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

Spin distribution as a probe to investigate the dynamical effects in fusion reactions

The spin distributions are measured for the compound nucleus 80Sr populated in the reactions 16O+64Zn and 32S+48Ti. The comparison of the experimental results for both the systems shows that the mean γ-ray multiplicity values for the system 32S+48Ti are lower than those for 16O+64Zn. The spin distribution of the compound nucleus populated through the symmetric channel is also found to be lower than the asymmetric channel. Present investigation directly shows the effect of entrance channel mass asymmetry on the reaction dynamics

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