A method for preparing barium fluorohalide-based crystal, which includes at
least a step in which a halide aqueous solution (B) and aqueous solutions
of a fluoride and a barium salt are mixed into a halide aqueous solution
(A). The halide aqueous solution (B) contains the same halogen as that
contained in the halide aqueous solution (A). In this method, halide ions
are used efficiently rather than remaining to form a waste residue.
