On Search and Identification of Fossil Tracks dne to Superheavy Cosmic Ray Nuclei (Z ≥ 110) in Meteoritic Crystals

A new method for investigation of the ultra-heavy component of Galactic cosmic-ray nuclei (Z = 50 - 92) has been developed since 1980. It depends on the ability of extraterrestrial silicate crystals (olivine) to register and store during many million years the tracks due to cosmic-ray nuclei with Z ≥ 22. Our approach bases on the partial annealing of both "fossil" tracks and the tracks due to accelerated Kr, Xe, Au, Pb and U ions, and on the chemical etching of total volume track length of the cosmic-ray nuclei in the olivine crystals. The crystals taken from Marjalahti and Eagle Station pallasites (the radiation ages are 180 and 45 million years respectively) were annealed at 703 K during 32 h and etched. The volume tracks due to Z ≥ 50 cosmic-ray nuclei were then measured. The intercomparison of track length spectra of the "fossil" tracks and the tracks due to the accelerated 238 U and 208 Pb nuclei proves unambiguously that the last two abundant peaks of "fossil" track length spectra (120 - 140 μm and 180 μm, first observed in 1980 in Dubna) are products of the recent nucleosynthesis in our Galaxy due to Pt-Pb and Th-U groups of cosmic-ray nuclei. During 1980 - 1996 more than 1600 Th-U "fossil" tracks were measured and 11 anomalously long tracks (L = 340 - 370 μm) were found. Concerning the origin of the anomalously long tracks we have determined the orientation of these tracks in olivine crystal with the Laue-Roentgen method. We estabilished that five anomalously long "fossil" tracks have an angle ≥ 15° to the main crystal plane (010) and subsequently can not be attributed to any actinide nuclei in meteoritic olivine crystals. Moreover, in the fossil track study of olivines annealed at 703 K during 32 h we found the 250 μm - long track which could not be attributed to Th-U nuclei at any orientation in the crystal lattice. Now we can set an upper limit of Z ≥ 110 (superheavy) nuclei abundance at the level N Z μ 110 / N Th, U ≤ (1÷3) · 10 −3 . Our goal is to obtain the final, necessary and sufficient proofs of the existence of SHE nuclei in Galactic matter.