  A newly developed segmented YSO scintillator detector was implemented for the
first time at the RI-beam Factory at RIKEN Nishina Center as an
implantation-decay counter. The results from the experiment demonstrate that
the detector is a viable alternative to conventional silicon-strip detectors
with its good timing resolution and high detection efficiency for ${\rm \beta}$
particles. A Position-Sensitive Photo-Multiplier Tube (PSPMT) is coupled with a
$48\times48$ segmented YSO crystal. To demonstrate its capabilities, a known
short-lived isomer in $^{76}$Ni and the ${\rm \beta}$ decay of $^{74}$Co were
measured by implanting those ions into the YSO detector. The half-lives and
${\rm \gamma}$-rays observed in this work are consistent with the known values.
The ${\rm \beta}$-ray detection efficiency is more than 80~\% for the decay of
$^{74}$Co.
