Radiation effects on SDRAMs and optical fiber-based dosimetry of high-energy electrons

Abstract

This thesis work contains studies in two separate fields, unified under the topic of electron radiation. The radiation effects of electrons on electronics is a field of study that is gaining traction due to the ever smaller technology nodes found in modern electronics risk getting upset by lighter particles and through different mechanisms than historically has been observed. In this work, the response of synchronous dynamic random access memories (SDRAM) was investigated under electron irradiation with much focus on stuck bits and the evolution of data retention times of the memory bits under and after irradiation. High-energy electrons were found to be capable of inducing stuck bits as single event effects in a device under test, and large losses of retention time capability were found both in stuck bits and in bits that had bit-flips during irradiation. These radiation effects were also studied under proton irradiation as well as photon irradiation, where a large retention-time degradation was observed in both cases, which was ascribed to the effects of total ionizing dose on the device. Characterizations of optical fiber-based dosimetry systems utilizing the radiation-induced luminescence (RIL) of doped silica glasses for online dose monitoring were performed under pulsed electron beams. The RIL intensity of the fiber-based dosimeters during the delivered electron bunches was found to be linearly proportional to the dose of the electron bunches when varying the dose per electron bunch. The luminescence properties of a silica glass rod doped with Gd3⁺-ions were investigated under electron irradiation at varying depths in an acrylic phantom. The RIL proportional to the deposited dose rate was separated from the induced Cherenkov radiation through two separate acquisition systems, one based on a monochromator and one based on a spectrometer. The decay time of the Gd3⁺-ion luminescence was also studied through the monochromator. The presented results show that these types of optical-fiber based dosimeters can be used to efficiently monitor the dose of such a Clinac. Keywords: dosimetry, electrons, optical fibers, photons, protons, radiation effects, radiation-induced luminescence, SDRAM, single event effects, stuck bits, total ionizing dose effects