  A prototype of LaBr3:Ce in situ gamma-ray spectrometer for marine
environmental monitoring is developed and applied for in situ measurement. A
3-inch LaBr3:Ce scintillator is used in the detector, and a digital pulse
process electronics is chosen as the pulse height analyzer. For this prototype,
the energy response of the spectrometer is linear and the energy resolution of
662keV is 2.6% (much better than NaI). With the measurement of the prototype in
a water tank filled with 137Cs, the detect efficiency for 137Cs is (0.288
0.01)cps/(Bq/L), which is close to the result of Monte Carlo simulation,
0.283cps/(Bq/L). With this measurement, the MDAC for 137Cs in one hour has been
calculated to 0.78Bq/L, better than that of NaI(Tl) in-situ gamma spectrometer,
which is ~1.0Bq/L.
