Nonabsorption probability

It can be demonstrated by means of a crude probability argument that these results (4.99) and (4.100) are indeed the nonabsorption probabilities defined above. For convenience, we will carry out the calculation in terms of the lethargy variable. Suppose that the interval 0 to w (which corresponds to the interval Eo to E) is divided into N subintervals Alii which are sufficiently small so that the cross sections may be given one particular value [2a(ui),2,(w<),. . . ] over each subinterval (see Fig. 4.17). Then let pi denote the probability that a neutron will pass through Aui without being absorbed. But, each must be an independent probability therefore,... 

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