Nuclear astrophysics with radioactive ions at FAIR

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes

Model-based computation of powder diffraction patterns for carbon nanotubes

The powder diffraction patterns of single- and multi-walled carbon nanotubes have been computed using the Debye equation including the Debye-Waller factor. The geometrical models of given diameter and chirality were constructed by generating the Cartesian coordinates of atoms. The results of such simulations are compared with the pulsed neutron diffraction data and agreement between them is regarded as criterion of validity of the model. All the features of the experimental intensity function of the multi-walled nanotubes are reproduced by the simulated powder diffraction pattern computed for the model consisting of nine coaxially stacked tubes. The Debye-Waller factor increasing with square root of the interatomic distance was used to account for decay of intensity oscillations. The two-shell and bundle models were considered to reproduce the weak first diffraction peak for the single-walled nanotubes. (C) 2003 Elsevier B.V. All rights reserved

Model-based computation of powder diffraction patterns for carbon nanotubes

The powder diffraction patterns of single- and multi-walled carbon nanotubes have been computed using the Debye equation including the Debye-Waller factor. The geometrical models of given diameter and chirality were constructed by generating the Cartesian coordinates of atoms. The results of such simulations are compared with the pulsed neutron diffraction data and agreement between them is regarded as criterion of validity of the model. All the features of the experimental intensity function of the multi-walled nanotubes are reproduced by the simulated powder diffraction pattern computed for the model consisting of nine coaxially stacked tubes. The Debye-Waller factor increasing with square root of the interatomic distance was used to account for decay of intensity oscillations. The two-shell and bundle models were considered to reproduce the weak first diffraction peak for the single-walled nanotubes. (C) 2003 Elsevier B.V. All rights reserved

Sensitivity study for s process nucleosynthesis in AGB stars

In this paper we present a large-scale sensitivity study of reaction rates in the main component of the s process. The aim of this study is to identify all rates, which have a global effect on the s process abundance distribution and the three most important rates for the production of each isotope. We have performed a sensitivity study on the radiative 13C-pocket and on the convective thermal pulse, sites of the s process in AGB stars. We identified 22 rates, which have the highest impact on the s-process abundances in AGB stars

Curved surfaces in disordered carbons by high energy x-ray scattering

Disordered carbons prepared by slow pyrolysis of saccharose and anthracene and subsequent heat treatment at 1000degreesC and 2300degreesC have been studied by high energy X-ray diffraction. Computer simulations of the powder diffraction patterns of fullerenes, nanotubes and carbon models have been compared with the experimental data after conversion to real space via, the Fourier transform. The presence of fullerene- and nanotube-like fragments with non-six membered rings in the investigated samples has been deduced by detailed analysis of the radial distribution functions of the saccharose- and anthracene-based carbons and related to resistance to graphitization of the saccharose-based carbons and to stability of the growing crystallites in the case of the anthracene-based carbons. The obtained results are compared to high resolution electron microscopy and Raman studies