The branching ratio of the direct decay of 40K to the ground state of 40Ar through electron capture has never been experimentally measured. This rate has been shown to be vital in constraining the DAMA/LIBRA (DArk MAtter/Large sodium Iodide Bulk for RAre processes) dark matter signal claim and is a rare example of a unique third forbidden decay. The KDK (pun for Potassium Decay) project attempts to measure the ratio of electron capture to the excited state of 40Ar versus the electron capture to its ground state. The experiment will combine an enriched 40K source attached to a low energy x-ray detector surrounded by an almost 4pi coverage gamma ray detector. The low energy x-ray detector will be a Large Area Avalanche Photodiode, while the gamma ray detector will be the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. This thesis focuses on the development, characterization and feasibility of avalanche photodiodes as low energy x-ray detectors for the KDK measurement.
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