  Thallium-doped sodium iodide (NaI(Tl)) crystals are widely used in radiation
detection applications, from gamma-ray spectroscopy to particle dark matter
searches. However, if the crystal is exposed to relative humidity of even a few
percent, its light emission degrades, making the crystal impractical as a
detector. Surrounding the crystal with organic scintillators not only protects
the surface of the crystal from humid air but also offers a new capability to
tag backgrounds such as external gamma rays and surface contaminations. We
developed a detector that is constructed by fully encasing a NaI(Tl) crystal in
a plastic scintillator and then immersing the plastic-crystal assembly in
liquid scintillator. Using data collected from this triple phoswich detector, a
pulse shape analysis is able to identify the various radiation signals from the
three scintillators. Additionally, we find that the crystal's emission quality
is maintained for a month.
