Silicon diodes as dosimeters in fast neutron therapy

Abstract

Silicon p-i-n diodes were found to be convenient and reliable integrating in vivo dosimeters for patients undergoing fast neutron therapy. These devices are almost completely insensitive to photons and thermal neutrons. Read-out does not alter the stored information. The diodes were calibrated directly on the treatment beam, using the change in forward voltage divided by the pre-irradiation forward voltage as the sensitive parameter. Annealing at 100 degrees c was used to reduce and stabilize the forward voltage of previously exposed diodes prior to re-irradiation. The calibration to dV/V and the annealing permitted multiple re-use of the diodes with precision approaching 5% for doses from 50 to 350 rad. Doses below 50 rad were subject to greater uncertainties, with 50% precision at 4 rad.