Abstract: A multilayer film for coating an exterior of a scintillation detector bar includes a pressure sensitive adherent layer containing a percentage of a light-diffusing material therein for affixing to an external surface of the bar. A clear plastic layer separates the adherent layer from a specularly reflecting layer. A protective layer is disposed atop the specularly reflecting layer. The light-diffusing material and the specularly reflecting layer cooperate to retain light within the bar, direct light in random directions within the bar and block optical crosstalk between adjacent bars. A preform consisting of a single piece of film may be used for covering five sides of the bar.