Measurements of neutron-induced reactions in inverse kinematics and applications to nuclear astrophysics

Neutron capture cross sections of unstable isotopes are important for neutron-induced nucleosynthesis as well as for technological applications. A combination of a radioactive beam facility, an ion storage ring and a high flux reactor would allow a direct measurement of neutron induced reactions over a wide energy range on isotopes with half lives down to minutes. The idea is to measure neutron-induced reactions on radioactive ions in inverse kinematics. This means, the radioactive ions will pass through a neutron target. In order to efficiently use the rare nuclides as well as to enhance the luminosity, the exotic nuclides can be stored in an ion storage ring. The neutron target can be the core of a research reactor, where one of the central fuel elements is replaced by the evacuated beam pipe of the storage ring. Using particle detectors and Schottky spectroscopy, most of the important neutron-induced reactions, such as (n,$\gamma$), (n,p), (n,$\alpha$), (n,2n), or (n,f), could be investigated.Comment: 5 pages, 7 figures, Invited Talk given at the Fifteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), Dresden, Germany, 201

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

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