Abstract: A light pulser consisting of a chip of CsI(Tl) crystal and an external alphasource ~(241)Am is constructed. Between the crystal and the source there is an alumi-nium foil with a small hole asits centre served both as reflector and collimator. Thewidth (FWHM) of the alpha peak is 8%. The gamma equivalent energy (GEE) isdetermined to be 3MeV with the pulser placed on a CsI (Tl) crystal. And it is9MeV when a BGO crystal is used. The present. type of light pulser is muchsimpler in construction and has higher reliability as compared. with the light pul-ser using NaI(Tl)crystal.