The transmission properties of gadolinium scandium gallium garnet doped with chromium and neodymium have been studied during and after a 20 ns high‐energy x‐ray pulse. Gain is observed in the transmission which indicates a small signal gain of 0.175/cm. About 5% of the absorbed dose is converted to inversion, which is comparable to flash‐lamp‐pumped inversion. The small signal gain scales with dose. ©1995 American Institute of Physics.