A comprehensive program is currently underway in several laboratories for the development of sensitive and non-destructive techniques for the quantification of transuranics in low and intermediate radioactive waste packages. This paper describes the method being developed to quantify different isotopes separately by using online prompt and delayed neutron measurements from the fission of isotopes such as 235U, 238U, 239Pu and 241Pu. The system uses a new generation 14 MeV pulsed neutron generator the emission of which is about 2×10 9 n s −1. The association of the differential die-away technique technique [W.E. Kunz, J.D. Atencio, J.T. Caldwell, A 1 nCi/g sensitivity transuranic waste assay system using pulsed neutron interrogation, INMM Annual meeting, Palm Beach, Florida. LA-UR-90-1794, CONF-800655-4 (1980)] (Differential Die-away Technique) and the SPHINCS method [Nucl. Instr. and Meth. B 160 (2000) 280–289] (Sequential PHoton Interrogation and Neutron Counting Signatures) allows measurement of the prompt and delayed neutrons from thermal and fast-induced fission after each interrogating pulse. This method is demonstrated by the measurement of uranium and plutonium samples. Samples of U + Pu have also been analysed inside a non-active drum of bituminized coating for the purpose of demonstrating the feasibility of the separation of 235U from 239Pu by this method. Moreover, the influence of 238U and the necessity of correcting its effects have been studied. Finally, the purpose is to determine the best estimated value for each mass of interest associated with its own standard deviation and statistical distribution. Hence a specific method, based on the Monte Carlo trials, has been developed to estimate masses and associated uncertainties for each isotope of interest.