Abstract: PRECISE DETERMINATION OF YIELDS OFANDLIZE；CUI ANZHI；LIU DAMING；LIU YONGHUI；WANG XIUZHI；JING KEXING；TANG PEIJA；YANG YI；ZHANG SHULAN；LI XINHUA；SUN HONGOING；LIU CONGGUI；LI DAMING；ZHANG SHENGDONG；AN XINYU；GUO JINGRU（China Institute of Atomic Energy,P.O.Box 275（48），Beijing 102413）ABSTRACT Fission yields of and are determinded for the fission of induced by ther-mal and 8 MeV neutrons by HPGe r-ray spectrometry. Absolute fisson rate is monitored with adouble-fission chamber. The efficiency of the fission chamber is checked with absolute determina-tion of activity from（n，r）reaction for the first time.Fission product activities ofirradiated foils are rneasured by HPGe r-ray spectrometry without chemical separation.Timeof flight technique and measurement of the fission ratio of are used to estimated the fis-sion events induced by neutrons of other energies．Ratio of"fast yield"to"thermal yield" is alsoobtaincd precisely because of elimination of some svstematic errors.The ratio and evaluated valueof"thermal yield "are used to get more accurate"fast yield" values. The results document thatthe yield values at 8 MeV energy point deviate from those from exponential function values.Key words Fission yield ThermaI neutrons 8 Mev neutrons r-ray spectrome-try Precise determination