Precise measurement of the thermal and stellar Fe 54 (n,γ) Fe 55 cross sections via accelerator mass spectrometry

Accelerator mass spectrometry (AMS) represents a complementary approach for precise measurements of neutron capture cross sections, e.g., for nuclear astrophysics. This technique, completely independent of previous experimental methods, was applied for the measurement of the $^{54}\\mathrm{Fe}(n,\\ensuremath{\\gamma})^{55}\\mathrm{Fe}$ reaction. Following a series of irradiations with neutrons from cold and thermal to keV energies, the produced long-lived $^{55}\\mathrm{Fe}$ nuclei (${t}_{1/2}=2.744+\\ensuremath{-}0.009)$ yr) were analyzed at the Vienna Environmental Research Accelerator. A reproducibility of about 1% could be achieved for the detection of $^{55}\\mathrm{Fe}$, yielding cross-section uncertainties of less than 3%. Thus, this method produces new and precise data that can serve as anchor points for time-of-flight experiments. We report significantly improved neutron capture cross sections at thermal energy (${\\ensuremath{\\sigma}}_{\\mathrm{th}}=2.30\\ifmmode\\pm\\else\\textpm\\fi{}0.07$ b) as well as for a quasi-Maxwellian spectrum of $kT=25$ keV ($\\ensuremath{\\sigma}=30.3\\ifmmode\\pm\\else\\textpm\\fi{}1.2$ mb) and for ${E}_{n}=481\\ifmmode\\pm\\else\\textpm\\fi{}53$ keV ($\\ensuremath{\\sigma}=6.01\\ifmmode\\pm\\else\\textpm\\fi{}0.23$ mb). The new experimental cross sections have been used to deduce improved Maxwellian-averaged cross sections in the temperature regime of the common $s$-process scenarios. The astrophysical impact is discussed by using stellar models for low-mass asymptotic giant branch stars.