Using the following values for the microscopic scattering cross sections for hydrogen and oxygen, = 20.1 and = 3.8 respectively, and the definition of average lethargy gain per collision = 1 (1) 2 2 ln ( +1 1 ) calculate average lethargy gain per collision for water < >2 Average lethargy gain per collision of a substance containing more than one material is given as: < >= ( 1 )(1,1 + 2,2 + ,) where 1, 2.. shows different atom species.