Quantum Tunneling in Nuclear Fusion

Recent theoretical advances in the study of heavy ion fusion reactions below the Coulomb barrier are reviewed. Particular emphasis is given to new ways of analyzing data, such as studying barrier distributions; new approaches to channel coupling, such as the path integral and Green function formalisms; and alternative methods to describe nuclear structure effects, such as those using the Interacting Boson Model. The roles of nucleon transfer, asymmetry effects, higher-order couplings, and shape-phase transitions are elucidated. The current status of the fusion of unstable nuclei and very massive systems are briefly discussed.Comment: To appear in the January 1998 issue of Reviews of Modern Physics. 13 Figures (postscript file for Figure 6 is not available; a hard copy can be requested from the authors). Full text and figures are also available at http://nucth.physics.wisc.edu/preprints

L-X-ray production cross-sections for PXAMS: Target and energy dependence for 50-200 MeV hafnium ions

In order to detect the long-lived radioisotope 182Hf (t1/2 = 8.9 Ma), a potential supernova isotope signature, we investigated PXAMS as a method of isobar separation for Hf and W. One of the problems of the method is low efficiency. Since there are no reliable quantitative predictions on cross-sections leading to the emission of X-rays from collisions involving fast Hf ions, we determined the energy dependent cross-sections for a number of target elements. A PXAMS system of maximum efficiency was then constructed on the basis of the data obtained. The efficiency of the final setup, defined as the ratio of the number of X-rays detected to the number of incident Hf ions, is 1.2%. The overall efficiency, including negative-ion formation probability and transmission through the accelerator, is 1 × 10-6

Campo del Cielo Iron Meteorite: Sample Shielding and Meteoroids Preatmospheric Size

Long-lived cosmogenic radioisotopes, 10Be, 26Al, 36Cl, 41Ca and 59Ni, have been measured in five samples from the Campo del Cielo iron meteorite by accelerator mass spectrometry (AMS). The 36Cl activities were significantly above the background. For the concentrations of the other four radioisotopes, only upper limits were obtained that were, however, consistent with the 36Cl result. The measured 36Cl activity allowed an estimate of the meteoroid's preatmospheric size: a radius larger than 300 cm and a mass of at least 840 000 kg. We conclude that this meteorite might be one of the largest meteorites to have been recovered

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 of129I concentrations. Once we complete this study, it will be the first set of data of this kind from an extended region of South America

X-ray spectrometry: a powerful tool for the measurement of complete fusion of weakly bound nuclei

We describe how the method of detection of delayed K x-rays produced by the electron capture decay of the residual nuclei can be a powerful tool in the investigation of the effect of the breakup process on the complete fusion (CF) cross-section of weakly bound nuclei at energies close to the Coulomb barrier. This is presently one of the most interesting subjects under investigation in the field of low-energy nuclear reactions, and the difficult experimental task of separating CF from the incomplete fusion (ICF) of one of the breakup fragments can be achieved by the x-ray spectrometry method. We present results for the fusion of the (9)Be + (144)Sm system. Copyright (c) 2008 John Wiley & Sons, Ltd.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqFundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)FAPERJCAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESPConsejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET)CONICE

Methodological Issues in the 14C Dating of Rock Paintings

From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.Chemical and isotopic analyses have been made of pigment samples from two separate rock art sites in Argentina. The purpose of the study has been to establish the feasibility of extracting carbonaceous material from the samples which will permit reliable radiocarbon dates for the time of painting. The two sites, Catamarca and Rio Negro, present quite different problems. Most of the paper is concerned with Catamarca, and here we have shown that the paint pigments contain very little or no organic binder; but they do contain calcium oxalate derived from local cacti, and calcium carbonate derived probably from local plant ash. We describe a method to purify carbon extracted from the calcium oxalate, and present the dates obtained on both components. We show that, though rare, natural deposits containing both calcium oxalate and calcite do occur, but that they are very distinct in both 13C and 14C compositions; and we argue that they are very unlikely to contaminate the pigments to such an extent that the 14C dates are altered. For the Rio Negro site we show that the ground for the paint pigments contains carbon derived from fires burnt inside the cave, and discuss how analytical methods provide information to develop a strategy for extracting material, from both ground and pigment, for more reliable dating.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

The 410,000 year terrestrial age of eucrite Rio Cuarto 001

We have measured a surprisingly long terrestrial age of 410,000 ±45,00020,000 yr (410 ±4520 ka) for basaltic eucrite Rio Cuarto 001 using accelerator mass spectrometry of26Al,36Cl, and41Ca. Though many meteorites are known to have survived for tens or

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 (6,7)Li on (144)Sm

Excitation functions of quasi-elastic scattering at backward angles have been measured for the (6,7)Li + (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.CNPq(FAPERJ) Fundacao de Amparo a Pesquisa do Estado do Rio de JaneiroPROSULPRONEXCONICE