Precision measurement of the specific activity of Ar-39 in atmospheric argon with the DEAP-3600 detector

The specific activity of the beta decay of Ar-39 in atmospheric argon is measured using the DEAP-3600 detector. DEAP-3600, located 2 km underground at SNOLAB, uses a total of (3269 +/- 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector is well-suited to measure the decay of Ar-39 owing to its very low background levels. This is achieved in two ways: it uses low background construction materials; and it uses pulse-shape discrimination to differentiate between nuclear recoils and electron recoils. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is (0.964 +/- 0.001(stat) +/- 0.024(sys)) Bq/kg(atmAr), which is consistent with results from other experiments. A cross-check analysis using different event selection criteria and a different statistical method confirms the result.

Automated summary

The specific activity of beta decay of Ar-39 in atmospheric argon was measured using the DEAP-3600 detector. The detector, located 2 km underground at SNOLAB, utilized 3269 +/- 24 kg of liquid argon distilled from the atmosphere for dark matter search. The detector's low background levels, achieved through the use of low background construction materials and pulse-shape discrimination, made it well-suited for measuring the decay of Ar-39. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction was (0.964 +/- 0.001(stat) +/- 0.024(sys)) Bq/kg(atmAr), consistent with results from other experiments. A cross-check analysis using different event selection criteria and a different statistical method confirmed the result.