A variety of high purity silicon grown on the basis of different manufacturing technologies were exposed to gamma irradiation (up to a dose of 108 rad(Si)) and to neutron irradiation (up to a fluence of 1015 n/cm2). Observation was made of the conduction type and carrier concentration as a function of dose. The conversion point (n-Si to p-Si) of gamma irradiated silicon was found to vary over 2 orders of magnitude of gamma dose for different manufacturers of high purity silicon independent of the initial carrier concentration. A systematic study of the radiation hardness of high purity silicon allows the development of silicon detectors working under harsh radiation environments operating over a wide range of dose. Another important aspect of this research is the development of neutron dosimeters with a wider range of response in terms of 1 MeV(Si) equivalent neutron fluence for calibration of neutron test facilities with unknown neutron energy spectrums. High purity silicon PIN diodes were calibrated using an epithermal neutron beam to determine whether response in terms of 1 MeV(Si) neutrons was independent of the calibration spectrum used. © 1996 IEEE.