ON DETERMINATION OF TH CONCENTRATION IN SPECIMENS BY MEANS OF GAMMA-RAYS AND ALPHA-PARTICLES

Experiments on improving the track technique for the determination of Th content in natural samples have been performed. For Th concentratio n measurements, gamma-rays with energies of 18 and 20 MeV were used. F or gamma-rays in the energy range 6-23.5 MeV, the ratio of fission fra gment track densities N-U/N-Th of these elements for thick targets has been obtained. The ratio ranges from 1.7 to 3.2 with the maximum at a gamma-ray energy of 15 MeV. The determined Th concentrations in the c alibrated Th standards and iron manganese nodules agree, within experi mental error, with the known values. For 9.1 MeV/n alpha-particles, th e track density ratio N-Th/N-U has been found to be equal to (1.06 +/- 0.07), but the Th content was lowered, possibly due to the vertical i nhomogeneity of the alpha-particle beam and also due to partial therma l fading of the tracks in mica. The investigation was performed at the Laboratory of Nuclear Reactions, JINR.