Speaker
Description
Charged-particle-induced reactions at low energies in the resolved resonance region are important for a range of applications in basic and applied sciences. Ion Beam Analysis of materials for cultural heritage, environment and climate control, and forensics, depends on the knowledge of proton-, deuteron- and alpha-induced reactions at energies of a few MeV. Management of fuel in nuclear reactors involves the control of neutrons produced after the reactor operation is shutdown. For the most widely used fuel materials, UO2, UF6, PuF4 and PuO2, the dominant neutron producing reactions are (α,xn) reactions on isotopes of O and F, at incident energies above the neutron emission threshold. In nuclear astrophysics, main stellar processes producing the energy of the stars and leading to the synthesis of the light and medium-mass elements up to the iron nuclei, are fuelled by thermonuclear reactions at temperatures of tens of millions of degrees Kelvin. These conditions simulated in the earth laboratories translate into charged-particle induced reactions on light and medium-mass nuclei at energies of a few hundreds of keV. Alpha-nucleus reactions up to 10 MeV are also a potential source of low-energy neutron background for rare event research in astroparticle physics (dark matter search, neutrino, etc.).
Significant effort has been made over the past decades to measure some of these cross sections. The Ion Beam Analysis Data Library (IBANDL) maintained by the IAEA contains over 6000 datasets of differential and total experimental cross sections for charged-particle-induced reactions in the energy region below several MeV. In nuclear astrophysics, several dedicated compilations (NACRE-I and II) and theoretical reaction rate databases (REACLIB, BRUSLIB, KADONIS, NUCASTRODATA.ORG) have been made available to meet the needs of the stellar nucleosynthesis calculations.
On the other hand, the evaluated nuclear data libraries maintained by national or international coordinated efforts (ENDF, JEFF, JENDL, CENDL) are to date, incomplete as far as charged-particle- induced reactions in the resolved resonance region are concerned.
In response to the above-mentioned gap in the evaluated libraries, the IAEA Nuclear Data Section is coordinating an international effort to (i) verify that the existing R-matrix codes are consistent, (ii) evaluate charged-particle cross sections in the resolved resonance region, (iii) produce evaluated nuclear data files for further processing and finally (iv) disseminate the evaluated data through general purpose evaluated nuclear data libraries.
In this paper we present the results of the effort made thus far on 1) verification of the available R-matrix codes, minimization methods and calculation of covariances, 2) the evaluation of the compound system 7Be*, and 3) improving (alpha,n) reaction data for the applications.
We also discuss the open issues in R-matrix calculations as we extend to higher energies, such as dealing with the rapidly growing number of open channels and merging with the regime of smooth cross sections described by the statistical model. Finally, we summarize the main conclusions of the IAEA Technical meeting on ‘(alpha,n) reaction evaluation and data needs’.
The work of I.J. Thompson was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
The work of G. Hale and M. Paris was supported by the U.S. Department of Energy through the Los Alamos National Laboratory. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract No. 89233218CNA000001). [LA-UR-21-29650]