DEAP-3600 is a single-phase liquid argon WIMP detector, operating at SNOLAB (Sudbury, Ontario) since 2016. With the 2km rock overburden, the facility boasts one of lowest muon flux in the word.
DEAP-3600 was built with the goal of being background-free in the region of interest for three years. The design choices made to meet this requirement meant that no calibration source could be deployed inside the argon volume, leading to an interesting energy calibration challenge.
In this talk, we will show how the DEAP collaboration used the internal 39Ar background and an external 22Na source to calibrate the energy response of the detector in the region of interest. While this method laid satisfactory results for the first WIMP search, an improvement in sensitivity will required a better understanding of the energy response, particularly at low energy. We will also present here the new calibrations sources DEAP intends to use to refine the energy calibration of the detector.