Before revision: In each collision the neutrons impart a fraction of their energy to the nuclei in the medium, losing up to a maximum of <math> \delta E _{max = (1 - \alpha) E \alpha = (A-1{A+1})^2 <\math> where A is the atomic number of the medium.
After revision: In each collision the neutrons impart a fraction of their energy to the nuclei in the medium, losing up to a maximum of <math> \delta E = (1 - \alpha) E \alpha = (A-1{A+1})^2 <\math> where A is the atomic number of the medium.