Abstract. The slowing down of hadrons in a moderator entails an intensity loss by nuclear absorption. The loss is expected to be particularly large for negative hadrons, due to a combination of Coulomb attraction and strong local absorption. A black sphere absorption model is set up and used for numerical calculations of absorption probability per momentum loss. For K-and ~ on heavy nuclei, a sharp maximum is found for kinetic energies below 0.1 MeV.