Nuclear Data for Astrophysics
An Extended Data Base of the Beta-Decay Properties and Nuclear Reaction Rated for Astrophysical Applications
Tech Area / Field
- INF-DAT/Data Storage and Peripherals/Information and Communications
- PHY-ANU/Atomic and Nuclear Physics/Physics
3 Approved without Funding
FEI (IPPE), Russia, Kaluga reg., Obninsk
- VNIIEF, Russia, N. Novgorod reg., Sarov
- Université Libre de Bruxelles / Institut d'Astronomie et d'Astrophysique, Belgium, Brussels\nForschungszentrum Karlsruhe Technik und Umwelt, Germany, Karlsruhe
Project summaryThere is a strong need to produce and disseminate high-quality evaluations of nuclear data for nuclear astrophysics. Specifically, more complete, precise, and up-to-date evaluated nuclear data are required for models of perse astrophysical phenomena. Up to now, the modeling of ultra-macroscopic systems such as stars, as well as simulation of explosive stellar events has been faced a lot of difficulties. By substantial part, they are connected to using of inaccurate nuclear input data for a large variety of nuclear processes .
The Project concerns the nuclear data for few basic processes of astrophysical nuclear synthesis which are responsible for the bulk of the elemental and isotopic abundance in the Universe, namely:
- static nuclear burning of elements from Hydrogen to Silicon;
- slow neutron capture and subsequent -decay (s-process);
- rapid (multiple) neutron capture followed by fast -decay and neutrino ()-capture (explosive r-process);
- rare p process which is driven by the proton capture and -decay.
Each of these processes requires a specific set of nuclear data at different energies of astrophysical relevance:
- Non-explosive nuclear burning mainly concerns the data on charge particle induced reactions below the Coulomb barrier. The relevant energies are substantially below the Coulomb barrier height, so that the cross sections to be determined are quite generally out of present experimental capacities. Thus, the main problem is an accurate extrapolation reaction cross sections to very low energies.
- In the slow s-process the relative mean lifetimes for neutron captures is larger than for -decays, thus the reaction path remains close to the -stability line. For the modeling of the s-process, precise experimental measurements of the neutron capture cross sections with the accuracy of <4% at typical energies 10 to 100 keV are required on stable and long-lived targets in the wide range of masses (12<A<210).
- The r-process is driven by the competition of the rapid neutron captures, photodisintegration, corresponding -decays and neutrino captures. For exotic “r-process nuclei”, most of the data can not be obtained in laboratories. Relevant neutron capture and weak interaction rates for 2-3 thousands nuclei are to be predicted on solid theoretical grounds. The main criteria is a self-consistency of the predicted nuclear masses, weak rates and neutron capture rates. The problem concerns not only an evaluation of nuclear data. The need to extrapolate nuclear data to experimentally unreachable exotic nuclei is an urgent theoretical nuclear physics challenge.
A complete data base should contain a detailed compilation and evaluation of nuclear data for nuclei close to stability (H to Si burning and the s-process), as well as self-consistent predictions of nuclear data for 2-3 thousands of experimentally unknown neutron–rich nuclei relevant to the r-process. It should contain detailed description of adopted evaluation methods; clear evaluation of the estimated errors; due account of the experimental data and theoretical predictions. In full scope, such a Program has not been fulfilled yet.
An ambitious Program of creating a complete “Nuclear Data Base for Astrophysics” has been recently undertaken by the NACRE network under the “Human Capital and Mobility” (HCM) Program of the Commission of the European Communities (1993-1997) co-ordinate by the Institut d’Astrophysique Universite Libre de Bruxelles (IAA Brussels). Up to now the main experimental and theoretical efforts within this program have been devoted to charged particle induced reaction. This direction of NACRE was to cure the shortcomings of the only existing evaluation of charged particle induced reactions by Caughlan, Fowler, 1988. The improved data base from the NACRE network (Angulo, Arnould, Rayet, et al.,1998) contains at the moment the detailed evaluation and compilation of 83 charged particle induced reactions on targets up to Silicon. It is widely recognized by the international nuclear astrophysics community that the NACRE data base needs to be extended in this, as well in the other above mentioned directions. Finally, with this extension NACRE has to become a standard reference data base in nuclear astrophysics.
The goals of the present Project are: first, to extend the NACRE by adding the calculated delayed -decay processes rates for the key nuclei and neutrino capture rates for about 2000 nuclei; second, by adding selected neutron and charge particle induced reaction rates which has not been evaluated in the NACRE.
The first direction of the Project is an extension of the NACRE to the complete set of weak rates for the r-process.
To reliably calculate the weak rates for exotic nuclei, an efficient, time consuming approach to nuclear ground state and weak rates will be used. It has been developed (I.N.Borzov, S.Goriely, J.M.Pearson, M.Arnould, 1995-1999) within the collaboration of IPPE Obninsk and IAA Brussels. The main emphasis of this direction is to extend the NACRE to the full set of the -decay properties including delayed neutron and delayed fission probabilities for key nuclides, as well as electron neutrino capture rates for about 2000 neutron-rich nuclei. In addition the direct component of neutron capture cross sections for the key unstable nuclides on the r-process paths will be calculated in the same self-consistent framework.
The second direction of the Project is to extend the NACRE to the data for the s- and p-processes modeling.
Much efforts by IPPE have been devoted to work out the IAEA standard for nuclear level density and neutron capture cross sections at the energies relevant for reactor and fusion applications (A.V.Ignatyuk et al., 1980-1999). A natural extension of this work within this direction would be theoretical systematic of nuclear level densities for astrophysical important nuclei, and extrapolation of compiled/evaluated neutron capture cross sections towards very low energies of astrophysical relevance for r-, s- and also for p-processes. Also the sets of global low energy n,p and optical parameters will be worked out and tested on the cross sections of n,p and induced reactions for mostly stable N Z nuclei with A>30 important
The third direction of the Project is to extend the NACRE to selected cross sections on charged particle induced reactions cross sections on light and medium mass nuclei.
The VNIIEF participants of this direction of the project accumulated an expertise in dealing with the compilation/evaluation of data for these nuclei, including their own experimental measurements .( S.Abramovich, B..Guzhovskii, A..Zvenigorodskii, V. Zherebchov, INDC(ССР)-326/L+F, IAEA, VIENNA, (1991).), and techniques of extrapolation of the charged particle induced reaction cross sections to very low energies. Based on the author’s previous measurements it is planned to create the recommended data set of the cross sections and astrophysical S-factors for the 6,7Li(t,n)8,9Be, 8B(,p)11C, 9Be(t,n)11B, 11C(p,)12N, 16O(p,)13N ,17, 18F(p,)18,19Ne, 19F(p,)20Ne reactions in NACRE-format.
The following results are planned under the Project:
1. New calculated -delayed neutron emission and -delayed fission probabilities for key r-process nuclei; neutrino capture cross sections for about 2000 neutron-rich nuclei.
2. New evaluations of the neutron capture cross sections for key unstable nuclei involved in the r- and p-processes.
3. New evaluations of charged particle induced reaction cross sections and astrophysical S-factors for light nuclei, which have not been yet considered in the NACRE evaluations.
4. Systematic of the level density parameters for nuclei far off the stability valley. Global proton and –particle optical potential parameters for sub-Coulomb energies and the results of its validating in the (n,p) and (n, ) cross section evaluations for medium nuclei of astrophysical interest.
5. The obtained experimental, evaluated and calculated data will be tested against the available data from different national and international data bases, validated in astrophysical calculations and presented in the IAA and IPPE Nuclear Data Center Web-pages (www.astro.ulb.ac.be, www.rndc.obninsk.ru )
The project complies with the ISTC basic principles helping to integrate former nuclear experts (including former weapon-oriented researchers) to fundamental studies in an interdisciplinary field like nuclear astrophysics. The involvement to large-scale international project could be very important.