Precise measurement of the neutron capture reaction 54Fe(n,γ)55Fe via AMS

The measurement of cross sections relevant to nuclear astrophysics has become one main research topic at the VERA (Vienna Environmental Research Accelerator) facility. The technique applied, accelerator mass spectrometry (AMS), offers excellent sensitivity for the detection of long-lived radionuclides through ultra-low isotope ratio measurements. We discuss the potential and preliminary results of ongoing precision measurements of neutron-capture cross sections of 54Fe. Such measurements might help to clarify the recently found discrepancy of s-process nucleosynthesis at lower-mass nuclei (A<120), which might be attributed to a systematic offset in previous experimental data. Samples were irradiated with neutrons from thermal to MeV energies. After the irradiations, the amount of produced long-lived 55Fe (t1/2 = 2.72 yr) was analyzed using AMS. At VERA, detection of 55Fe was developed with a reproducibility of about 1%, which makes the 54Fe(n,γ)55Fe reaction a precise and unique laboratory measurement, which can serve as a reference to complementary techniques. In this regard a new 55Fe standard for AMS measurements was produced. The final cross-section data are expected to be accurate to better than 3%. We report a preliminary, however, already significantly improved thermal neutron cross section value of (2.32 ± 0.10) barn, and a value of (6.3 ± 0.6) mbarn for En = (520 ± 50) keV.