Measurement of radon-induced backgrounds in the NEXT double beta decay experiment

TL;DR

This study measures radon-related background levels in the NEXT-White detector, demonstrating that radon-induced backgrounds are low enough to not significantly hinder the neutrinoless double beta decay search in NEXT-100.

Contribution

It provides a detailed measurement of radon activity and its impact on background levels in the NEXT detector, supporting future double beta decay experiments.

Findings

Radon activity measured at 38.1 mBq/m^3 with uncertainties.

Radon-induced background rate projected to be below 0.1 counts/year.

Radon backgrounds are sufficiently low for NEXT-100 physics goals.

Abstract

The measurement of the internal $^{222}$Rn activity in the NEXT-White detector during the so-called Run-II period with $^{136}$Xe-depleted xenon is discussed in detail, together with its implications for double beta decay searches in NEXT. The activity is measured through the alpha production rate induced in the fiducial volume by $^{222}$Rn and its alpha-emitting progeny. The specific activity is measured to be $(38.1\pm 2.2~\mathrm{(stat.)}\pm 5.9~\mathrm{(syst.)})$~mBq/m$^3$. Radon-induced electrons have also been characterized from the decay of the $^{214}$Bi daughter ions plating out on the cathode of the time projection chamber. From our studies, we conclude that radon-induced backgrounds are sufficiently low to enable a successful NEXT-100 physics program, as the projected rate contribution should not exceed 0.1~counts/yr in the neutrinoless double beta decay sample.