Radiation damage induced dose rate non-linearity in an n-type silicon detector

Depth dose measurements in continuous cobalt radiation and pulsed roentgen rays were performed with nonirradiated and preirradiated detectors made of n-type silicon. A change in the relative signal at 15 cm depth of 5 to 10 per cent was found in pulsed roentgen ray fields when the detector was radiation damaged. Further experiments showed that the preirradiated detector had a superlinear dose response characteristic at high dose rates. A theoretic model was worked out and the non-linearity is explained by the properties of the recombination centers created during the preirradiation. The recombination centers are also responsible for the sensitivity drop after irradiation. At low dose rates in continuous radiation the non-linearity effect is not observed, which is in accordance with the theory. The theory in conjunction with our and other experimental results suggests that a p-silicon detector will remain linear also after heavy preirradiation.