[en] 1 - Description of problem or function: CRYSTAL-BALL is a program for determining neutron spectra from activation measurements and their associated errors. A subsidiary program, XSTAPE, converts activation cross sections from the SAND-II data library into pointwise cross sections in a format that can be read by the main program. An energy grid consistent with the SAND-II grid is used, however the subroutine specifying the energy spacings can be easily changed. CRYSTAL-BALL itself uses the cross section data, together with an initial guess of the neutron spectrum to calculate the integral and differential spectrum and the corresponding reaction rates and monitor responses. An option to plot spectrum data using CALCOMP plotter routines is included. 2 - Method of solution: Measured activities are related to the neutron flux and cross section by an integral equation of the first kind. CRYSTAL-BALL uses the method of F.W. Stallman to solve a set of these equations. The method is based on a direct approximation of the Dirac delta operator by a linear combination of integral operators. It involves minimizing an integral expression involving both the true spectrum and a user-supplied estimate, subject to a tolerance limit