Abstract: DETERMINATION OF ~(88)Y IN NEUTRON ACTIVATED ROCKS──APPLICATION　OF　SIMPLEX OPTIMIZATION IN SPECTROPHOTOMETRIC ANALYSISWANG WUSHANG；CHEN LIYUN（Northwest Institute of Nuclear Technology，P.O.Box 69（17），Xi′an 710024）ABSTRACT A　sensitive andselective spectrophotometric method for the determination of chemical recov-ery of ~(88)Y in neutron activated rocks is developed with modified simplex optirnization method.Thespectrophotometric method is based on the reaction between rare earth elements and chlorophos-phonazo Ⅲ in aqueous solution containing Cu， Phen and ethanol．Under the experimental condi-tions，the maximum absorption wavelength is at 680nm，the molar absorptivity is 1．06×10~4m~2／mol．The absorbance is linearly dependent on the concentration of yttrium when the concen-tration is below 0．6mg／l The variation coefficient is 0. 87％。Key words Simplex optimization method Spectrophotometric method Yttrium Chlorophosphonazo Ⅲ