A NOVEL-APPROACH TO THE PROBLEM OF HIGHLY SENSITIVE ROUTINE ANALYSIS FOR MAN-MADE PLUTONIUM IN ENVIRONMENT AND HUMAN-BODY

A method of determining subpicogram quantities of Pu in soil, mud, wat er, plant and animal tissues is proposed. Pu is chemically isolated fr om the samples, while Pu-236 is used to control yield. The Pu fraction deposited on some backing as well as an U containing standard are put in contact with solid state track detectors (SSTD) - foils of polyeth yleneterephthalate, and irradiated by thermal neutrons of approximatel y 10(15) cm(-2) fluence. After an appropriate chemical etching, the co ntent of Pu-239 in the samples is determined by scanning fission fragm ent tracks in the SSTD. To control possible U impurities in the Pu fra ction,the latter and the standard (in contact with a fresh SSTD) are b ombarded by a high fluence of gamma-quanta with energies less than or equal to 25 MeV (microtron bremsstrahlung). We have succeeded in deter mining the lower limit of U-235 impurities at a level of < 10(?(-13)) g, due to similar photofission cross section of all U and Pu isotopes. The proposed method provides the determination of Pu-239 content in r outine analyses with a sensitivity at a level of 10(-13) g/g. More tha n one hundred assays for Pu-239 content in specimens of above indicate d media from Ukraine, Belorussia, Urals region and Germany have been p erformed. In future, one will hopefully reach a sensitivity of 10(-14) -10(-15) g/g.