Abstract: DETERMINATION OF THE HEAVY RARE EARTH RADIONUCLIDES IN MELTED ROCKLI YINMING；WANG YALONG；ZHANG QUANSHI（Northwest Institute of Nuclear Technology，P.O.Box 69（17），Xi′an 710024）ABSTRACT There are some　heavy rare earth radionuclides in the melted rocks，such as~(160)Tb，~(168，170)Tm，~(88，91)Y，~(174，177)Lu，~(169)Yb ，etc. Because their contents are very low in the melted rocks and the lightrare earth fission products are interfered with their determination，it is very complicated to mea-sure them quantitatively．So a new method has been studied in which P507 resin is used to sepa-rate and purify the rare earths， radioactive sources are prepared by the pieces of filter paper fordetermining chernical yield with X-fluorescene analysis，and radioactive activity is determined withthe γ－spectra analysis.It is proved that this method has satisfied the demands of experiments.Key words Heavev rare earth radionuclides Melted rock P507 resin