简介：TodevelopaNaI(Tl)detectorforinsituradioactivitymonitoringinthemarineenvironmentandenhancetheconfidenceoftheprobabilityofthegamma-spectrumanalysis,MonteCarlosimulationsusingtheMonteCarloN-Particle(MNCP)codewereperformedtoprovidetheresponsespectraofsomeinterestedradionuclidesandthebackgroundspectraoriginatingfromthenaturalradionuclidesinseawaterrecordedbyaNaI(Tl)detector.Anewlydeveloped75mm×75mmNaI(Tl)detectorwascalibratedusingfourreferenceradioactivesources137Cs,60Co,40Kand54Mninthelaboratorybeforethefieldmeasurementsinseawater.Asimulationmodelwasestablishedforthedetectorimmersedinseawater.ThesimulatedspectrawereallbroadenedwithGaussianpulsestoreflectthestatisticalfluctuationsandelectricalnoiseintherealmeasurement.Thesimulatedspectrashowthatthesingle-energyphotonsintothedetectoraremostlyscatteringlow-energyphotonsandthehighbackgroundinthelowenergyregionmainlyoriginatesfromtheComptoneffectofthehighenergyγ-raysofnaturalradionuclidesinseawater.Thesimulatedbackgroundspectrumwascomparedwiththeexperimentalonerecordedinfieldmeasurementandtheyseemtobeingoodagreement.Thesimulationmethodandspectracanbeusedfortheaccurateanalysisofthefiledmeasurementresultsoflowconcentrationradioactivityinseawater.