Time Dependent, Space Independent Neutron Thermalization

The time dependent thermalization following a burst of fast neutrons is analyzed in the space independent case. The spectrum is decomposed in an asymptotic and a transient part, and the latter is expanded in a series of Laguerre polynomials. The argument of the polynomials is proportional to the time after the burst and the coefficients of the expansion are linear combinations of the transient time moments.