Study of the Radiation Resistance of Endohedral Fullerenes of Rare-Earth Elements and Their Water-Soluble Derivatives
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Study of the Radiation Resistance of Endohedral Fullerenes of Rare-Earth Elements and Their Water-Soluble Derivatives I. M. Dubovskii*, V. T. Lebedev, V. A. Shilin, A. A. Szhogina, M. V. Suyasova, and V. P. Sedov National Research Centre “Kurchatov Institute,” Petersburg Nuclear Physics Institute, Russian Academy of Sciences, Gatchina, Leningrad oblast, 188300 Russia *e-mail: [email protected] Received November 28, 2016
Abstract—Endohedral metallofullerenes Me@C2n (n = 30–50), their hydroxylated derivatives Me@C2n(OH)38–40 (Me = Tm, Ho, Eu, Sm, Co), and fullerenol С60(ОН)38 have been synthesized The radiation resistance of these structures under irradiation in reactor by thermal and fast neutron fluxes in the fluence range of 1018–1019 cm–2 (cadmium ratio of ~10) has been analyzed. Endofullerenols are shown to be more stable in comparison with initial endohedral fullerenes; the molecules containing Eu and Sm (atoms characterized by the largest slow-neutron absorption cross section) turned out to be most stable. The mechanism of the formation of secondary Eu and Sm endofullerenols is discussed taking into account the neutron capture and emission of γ quanta by excited nuclei, which acquire the recoil energy. DOI: 10.1134/S1063774518010054
INTRODUCTION The discovery of fullerenes С60 [1] in 1985 was followed by the synthesis of their endohedral complexes La@C60 (endohedral metallofullerenes (EMFs)) [2] in the same year. Then a number of EMFs with rareearth elements have been obtained; these artificial materials (absent in nature) are interesting for the fundamental science and some practical (including biomedical) applications [3, 4]. The atoms, ions, and atomic groups captured and isolated in a carbon framework partially transfer their charge to it, which leads to the manifestation of new (and sometimes unexpected) properties: redox, magnetic, luminescence, nonlinear optical, etc. Thus, one can develop new materials [1–5] for electronics: superconductors; semiconductors with controlled band gap; magnets; nonlinear optical materials for protecting light detectors from laser attack; new classes of polymers with specified mechanical, optical, electrical, and magnetic properties; materials for data recording and storage; etc. In our opinion, the most important application is the introduction of fullerenes and their derivatives (in particular, EMFs) into biomedicine; the ability of EMFs to encapsulate medical radioactive isotopes may be a basis for developing new methods of prevention, diagnostics, and treatment of many human diseases. The undoubted advantage of EMFs is related to the fact that isotopes, being protected by a strong carbon framework, do not cause radioactive contamination and toxicity risks, because the penetration of
metal atoms into the organism medium is blocked. At the same time, the migration of these molecules in the organism can easily be controlled. To introduce EMFs and isotopic preparations on their basis into medical practice, one must primarily determine the stability of EM
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