Precise measurement of the thermal and stellar $^{54}$Fe($n, \gamma$)$^{55}$Fe cross sections via AMS

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 Fe-54(n,gamma) Fe-55 reaction. Following a series of irradiations with neutrons from cold and thermal to keV energies, the produced long-lived Fe-55 nuclei (t(1/2) = 2.744+-0.009) yr) were analyzed at the Vienna Environmental Research Accelerator. A reproducibility of about 1% could be achieved for the detection of Fe-55, 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 (sigma(th) = 2.30 +/- 0.07 b) as well as for a quasi-Maxwellian spectrum of kT = 25 keV (sigma = 30.3 +/- 1.2 mb) and for E-n = 481 +/- 53 keV (sigma = 6.01 +/- 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.