  A scintillating fiber array measurement system for gross beta is developed to
achieve real-time monitoring of radioactivity in drinking water. The detector
consists of 1,096 scintillating fibers, both sides of the fibers connect to a
photomultiplier tube, and they are placed in a stainless steel tank. The
detector parameters of working voltage, background counting rate and stability
of the detector were tested, and the detection efficiency was calibrated using
a standard solution of potassium chloride. Through experiment, the background
counting rate of the detector is 38.31 cps and the detection efficiency for
$\beta$ particles is 0.37 cps per Bq per liter; the detector can reach its
detection limit of 1.0 Bq per liter for $\beta$ particles within 100 minutes
without pre-concentration.
