  Among the direct search experiments for WIMP dark matter, the DAMA experiment
observed an annual modulation signal interpreted as WIMP interactions with
9.2$\sigma$ significance. However, this result is contradictory with other
direct search experiments reporting null signals in the same parameter space
allowed by the DAMA observation, necessitating clarification of the origin of
the modulation signal observed using the NaI(Tl) crystals of the DAMA
experiment independently. Here, we report the first results of NaI(Tl) crystal
measurement at the Yangyang Underground Laboratory to grow ultra-low-background
NaI(Tl) crystal detectors.
