Radiation image storage panel

A radiation image storage panel which has a phosphor layer containing energy-storing phosphor particles, wherein the energy-storing phosphor particles comprises a mixture of a phosphor particle group having a relatively large median diameter and a phosphor particle group having a relatively small median diameter, the former group having a median diameter in the range of 4 to 30 μm, the latter group having a median diameter in the range of 1 to 8 μm, and the mixture of these groups having a particle size frequency distribution that satisfies the condition of:

• (x+y)/5>z
• in which x is a size frequency in terms of percent at the peak in a larger range of the size frequency distribution curve, y is a size frequency in terms of percent at the peak in a smaller range, and z is the lowest size frequency in terms of percent in the range between the two peaks.