Aiming at the problem that the irradiation light output of CsI(Tl)scintillator detector changes constantly during the long time experiment,with the stability control of dark field signal,apebble flow detection system with a 5∶1 ratio reduction of the actual core was irradiated for 48 hwith no-loadγray.Besides,the controlled result of dark field stability and the irradiation light output of the detector were recorded.Experiment results show that after theγirradiation,the irradiation light output of the scint...