The DEAP-3600 experiment is searching for dark matter with a single phase liquid argon (LAr) target, located at SNOLAB. For a background-free exposure of 3000 kg·yr, the projected sensitivity to the spin-independent WIMP-nucleon cross section at 100 GeV/c2 WIMP mass is 1e-46 cm2. The construction and filling of DEAP-3600 was completed in 2016 and the experiment is currently taken physics data. Recently, the first results of an initial commissioning data set were presented which could successfully demonstrate the detector performance and resulted in the leading limit on the WIMP-nucleon spin-independent cross section for argon.

In the first part of this seminar I will present the DEAP-3600 experiment and its recent results with an emphasis on radioactive backgrounds. In the second part of the seminar I will briefly describe a few recent investigations of rare beta and double beta decay processes such as 36Ar, 39Ar and 42Ar with DEAP but also other isotopes with gamma-spectroscopy setups. I will illustrate their importance in the context of radioactive backgrounds in other low background experiments and in the context of understanding nuclear structure. Especially the better understanding of nuclear models and their intrinsic parameters is needed to obtain more reliable nuclear matrix elements e.g. for neutrinoless double beta decay processes in order to connect the observed half-life to the the effective Majorana neutrino mass.