I've been thinking. If one were to estimate what the rate at which neutrons are produced in a fission reaction, they are going to have to know at least the following facts:
$_{0}^{1}\textrm{n} + _{92}^{235}\textrm{U} \to _{92}^{236}\textrm{U} \text{ : with a rate } R_1 (N_n(t), N_{235}(t))$.
$_{92}^{236}\textrm{U} \to ^{k_1}\textrm{X} + ^{235-k_1}\textrm{Y} + m \times _{0}^{1}\textrm{n} \text{ : with a rate } R_2(N_{236}(t))$.
$\text{Some of the } _{0}^{1}\textrm{n} \text{ excape without being absorbed at a rate } R_3(N_n (t))$.

My question to you is: How does one find:
$R_1 (N_n(t), N_{235}(t))$,
$R_2(N_{236}(t))$, and
$R_3(N_n (t))$?

Does one need to know the probablity of a neutron encountering a uranium-235 nucleus?