On search and identification of tracks due to short-lived SHE nuclei in extraterrestrial crystals

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The unique approach for search and unambiguous identification of short-lived ( T 1/2=10 3–10 7 years) superheavy nuclei in cosmic-ray products of the recent nucleosynthesis in our Galaxy are discussed. It is based on: (a) the ability of non-conducting crystals to register and to store for many million years the tracks due to fast nuclei with atomic number Z⩾20 (“fossil” tracks); (b) calibrations of the said crystals with accelerated heavy ions (20⩽ Z⩽92) and on revealing the volume etchable track length (VETL) of the fast nuclei coming to rest inside crystals—both of fossil and “fresh” tracks—to determine the charge distribution of cosmic-ray nuclei tracks and (c) the so-called “four-zone” model of tracks in crystals (and also glasses) which provides not only the VETL track length dependence for 20⩽ Z⩽92 nuclei but also demonstrates the regular annealing behavior of VETL of 20⩽ Z⩽92 nuclei in a broad temperature interval. This approach was first applied in the early 1980s to investigate the “fossil” tracks due to 22⩽ Z⩽92 cosmic-ray nuclei in olivine crystals from meteorites-pallasite Marjalahti and Eagle Station. The discovery of Th–U cosmic-ray nuclei tracks in 1980 was unambiguously confirmed by calibrations of the same crystals with 238 U , 197 Au and 208 Pb accelerated ions in the late 1980s. More than 1600 tracks due to cosmic-ray actinide nuclei were measured during the last two decades of the 20th century. Also, 11 anomalously long tracks (track length exceeds by a factor (1.6±0.1) the track length due to Th–U nuclei were measured. The detailed analysis shows that at least 5 of these tracks could not be attributed to the Th–U nuclei. It means that now we have a preliminary proof on the existence Z⩾110 nuclei in cosmic-rays. The abundance is Z⩾110/Th–U=(1–3)×10 −3 in Z⩾110 freshly formed cosmic-rays (time interval 10 3–10 7 years). The method proposed can provide the necessary and sufficient conditions for the discovery of Z⩾110 nuclei in nature.