Journal o f Radioanalytical and Nuclear Chemistry, Articles, Vol. 113, No. 2 (1987) 357-370 A COMPARATIVE STUDY OF SOME NUCLEAR METHODS FOR 23 s U/2 s s U ISOTOPIC RATIOS DETERMINATION M. B. A. VASCONCELLOS, M. J. A. ARMELIN, A. M. G. FIGUEIREDO, B. P. btAZZILLI, M. SAIKI lnstituto de Pesquisas Energdticas e Nucleates, Comis~o National de Energia Nuclear, CaLvaPostal 11049 - Pinheiros 01000 Sdo Paulo - SP (Brasil) (Received December 12, 1986) In the present work, a comparative study is made among nuclear methods for 23SU/23Su ratios determination: activation analysis followed by high-resolution gamma-ray spectrometry, delayed neutron counting, passive gamma-ray and alpha spectrometry, Activation analysis followed by high-resolution gamma-ray spectrometry yielded a relative standard deviation down to 0.1% and a relative error of about 1% for standards of uraniom enriched to 14%. Passive gamma-ray spectrometry using .Ge(Li) detectors yielded a relative error down to 0.1% for enriched uranium and values even lower for the standard deviation. Passive gamma-ray spectrometry using Low Energy Photon Detector (LEPD) yielded a precision of 0.2% and a still better accuracy for enriched standards. In the ease of alpha spectrometry, a relative error down to 0.5% and a precision of about 1% were obtained, also for enriched uranium standards. Delayed neutron counting allowed a relative standard deviation of about 7% and a relative error of about 2%, for standards of depleted uranium. Introduction The determination of 235U/238U isotopic ratios is of great inloortance in nuclear technology. It is normally assigned that precise and accurate iso- topic analysis of uranium has to be carried out by mass spectrclnetry. In nuclear laboratories, on the other hand it can be more convenient and less expensive to use other available methods of aD~alysis. In the present work, a comparative study is made among some nuclear me thods for 235[;/238[/ ratios determination, such as; activation analysis follo- wed by high-resolution ganmm-ray spectrometry, delayed-neutron counting, passive ganmm-ray and alpha spectrometry. The methods were studied by using uranium isotopic standards from the Co~0agnie Generale de Matieres Nucleaires (COGEMA) from Pierrelatte, France. Elsevier Sequoia S. A., Lausanne Akaddmiai Kiad6, Budapest