As an illustration, if the spectrum is a typical spectrum in the range of 10-60 keV, a preferred inorganic composition comprises at least one element or compound thereof selected from groups (A), (C) and (D) above with the remainder being at least one element or compound thereof selected from groups (E) or (F), especially 20-70 parts and in particular 30-50 parts from groups (A), (C) and (D), per