Low-temperature infrared (IR) absorption measurements under above-gap illumination were done to investigate the degradation behaviors of Si crystal for solar cells. The concentration of boron acting as an acceptor decreased with increasing radiation doses of 1 MeV electrons or 10 MeV protons. A new band around 520 cm(-1) was observed in irradiated samples. These results indicate that the boron configuration was changed at Si site by the irradiation. Annealing experiments showed that the concentration of boron accepters restored by annealing around 300 degrees C.