We characterize two 40 kBq sources of electrodeposited Th-228 for use in low-background experiments. The sources efficiently emanate Rn-220, a noble gas that can diffuse in a detector volume. Rn-220 and its daughter isotopes produce alpha, beta, and gamma-radiation, which may used to calibrate a variety of detector responses and features, before decaying completely in only a few days. We perform various tests to place limits on the release of other long-lived isotopes. In particular, we find an emanation of <0.008 atoms/min/kBq (90% CL) for Th-228 and 1.53 atoms/min/kBq for Ra-224. The sources lend themselves in particular to the calibration of detectors employing liquid noble elements such as argon and xenon. With the source mounted in a noble gas system, we demonstrate that filters are highly efficient in reducing the activity of these longer-lived isotopes further. We thus confirm the suitability of these sources even for use in next-generation experiments, such as XENON1T/XENONnT, LZ, and nEXO.
@article{arxiv.1602.01138,
title = {A Rn-220 source for the calibration of low-background experiments},
author = {Rafael F. Lang and Andrew Brown and Ethan Brown and Mayra Cervantes and Sean Macmullin and Darryl Masson and Jochen Schreiner and Hardy Simgen},
journal= {arXiv preprint arXiv:1602.01138},
year = {2016}
}