On search and identification of short-lived super heavy cosmic-ray nuclei ( Z ≥ 110) by fossil track study of the extraterrestrial crystals: Results and perspectives [II

Abstract

The existence of relatively stable super heavy elements (SHE) in Nature was predicted theoretically at the midst of the sixties (Nilsson, Nix, Sobichevsky, see Ref. [1]). Basing on nuclear shell model it was estimated, that double magic nuclei with atomic number 110 ≤ Z ≤ 114 and neutron number N = 184, namely, the double “magic” closed shells of nuclei can possess the life time at ≥10 3 up to 10 9 years. Thus, these elements, similarly to Th and U, can survive in the Earth and meteorites since formation of Solar system ∼ 4.6 billion years ago. The present project work was drastically stimulated by recent synthesis and discovery of very stable isotopes of SHE in Flerov Laboratory of Nuclear Reactions During 1999–2000 Oganessian and his colleagues succeed in obtaining of a number of rather neutron-rich isotopes of elements 112, 114 and 116 in the reactions of 48Ca with monoisotopic targets of 238U, 244Pu and 248Cm, respectively [2]. The most stable isotope obtained is odd-even nuclear 285112, which possess the life time in between 10–30 min. Still this isotope has only 173 neutrons which is 11 fewer as compared with the magic number N = 184. For the region of known actinide nuclei (Z = 89 – 98) such a neutron difference for the most stable isotopes provides the stabilization factor of 10 10 – 10 13 in the life time. The discovery of very stable isotope of the new element 112 provides firstly the final unambiguous proof on the existence of new island of very stable SHE nuclei. Now we pointed out that there is no way to get the neutron number N = 184 using present accelerators and target nuclei. The only one way to find out double magic SHE nuclei now is the search for these nuclei in natural samples. The experimental attempts to discover such long-lived SHE nuclei with the life time ≥2×10 8 y in natural samples undertaken during the late sixties up to end of seventies provided some evidence of their existence in a number of both terrestrial samples and meteorites. These experiments were done by the investigation of alpha radioactivity and spontaneous fission activity, which exceeds significantly the effect due to the spontaneous fission of 238U nuclide. Still no decisive information on the existence of SHE in the nature was obtained.