An Implantable Radiation Detector for Cancer Radiotherapy

The conversion of trigger events to their digital equivalent is a central component of any timing-based front end, with applications found in mass spectrometry, single channel analyzers, and a huge variety of 3D mapping and ranging systems. At the same time, ever- tightening size, weight, and power budgets for space launches with a skyrocketing (no pun intended) number of launches in the last decade have made application-specific integrated circuit solutions increasingly appealing. However, conventional analog methods of pulse discrimination introduce timing walk or are limited to a narrow range of pulse shapes, while early-stage digitization requires impractically high sample rates for the events in question. This work presents the analysis, design, and measurement of an integrated constant frac- tion discriminator with theoretically zero timing walk and a programmable, constant trigger fraction which does not depend on input pulse shape. The specific silicon presented here was designed for the Solar Probe Analyzer for Ions as part of its time-of-flight mass spectrometer to determine the ion composition of space plasmas. This dissertation discusses the front end requirements for a radiation hardened pulse discriminator in the context of SPAN-Ion. We then address the architectural modifications used to achieve a pulse shape-independent constant trigger fraction, as well as the analog and digital hardening techniques required to detect, correct, and/or mitigate radiation-induced effects. Finally, this work presents the first attempt at an integrated pulse-shaping front end for SPAN-Ion, concluding with sim- ulation results from a more recent chip and a discussion of future work both for SPAN-Ion and for further code base development.