Needle-shaped CsBr:Eu2+ storage phosphor crystal particles in form of a cylinder suitable for use in flat storage phosphor panels have been provided, wherein said particles have an average cross-section in the range from 1 .mu.m up to 30 .mu.m and an average length, measured along the casing of said cylinder, in the range from 100 .mu.m up to 1000 .mu.m.