Experimental study of 38Ar + α reaction cross sections relevant to the 41Ca abundance in the solar system

In massive stars, the Ca-41(n, alpha)Ar-38 and K-41(p, alpha)Ar-38 reactions have been identified as the key reactions governing the abundance of Ca-41, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the Ca-41(n, alpha)Ar-38 reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse Ar-38(alpha, n)Ca-41 and Ar-38(alpha, p)K-41 reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV Ar-38 beam and He-4 as the active-gas target. Both excitation functions were measured simultaneously in the energy range of 6.8 <= E-c.m. <= 9.3 MeV. Using detailed balance the Ca-41(n, alpha)Ar-38 and K-41(p, alpha)Ar-38 reaction rates were determined, which suggested a 20% increase in the Ca-41 yield from massive stars.