Measurement of (α,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions

Date of Acceptance: 30/01/2015The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the 164,166Er(α,n)167,169Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined 162Er(α,n) and 162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.Peer reviewedFinal Accepted Versio

Elemental concentrations in atmospheric particulate matter sampled on the North Sea and the English Channel

Air sampling on a series of 10 cruises, spanning the whole area of the North Sea, yielded detailed spatial distributions of atmospheric concentrations of Al, Si, S, Cl, P, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, and Pb determined by EDXRF. A strong influence of the air mass history on the heavy metal concentrations was demonstrated for the whole sampling period of 5 years. Factor analysis performed on all samples collected with a stack filter unit resulted in the identification of three factors for the coarse particle fraction (sulphate particles with trace metals, sea salt particles and soil dust or metallurgic particles containing Fe) and four factors for the fine particle fraction (sea salt, sulphate with Pb and Zn), trace metal particles with Cu, Ni, Zn and fly-ash particles. The same statistics performed on all samples collected above the Southern Bight of the North Sea yielded three factors, namely: sea salt particles, particles enriched in Ni and V, originating from natural oil combustion and particles containing a variety of elements such as S, K, Ca, Fe, Pb, Cu and Zn. Compared with relevant measurements of trace elements in this area, a relatively good agreement can be found