A new code has been developed named RAINIER that simulates the γ-ray
decay of discrete and quasi-continuum nuclear levels for a user-specified range
of energy, angular momentum, and parity including a realistic treatment of
level spacing and transition width fluctuations. A similar program, DICEBOX,
uses the Monte Carlo method to simulate level and width fluctuations but is
restricted to γ-ray decay from no more than two initial states such as
de-excitation following thermal neutron capture. On the other hand, modern
reaction codes such as TALYS and EMPIRE populate a wide range of states in the
residual nucleus prior to γ-ray decay, but do not go beyond the use of
deterministic functions and therefore neglect cascade fluctuations. This
combination of capabilities allows RAINIER to be used to determine
quasi-continuum properties through comparison with experimental data. Several
examples are given that demonstrate how cascade fluctuations influence
experimental high-resolution γ-ray spectra from reactions that populate
a wide range of initial states.Comment: 14 pages, 13 figures, Nuclear Instrumentation and Methods A, 201