In this work the infrared absorption of neutron irradiated silicon was compared to that of non-irradiated silicon at room and liquid nitrogen temperatures. It was found that instead of the 1.75 micron absorption band that has been mentioned in numerous papers transmission was completely cut off below about 2.5 microns at room temperature and about 1.8 microns at liquid nitrogen temperature. A weak absorption band was noted at 4.4 microns for all three samples at liquid nitrogen temperature and the two irradiated samples at room temperature. Absorption due to free carriers depressed at the longer wavelengths (10-15 microns) with irradiation and cooling as was expected from past experiments. The resistivity of Si₄ increased from an assumed initial value of 10³ ohm-om to 1.89 x 10⁵ ohm-om. / Master of Science