Solve the given problem:
Problem: Suppose that a fission neutron, emitted with an energy of 2 Me V, slows down to an energy of 1 eV as the result of successive collisions in a moderator. If, on the average, the neutron gains in lethargy the amount in each collision,
Part A: How many collisions are required if the moderator is
(a) Hydrogen?
(b) Graphite?
I need the right answer and steps of solving this problem. Thank you!