DEAP-3600 is a liquid argon (LAr) based spin-independent direct dark matter search experiment. It is designed to detect nuclear recoils induced by the elastic scattering of weakly interacting massive particles (WIMPs) on argon nuclei. In 2019, DEAP-3600 reported the best upper limit on the WIMP-nucleon spin-independent cross section on a LAr target of 3.9 × 10 −45 cm 2 for a 100 GeV/c 2 WIMP mass at 90% CL. An essential component of this result involved measuring the rates of α-decays within the detector and determining their impact on the expected background rate in the WIMP search region. The techniques used to measure and characterize these rates in-situ, and their results, will be discussed here in detail. I would like to thank Kevin Graham for his guidance and mentorship during my journey through graduate school. He taught me how to communicate, work, and think like a scientist. He also made sure to prioritize the person before the project, always considering it of utmost importance that I enjoy the work that I do, and taking a strong interest in my personal life and well-being. He formed me into a scientist and I could not have asked for a better supervisor! I would like to thank the DEAP Collaboration, particularly the people at Carleton, for their friendship and support of my work. Everyone I met was always willing to answer questions and lend a hand. I would like to thank Matt Dunford for getting me started with DEAP, and for sharing his advice and knowledge when I first joined, and Andrew Erlandson and David Gallacher for their help and advice as I ran into issues with the software or when I just needed good ideas. I want to thank Tina for helping me learn how to use the DEAP DB and for supporting me as DB co-admin, Simon Viel and Marcin Kuźniak for their support and advice, Björn Lehnert and Alexander Derbin for lending their expertise to the axion work, and Hamid Moradi for excellent discussions that slowed down my PhD work. I would especially like to thank Rob Stainforth and Shawn Westerdale. They both put so much of their time and effort into helping me with the α and axion work that is described in this thesis. Without their time, extensive knowledge, advice, and constant support, I wouldn't have been able to do it. Both were always ready and iv available to answer questions, and frequently took the time to provide very detailed feedback on my work. My parents worked very hard to provide me and my siblings with a quality education growing up, and always encouraged me to pursue a career I was passionate about. My parents and siblings, Natasha, Rebecca, and Joseph, made me the person I am today through their constant love and support throughout my entire life. And lastly, I owe a deep debt of gratitude to my wife, Gloria. She put up with the often long hours of work I had to put in to accomplish this, and her constant love and support got me through it. My wife and children, Christopher and Veronica, have all been constant sources of joy and have been me going, especially during the most difficult ti...