Evaluation of the fission track analysis for determination of trace-amounts of Pu-239

The fission track technique was studied and evaluated for critical circumst ances in the overall process of the analysis. Fission Track Analysis (FTA) is used for determination of Pu-239 at a femto gram level in biological and environmental samples. The technique is a type of neutron activation where Pu-239 is determined by the registration of fission fragments in quartz af ter irradiation with thermal neutrons in a nuclear reactor. Plutonium is ex tracted from the sample by chemical separation processes in several steps i n order to retrieve a pure plutonium sample. The method for the chemical se paration was selected to suppress the influence from naturally occurring ur anium in the sample since the cross-section of thermal neutron fission of U -235 is in the same order of magnitude as the cross-section for Pu-239. Th, following parts of the fission track analysis were regarded as critical an d subjects of further evaluation: the quenching of fission tracks, the effi ciency of the solvent extraction used in the final step of the chemical sep aration, the efficiency of the uranium de-contamination, the background con tribution from the yield determinant Pu-236, the interference from Th-232 ( which fissions with fast neutrons) and the calibration process. The study w as performed in order to assure the accuracy of the Pu-239 determination an d showed that none of the mentioned critical parts prevent a successful per formance of FTA with a mu Bq detection limit. (C) 1999 Elsevier Science B.V . All rights reserved.