1. V. A. Tsarev, J. Rad. Phys. Chem. 75, 805 (2006).
2. G. A. Gusev, B. N. Lomonosov, K. M. Pichkhadze, et al., Kosm. Issled. 44, 22 (2006) [Cosmic Res. 44, 19 (2006)].
3. V. A. Chechin, V. A. Feinberg, G. A. Gusev, et al., in Proceedings of the International ARENA Workshop, DESY, Zeuthen, Germany, 2005 (DESY, Zeuthen, 2005), p.232.
4. N. G. Lehtinen, P.W. Gorham, A. R. Jacobson, et al., Phys. Rev. D 69, 013008 (2004).
5. Y. Takahashi et al., New J. Phys. 11, 065009 (2009).