OPPORTUNITIES TO CONSTRAIN ASTROPHYSICAL REACTION RATES FOR THEs-PROCESS VIA DETERMINATION OF THE GROUND-STATE CROSS-SECTIONS

Abstract

Modern models of s-process nucleosynthesis in stars require stellar reaction rates of high precision. Most neutroncapture cross-sections in the s-process have been measured, and for an increasing number of reactions the required precision is achieved. This does not necessarily mean, however, that the stellar rates are constrained equally well, because only the capture of the ground state of a target is measured in the laboratory. Captures of excited states can contribute considerably to stellar rates that are already at typical s-process temperatures. We show that the ground-state contribution X to a stellar rate is the relevant measure to identify reactions that are or could be well constrained by experiments and apply it to (n,γ ) reactions in the s-process. We further show that the maximum possible reduction in uncertainty of a rate via determination of the ground-state cross-section is given directly by X. An error analysis of X is presented, and it is found that X is a robust measure with mostly small uncertainties.

Spin differences in the Zr90 compound nucleus induced by (p,p′) , Ota1, Burke2, Casperson3 et al. 2015Phys. Rev. C233280View full textAdd to dashboardCite

“…Cross sections of neutron-induced reactions such as (n, f ), (n, γ), (n, 2n) at neutron energies (E n ) of a few tens of keV to a few tens of MeV are crucial inputs for nuclear energy applications [1], astrophysical studies [2,3], and radiochemical applications [4][5][6]. However, the cross sections for most short-lived isotopes remain poorly known because of their inaccessibility as target materials.…”

The new KADoNiS v1.0 and its influence on the s-process

“…12 C, 16 O, 20 Ne), since their impact on the neutron economy of the s-process depends on both, their abundance and their neutron capture rates. The propagation effect due to light neutron poisons was first discussed by [4] for 22 Ne.…”

“…rate. This approach has been found to be inadequate [16] and has been replaced by the procedure given in [17], which also allows to properly define uncertainties in the stellar rates from a combination of theoretical and experimental uncertainties. In the KADoNiS datasheet we show now both, the SEF and the new ground-state contribution labelled as "X factor".…”

Current quests in nucleosynthesis: present and future neutron-induced reaction measurements

“…Moreover, the weak s predictions are also affected by the uncertainties of the neutron capture cross sections of the light neutron poisons like 23 Na [10]. The situation becomes more puzzling because the stellar rates may be not constrained equally well than the neutron capture cross sections [11]. The reason is that only the capture of the ground state is measured in the laboratory while the captures of excitated states can contribute considerably at typical s-process temperatures.…”

“…The reason is that only the capture of the ground state is measured in the laboratory while the captures of excitated states can contribute considerably at typical s-process temperatures. Rauscher et al [11] have proposed the ground-state contribution (X) to the stellar reaction rate as a factor to be taken into account in the planning of future experiments. Low values of X indicate that it is impossible to determine the stellar reaction rate directly from the experimental capture data, while the stellar enhancement factor could provide values close to the unity.…”