Radon-induced backgrounds in the NEXT-100 experiment

A bstract The NEXT-100 detector at the LSC aims at the first competitive search for the 0 νββ decay using a high-pressure 136 Xe electroluminescent time projection chamber. The first low-background run of NEXT-100 at 3.95 bar has been devoted to the measurement of the radon-induced backgrounds impacting this search. The contributions from both the internal and external airborne radon have been evaluated. The internal 222 Rn activity is found to be (0.95 ± 0.04(stat) ± 0.09(sys)) Bq/m 3 , while no traces of 220 Rn have been observed. Most of the 222 Rn progeny plate-out on the surface of the cathode of the detector, leading to a rate of Rn-induced 214 Bi of (0.97 ± 0.05(stat) ± 0.10(sys)) Hz for visible energies above 400 keV. The corresponding background index in the 0 νββ region of interest is evaluated as (7.3 ± 1.5(stat) ± 0.8(sys)) × 10 − 4 counts/(keV · kg · yr) after selection of the fully contained events. This background index is reduced to ∼ 4 × 10 − 5 counts/(keV · kg · yr) by applying a topological selection requiring only one double-electron-like track in the events. This value is one order of magnitude below the total radiogenic background expectation in NEXT-100. By analyzing the correlation of the airborne radon activity and the measured rate of events in NEXT-100, it is concluded that the detector operates in a virtually radon-free environment thanks to the radon abatement system of the LSC.