Radon Daughter Plate-out Measurements at SNOLAB for Polyethylene and Copper

TL;DR

This study measures radon daughter plate-out rates on polyethylene and copper at SNOLAB, comparing experimental results with predictions, and discusses a time-dependent model of alpha activity in these materials.

Contribution

It provides the first detailed measurements of radon daughter plate-out rates on polyethylene and copper in an underground environment, along with a time-dependent activity model.

Findings

Average $^{210}$Pb plate-out rates of 249 and 423 atoms/day/cm$^{2}$ for polyethylene and copper.

Experimental measurements align with predicted rates based on environmental conditions.

A time-dependent model of alpha activity is proposed for these materials.

Abstract

Polyethylene and copper samples were exposed to the underground air at SNOLAB for approximately three months while several environmental factors were monitored. Predictions of the radon-daughter plate-out rate are compared to the resulting surface activities, obtained from high-sensitivity measurements of alpha emissivity using the XIA UltraLo-1800 spectrometer at SMU. From these measurements, we determine an average $^{210}$Pb plate-out rate of 249 and 423 atoms/day/cm$^{2}$ for polyethylene and copper, respectively, when exposed to radon activity of 135 Bq/m$^{3}$ at SNOLAB. A time-dependent model of alpha activity is discussed for these materials placed in similar environmental conditions.