Neutron capture of Ca-46 at thermonuclear energies

The measurement of the neutron capture reaction Ca-46(n, gamma)Ca-47 is of astrophysical interest, because Ca-46 is bypassed by charged-particle react ions. The nucleus Ca-46 is produced and destroyed by neutron-induced nucleo synthesis in hydrostatic helium, carbon, and neon burning through the react ion chain Ca-45(n, gamma)Ca-46(n, gamma)Ca-47. At the Karlsruhe and Tubinge n 3.75 MV Van de Graaff accelerators the thermo-nuclear Ca-46(il, gamma)Ca- 47(4.53 d) cross section was measured by the activation technique via the 1 297.09 keV gamma-ray line of the Ca-47 decay. Samples of CaCO3 enriched in Ca-46 by 5% were irradiated between two Sold foils which served as capture standards using the Li-7(p,n) and T(p,n) reactions. The capture cross secti on was measured at the mean neutron energies 30, 104, 149, 180, and 215 keV , respectively. Maxwellian averaged capture cross sections were measured at the quasithermal neutron energies kT = 25 and 52 keV, respectively. It was found that the Ca-46(n,gamma)Ca-47 cross section in the thermonuclear ener gy region and at thermal energy is dominated by an s-wave resonance at 28.4 keV with a neutron width Gamma(n) =( 17.4(-2.8)(+3.6)) keV and a radiation width Gamma(y) = (2.4 +/- 0.3) eV. The stellar reaction rate is determined in the temperature range from kT = 1 to 250 keV and is compared with previ ous investigations using Hauser-Feshbach calculations or experimental cross section data. The astrophysical consequences of the new stellar reaction r ate with respect to the nucleosynthetic abundance of Ca-46 are discussed. [ S0556-2813(99)05106-7].