Using 220Rn to calibrate liquid noble gas detectors
  In this paper, we describe 220Rn calibration source that was developed for
liquid noble gas detectors. The key advantage of this source is that it can
provide 212Bi-212Po consecutive events, which enables us to evaluate the vertex
resolution of a detector at low energy by comparing low-energy events of 212Bi
and corresponding higher-energy alpha-rays from 212Po. Since 220Rn is a noble
gas, a hot metal getter can be used when introduced using xenon as the carrier
gas. In addition, no long-life radioactive isotopes are left behind in the
detector after the calibration is complete; this has clear advantage over the
use of 222Rn which leaves long- life radioactivity, i.e., 210Pb. Using a small
liquid xenon test chamber, we developed a system to introduce 220Rn via the
xenon carrier gas; we demonstrated the successful introduction of 6 times 10^2
220Rn atoms in our test environment.
