Thermal-neutron scattering length and capture by Ca46

We have deduced the coherent scattering amplitude of Ca46 as 3.55±0.21 fm by measuring the neutron-diffraction patterns of calcite enriched to 32% in Ca46. We have employed this value in calculating the direct-capture cross sections of the primary electric-dipole transitions in Ca47 using optical-model potentials with physically realistic parameters. The calculated cross sections agree reasonably well with measurements showing that thermal-neutron capture by Ca46 is controlled largely by a simple direct mechanism.