometry). Using the 10Be production rate in the atmosphere, an upper limit of 5.5 × 103 atoms cm-2 yr-1 was estimated for the deposition of extraterrestrial 53Mn. This result is compatible with one of the two discrepant values existing in the literature.

Angular distributions of the alpha particle production in the 7Li+144Sm system at near-barrier energies

We have studied the production of alpha particles in reactions induced by 7Li projectiles on a 144Sm target at bombarding energies of 18, 24 and 30 MeV over the 15°-140° angular range. The purpose of the investigation has been to determine the contribution of different mechanisms in reactions that involve weakly bound projectiles. We have included in our analysis several processes that can either directly or sequentially lead to the emission of alpha particles: complete fusion, direct transfer of 3H, capture breakup (incomplete fusion, sequential complete fusion) and non-capture breakup. In order to distinguish alpha particles stemming from these processes it is necessary to determine the mass and charge of the reaction products and to obtain precise measurements of their energies and scattering angles over relatively wide ranges of these variables. We have done this using a detection system consisting of an ionization chamber plus three position sensitive detectors. We present results of these measurements and a preliminary interpretation based on kinematical considerations and comparisons with predictions from a statistical model.

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.

129I present in Bovine Thyroid in Argentina

129I concentrations in bovine thyroid coming from all over Argentina were analyzed by Accelerator Mass Spectrometry and total iodine present in samples by Gas Chromatography. We present a preliminary latitudinal profile of 129I concentrations. Once we complete this study, it will be the first set of data of this kind from an extended region of South America.

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.

Environmental Levels Of 129I Present In Bovine Thyroid And Fresh Water In Argentina

Concentrations of 129I in bovine thyroid and fresh water samples coming from all over Argentina were analyzed by Accelerator Mass Spectrometry (AMS) and total iodine present in samples by Gas Chromatography (GC) and Inductive Coupled Plasma Mass Spectrometry (ICP‐MS), respectively. Once we complete this study, it will be the first set of data of this kind from an extended region of the south American subcontinent.

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.